Climate change affects marine fishes through the oxygen limitation of thermal tolerance

A cause-and-effect understanding of climate influences on ecosystems requires evaluation of thermal limits of member species and of their ability to cope with changing temperatures. Laboratory data available for marine fish and invertebrates from various climatic regions led to the hypothesis that, as a unifying principle, a mismatch between the demand for oxygen and the capacity of oxygen supply to tissues is the first mechanism to restrict whole-animal tolerance to thermal extremes. We show in the eelpout, Zoarces viviparus, a bioindicator fish species for environmental monitoring from North and Baltic Seas (Helcom), that thermally limited oxygen delivery closely matches environmental temperatures beyond which growth performance and abundance decrease. Decrements in aerobic performance in warming seas will thus be the first process to cause extinction or relocation to cooler waters.

Local Replenishment of Coral Reef Fish Populations in a Marine Reserve

The scale of larval dispersal of marine organisms is important for the design of networks of marine protected areas. We examined the fate of coral reef fish larvae produced at a small island reserve, using a mass-marking method based on maternal transmission of stable isotopes to offspring. Approximately 60% of settled juveniles were spawned at the island, for species with both short (<2 weeks) and long (>1 month) pelagic larval durations. If natal homing of larvae is a common life-history strategy, the appropriate spatial scales for the management and conservation of coral reefs are likely to be much smaller than previously assumed.

Genetic evidence for local retention of pelagic larvae in a Caribbean reef fish

The pelagic larvae of many marine organisms can potentially disperse across hundreds of kilometers, but whether oceanographic or behavioral mechanisms can constrain dispersal over periods sufficient for the evolution of genetic differentiation remains unclear. Here, we concurrently examine larval duration and genetic population differentiation in a cleaner goby, Elacatinus evelynae, a member of the most species-rich genus of Caribbean reef fishes. Despite evidence for extended pelagic duration (21 days), populations of E. evelynae show strong genetic differentiation: among color forms (1.36 to 3.04% divergent at mitochondrial cytochrome b) and among island populations within color forms (Phi(ST) up to 70%). These results suggest that marine populations can remain demographically closed for thousands of generations despite extended larval duration, and that recognition cues such as color may promote speciation when geographic barriers are transient or weak.

Twenty years of invasion: a review of round goby Neogobius melanostomus biology, spread and ecological implications

The round goby Neogobius melanostomus is one of the most wide-ranging invasive fish on earth, with substantial introduced populations within the Laurentian Great Lakes watershed, the Baltic Sea and several major European rivers. Rapid expansion and deleterious ecosystem effects have motivated extensive research on this species; here this research is synthesized. Maps of the global distribution are provided and the invasion history of N. melanostomus, which spread more rapidly at first in North America, but has undergone substantial expansion over the past decade in the Baltic Sea, is summarized. Meta-analyses comparing their size at age, diet, competitors and predators in North American and European ecosystems are provided. Size at age is region specific, with saline habitats typically supporting larger and faster growing individuals than fresh water. Neogobius melanostomus prey differs substantially between regions, demonstrating a capacity to adapt to locally abundant food sources. Neogobius melanostomus comprise at least 50% of the diet of eight taxa in at least one site or life stage; in total, 16 predator taxa are documented from the Laurentian Great Lakes v. five from Eurasia. Invasive N. melanostomus are the only common forage fish to heavily exploit mussels in the Laurentian Great Lakes and the Baltic Sea, facilitating the transfer of energy from mussels to higher trophic levels in both systems. Neogobius melanostomus morphology, life history, reproduction, habitat preferences, environmental tolerances, parasites, environmental effects, sampling strategies and management are also discussed. Neogobius melanostomus inhabit a wide range of temperate freshwater and brackish-water ecosystems and will probably continue to spread via ballast water, accidental bait release and natural dispersal worldwide. Climate change will probably enhance N. melanostomus expansion by elevating water temperatures closer to its energetic optimum of 26° C. Future research needs are presented; most pressing are evaluating the economic effects of N. melanostomus invasion, determining long-term population level effects of egg predation on game-fish recruitment and comparing several variables (density, ecological effects morphology and life history) among invaded ecosystems. This review provides a central reference as researchers continue studying N. melanostomus, often as examples for advancing basic ecology and invasion biology.

Temperature rise and microplastics interact with the toxicity of the antibiotic cefalexin to juveniles of the common goby (Pomatoschistus microps): Post-exposure predatory behaviour, acetylcholinesterase activity and lipid peroxidation

The goal of this study was to investigate the toxicity of cefalexin to Pomatoschistus microps juveniles in relation to the presence of microplastics in the water and temperature rise. After acclimatization, groups of wild juveniles were exposed for 96h to artificial salt water (control), microplastics alone (0.184mg/l), cefalexin alone (1.3-10mg/l) and in mixture with microplastics (cefalexin: 1.3-10mg/l; microplastics: 0.184mg/l) at 20 and 25°C. Effect criteria were mortality, post-exposure predatory performance (PEPP), acetylcholinesterase activity (AChE) and lipid peroxidation levels (LPO). At 20°C, concentrations of cefalexin alone≥5mg/l significantly reduced PEPP (up to 56%; 96h-EC₅₀=8.4mg/l), indicating toxicity of the antibiotic to juveniles after short-term exposure to water concentrations in the low ppm range. At 20°C, fish exposed to microplastics alone did not have significant differences in any of the parameters tested relative to the control group but tended to have an inhibition of the PEPP (23%) and AChE (21%); at 25°C, microplastics alone caused mortality (33%) and PEPP inhibition (28%). Thus, microplastics are toxic to P. microps juveniles. At 20°C, under simultaneous exposure to cefalexin and microplastics, the PEPP was significantly reduced (at cefalexin concentrations≥1.25mg/l). Moreover, at 25°C, the toxicity curves of cefalexin (PEPP based), alone and in mixture with microplastics, were significantly different (p<0.05; 96h-EC₅₀ of 3.8 and 5.2mg/l, respectively), and the integrated data analysis indicated significant interactions between the two substances for all biomarkers. Thus, the presence of microplastics in the water influenced the toxicity of cefalexin. The rise of water temperature (from 20°C to 25°C), increased the microplastics-induced mortality (from 8 to 33%), and the inhibitory effects of cefalexin on the PEPP (up to 70%). Significant differences (p<0.05) between the toxicity curves of cefalexin alone at distinct temperatures were found, with a lower 96h-EC₅₀ at 25°C (3.8mg/l) than at 20°C (8.4mg/l). Moreover, at 25°C, increases of AChE activity (14%) and LPO (72%) in fish exposed to the mixture treatment containing the highest cefalexin concentration were found, and the integrated analysis of data indicated significant interactions between cefalexin and temperature for PEPP, and among all stressors for LPO. Thus, the temperature rise increased the toxicity of microplastics and of cefalexin, alone and in mixture with microplastics, to P. microps juveniles. These findings raise concern on the long-term exposure of wild populations to complex mixtures of pollutants, likely decreasing their fitness, and highlight the need of more research on the combined effects of widely used pharmaceuticals, microplastics and temperature increase on wild species to improve environmental and human risk assessments of chemicals and their safe use under a global warming scenario.

Effects of ocean acidification on the early life history of a tropical marine fish

Little is known about how fishes and other non-calcifying marine organisms will respond to the increased levels of dissolved CO(2) and reduced sea water pH that are predicted to occur over the coming century. We reared eggs and larvae of the orange clownfish, Amphiprion percula, in sea water simulating a range of ocean acidification scenarios for the next 50-100 years (current day, 550, 750 and 1030 ppm atmospheric CO(2)). CO(2) acidification had no detectable effect on embryonic duration, egg survival and size at hatching. In contrast, CO(2) acidification tended to increase the growth rate of larvae. By the time of settlement (11 days post-hatching), larvae from some parental pairs were 15 to 18 per cent longer and 47 to 52 per cent heavier in acidified water compared with controls. Larvae from other parents were unaffected by CO(2) acidification. Elevated CO(2) and reduced pH had no effect on the maximum swimming speed of settlement-stage larvae. There was, however, a weak positive relationship between length and swimming speed. Large size is usually considered to be advantageous for larvae and newly settled juveniles. Consequently, these results suggest that levels of ocean acidification likely to be experienced in the near future might not, in isolation, significantly disadvantage the growth and performance of larvae from benthic-spawning marine fishes.

Effects of microplastic exposure on the body condition and behaviour of planktivorous reef fish (Acanthochromis polyacanthus)

The effect of a pollutant on the base of the food web can have knock-on effects for trophic structure and ecosystem functioning. In this study we assess the effect of microplastic exposure on juveniles of a planktivorous fish (Acanthochromis polyacanthus), a species that is widespread and abundant on Indo-Pacific coral reefs. Under five different plastic concentration treatments, with plastics the same size as the natural food particles (mean 2mm diameter), there was no significant effect of plastic exposure on fish growth, body condition or behaviour. The amount of plastics found in the gastro-intestinal (GI) tract was low, with a range of one to eight particles remaining in the gut of individual fish at the end of a 6-week plastic-exposure period, suggesting that these fish are able to detect and avoid ingesting microplastics in this size range. However, in a second experiment the number of plastics in the GI tract vastly increased when plastic particle size was reduced to approximately one quarter the size of the food particles, with a maximum of 2102 small (< 300μm diameter) particles present in the gut of individual fish after a 1-week plastic exposure period. Under conditions where food was replaced by plastic, there was a negative effect on the growth and body condition of the fish. These results suggest plastics could become more of a problem as they break up into smaller size classes, and that environmental changes that lead to a decrease in plankton concentrations combined with microplastic presence is likely have a greater influence on fish populations than microplastic presence alone.

Endocrine mediators of seasonal growth in gilthead sea bream (Sparus aurata): the growth hormone and somatolactin paradigm

Regulation of somatolactin (SL) and the somatotropic axis was examined year-around at three different stocking times (spring, summer, and autumn) in a Mediterranean fish, the gilthead sea bream (Sparus aurata). The overall timing of plasma growth hormone (GH) increase was similar among trials (late spring-early summer), but the range of variation year-around was different and followed changes in food intake. Total plasma insulin-like growth factor-I primarily followed changes on growth rates, and a close positive correlation between IGF-I and thermal-unit growth coefficient (TGC) was found irrespective of fish stocking time. Thus, the activation of the somatotropic axis preceded always warm growth spurts, whereas the rise of SL in concurrence with low plasma cortisol levels was found at late autumn. This up-regulation of circulating SL titres preceded the winter inhibition of feeding, and it was more severe in big fish (spring and summer stocking times) than in small fish (autumn stocking time), growing with a relative high efficiency during the cold season despite of a severe hypertriglyceridemia and a high hepatosomatic index. These new insights provide good evidence for a different timing of GH and SL increases, and it is likely that the dominant role of SL in energy homeostasis is to be a mediator of the adaptation to fasting after replenishment of body fat stores, whereas GH and IGF-I are perceived as growth-promoting signals in times of food intake and increasing temperature and day-length.

Dietary administration of the probiotic, Lactobacillus plantarum, enhanced the growth, innate immune responses, and disease resistance of the grouper Epinephelus coioides

The percent weight gain (PWG) and feed efficiency (FE) of Epinephelus coioides were calculated, and the lactobacilli and total microbiota in the posterior intestines, and non-specific immune parameters of grouper, and its susceptibility to Streptococcus sp. and an iridovirus were determined when the fish were fed diets containing Lactobacillus plantarum at 0 (control), 10(6), 10(8), or 10(10) colony-forming units (cfu) kg(-1) for 4 weeks. Results showed that grouper fed a diet containing L. plantarum at the levels of 10(6), 10(8), and 10(10) cfu kg(-1) had significantly increased PGW and FE especially at 10(8) cfu kg(-1) group which were 404.6% and 1.26, respectively. L. plantarum significantly increased in the fish posterior intestines during the L. plantarum feeding period, but decreased rapidly from the intestine within 1 week after changing to the control diet (without L. plantarum). Fish fed a diet containing L. plantarum at 10(6) and 10(8) cfu kg(-1) had significantly higher survival rates than those fed the control diet after challenge with Streptococcus sp., as well as those fed 10(8) cfu kg(-1) after challenge with an iridovirus, causing increases in the survival rates of 23.3%, 20.0%, and 36.7%, respectively, compared to the control group. The alternative complement activity (ACH(50)) level of fish fed diets containing L. plantarum after 4 weeks was significantly higher than that of fish fed the control diet, and that of the 10(8) cfu kg(-1) group was significantly higher than those of the 10(6) and 10(10) cfu kg(-1) groups, which increased by 83.4% compared to the control group. The lysozyme activity and glutathione peroxidase (GPx) activity of fish fed the L. plantarum-containing diets at 10(8) and 10(10) cfu kg(-1) significantly increased compared to those fed the 10(6) cfu kg(-1)L. plantarum diet and control diet, and had increased by 76.3% and 136.6%, and 57.1% and 113.3%, respectively, compared to those fed the control diet. The phagocytic activity (PA), phagocytic index (PI), and respiratory bursts of head kidney leucocytes of fish fed 10(6), 10(8), and 10(10) cfu kg(-1)L. plantarum diets were significantly higher than those of fish fed the control diet after 4 weeks of feeding, and increased 2.2-, 2.2-, and 2.3-fold; 1.8-, 1.8-, and 2.0-fold; and 1.4-, 1.4-, and 1.4-fold, respectively, compared to the control group. We therefore recommend dietary L. plantarum administration at 10(8) cfu kg(-1) to promote growth and enhance immunity and resistance against Streptococcus sp. and an iridovirus of E. coioides.

MOTHERS MATTER: CROWDING LEADS TO STRESSED MOTHERS AND SMALLER OFFSPRING IN MARINE FISH

Most marine populations are sustained by the entry of juveniles that have survived the larval phase, during which time most die. The number of survivors depends strongly on the quality of the eggs produced by spawning females, but it is not known how the social conditions under which breeding occurs influence the quality of larvae produced. Here I show that the density of females interacting with breeding mothers directly influences the size of larvae produced, through a stress-related mechanism. On the Great Barrier Reef of Australia, breeding pairs of a damselfish, Pomacentrus amboinensis, were isolated on habitat patches, and additional females that could not access the spawning site were added at four densities (0, 1, 3, or 6 females). Additional females increased aggressive interactions by mothers and increased the levels of the stress hormone, cortisol, in their ovaries, leading to reduced larval size. Neither egg output nor yolk size of the larvae was influenced by female density. Pairs breeding in isolation produced the largest larvae; current theory suggests that these larvae should contribute most to subsequent population replenishment events. This social mechanism may influence which females effectively contribute to the next generation and may promote resilience in patchy or isolated populations.

The threat of punishment enforces peaceful cooperation and stabilizes queues in a coral-reef fish

Social queues, in which subordinates wait for their turn to inherit dominant breeding status, are a familiar feature of many animal societies. However, little is known about the mechanisms stabilizing social queues given the inevitable conflict over rank between group members. Here, we report the role of punishment and cooperation in promoting the stability of size-based queues in a coral-dwelling goby, Paragobiodon xanthosomus (Gobiidae). Quantitative analysis of the size-structure of queues revealed that individuals of adjacent rank differ in size by a specific size ratio, and comparisons of individual growth rates within queues demonstrated that specific size ratios are maintained over time via the regulation of subordinate growth rates. Furthermore, contest experiments demonstrated that the specific size ratio represents a threshold above which the subordinates become a threat to their immediate dominant, and as a result, dominants evict subordinates that exceed this size ratio from the group. We propose that threshold size ratios are maintained by subordinates as a form of peaceful cooperation whereby they avoid inflicting costs on dominants, and that such cooperation arises in response to the threat of punishment in the form of eviction by dominants. Societal stability is therefore achieved through the effects of punishment and cooperation acting in concert to promote the resolution of conflict over rank between group members.

Fish growth rates modulate mercury concentrations in walleye (Sander vitreus) from eastern Canadian lakes

The majority of the studies attempting to explain fluctuations of mercury (Hg) concentrations in fish from diverse aquatic ecosystems have invoked the influence of physico-chemical or environmental factors but has eluded that of strictly biological factors. In this study, we examine the relationship between Hg concentrations in walleye (Sander vitreus) muscles and their growth rates in 12 natural lakes located in four different regions of Quebec (Saint Lawrence Valley, Chibougamau, Abitibi, and Temiscamingue). Hg concentrations vs. total lengths of fish were described using polynomial regressions while growth rates (lengths vs. ages) were estimated using the Von Bertalanffy growth model. No significant differences for fish growth rates or for the relation fish length vs. fish Hg concentrations were found among the different regions except for the three lakes of the Abitibi region where fish grow more slowly than in the other lakes. Major differences were observed for growth rates or lengths vs. Hg concentrations in the different walleye populations of each lake. For example, a 5-year-old walleye with the lowest growth rate will reach an average length of 325 mm, whereas the average length for a walleye with the highest growth rate is 550 mm. Predicted values of Hg concentrations in walleyes of a standardized length of 350 mm ranged from 0.17 to 0.79 ppm. When all walleye populations of the 12 lakes were considered together, growth rates were significantly correlated to Hg concentrations (r=0.9244; P<0.001). This suggests that faster-growing walleyes will have lower Hg concentrations than slower-growing fish at a given length. The growth rate as a biological factor dominates all other environmental factors to account for differences in Hg concentrations in walleye populations studied. Nevertheless, the minor differences in Hg concentrations observed in walleye taken from two separate arms of a single lake in the Temiscamingue region, Lake Desjardins, could not be explained by fish growth rates only and thus should be related to other environmental parameters.

Functionally diverse reef-fish communities ameliorate coral disease

Coral reefs, the most diverse of marine ecosystems, currently experience unprecedented levels of degradation. Diseases are now recognized as a major cause of mortality in reef-forming corals and are complicit in phase shifts of reef ecosystems to algal-dominated states worldwide. Even so, factors contributing to disease occurrence, spread, and impact remain poorly understood. Ecosystem resilience has been linked to the conservation of functional diversity, whereas overfishing reduces functional diversity through cascading, top-down effects. Hence, we tested the hypothesis that reefs with trophically diverse reef fish communities have less coral disease than overfished reefs. We surveyed reefs across the central Philippines, including well-managed marine protected areas (MPAs), and found that disease prevalence was significantly negatively correlated with fish taxonomic diversity. Further, MPAs had significantly higher fish diversity and less disease than unprotected areas. We subsequently investigated potential links between coral disease and the trophic components of fish diversity, finding that only the density of coral-feeding chaetodontid butterflyfishes, seldom targeted by fishers, was positively associated with disease prevalence. These previously uncharacterized results are supported by a second large-scale dataset from the Great Barrier Reef. We hypothesize that members of the charismatic reef-fish family Chaetodontidae are major vectors of coral disease by virtue of their trophic specialization on hard corals and their ecological release in overfished areas, particularly outside MPAs.

Inhibition of Vibrio biofilm formation by a marine actinomycete strain A66

China remains by far the largest aquaculture producer in the world. However, biofilms formed by pathogenic Vibrio strains pose serious problems to marine aquaculture. To provide a strategy for biofilm prevention, control, and eradication, extracts from 88 marine actinomycetes were screened. Thirty-five inhibited the biofilm formation of Vibrio harveyi, Vibrio vulnificus, and Vibrio anguillarum at a concentration of 2.5% (v/v). Thirty-three of the actinomycete extracts dispersed the mature biofilm. Six extracts inhibited the quorum-sensing system of V. harveyi by attenuating the signal molecules N-acylated homoserine lactones' activity. Strain A66, which was identified as Streptomyces albus, both attenuated the biofilms and inhibited their quorum-sensing system. It is suggested that strain A66 is a promising candidate to be used in future marine aquaculture.

Selective predation for low body condition at the larval-juvenile transition of a coral reef fish

Mortality is known to be high during the transition from larval to juvenile life stages in organisms that have complex life histories. We are only just beginning to understand the processes that influence which individuals survive this period of high mortality, and which traits may be beneficial. Here we document a field experiment that examines the selectivity of predation immediately following settlement to the juvenile population in a common tropical fish, Pomacentrus amboinensis (Pomacentridae). Newly metamorphosed fish were tagged and randomly placed onto replicated patches of natural habitat cleared of resident fishes. After exposure to transient predators for 3 days, fish were recollected and the attributes of survivors from patch reefs that sustained high mortality were compared to individuals from patch reefs that experienced low mortality. Seven characteristics of individuals, which were indicative of previous and present body condition, were compared between groups. Predation was found to be selective for fish that grew slowly in the latter third of their larval phase, were low in total lipids, and had a high standardized weight (Fulton's K). Traits developed in the larval phase can strongly influence the survival of individuals over this critical transition period for organisms with complex life cycles.

Dietary administration of the probiotic, Bacillus subtilis E20, enhances the growth, innate immune responses, and disease resistance of the grouper, Epinephelus coioides

The aim of this study was to improve the growth performance, immune response and disease resistance of grouper, Epinephelus coioides by using probiotic, Bacillus subtilis E20. The percent weight gain (PWG) and feeding efficiency (FE) of grouper administered the probiotic B. subtilis E20 were calculated. Survival of B. subtilis E20 in the posterior intestines was determined using a specific primer pair of BPHYF/BPHYR, as were the non-specific immune parameters of grouper, and its susceptibility to Streptococcus sp. and an iridovirus when fish were fed diets containing B. subtilis at 0 (control), 10(4), 10(6), and 10(8) colony-forming units (cfu) g(-1) up to 28 days. Results showed that grouper fed a diet containing B. subtilis at the levels of 10(4), 10(6), and 10(8) cfu g(-1) had significantly increased PGW (203.0%, 229.6%, and 238.0%) and FE (1.15, 1.20, and 1.22) compared to control (191.8% and 1.0), and these directly increased in a dose-dependent manner with B. subtilis concentrations. B. subtilis was able to survive in the fish's posterior intestines during the feeding period. The survival rate increased in grouper challenged with Streptococcus sp. or an iridovirus when the fish were fed B. subtilis at 10(4), 10(6), and 10(8) cfu g(-1) for 14 and 28 days, and it was higher at 28 days than at 14 days. After 28 days of feeding, the relative survival percentages of fish challenged with Streptococcus sp. and an iridovirus were 22.8, 40.9 and 45.5, and 21.7, 30.4, and 52.2, respectively. The phagocytic activity, respiratory bursts, and superoxide dismutase (SOD) level of head kidney leucocytes as well as serum lysozyme activity and serum alternative complement activity (ACH(50)) of fish fed diets containing B. subtilis at 10(4), 10(6) and 10(8) cfu g(-1) were significantly and dose-dependently higher than those of fish fed the control diet for 28 days. We therefore recommend dietary B. subtilis E20 administration of 10(4) - 10(8) cfu g(-1) to E. coioides to promote growth, and enhance immunity and resistance against Streptococcus sp. and an iridovirus. The best results were seen in the 10(8) cfu g(-1) group fed for 28 days.

Acute effects of Benzo[a]pyrene, anthracene and a fuel oil on biomarkers of the common goby Pomatoschistus microps (Teleostei, Gobiidae)

The objective of this study was to investigate the effects of two different PAHs and a complex petrochemical mixture on the common goby, Pomatoschistus microps, using selected biomarkers as effect criteria. Benzo[a]pyrene (BaP) and anthracene were used as reference substances, while the water accommodated fraction of #4 fuel-oil (#4 WAF) was used as an example of a petrochemical mixture. P. microps was used since it is both a suitable bioindicator and a good test organism. Groups of fish were exposed to different concentrations of each of the test substances for 96 h and the activities of several enzymes commonly used as biomarkers were determined at the end of the bioassays. All the substances inhibited P. microps acetylcholinesterase (AChE) indicating that they have at least one mechanism of neurotoxicity in common: the disruption of cholinergic transmission by inhibition of AChE. An induction of lactate dehydrogenase (LDH) activity was found in fish exposed to BaP or to anthracene, suggesting an increase of the anaerobic pathway of energy production. On the contrary, inhibition of LDH was found in fish exposed to #4 WAF, suggesting a distinct effect of the mixture. An induction of P. microps glutathione S-transferase (GST) activity was found in fish exposed to BaP or to #4 WAF, while an inhibition was observed after exposure to anthracene. These results suggest that GST is involved in the detoxification of BaP and #4 WAF, but not of anthracene. All the substances increased catalase activity and isolated PAHs also increased superoxide dismutase, glutathione reductase and glutathione peroxidase activities, while #4 WAF did not cause significant alterations on these enzymes. These results suggest that all the substances may induce oxidative stress on P. microps, with BaP and anthracene apparently having more oxidative stress potential than #4 WAF.

The structure of reef fish metapopulations: modelling larval dispersal and retention patterns

An improved understanding of the dispersal patterns of marine organisms is a prerequisite for successful marine resource management. For species with dispersing larvae, regional-scale hydrodynamic models provide a means of obtaining results over relevant spatial and temporal scales. In an effort to better understand the role of the physical environment in dispersal, we simulated the transport of reef fish larvae among 321 reefs in and around the Cairns Section of the Great Barrier Reef Marine Park over a period of 20 years. Based on regional-scale hydrodynamics, our models predict the spatial and temporal frequency of significant self-recruitment of the larvae of certain species. Furthermore, the results suggest the importance of a select few local populations in ensuring the persistence of reef fish metapopulations over regional scales.

Reduction in muscle fibre number during the adaptive radiation of notothenioid fishes: a phylogenetic perspective

The fish fauna of the continental shelf of the Southern Ocean is dominated by a single sub-order of Perciformes, the Notothenioidei, which have unusually large diameter skeletal muscle fibres. We tested the hypothesis that in fast myotomal muscle a high maximum fibre diameter (FD(max)) was related to a reduction in the number of muscle fibres present at the end of the recruitment phase of growth. We also hypothesized that the maximum fibre number (FN(max)) would be negatively related to body size, and that both body size and size-corrected FN(max) would show phylogenetic signal (tendency for related species to resemble each other). Finally, we estimated ancestral values for body size and FN(max). A molecular phylogeny was constructed using 12S mitochondrial rRNA sequences. A total of 16 species were studied from the Beagle Channel, Tierra del Fuego (5-11 degrees C), Shag Rocks, South Georgia (0.5-4 degrees C), and Adelaide Island, Antarctic Peninsula (-1.5 to 0.5 degrees C). The absence of muscle fibres of less than 10 micro m diameter was used as the criterion for the cessation of fibre recruitment. FD(max) increased linearly with standard length (SL), reaching 500-650 micro m in most species. Maximum body size was a highly significant predictor of species variation in FN(max), and both body size and size-corrected FN(max) showed highly significant phylogenetic signal (P<0.001). Estimates of trait values at nodes of the maximum likelihood phylogenetic tree were consistent with a progressive reduction in fibre number during part of the notothenioid radiation, perhaps serving to reduce basal energy requirements to compensate for the additional energetic costs of antifreeze production. For example, FN(max) in Chaenocephalus aceratus (12 700+/-300, mean +/- S.E.M., N=18) was only 7.7% of the value found in Eleginops maclovinus (164 000+/-4100, N=17), which reaches a similar maximum length (85 cm). Postembryonic muscle fibre recruitment in teleost fish normally involves stratified followed by mosaic hyperplasia. No evidence for this final phase of growth was found in two of the most derived families (Channichthyidae and Harpagiferidae). The divergence of the notothenioids in Antarctica after the formation of the Antarctic Polar Front and more recent dispersal north would explain the high maximum diameter and low fibre number in the derived sub-Antarctic notothenioids. These characteristics of notothenioids may well restrict their upper thermal tolerance, particularly for Champsocephalus esox and similar Channichthyids that lack respiratory pigments.

Survival against the odds: ontogenetic changes in selective pressure mediate growth-mortality trade-offs in a marine fish

For organisms with complex life cycles, variation among individuals in traits associated with survival in one life-history stage can strongly affect the performance in subsequent stages with important repercussions on population dynamics. To identify which individual attributes are the most influential in determining patterns of survival in a cohort of reef fish, we compared the characteristics of Pomacentrus amboinensis surviving early juvenile stages on the reef with those of the cohort from which they originated. Individuals were collected at hatching, the end of the planktonic phase, and two, three, four, six and eight weeks post-settlement. Information stored in the otoliths of individual fish revealed strong carry-over effects of larval condition at hatching on juvenile survival, weeks after settlement (i.e. smaller-is-better). Among the traits examined, planktonic growth history was, by far, the most influential and long-lasting trait associated with juvenile persistence in reef habitats. However, otolith increments suggested that larval growth rate may not be maintained during early juvenile life, when selective mortality swiftly reverses its direction. These changes in selective pressure may mediate growth-mortality trade-offs between predation and starvation risks during early juvenile life. Ontogenetic changes in the shape of selectivity may be a mechanism maintaining phenotypic variation in growth rate and size within a population.

Effect of waterborne copper exposure on growth, hepatic enzymatic activities and histology in Synechogobius hasta

The present study was conducted to determine growth, hepatic enzymatic activities and histology in Synechogobius hasta exposed to waterborne copper concentrations of 0 (control), 0.15 and 0.3 mg Cu/l, respectively, for 15 days, and explore whether waterborne copper exposure could induce the fatty liver syndrome for the fish species. Growth (WG and SGR) declined, but HSI increased in S. hasta with increasing waterborne copper levels (P<0.05). Waterborne copper exposure also significantly increased lipid content and reduced protein content in both whole body and liver, and increased copper accumulation in whole body and vertebrae. Copper exposure changed hepatic enzymatic activities (SOD, CAT, SDH, PK, LDH, LPL and HL) and increased hepatic lipid peroxidation level, impaired the histological structure of the gill and liver in S. hasta. Thus, our study demonstrated for the first time that waterborne Cu exposure could induce fatty liver syndrome in fish.

Developmental and tissue-regulated expression of IGF-I and IGF-II mRNAs in Sparus aurata

Recent studies have shown that homologues of the mammalian IGF-I and -II genes are also found in teleosts. We report here the cDNAs coding for IGF-I and IGF-II cloned from the gilthead seabream, Sparus aura ta. Sequence comparisons revealed that both IGFs have been well conserved among teleosts, although Sparus IGF-I is shorter bv three amino acid residues due to truncated B-and C-domains. Using the cloned cDNAs as probes, the relative expression of IGF-I and IGF-II mRNAs were assayed in different Sparus tissues. Sparus liver clearly contained the highest level of IGF-I mRNA while relatively high levels of IGF-II mRNA were found in liver, heart and gill using the ribonuclease protection assay. After GH administration the amount of IGF-I mRNA was increased by 220% in liver but no changes in IGF-II mRNA levels were detected in any tissue. We also assayed the expression of IGF-I and IGF-II in Sparus during early development. The IGF-II mRNA level was highest in larva I day after hatching and decreased thereafter. In contrast, IGF-I mRNA was detected in 1-day-old larva but there was an increase in expression in 12- and 16-day-old larva. These results demonstrated that the expression of IGF-I and IGF-II is highly regulated in teleosts and suggest that they play distinct roles during growth and development.

Arsenic-induced histopathology and synthesis of stress proteins in liver and kidney of Channa punctatus

As3+, considered effective for aquatic weed control, has been found to be harmful to several species of freshwater teleosts. Channa punctatus (Bloch) exposed for 14 days to nonlethal concentrations (1/20 LC50 and 1/10 LC50) of As2O3 were sampled on days 0, 1, 2, 7, and 14. Tissue disorientation, peliosis, and vacuolization accompanied by karyolysis, apoptosis, and necrosis of hepatocytes were significant on days 1, 2, and 7. In the kidney shrinkage of the glomerulus and increase in the Bowman's space were observed on days 1, 2, and 7. Irregularities in the renal tubule including apoptotic and necrotic cells were also common. Decreased intertubular space and enlargement of the height of the brush border cells were noteworthy. Corresponding with the histopathological lesions, dose-dependent disturbances in liver and renal functions and induction of heat shock protein 70 were significant at the early phase of arsenic treatment while metallothionein was induced at a later phase of treatment.

Interaction effects of dietary supplementation of heat-killed Lactobacillus plantarum and β-glucan on growth performance, digestibility and immune response of juvenile red sea bream, Pagrus major

Both heat-killed Lactobacillus plantarum (HK-LP) and β-glucan (BG) play important roles in growth performance, feed utilization and health status of fish. Therefore, a feeding trial was conducted to determine the interactive effects of dietary HK-LP and BG on growth performance, digestibility, oxidative status and immune response of red sea bream for 56 days. A significant interaction was found between HK-LP and BG on final body weight, total plasma protein, glucose, serum bactericidal activity (BA), total serum protein, serum alternative complement pathway (ACP) activity, protein and dry matter digestibility coefficients (P < 0.05). In addition, body weight gain, specific growth rate, feed intake, protein efficiency ratio as well as serum lysozyme activity, ACP activity and mucus secretion were significantly affected by either HK-LP or BG (P < 0.05). Further, feeding 0.025% HK-LP combined with 0.1% BG significantly increased serum peroxidase activity compared with the other groups (P < 0.05). However, protein body content, somatic parameters, total bilirubin, blood urea nitrogen, glutamyl oxaloacetic transaminase (GOT), glutamic-pyruvate transaminase (GPT), triglycerides and mucus BA were not significantly altered by supplementations (P > 0.05). Interestingly, fish fed with both HK-LP at (0.025 and 0.1%) in combination with BG at (0 and 0.1%) showed higher oxidative stress resistance. Under the experimental conditions, dietary HK-LP and BG had a significant interaction on enhancing the growth, digestibility and immune responses of red sea bream.