Influence of the photoperiod on growth rate and insulin-like growth factor-I gene expression in Nile tilapia Oreochromis niloticus

The crosstalk between photoperiod and early mild stress on juvenile oscar (Astronotus ocellatus) after acute stress

Early mild stress (EMS) is like preparedness and might help fish deal with stress appropriately. This study investigated how EMS and photoperiod changes can impact growth, haematology, blood biochemistry, immunological response, antioxidant system, liver enzymes, and stress response of oscar (Astronotus ocellatus; 7.29 ± 0.96 g) before and after acute confinement stress (AC stress). Ten experimental treatments included five different photoperiods 8L16D (08:16 light to dark), 12L12D (12:12 light to dark), 16L8D (16:08 light to dark), 20L4D (20:04 light to dark), and 24L0D (24:00 light to dark), and these five photoperiod schedules were conducted in an EMS condition. After 9 weeks, no significant differences were found in growth parameters, survival rate, and body composition. At the end of the experiment and after AC stress, fish farmed in 24 light hours had the lowest haematocrit, white blood cells, total protein, blood performance, lysozyme, immunoglobulin M, complement C3, superoxide dismutase, and catalase. Fish that experienced EMS had significantly higher survival rates than those farmed in normal conditions (80.67% vs 61.33%). In conclusion, considering all measured parameters, 8-h light can be suggested as an optimum photoperiod for this fish species. Under 24L0D (no EMS) conditions, there were many negative effects apparent. In addition, a positive effect of EMS was evident in terms of survival after AC stress. AC stress decreased some health parameters under 24-h light treatment, while these results were not observed in EMS-exposed fish. Therefore, the EMS schedule can be a useful tool in preventing the negative effects of stress.

Feeding and locomotor rhythm of the ornamental cichlid fish Amatitlania sp. in different social groups

The aim of this study was to evaluate the feeding activity and the rhythm of daily locomotor activity of the convict cichlid (Amatitlania sp.) kept in different social groups under a self-feeding system. A total of 120 animals was distributed among six repetitions of four social groups, as follows: group 1 with one male and one female per tank; group 2 with three males and three females per tank; group 3 with six males per tank; and group 4 with six females per tank. Feeding activity (FA) and locomotor activity (LA) were evaluated using photoelectric presence-sensors connected to automatic feeders. The fish were fed a commercial extruded diet (46% crude protein and 3600 kcal kg^-1 of digestible energy). Animal growth was evaluated for all groups. After 30 days of experimentation, the fish stabilized their demands by adjusting their consumption. Amatitlania sp. showed predominantly diurnal FA and LA. All groups showed a peak of activity when the light was turned on and when it was turned off. In summary, FA and LA of Amatitlania sp. are predominantly diurnal and independent of social group. Pairs and groups of males and females together consume less food in relation to groups of one sex or the other due to reproductive behaviour. On the other hand, groups of only males or females consume more food because they lack reproductive stimuli and thus prioritize growth. These results may support good feeding management practices for this ornamental cichlid. Studies relating feeding behaviour with different social groups are of great importance for determining effective feeding strategies for this species in captivity. Thus, such a study assists in a more efficient production of Amatitlania sp.

Blood biomarkers as diagnostic tools: An overview of climate-driven stress responses in fish

Global climate change due to anthropogenic activities affects the dynamics of aquatic communities by altering the adaptive capacities of their inhabitants. Analysis of blood provides valuable insights in the form of a comprehensive representation of the physiological and functional status of fish under various environmental and treatment conditions. This review synthesizes currently available information about blood biomarkers used in climate change induced stress responses in fish. Alterations in informative blood-based indicators are used to monitor the physiological fitness of individual fishes or entire populations. Specific characteristics of fish blood, such as serum and plasma metabolites, cell composition, cellular abnormalities, cellular and antioxidant enzymes necessitate adapted protocols, as well as careful attention to experimental designs and meticulous interpretation of patterns of data. Moreover, the sampling technique, transportation, type of culture system, acclimation procedure, and water quality must all be considered for valid interpretation of hemato-biochemical parameters. Besides, blood collection, handling, and storage time of blood samples can all have significant impacts on the results of a hematological analysis, so it is optimal to perform hemato-biochemical evaluations immediately after blood collection because long-term storage can alter the results of the analyses, at least in part as a result of storage-related degenerative changes that may occur. However, the scarcity of high-throughput sophisticated approaches makes fish blood examination studies promising for climate-driven stress responses in fish.

Tris(1,3-dichloro-2-propyl)phosphate Reduces Growth Hormone Expression via Binding to Growth Hormone Releasing Hormone Receptors and Inhibits the Growth of Crucian Carp

Tris(1,3-dichloro-2-propyl)phosphate (TDCIPP) has commonly been used as an additive flame retardant and frequently detected in the aquatic environment and in biological samples worldwide. Recently, it was found that exposure to TDCIPP inhibited the growth of zebrafish, but the relevant molecular mechanisms remained unclear. In this study, 5 day-old crucian carp (Carassius auratus) larvae were treated with 0.5, 5, or 50 μg/L TDCIPP for 90 days; the effect on growth was evaluated; and related molecular mechanisms were explored. Results demonstrated that 5 or 50 μg/L TDCIPP treatment significantly inhibited the growth of crucian carp and downregulated the expression of growth hormones (ghs), growth hormone receptor (ghr), and insulin-like growth factor 1 (igf1). Molecular docking, dual-luciferase reporter gene assay, and in vitro experiments demonstrated that TDCIPP could bind to the growth hormone releasing hormone receptor protein of crucian carp and disturb the stimulation of growth hormone releasing hormone to the expression of ghs, resulting in the decrease of the mRNA level of gh1 and gh2 in pituitary cells. Our findings provide new perceptions into the molecular mechanisms of developmental toxicity of TDCIPP in fish.

Photoperiodic effects on somatic growth and gonadal maturation in Mickey Mouse platy, Xiphophorus maculatus (Gunther, 1866)

Photoperiod is important in initiation or suppression of reproductive timing and gonadal maturation which varies with species. The aim of the present study was to investigate the effect of two photoperiodic manipulating regimes, i.e., long (18L:6D) and short (10L:14D) photoperiods for a period of 60 days on somatic growth and gonadal maturation of a live-bearer ornamental fish, Mickey Mouse platy (Xiphophorus maculatus). The control fish were further kept under the laboratory environmental condition. The results showed a significant increase in weight gain, specific growth rate, and gonadosomatic index in fish under long photoperiod than those exposed to short photoperiod and control condition (P < 0.05). A condition factor showed significant variations between long photoperiod and control groups. Furthermore, a long photoperiod also induced a significant increase in the number of fish with mature embryo and middle-eyed embryo in the ovary. Similarly, histological analysis of testes of males showed an increase in the number of mature spermatid and spermatozoa under long photoperiod when compared to those of control and short photoperiod ones. Thus, it can be concluded that long-day photoperiodic manipulation may be applied for healthy growth and early gonadal maturation of live-bearer ornamental fishes.

Nonadditive and allele-specific expression of insulin-like growth factor 1 in Nile tilapia (Oreochromis niloticus, ♀) × blue tilapia (O. aureus, ♂) hybrids

Hybrid Nile tilapia (Oreochromis niloticus, ♀) × blue tilapia (O. aureus, ♂) is a widely cultured tilapia variety due to its growth vigor compared to the parent species. As a peptide hormone, insulin-like growth factor 1 (IGF-1) plays a critical role in regulating somatic growth. The present study focuses on the expression characteristics of IGF-1 in hybrid tilapia. The cloned complete open reading frame of IGF-1 in hybrid tilapia is 549 bp in length, encoding a protein of 182 amino acids. The deduced protein is highly similar to that of Nile tilapia and blue tilapia. IGF-1 was found to be primarily expressed in the liver and muscle in the hybrid; lower expression levels were found in other tissues such as the intestine, spleen, and head-kidney. Increased mRNA expression was observed in the liver and muscle of the hybrid compared to Nile tilapia and blue tilapia, indicating a nonadditive expression pattern in the hybrid. An IGF-1 SNP site (397 site: C in Nile tilapia, G in blue tilapia) for differentiating the Nile tilapia or blue tilapia subgenome in hybrids was identified. Pyrosequencing analysis of the liver transcriptome indicated that most of the hybrids (9 of 10 individuals) predominantly expressed the G allele, demonstrating bias of the blue tilapia subgenome. The present study provides novel data indicating, for the first time, overall gene expression of IGF-1 and allele-specific expression in hybrid tilapia.

Compensatory response of fathead minnow larvae following a pulsed in-situ exposure to a seasonal agricultural runoff event

Agriculturally-dominated waterways such as those found throughout the Midwestern United States often experience seasonal pulses of agrichemical contaminants which pose a potential hazard to aquatic organisms at varying life stages. The objective of this study was to characterize the developmental plasticity of fathead minnow larvae in a natural environment subject to a seasonal episodic perturbation in the form of a complex mixture of agricultural stressors. Fathead minnow larvae were maintained at the Elkhorn River Research Station for a 28-d in situ exposure to an agrichemical pulse event. Minnow larvae were sampled after 14 and 28days to characterize developmental plasticity through growth measures and relative gene expression. Concentrations of agrichemical contaminants measured in water using polar organic chemical integrative samplers and composite sediment samples throughout the 28-d exposure were quantified using gas chromatography-mass spectrometry. Elevated concentrations of acetochlor, atrazine, and metolachlor were indicative of inputs from agricultural sources and were associated with reductions in body mass, condition factor, and androgenic gene expression in river exposed fathead minnow larvae. However, following a 14-d in situ depuration during the post-pulse period, river exposed larvae overcompensated in previously suppressed biological endpoints. These results indicate that fathead minnow larvae are capable of compensatory responses following episodic exposure to agrichemical stressors.

Fotoperíodo sobre parâmetros fisiológicos relacionados ao estresse em alevinos de tilápia-do-nilo

Com este trabalho objetivou-se avaliar a influência de diferentes fotoperíodos sobre parâmetros fisiológicos relacionados ao estresse em alevinos de tilápia-do-nilo (Oreochromis niloticus). Foi utilizado um delineamento inteiramente casualizado, com cinco tratamentos (0L; 6L; 12L; 18L; 24L) e quatro repetições, sendo o aquário a unidade experimental. Cento e sessenta alevinos de tilápia, 3,21±0,05g e 4,35±0,07cm, foram distribuídos em 20 aquários de 20 litros, em sistema de recirculação com temperatura controlada em 27oC e densidade de oito peixes por aquário. Por um período de 75 dias, a alimentação foi realizada duas vezes ao dia com ração extrusada contendo 40% de proteína bruta. Ao final do período experimental, os dados de crescimento, sobrevivência, cortisol, glicose e hematócrito foram submetidos à análise de variância e, posteriormente, em caso de significância (P<0,05), foi realizado um teste Tukey a 5% para comparação das médias. A manipulação do fotoperíodo demonstra não alterar a homeostase dos alevinos, uma vez que não há diferença sobre a sobrevivência, glicose sanguínea, hematócrito e cortisol plasmático (P>0,05).

Elevated expressions of GH/IGF axis genes in triploid crucian carp

Growth hormone (GH), growth hormone receptor (GHR) and insulin-like growth factor 1 (IGF-1) are pivotal signaling factors of the GH/IGF axis, which plays a crucial role in regulating growth in vertebrates. In this study, GH, GHR and IGF-1 cDNAs were cloned from triploid and tetraploid crucian carp. In addition, mRNA expression levels were characterized in diploid red crucian carp, triploids and tetraploids. Reverse transcriptase PCR indicated that GH genes were only expressed in the pituitary, while GHR and IGF-1 were widely expressed in all tested tissues. Real-time PCR study of different seasonal profiles showed that triploids had significantly higher expression of the studied genes during both the prespawning and the spawning season. Although different temperatures (22, 26 and 30°C) showed no significant effects on GH, GHR and IGF-1 mRNA expression in either diploids or triploids, triploids had higher expression levels than diploids at each temperature. After 1 week of fasting, the expression of all studied genes was reduced in both diploids and triploids, while the expressions levels were higher in triploids than in diploids. These results suggest that the elevated expression of GH/IGF axis genes in triploids plays a crucial role in the faster growth rate of triploids.

Perspectives on concordant and discordant relations between insulin-like growth factor 1 (IGF1) and growth in fishes

Many physiological processes are modulated by the endocrine system, including growth. Insulin-like growth factor 1 is one of the primary hormones involved in growth regulation in vertebrates, including fishes. Current work on IGF1 in fishes is driven both by a desire to better understand mechanisms of growth as well as to develop a reliable index of growth rate. A review of studies relating IGF1 to growth broadly reveals positive and significant relations between IGF1 and growth; however, relations found in individual studies range from no correlation to highly significant correlations. Potential sources for this variation include both biological and methodological issues and range from differences in how growth is defined (changes in length or weight), the duration of growth assessed (weeks to months) and how growth is calculated (total change, rate, percent change); yet, these methodological concerns cannot account for all the variation found. A further review of the literature reveals a number of physiological conditions and environmental factors that might influence IGF1 level and the subsequent relation of that IGF1 level to growth rate. The term concordance is introduced to categorize factors that influence IGF1 and growth in a similar fashion, such that positive and significant relations between IGF1 and growth are maintained even though the factor stimulates changes in IGF1 level. Conversely, the term discordance is introduced to categorize factors that stimulate changes in the relations between IGF1 and growth, such that IGF1 is not an efficacious index of growth for both pre and post-stimulus fish combined. IGF1 and growth relations generally remain concordant after changes in nutrition (consumption rate or diet). Differences in IGF1 level of juvenile, maturing male and maturing female fish are common and IGF1-growth relations appear discordant between these groups. Acute changes in temperature and salinity induce discordant relations between IGF1 and growth but acclimation to persistent differences in environmental condition generally result in concordant relations. Overall, by discriminating between fish of differing physiological status and discerning and categorizing differences among environments one may effectively use IGF1 as a growth index for fishes.