Incubation media modify silver nanoparticle toxicity for whitefish (Coregonus lavaretus) and roach (Rutilus rutilus) embryos

Toxicological studies were performed to examine silver nanoparticle (AgNP, size: 14.4 ± 2.5 nm) transformation within three different test media and consequent effects on embryos of whitefish (Coregonus lavaretus) and roach (Rutilus rutilus). The test media, namely ASTM very hard water, ISO standard dilution medium, and natural lake water differed predominantly in ionic strength. Total silver was determined using inductively coupled plasma mass spectrometry (ICP-MS), while AgNPs were characterized by transmission electron microscopy and single particle ICP-MS. Silver species distributions were estimated via thermodynamic speciation calculations. Data demonstrated that increased AgNP dissolution accompanied by decreasing ionic strength of the test medium did not occur as noted in other studies. Further, other physicochemical parameters including AgNP size and metallic species distribution did not markedly affect AgNP-induced toxicity. Irrespective of the test medium, C. lavaretus were more sensitive to AgNP exposure (median lethal concentration after 8 weeks: 0.51-0.73 mg/L) compared to R. rutilus, where adverse effects were only observed at 5 mg/L in natural lake water. In addition, AgNP-induced toxicity was lower in the two standard test media compared to natural lake water. Currently, there are no apparent studies assessing simultaneously the sensitivity of C. lavaretus and R. rutilus to AgNP exposure. Therefore, the aim of this study was to (1) investigate AgNP-induced toxicity in C. lavaretus and R. rutilus cohabiting in the same aquatic environment and (2) the role played by test media in the observed effects of AgNPs on these aquatic species.

Sulfate toxicity to early life stages of European whitefish (Coregonus lavaretus) in soft freshwater

Sulfate occurs naturally in the aquatic environment but its elevated levels can be toxic to aquatic life in freshwater environments. We investigated the toxicity of sulfate in humic, soft freshwater to whitefish (Coregonus lavaretus) from fertilization of eggs to hatching i.e. during the critical phases of whitefish early development. Anadromous Kokemäenjoki whitefish eggs and sperm during fertilization, embryos and larvae were exposed in the long-term 175-day incubation to seven different sodium sulfate (Na₂SO₄) concentrations from 44 to 2 000 mg SO₄ L^-1. Endpoint variables were the fertilization success, offspring survival and larval growth. Egg fertilization and early embryonic development were the most sensitive developmental stages of whitefish to sulfate, although the fertilization success and survival of embryos decreased only in the highest concentration of 2 000 mg SO₄ L^-1. The survival during late embryonic period, hatching and the 5-day larval period was high and no difference between the control and sulfate treatments were observed. LC₅₀-values of sulfate for early embryonic period and for the entire embryonic and larval period was 1 413 and 1 161 mg L^-1, respectively. The NOEC (No-observed Effect Concentration) of sulfate for the both periods was 1 207 mg L^-1. The tolerance of whitefish early stages to sulfate toxicity seems to be on the same level as the tolerance of other salmonids' early stages.

Hypoxia affects the ontogeny of the hypothalamus-pituitary-interrenal axis functioning in the lake whitefish (Coregonus clupeaformis)

Early life stages are sensitive to environmental insults and changes during critical developmental periods; this can often result in altered adult behaviour and physiology. Examining the development of the hypothalamus-pituitary-interrenal (HPI) axis and its responsiveness, or lack thereof, during development are important for understanding the short- and long-term impacts of stressors on embryonic and larval fish. We examined the ontogeny of the HPI axis in embryonic (21, 38, 63, 83 and 103 days post-fertilisation (dpf)) and larval (1, 2, 3 and 4 weeks post-hatch (wph)) lake whitefish (Coregonus clupeaformis) by quantifying changes in mRNA levels of several genes associated with HPI axis functioning and whole animal cortisol levels throughout development and in response to a severe or mild hypoxic stress. Cortisol, and crh, crhbp1, pomc and star transcripts were detected from the earliest embryonic age studied. Cortisol levels in control embryos decreased between 21 and 63 dpf, suggesting the utilisation of maternal cortisol deposits. However, by 83 dpf (70% developed) endogenous de novo synthesis had generated a 4.5-fold increase in whole embryo cortisol. Importantly, we provide novel data showing that the HPI axis can be activated even earlier. Whole body cortisol increased in eyed lake whitefish embryos (38 dpf; ~32% developed) in response to hypoxia stress. Coincident with this hypoxia-induced increase in cortisol in 38 dpf embryos were corresponding increases in crh, crhbp1, pomc and star transcript levels. Beyond 38 dpf, the HPI axis in lake whitefish embryos was hyporesponsive to hypoxia stress at all embryonic ages examined (63, 83 and 103 dpf; 54, 72 and 85% developed, respectively). Post-hatch, larvae responded to hypoxia with an increase in cortisol levels and HPI axis genes at 1 wph, but this response was lost and larvae appeared hyporesponsive at subsequent ages (2, 3 and 4 wph). Collectively our work demonstrates that during fish embryogenesis and the larval stage there are windows where the HPI axis is responsive and windows where it is truly hyporesponsive; both could be beneficial in ensuring undisrupted development particularly in the face of increasing environmental changes.

Modifying effects of a cobble substrate on thermal environments and implications for embryonic development in lake whitefish (Coregonus clupeaformis)

A laboratory flume was constructed to examine substrate effects on aquatic development. The flume was designed as a once-through system with a submerged cobble-filled corebox. Lake whitefish (Coregonus clupeaformis) embryos and temperature probes were deployed at multiple sites within the cobble and in the open water channel. Embryos were incubated in the flume for two different experimental periods: one to examine substrate impacts during natural lake cooling (37 days: 5 December 2016 to 10 January 2017) and the second to investigate substrate effects while administering a twice weekly 1 h heat shock (51 days: 11 January to 2 March 2017). During incubation, no significant difference was found in the average temperature between locations; however, temperatures were more stable within the cobble. Following both incubation periods, embryos retrieved from the cobble were significantly smaller in both dry mass and body length by up to 20%. These results demonstrate differences between embryos submerged in a cobble substrate and in the open water column, highlighting the need to consider the physical influences from the incubation environment when assessing development effects as part of any scientific study or environmental assessment.

Expression and activity of lipid and oxidative metabolism enzymes following elevated temperature exposure and thyroid hormone manipulation in juvenile lake whitefish (Coregonus clupeaformis)

Temperature has unequivocal effects on several aspects of fish physiology, but the full extent of its interaction with key endocrine signaling systems to influence metabolic function remains unknown. The aim of the current study was to assess the individual and combined effects of elevated temperature and hyperthyroidism on hepatic metabolism in juvenile lake whitefish by quantifying mRNA abundance and activity of key metabolic enzymes. Fish were exposed to 13 (control), 17 or 21 °C for 0, 4, 8 or 24 days in the presence or absence of low-T₄ (1 µg × g body weight^-1) or high-T₄ (10 µg × g body weight^-1) treatment. Our results demonstrate moderate sensitivity to elevated temperature in this species, characterized by short-term changes in mRNA abundance of several metabolic enzymes and long-term declines in citrate synthase (CS) and cytochrome c oxidase (COX) activities. T₄-induced hyperthyroidism also had several short-term effects on mRNA abundance of metabolic transcripts, including depressions in acetyl-coA carboxylase β (accβ) and carnitine palmitoyltransferase 1β (cpt1β), and stabilization of cs mRNA levels; however, these effects were primarily limited to elevated temperature groups, indicating temperature-dependent effects of exogenous T₄ treatment in this species. In contrast, maximal CS and COX activities were not altered by hyperthyroidism at any temperature. Collectively, our data suggest that temperature has the potential to manipulate thyroid hormone physiology in juvenile lake whitefish and, under warm-conditions, hyperthyroidism may suppress certain elements of the β-oxidation pathway without substantial impacts on overall cellular oxidative capacity.

Assessment of Fish Embryo Survival and Growth by In Situ Incubation in Acidic Boreal Streams Undergoing Biomining Effluents

The applicability of an in situ incubation method in monitoring the effects of metal mining on early life stages of fish was evaluated by investigating the impacts of a biomining technology utilizing mine on the mortality, growth, and yolk consumption of brown trout (Salmo trutta) and whitefish (Coregonus lavaretus) embryos. Newly fertilized eggs were incubated from autumn 2014 to spring 2015 in six streams under the influence of the mine located in North-Eastern Finland and in six reference streams. Although the impacted streams clearly had elevated concentrations of several metals and sulfate, the embryonic mortality of the two species did not differ between the impacted and the reference streams. Instead, particle accumulation to some cylinders had a significant impact on the embryonic mortality of both species. In clean cylinders, mortality was higher in streams with lower minimum pH. However, low pH levels were evident in both the reference and the mine-impacted groups. The embryonic growth of neither species was impacted by the mining activities, and the growth and yolk consumption of the embryos was mainly regulated by water temperature. Surprisingly, whitefish embryos incubated in streams with lower minimum pH had larger body size. In general, the applied in situ method is applicable in boreal streams for environmental assessment and monitoring, although in our study, we did not observe a specific mining impact differing from the effects of other environmental factors related to catchment characteristics.

Interspecific germ cell transplantation: a new light in the conservation of valuable Balkan trout genetic resources?

Interspecific transplantation of germ cells from the brown trout Salmo trutta m. fario and the European grayling Thymallus thymallus into rainbow trout Oncorhynchus mykiss recipients was carried out in order to improve current practices in conservation of genetic resources of endangered salmonid species in the Balkan Peninsula. Current conservation methods mainly include in situ efforts such as the maintenance of purebred individuals in isolated streams and restocking with purebred fingerlings; however, additional ex situ strategies such as surrogate production are needed. Steps required for transplantation such as isolation of high number of viable germ cells and fluorescent labeling of germ cells which are to be transplanted have been optimized. Isolated and labeled brown trout and grayling germ cells were intraperitoneally transplanted into 3 to 5 days post hatch rainbow trout larvae. Survival of the injected larvae was comparable to the controls. Sixty days after transplantation, fluorescently labeled donor cells were detected within the recipient gonads indicating successful incorporation of germ cells (brown trout spermatogonia and oogonia-27%; grayling spermatogonia-28%; grayling oogonia-23%). PCR amplification of donor mtDNA CR fragments within the recipient gonads additionally corroborated the success of incorporation. Overall, the transplantation method demonstrated in this study presents the first step and a possible onset of the application of the germ cell transplantation technology in conservation and revitalization of genetic resources of endangered and endemic species or populations of salmonid fish and thus give rise to new or improved management strategies for such species.

Impacts of temperature, morpholine, and chronic radiation on the embryonic development of round whitefish (Prosopium cylindraceum)

During incubation, round whitefish embryos may experience fluctuating or elevated temperatures from natural (e.g., seasonal temperature changes) and/or anthropogenic sources. Anthropogenic sources like once-through cooling discharges from nuclear power plants can also expose embryos to chemicals (e.g., morpholine) and/or radiation. To examine the effects of these potential stressors on embryogenesis, round whitefish were incubated under fluctuating or constant temperatures, with morpholine or ¹³⁷ Cs gamma rays. We report the percentage of prehatch and posthatch mortality, developmental rate, hatch dynamics, and morphometrics at 4 development stages. Embryos reared at constant temperatures had delayed developmental stage onset and median hatch, higher mortality at constant 8 °C, and lower mortality at ≤5 °C, compared with embryos reared under seasonal temperature regimes. Embryos incubated with ≥500 mg L^-1 morpholine (>200× regulatory limits) had advanced hatch, reduced body size, and increased prehatch (100% at 1000 mg L^-1 ) and posthatch (≈95% at 500 mg L^-1 ) mortality compared with controls. Relative to controls, embryos irradiated with ≥0.16 mGy/d had larger body mass early in development, and all irradiated embryos had decreased posthatch mortality; the lowest dose was >300× discharge limits. Our study suggests that fluctuating or elevated temperatures and high-dose morpholine can alter development rate, hatch dynamics, and growth, and/or increase mortality compared with embryos reared at constant temperatures of ≤5 °C; conversely, low-dose irradiation had transient developmental effects but may benefit early posthatch survival. Environ Toxicol Chem 2018;37:2593-2608. © 2018 SETAC.

Characterization of igf1 and igf2 genes during maraena whitefish (Coregonus maraena) ontogeny and the effect of temperature on embryogenesis and igf expression

The insulin-like growth factors IGF-1 and IGF-2 play important roles in the growth, development, and metabolism of teleost fish. We isolated cDNA sequences of igf1, and igf2 genes from maraena whitefish. We quantified the mRNA and protein expressions of IGFs in different tissues of marketable juvenile maraena whitefish. Moreover, we analyzed the gene expression profiles during maraena whitefish development from unfertilized egg to fingerling and examined the effect of incubation temperature on igf1, and igf2 gene expression during embryonic and early larval development. Transcripts encoding IGF-1 or IGF-2 were detected in all tested tissues, with the greatest abundance in the liver. We measured higher igf2 than igf1 copy numbers in all tissues and at all developmental stages examined, even at advanced juvenile stages. Using the Western blot technique, we demonstrated that several isoforms of IGF-1 are expressed in the liver and gills but not in muscle tissue, indicating tissue-specific protein expression of IGF-1. We observed an accelerated embryonic development with increasing temperature, resulting in shortened hatching periods. Out of the three tested temperatures, we observed the highest hatching rate, larval hatching size, and larval growth at 6 °C. At 9 °C, hatching rate, larval hatching size and larval growth were reduced compared to the values we observed at 4 °C and 6 °C, since incubation temperature might have exceeded the optimum. To our knowledge, our data show for the first time that both igf1 and igf2 expression were upregulated due to elevated incubation temperature within embryonic development of fish. Further, we found significantly higher igf expression for the best-developing larvae (6 °C group) at specific life stages of maraena whitefish.

Embryonic development of lake whitefish Coregonus clupeaformis: a staging series, analysis of growth and effects of fixation

A reference staging series of 18 morphological stages of laboratory reared lake whitefish Coregonus clupeaformis is provided. The developmental processes of blastulation, gastrulation, neurulation as well as development of the eye, circulatory system, chromatophores and mouth are included and accompanied by detailed descriptions and live imaging. Quantitative measurements of embryo size and mass were taken at each developmental stage. Eggs were 3·19 ± 0·16 mm (mean ± s.d.) in diameter at fertilization and embryos reached a total length (LT ) of 14·25 ± 0·41 mm at hatch. Separated yolk and embryo dry mass were 0·25 ± 0·08 mg and 1·39 ± 0·17 mg, respectively, at hatch. The effects of two common preservatives (formalin and ethanol) were examined throughout development and post hatch. Embryo LT significantly decreased following fixation at all points in development. A correction factor to estimate live LT from corresponding fixed LT was determined as live LT = (fixed LT )(1·025) . Eye diameter and yolk area measurements significantly increased in fixed compared with live embryos up to 85-90% development for both measurements. The described developmental stages can be generalized to teleost species, and is particularly relevant for the study of coregonid development due to additionally shared developmental characteristics. The results of this study and staging series are therefore applicable across various research streams encompassing numerous species that require accurate staging of embryos and descriptions of morphological development.

Reproductive isolation in a nascent species pair is associated with aneuploidy in hybrid offspring

Speciation may occur when the genomes of two populations accumulate genetic incompatibilities and/or chromosomal rearrangements that prevent inter-breeding in nature. Chromosome stability is critical for survival and faithful transmission of the genome, and hybridization can compromise this. However, the role of chromosomal stability on hybrid incompatibilities has rarely been tested in recently diverged populations. Here, we test for chromosomal instability in hybrids between nascent species, the 'dwarf' and 'normal' lake whitefish (Coregonus clupeaformis). We examined chromosomes in pure embryos, and healthy and malformed backcross embryos. While pure individuals displayed chromosome numbers corresponding to the expected diploid number (2n = 80), healthy backcrosses showed evidence of mitotic instability through an increased variance of chromosome numbers within an individual. In malformed backcrosses, extensive aneuploidy corresponding to multiples of the haploid number (1n = 40, 2n = 80, 3n = 120) was found, suggesting meiotic breakdown in their F1 parent. However, no detectable chromosome rearrangements between parental forms were identified. Genomic instability through aneuploidy thus appears to contribute to reproductive isolation between dwarf and normal lake whitefish, despite their very recent divergence (approx. 15-20 000 generations). Our data suggest that genetic incompatibilities may accumulate early during speciation and limit hybridization between nascent species.

[Embryonic development of whitefishes (Coregonidae) as representatives of the "pagophilous" ecological group]

Studies of reproduction and embryonic development in six species of coregonid fishes have revealed the possibility of their fertilized eggs to develop normally while being embedded in the ice of a spawning water body (optionally). Such ability is facilitated by extremely low respiratory activity of embryos at early stages of embryogenesis (from the stage of fission to the stage of organogenesis). Low level of oxygen consumption and carbon dioxide emission is an adaptation to low diffusion gas permeability of the ice. The main factor controlling the rate of coregonids embryonic development is not temperature, but intensity and periodicity of insolation. Without the sunlight--an obligatory external factor--normal development is just not possible. Under experimental conditions, when developing in the water at near zero temperature or in the ice, normal morphogenesis of Arctic cisco and Sevan whitefish embryos was observed at the illumination of 50-300 lux. Hemoproteid cytochrome beta560, the pigment that has been discovered in water-soluble part of coregonids oocyte yolk and is treated as a biochemical marker for eggs of the family Coregonidae, in all likelihood performs protective (antioxidant) functions preventing spontaneous oxidation of embryo's fatty inclusions. Under the oxygen shortage inside the ice envelope, cytochrome beta560 probably sets conditions for oxidation processes of embryo's tissue respiration. Spherome, being kept till the time of hatching, acts as a temporary hydrostatic organ and ensures larvae buoyancy at the stage of postembryonic metamorphosis. It also serves as an energy store after downstream migration of larvae from the spawning areas till their shift to exogenous feeding on zooplankton. Conforming to ecological traits of reproduction and development, and also to revealed morphogenetic, physiological, and biochemical features, it is proposed to ascribe all of the currently known 26 species of whitefishes to "pagophilous" ecological group.

Elevated water temperature impairs fertilization and embryonic development of whitefish Coregonus lavaretus

The adverse effects of high temperatures on the early life stages of anadromous whitefish Coregonus lavaretus were experimentally examined by assessing fertilization success, the percentage of developmental abnormalities, cumulative mortality and the rate of embryogenesis across a range of temperatures. Temperatures >or= 7 degrees C increased the proportion of unfertilized and abnormally dividing eggs, deformed embryos and consequent mortality. The higher the temperature, the more severe were the effects. When eggs were fertilized and constantly incubated at various temperatures, the effective level for 50% of the eggs and embryos (EL50) of temperature was 7.6 degrees C at the developmental stage when eye pigmentation was visible. Fewer developmental abnormalities and a lower cumulative mortality rate were observed when embryos were exposed to high temperatures from the later, gastrula stage, than from fertilization or the four-cell stage. Irrespective of retarded development in terms of day-degrees (i.e. the sum of daily mean temperatures), a high incubation temperature reduced the development time of C. lavaretus, leading to earlier hatching, and hatched fry were shorter than at the reference temperature of 4-5 degrees C. Global warming will particularly pose risks for stenothermic species such as C. lavaretus, with early life stages being especially susceptible. Thus, relatively small increases and fluctuations in river water temperatures during the spawning season of this anadromous species may have substantial negative impacts on its recruitment and population persistence.

‘Good-genes’ and ‘compatible-genes’ effects in an Alpine whitefish and the information content of breeding tubercles over the course of the spawning season

Some models of sexual selection predict that individuals vary in their genetic quality and reveal some of this variation in their secondary sexual characteristics. Alpine whitefish (Coregonus sp.) develop breeding tubercles shortly before their spawning season. These tubercles are epidermal structures that are distributed regularly along the body sides of both males and females. There is still much unexplained variation in the size of breeding tubercles within both sexes and with much overlap between the sexes. It has been suggested that breeding tubercles function to maintain body contact between the mating partners during spawning, act as weapons for defence of spawning territories, or are sexual signals that reveal aspects of genetic quality. We took two samples of whitefish from their spawning place, one at the beginning and one around the peak of spawning season. We found that females have on average smaller breeding tubercles than males, and that tubercle size partly reveals the stage of gonad maturation. Two independent full-factorial breeding experiments revealed that embryo mortality was significantly influenced by male and female effects. This finding demonstrates that the males differed in their genetic quality (because offspring get nothing but genes from their fathers). Tubercle size was negatively linked to some aspects of embryo mortality in the first breeding experiment but not significantly so in the second. This lack of consistency adds to inconsistent results that were reported before and suggests that (i) some aspects of genetic quality are not revealed in breeding tubercles while others are, or (ii) individuals vary in their signaling strategies and the information content of breeding tubercles is not always reliable. Moreover, the fact that female whitefish have breeding tubercles of significant size while males seem to have few reasons to be choosy suggests that the tubercles might also serve some functions that are not linked to sexual signaling.

A novel salmonid myoD gene is distinctly regulated during development and probably arose by duplication after the genome tetraploidization

A novel myoD paralogue was characterised in Salmo salar (smyoD1c) and S. trutta (btmyoD1c). SmyoD1c had 78.2/90.6% protein sequence identity to smyoD1a/smyoD1b, respectively. Each paralogue was differentially expressed throughout somitogenesis. In adult fish, smyoD1a was the predominant gene expressed in fast muscle, whereas smyoD1c was 2-3 times upregulated in slow muscle compared to smyoD1a/1b. A maximum likelihood analysis indicated that myoD1c arose by duplication of myoD1b after the salmonid tetraploidization. Another myoD paralogue (myoD2) is present in at least some teleosts, reflecting a more ancient genome duplication. To accommodate these findings we propose a simplified teleost-myoD nomenclature.

Toxicity of a phytosterol mixture to grayling (Thymallus thymallus) during early developmental stages

The study concerns the toxicity of a phytosterol mixture, ultrasitosterol, consisting mainly of beta-sitosterol 75.7% and beta-sitostanol 13.0%, to grayling (Thymallus thymallus) embryos. Eyed eggs were exposed to three concentrations (1 microg/l, 10 microg/l, and 50 microg/l) of ultrasitosterol for 4 weeks. Embryos and later on hatched fry were taken for triiodothyronine (T3), thyroxine (T4), and histopathological analyses after 7, 14, 21, and 28 days of exposure. Most of the eggs (>95%) hatched during the first week of exposure, and ultrasitosterol treatment shortened hatching time significantly (p < or = 0.0001) at all exposure concentrations in comparison to the control. Ultrasitosterol did not have any significant effect on T3 or T4 levels in the embryo extracts. However, an interesting observation was that T3 levels increased in all treatments and in the control near the time of hatching. In conclusion, ultrasitosterol showed potential to affect the development of grayling embryos and fry, but further long-term exposure experiments are needed to verify these changes in more detail.

[Aminotransferases in early development of salmonid fish]

The activities of alanine and aspartate aminotransferases were assessed in the embryos and juveniles of the rainbow trout Parasalmo mukiss L. and chum salmon Oncorchyncus keta W. Changes in subcellular localization of these enzymes and their activities were found at different pH optima in each subcellular fraction of the rainbow trout during ontogenesis.

[The studies of temporal and spatial characteristics of somitogenesis in fish embryos]

New data were obtained corroborating that somitogenesis is a rhythmic process, in which the time of somite formation is strictly constant. This constant (tau s) can be considered as a natural unit of developmental "biological clock" characterizing rhythmic processes. The constant tau s can be determined with an exceptional accuracy that has no analogs among the known biological processes. This fact alone suggests that the accuracy of developmental clock is very high. In addition to the constancy of tau s, all forming somites have equal linear size along the notochord axis. In the process with strictly constant temporal and spatial factors, time plays the leading role in triggering the formation of new somite. This became clear in studies of twin embryos. Both embryos had the same number of somites but they were shorter than in the normal embryos. Also, we measured the length of head and both segmented and unsegmented caudal parts of the trunk. Combined with the published data on somitogenesis, our results suggest that the previously proposed scheme for the role of developmental clock in embryogenesis predicts: (1) a possible loss of some embryonic stages without serious consequences for subsequent development and (2) periodic switching on/off any embryonic processes (at the molecular, cellular, or supercellular level) with intervals multiple to tau s.

[Cytogenetic approach to estimation of developmental stability of the natural population of coregonid fishes]

A comparative cytogenetic analysis of coregonid fish was carried out in the river and lake ecosystems of the northern Tyumen' District. The occurrence of chromosomal aberrations in embryonic cells of fish steadily increased during the period from 1989 until 2001. Possible causes of this dynamic are discussed.

Fertilization and embryonic development of whitefish (Coregonus lavaretus lavaretus) in acidic low-ionic-strength water with aluminum

The fertilization rate and extent of the cortical reaction of anadromous whitefish decreased with increasing acidity (0.034 mmol Ca(2+)L(-1)); at pH 4.5 the fertilization rate was 46% of that at pH 6.5. Aluminum (250 microg L(-1)) decreased the percentage fertilization independently of pH and reduced the cortical reaction magnitude at all pH levels. In eggs at pH 5.0, especially at pH 4.5, and in solutions with Al, the growth of embryos was impaired by a perivitelline space that was too narrow. The proportion of embryos with a curved tail tip and those with blood circulation failure increased with decreasing pH. No fry hatched at pH 4.5 and those few that hatched at pH 5.0 did not survive. No fry survived Al-containing water at pH 5.5 and survival was decreased at pH 6.5 with Al. It is concluded that for successful recruitment of anadromous whitefish, pH should preferably remain >5.5 in dilute soft water when toxic concentrations of Al are present.

Induced hatching to avoid infectious egg disease in whitefish

Reacting to a threat before physical contact, e.g., induced by air- or water-borne substances, appears to be an elegant way of defense. The reaction may be behavioral, developmental, morphological, or physiological, and it can involve a shift in niche or life history. Hatching from eggs is a shift in niche and in life history. From niche shift and life history models, one would predict that the timing of hatching is, to some degree, phenotypically plastic, i.e., early or delayed hatching is likely to be inducible. Temporary increased larval mortality (e.g., increased predation on larvae) would favor delayed hatching, while relatively high egg mortality would favor early hatching. Here, I show experimentally that eggs of the whitefish (Coregonus sp.) hatch earlier in the presence of a virulent egg parasite and that this early hatching is induced by water-borne cues emitted from infected eggs.

Toxicity of waters from two streams to early life stages of brown trout (Salmo trutta f. fario L.), tested under semi-field conditions

The development of brown trout (Salmo trutta f. fario L.) in water of two differently polluted streams and in a control situation was monitored in order to get insights into the impact of anthropogenic chemical stressors on the reproductive success of this fish species indigenous to both streams. The test streams, situated in the south of Stuttgart, Germany, were the complexly polluted Körsch stream and the less polluted Krähenbach stream. Bypass systems connected to the streams and a laboratory control system were used for continuous exposure of early brown trout stages shortly after fertilisation up to the end of the embryonic development. Temperature and oxygen conditions were standardised in all test series in order to minimise unspecific effects. The examined endpoints were: (1) mortality, (2) developmental rate, (3) time course of hatching, (4) malformations, and (5) growth. A retarded development, reduced growth rates and higher mortality rates of Körsch stream water exposed embryos indicated an embryotoxic potential for the more polluted stream. High infection-related mortality rates of embryos suggested the presence of confounding factors also in the less polluted Krähenbach stream. In parallel to the exposure experiment, physicochemical and limnochemical parameters as well as concentrations of organic contaminants and heavy metals were monitored. Analytical data confirm the different degrees of pollution of both streams.

Permanent impairment in the feeding behavior of grayling (Thymallus thymallus) exposed to methylmercury during embryogenesis

Embryos of grayling (Thymallus thymallus) were exposed to different concentrations of methylmercury (0.16, 0.8, 4.0 and 20 micrograms Hg l-1) during the first 10 days of development. The exposure resulted in body concentrations in the newly hatched fry of 0.09, 0.27, 0.63 and 3.80 micrograms Hg g-1 wet wt., respectively. A control group had a body concentration of 0.01 microgram Hg g-1. Morphological disturbances were only found in the highest exposure group. Three years later, at a size of 13.8 +/- 0.8 cm, the different groups were tested for sublethal toxicant effects on foraging behavior. In the first series of experiments we tested the foraging efficiency of the fish when kept alone for 5 min in small flow-through aquariums. In the second series of experiments we tested the competitive ability of eight individuals from an exposed group vs. eight individuals from a control group when kept together for 30 min in a 300-1 aquarium. In both experiments live Dapnia magna were used as prey. We found impaired feeding efficiencies and reduced competitive abilities in grayling from the exposed groups which as yolk-fry had Hg concentrations of 0.27 microgram g-1 or more. In the foraging efficiency experiments these groups were 15-24% less efficient as compared to the control group. In the competitive ability experiments the control group caught two to six times as many preys as these exposed groups. Such harmful body concentrations of Hg (> 0.27 microgram g-1) may be found in eggs from piscivorous fishes in lakes receiving diffuse atmospheric depositions of mercury. We suggest such concentrations may have ecological consequences by reducing the fitness of the affected populations.

Characteristics of current international trade of live salmonid eggs

World trade in live salmonid embryos (eyed eggs) has grown in response to increased global salmon production, particularly in South America, and parallels international trade in farmed salmonid products. Rainbow trout (Oncorhynchus mykiss), Atlantic salmon (Salmo salar) and coho salmon (O. kisutch) are the most commercially important species. In 1992, the Food and Agriculture Organization of the United Nations estimated world production of rainbow trout at 300,000 tonnes, while the production of Atlantic salmon was estimated at 250,000 tonnes and coho salmon at 50,000 tonnes. One can estimate that roughly 3 billion, 150 million and 30 million eggs, respectively, were required to produce this yield. Broodstock are cultivated world-wide, using a wide variety of water sources, including the marine environment, riverine water containing anadromous fish, and ground water free of migrating fish. As many as 70% of all coho eggs are derived from feral fish. Approximately 50% of all commercial salmonid eyed eggs are produced in Europe, and approximately 15% are produced in the state of Washington, United States of America. Conditions which are ideal for commercial salmonid grow-out are not necessarily ideal for the cultivation of salmonid broodstock; this is one reason why international egg trade is necessary. The trend of current salmonid health regulations is towards facilitating egg commerce on a regional level, in an attempt to control disease transmission. Regulations controlling egg importation often include pathogens which are not vertically transmitted. This serves only to increase egg prices, in compensation for the cost of laboratory tests. Genetic improvements have been the cornerstone of increasing commercial production of all agricultural commodities. Fish health regulations are sometimes instituted in an effort to protect the local industry, but in fact they act more often to restrict the flow of genetic material and may actually serve to reduce industry productivity and profitability.

Developmental changes in the brain-stem serotonergic nuclei of teleost fish and neural plasticity

1. During early ontogeny, the serotonergic neurons in the brain stem of the three-spined stickleback shows a temporal and spatial developmental pattern that closely resembles that of amniotes. 2. However, in the adult fish, only the midline nuclei of the rostral group (dorsal and median raphe nuclei) and the dorsal lateral tegmental nucleus are consistently serotonin-immunoreactive (5-HTir), whereas the groups of the upper and lower rhombencephalon (raphe pontis, raphe magnus, and raphe pallidus/obscurus nuclei) are variable and, when present, contain relatively small numbers of 5-HTir neurons. 3. Using specific antisera against tryptophan 5-hydroxylase and aromatic L-amino acid decarboxylase, we have shown that the lateral B9 group and the groups of the upper and lower rhombencephalon are consistently present in adult sticklebacks. The results are discussed in relation to other known instances of neurotransmitter plasticity or transient neurotransmitter expression in teleost fish. 4. While there are several instances of transient expression of neurotransmitter markers by discrete neuronal populations, there is so far no evidence of changes from one neurotransmitter phenotype to another in the brain of teleost fish. However, there are indications of plasticity of expression of catecholamines and indoleamines, and their respective synthesizing enzymes, as reflected in age-dependent changes and variation between individuals of different physiological status. 5. As the brain grows continuously in teleost fish, and new neurons are added from proliferative regions, synaptic connections may be expected to undergo remodeling in all brain regions throughout life. Thus, the teleostean brain may be considered a suitable model for experimental studies of different aspects of neural plasticity.

Mitogenic activity from trout embryos

An extract of 21-day rainbow trout embryos stimulated growth of several piscine cell lines in the absence of added serum. Established lines from trout (RTG-2 and STE-137), salmon (CHSE-214), carp (EPC), and goldfish (CAR) and early-passage cells initiated from trout embryos grew in serum-free medium containing the embryo extract. In addition the extract was sufficient for maintaining long-term cultures of CHSE-214 cells for several months through a minimum of 20 passages (approximately 50 population doublings) in the absence of serum. Optimal response was achieved with 100 micrograms of extract protein per ml, but a significant growth-promoting effect was observed with as little as 2.5 micrograms/ml. The activity was nondialyzable, protease-sensitive, and stable in 200 mM acetic acid. The level of mitogenic response induced by the extract could not be duplicated with purified mammalian growth factors added individually or in combination, and the extract did not stimulate DNA synthesis in quiescent mouse fibroblasts. These results suggest that trout embryo extract may contain a novel growth-promoting activity for fish cells.

Monoamine oxidase activity in embryos of pike (Esox lucius)

1. Mitochondrial MAO specific activity was measured in eggs and early embryos of the teleostean fish Esox lucius using tryptamine, 5-hydroxytryptamine (5-HT) and phenylethylamine (PEA) as substrates. 2. Tryptamine is the most readily deaminated substrate in mitochondria isolated from unfertilized eggs and embryos at the stages of cleavage, blastula and gastrula. 3. Monoamine oxidase activity gradually decreases during development and at the gastrula stage it is respectively 80% (tryptamine), 70% (5-HT) and 50% (PEA) of that found in the egg using the corresponding substrate. 4. The inhibition of egg MAO activity by clorgyline and deprenyl measured in E. lucius eggs using tryptamine as substrate, indicates the presence of a single form of MAO not corresponding to the MAO A and MAO B described in terrestrial vertebrates.

Morphological and physiological development of olfactory receptor cells in rainbow trout (Salmo gairdneri) embryos

The morphological and functional differentiation of the olfactory receptor cells were investigated in developing rainbow trout (Salmo gairdneri) embryos by means of light and electron (transmission and scanning) microscopy and electrophysiology. Ciliated receptor cells first appeared when the olfactory placode was folded to form a groovelike structure rostrad to the eye at stage 24 (day 18; 18 days postfertilization). Ciliated receptor cells predominated until immature microvillar receptor cells developed in stage 28 (day 26) embryos. At stage 29, the day of hatching, the anterior edge of the olfactory epithelium contained only ciliated receptor cells, and the midregion contained both ciliated and microvillar receptor cells. Spontaneous neural firing activity was recorded from the olfactory mucosa as early as stage 25. The neural responses to amino acids were initially recorded from stage 26 embryos, containing sparse ciliated receptor cells with a few short cilia. The D-enantiomers of amino acids were less effective. From these results we concluded that in rainbow trout the olfactory receptor cell has two separate morphological forms, ciliated and microvillar. These are ontogenetically distinct; the ciliated receptor cells preceded the microvillar. The ciliated receptor cells respond to amino acid stimulation.

Injection of the mouse MT-1 gene into rainbow trout eggs and assay of trout fry for resistance to cadmium and zinc toxicity

The mouse MT-1 gene, cloned into the plasmid pBR 322, has been injected into fertilised eggs of the rainbow trout, Salmo gairdneri. About 10(6) copies of the construct, either circular or linearized, have been injected into 1 cell stage eggs within 4 hours of fertilisation, and fry hatched from such eggs are being assayed for evidence of integration of the injected sequence. In addition, with a view to the development of an assay which can be used to monitor for expression of the injected gene, uninjected fry have been exposed to various concentrations of cadmium chloride or zinc sulphate, with or without prior exposure to inducing doses of these compounds. Whereas a distinct protection is evident following induction with zinc, no such protection has been detected with cadmium induction.

Innervation of the early pelvic fin bud of the trout embryo, Salmo gairdneri

Innervation of the early pelvic fin bud in the trout embryo involves four nerves. Electron microscopy discloses axons in the mesodermal mesenchyme and in the epidermis of the bud as early as stage I of the development of the pelvic fins. Sensory axons alone penetrate the epidermis. Unmyelinated axons invade the pelvic fin territory before the bud is obvious on the abdomen. Schwann cells occur in the vicinity of the ventral edge of the myotomes and later in the core of the bud and in subepidermal regions. Consequently, the nerve fibers are present early in the development of the pelvic fin bud of the trout embryo. Although the role of these axons is unknown, it is speculated that they play a role in development. Our results are discussed in the light of data available in the literature dealing with the development of tetrapod appendages.

The influence of the zona radiata on the toxicities of zinc, lead, mercury, copper and silver ions to embryos of steelhead trout Salmo gairdneri

Eyed embryos of the steelhead trout (Salmo gairdneri) were significantly more resistant to zinc and lead but significantly less resistant to mercury, copper and silver if the zona radiata (egg capsule) was removed than if it was intact. The zona radiata appears to act as a cation exchanger and inhibits metals with high binding constants (Hg2+, Cu2+, Ag+) from entering the perivitelline fluid. Metals with low binding constants (Zn2+, Pb2+, Cd2+) rapidly penetrate the zona radiata and accumulate in the perivitelline fluid according to the Donnan equilibrium.

Microinjection of carcinogens into rainbow trout embryos: an in vivo carcinogenesis assay

Liver tumors were induced in rainbow trout (Salmo gairdneri) 1 year after carcinogens were microinjected into embryos. Neoplasms were induced by a single injection of 13 and 25 ng per egg of aflatoxin B1 (CAS: 1162-65-8), 500 ng per egg of 7,12-dimethylbenz[a]anthracene (CAS: 57-97-6), and 250 ng per egg of 2-anthramine (CAS: 613-13-8). Over 70% of [3H]benzo[a]-pyrene (CAS: 50-32-8) injected into eggs was retained in hatched embryos, 120 hours postinjection. Exogenous activation of test compounds with the use of rat liver microsome preparation (S-9) increased the incidence of liver tumors in fish given injections of 25 ng aflatoxin B1. The amount of chemical required for the embryo injection assay was comparable to that required for the Ames bacterial mutagenesis assay.

Rainbow trout embryos: advantages and limitations for carcinogenesis research

Rainbow trout embryos are sensitive to the initiation of neoplasms in various tissues by brief exposures to solutions of water-soluble carcinogens. This characteristic was first demonstrated with the sparingly soluble liver carcinogen, aflatoxin B1 (AFB1). A 30-minute exposure of 21-day-old embryos (embryos hatch in 24-25 days at 12 degrees C) to a 0.5-ppm aqueous solution of AFB1 will result in approximately 65 of the survivors having at least 1 liver tumor, 1 year after treatment. The embryos are responsive to both AFB1 dose and the length of exposure and become increasingly sensitive with increased embryonic age. We have used rainbow trout embryos to demonstrate the hepatocarcinogenicity of other aflatoxin metabolites and precursors; aflatoxicol, aflatoxin G1, versicolorin A, and sterigmatocystin. In addition to mycotoxins, trout embryos are sensitive to several nitrosamine hepatocarcinogens including: dimethylnitrosamine, diethylnitrosamine, nitrosopyrrolidine, and 2,6-dimethylnitrosomorpholine. However, with the highly water-soluble nitrosamines, longer exposure time (up to 24 hr) are required. It is generally accepted that each of the above-named carcinogens requires metabolic activation to the ultimate carcinogenic form. This provides indirect evidence that the trout embryo is capable of cytochrome P-450-mediated metabolism. Finally, trout embryos are sensitive to the direct-acting carcinogen, N-methyl-N'-nitro-N-nitrosoguanidine. This compound produces tumors of the liver, stomach, kidney, and swim bladder, and a pronounced female-to-male sex reversal. Results to date have shown that the trout embryo is a sensitive, convenient, and economical whole animal model system with many distinct advantages for carcinogen testing and research.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation and structures of the third major type of carbohydrate units in polysialoglycoproteins from rainbow trout eggs

The structures of the third major type of oligosialyloligosaccharides obtained by alkali-borohydride treatment of polysialoglycoproteins of the unfertilized eggs of rainbow trout have been determined to be: alpha-L-fucosyl-(1----3)-beta-N-acetyl-D-galactosaminyl-(1----3)-beta-D- galactosyl-(1----4)-beta-D-galactosyl-(1----3)-[[(----8)-alpha-N- glycolylneuraminyl-(2----)]n-(----6)]-N-acetyl-D-galactosaminitol with n = 1 to 4. The proportion of the fucose-containing units in 3 major carbohydrate units present in fish egg polysialoglycoproteins was found to be highly species-specific and only 6% in the eggs of rainbow trout.

Ingrowth of optic nerve fibers and onset of myelin ensheathment in the optic tectum of the trout (Salmo gairdneri)

The early differentiation of the optic pathway of the trout was studied by means of autoradiography, silver impregnation and electron microscopy. Ingrowth of the optic nerve fibers into the optic tectum was consistently shown by tracer application and Golgi studies to occur at stage 28, about one week before hatching. Fibers being arranged in discrete bundles were rapidly growing through the longitudinal axis of tectum and at stage 33 reached its posterior end. Cross sections of these fiber bundles at different positions revealed myelin ensheatment to be initiated at the end of stage 34 at the anterior pole of the tectum. Since in the optic nerve of the trout the onset of myelination occurred even earlier (stage 33), it is assumed that this differentiation process follows a rostro-caudal gradient during development of the optic pathway.

Consequences of cell death after nitrogen mustard treatment on skeletal pelvic fin morphogenesis in the trout, Salmo Gairdneri (Pisces, Teleostei)

Five concentrations of nitrogen mustard (methyl-bis-chlorethylamine) have been administered to different stages of development of trout embryos (Salmo gairdneri), in order to study their effect on the formation of both pelvic fins soft tissue and skeleton. Sensitivity of epidermis and mesoderm toward this cytotoxic agent has been assessed histologically. Although both components are sensitive to nitrogen mustard, mesoderm is more sensitive than epidermis. These results are compared with the results of similar studies on tetrapod limb buds. The pelvic fin skeleton of some treated animals was doubly stained in toto for cartilage and bone by Alcian blue and alizarin, followed by clearing. Other specimens were processed for histological serial sections. Analysis included comparison of the following parameters: (1) dose of nitrogen mustard, (2) stage of fin bud development at the time of treatment, (3) importance of necrosis in the fin bud, and (4) abnormalities of the endoskeleton of the fin (pelvic girdle and radials) and of the dermal skeleton (lepidotrichia and actinotrichia) one month after the hatching of control animals. Resuls suggest (1) that material of endoskeleton and lepidotrichia are laid down simultaneously, and (2) that differentiation of actinotrichia is independent of differentiation in endoskeleton and lepidotrichia.

A morphological and experimental study of gonadal sex differentiation in the rainbow trout, Salmo gairdneri

Gonadal sex differentiation in rainbow trout takes place between day (D) 45 and D 55 after fertilization. Until D 400 the male GSI is maintained at about 0.4%, and that of the female at about 1%. Treatment with N,N-dimethylformamide (DMF) influences the sex ratio and GSI, and is therefore unsuitable as a solvent for steroids to be added to the aquarium water for examination of their effects on gonadal sex differentiation. Triton X-100 has no such effect, and is used as the steroid solvent in the present experiments. Progesterone (300 microgram/l) administered for 4 weeks from hatching, or from D 43, significantly affects the sex ratio in favour of females. Methyltestosterone given from hatching results in sterilization of the gonads, especially when the treatment is carried out for 8 weeks, or when a relatively high dose (300 microgram/l) is used for 4 weeks. When given from D 43 methyltestosterone has a masculinizing effect. It is concluded that progesterone and androgen(s) are important in inducing the onset of ovarian and testis development, respectively.

Analysis of filament population in different stages of fish and amphibian myogenesis

In order to determine the participation of different types of filaments in particular phases of myogenic cell differentiation, analysis of filament population was done in embryonic somite cells of the trout (S. trutta) and in the cells of developing limb of the salamander larvae (S. salamandra L.). The following types of myogenic units were selected for the observation: undifferentiated mesenchymal cells (presumptive myoblasts), myoblasts prior to and post fusion and myotubules. Basing on morphological features four types of filaments were encountered: skein (4 nm), actin (8 nm), intermediate (12...14 nm) and myosin (14, 17, 21, 25 nm) filaments. Within the myosin filament population three different classes of filaments differing significantly from one another in their thickness (p less than 0.01) were found. In fish myogenic cells we have found myosin filaments of a thickness 17, 21, 25 nm, whereas in amphibian's cells, myosin filaments measured in thickness 14, 17, 21 nm respectively. The observed quantitative differences in the composition of myosin filament population might reflect their maturation process during sarcomere formation. As the process of differentiation of contractile units - sarcomeres and microfibrils develops, a distinctive quantitative predominance of 17 nm myosin filaments in fishes and 14 nm myosin filaments in amphibians becomes established.

Rainbow trout (Salmo gairdneri) embryos: a sensitive animal model for experimental carcinogenesis

Dietary exposures have demonstrated rainbow trout to be the most sensitive experimental animal to the hepatocarcinogenicity of aflatoxin B1 (AFB1). More recently the development of an alternate exposure method has shown trout to be even more sensitive to AFB1. This method involves the single exposure of fertile rainbow trout eggs (embryos) to a 0.5 ppm aqueous solution of AFB1 for 30 minutes, rinsing the eggs in water, and allowing hatching, swim-up and the onset of feeding to proceed as usual. Resulting fish are fed a control diet for 1 year at which time approximately two-thirds of the population will have developed hepatocellular carcinoma of the liver. Variables, such as embryo age of greatest sensitivity, carcinogen concentration, and length of exposure, have been defined for AFB1 exposures. Sensitivity to AFB1 increased with increasing age of the embryo, the model system showed a dose-response to increasing carcinogen concentrations, and one-half hour exposures appeared to be optimum for AFB1. Experiments with other carcinogens have shown the embryo model system to be sensitive to the hepatocarcinogenicity of AFB1 metabolites (aflatoxicol, aflatoxin M1, and aflatoxin G1), sterigmatocystin, versicolorin A, dimethylnitrosamine, and N-methyl-N'-nitro-N-nitrosoguanidine. The latter compound also initiated nephroblastomas of the kidneys. The results demonstrate the potential for the trout embryo to be developed into a convenient, economical, and sensitive whole animal model system for experimental carcinogenesis.

Thermal induction of diploid gynogenesis and triploidy in the eggs of the rainbow trout (Salmo gairdneri Richardson)

Sporadic diploid gynogenetic fry resulted from fertilization with gamma-irradiated sperm. Their frequency increased appreciably when thermal shock treatments, beginning during the first hour of development (--0.4 degrees C lasting 6 hrs 45 min; 26-30 degrees C lasting 10 min), were used. When the eggs were fertilized with normal sperm, a good triploidization rate was induced by means of heat shocks (27-30 degrees C lasting 10 min). It is supposed that the retention of the second polar body caused the gynogenetic diploidy observed.

The light chain composition of embryonic myosin

1. Myosins from an adult individual and embryos of Salmo trutta L. in different stages of development were isolated. Their light chain composition was investigated by polyacrylamide gel electrophoresis using two systems: tris-glycine buffer, pH 8.6, containing 8 M urea and 100 mM sodium phosphate buffer, pH 7.0, containing 0.1% SDS. 2. Both types of myosin are composed of three light chains with mol. wt 26200 D, 18300 D, 16800 D. 3. Almost no changes in electrophoretic patterns were discovered between the separate stages of development, except for the intensity of the light chain lc3, which increased gradually during miogenesis.

Scanning electron microscope study of the developing trout pelvic fin bud

The growth of the pelvic fin bud has been studied with the SEM along with the characteristics of the pseudoapical epidermal ridge which occupies the free margin of the bud. SEM revealed fluffy protuberances in many of the epidermal cells, distinguishing the fin bud territory from adjacent areas. When the pseudoapical ridge appears, all the cells show this feature but their relative number decreases and these cells, termed the "tassel cells," are finally restricted to the base of the fin bud. This particular surface structure of the superficial cells may be unique to the fish, since it has not been heretofore reported in SEM studies of tetrapod limb bud.

On the development of the cerebellum of the trout, Salmo gairdneri. II. Early development

The early histogenesis of the cerebellum of Salmo gairdneri RICHARDSON, 1836 has been studied in fish ranging in length from about 5 to 14 mm, both with light microscopical and electron microscopical techniques. Structurally, the matrix cells correspond to those of other vertebrates. Mitoses occur predominantly at the ventricular surface, but peripheral mitoses are found as well, particularly in the period of highest mitotic activity. Mantle cell somata can be distinguished from the elongated matrix cells on the basis of their rounded shape. The neurogenetic and gliogenetic periods overlap considerably. Presumably the first mantle cells are all neuroblasts: as soon as the mantle layer starts to form, axonal profiles are found. In a slightly later stage glial differentiation is manifest in the radial processes contacting the meningeal surface. In young stages a distinction between neuroblasts and glioblasts can only be made on the basis of the structure of their processes. Processes of glioblasts can be distinguished from axons and dendrites by their paucity of microtubules. Dendrites, appearing in late-embryonic stages, contain the same organelles as axons, but in larger amounts. The first differentiation of mantle cell somata is an increase of rough endoplasmic reticulum, and that to a lesser degree in glioblasts than in neuroblasts. Neuronal nuclei are rounded and more electronlucent than those of mantle cells. Apart from zonulae adhaerentes between the internal processes of matrix cells, puncta adhaerentia occur frequently in the cerebellar anlage. However, they rarely occur on young neuron;. The possible significance of these junctions is discussed. The present study indicates that growth cones and filopodia are characteristic of most and probably of all types of cells in the early developing cerebellum. Growth cones contain much vesicular and tubular endoplasmic reticulum and in filopodia a fine filamentous network is present. In the somata of mantle cells growth areas were found, i.e. areas under the cell membrane with a similar content as growth cones. It is suggested that these areas anticipate the outgrowth of a new process.

On the development of the cerebellum of the trout, Salmo gairdneri. I. Patterns of cell migration

Patterns of cell migration in the cerebellum of Salmo gairneri RICHARDSON, 1836 were studied in fish ranging in length from 4.5 to 230 mm. Sagittal and transverse series were stained with haematoxylin-eosin or according to Nissl or Golgi. The cerebellum of the trout comprises three main parts, i.e. the massive corpus cerebelli, the folded valvula cerebelli and the transversely oriented lobus vestibulolateralis. The early cerebellar anlage is a simple plate, which is delimited from the tectum mesencephali by the fissura rhombo-mesencephalica. The histogenesis may be divided into three phases. During the first phase the matrix layer produces the mantle layer. During the second phase the three typical cerebellar layers are formed. The third phase is characterized by growth. As regards the first phase, the mantle layer develops throughout almost the entire extent of the cerebellar anlage. Only in a narrow paramedian strip (matrix zone M) this layer does fail to appear. In regions where the mantle layer is formed, the matrix no longer occupies the whole width of the wall and is termed the ventricular matrix. The largest part of the ventricular matrix is gradually exhausted. However, in some places this matrix persists as a layer of proliferating cells. This holds for the matrices of the caudal border of the cerebellum; matrix zone L, surrounding the lateral recesses of the fourth ventricle, and matrix zone P, connecting the matrix zones L. The mantle layer produced in the first phase of histogensis mainly develops into the ganglionic layer. The second phase of histogenesis is characterized by the formation of a secondary matrix. Newly produced cells of the matrix zones M, L and P migrate away from their sites of origin towards the regions where a mantle layer prevsiously has been formed. The majority of these cells develops into granule cells. Migration of the cells produced in the first phase of histogenesis occurs in the radial direction. Because of the curvature of the cerebellum this direction changes with respect to the main longitudinal axis of the brain from region to region. The migration paths of granule cells show variable directions, namely (a) tangential followed by radial, for granule cells in the corpus cerebelli and in the medial parts of the valvula cerebelli and the lobus vestibulolaterialis, (b) tangential, for granule cells in the lateral parts of the valvula and (c) radial, for granule cells in the lateral parts of the lobus vestibulolateralis. The analysis of these migration patterns elucidates both the histogenesis and the morphogenesis of the cerebellum of the trout.

Myogenesis and contraction in the early embryonic heart of the rainbow trout. An electron microscopic study

Myogenesis in the embryonic heart of the rainbow trout, Salmo gairdneri (Rich.), was investigated electron microscopically from the 29th to the 41st somite stage. Thick and thin myofilaments are formed simultaneously as well as precursors of Z-lines, to which the thin filaments are attached. The genesis of filaments takes place in the region around the intracellular yolk droplets. The first myofibrils appear by the 33rd somite stage, probably formed by a mechanism of self-assembly in which the binding sites of actin and myosin participate. A- and I-bands do not develop before the 38th osmite stage. The contraction already begins during the 33rd somite stage in the middle of the tubular heart. Gradually, the peristaltic waves spread increasingly to other parts of the heart. In the 41st somite stage the entire heart is contractile and all myocytes contain myofibrils.

Initiation of the actinotrichial development in the early fin bud of the fish, Salmo

Ultrastructural analysis of initial development of actinotrichia, the skeleton anlage of the pelvic fin buds, was performed on the rainbow trout, Salmo gairdneri. It shows that the first actinotrichial rudiments appear in the subepidermal space of the pseudoapical cap. No mesenchymal cell bodies or their filopods are present. Hyaloplasmic protrusions of the basal epidermal cells are seen in the subepidermal space, limited by a dermoepidermal boundary reduced to a discontinuous thin adepidermal lamina without a collagenous layer. These morphological data suggest that the epidermal pseudoapical cap probably initiates the development of actinotrichia. Later, mesenchymal cells invade the subepidermal space and are probably involved in the further growth of actinotrichia.

[Histochemical localization of lactate dehydrogenase in the trout embryo (Salmo irideus, Gibb) during early organogenesis of the cord and the neural tube]

The histochemical study of the LDH in the Trout embryo during the early organogenesis shows a specific localization in notochord cells, in mesodermic cells of the terminal knob and in some prosencephalic neuroblasts. The role of the LDH in the metabolism of NAD as well as in the energetic metabolism of embryonic cells is discussed.