The effect of environmental stressors on growth in fish and its endocrine control

Modulated regulation of the stress-feeding-growth neuroendocrine cascade in Chinese sea bass (Lateolabrax maculatus) under temperature and salinity changes

Temperature and salinity are among the most important factors affecting food-intake, metabolism, and growth of aquatic animals through their neuroendocrine systems. However, how the regulation of feeding, metabolism and growth are integrated under thermo-saline interaction is still unclear. In this study, modulated transcriptomic responses to temperature and salinity changes were investigated in Chinese sea bass (Lateolabrax maculatus), the economically important fish in East Asia that can adapt to diverse thermo-saline environments. L. maculatus were acclimated at different temperatures (14 °C, 21 °C, 28 °C) and salinities (freshwater and seawater) for 30 days, and their growth rate was better at 21 °C than 14 °C/28 °C (2.76-3.22 times), with mild difference between seawater and freshwater. An interaction between temperature and salinity on L. maculatus growth was detected, and low salinity (0 ppt) may mitigate the temperature (28 °C) effect. Weighted gene co-expression network analysis for L. maculatus brain transcriptomes identified growth-related temperature-salinity responsive modules, revealing the neuroendocrine gene cascade for stress-feeding-growth functions in L. maculatus. Specifically, stress-induced heat shock proteins (hspe1 and hsp30l) may stimulate the hypothalamic-pituitary-interrenal (HPI) axis (crhb and pomc), further activate anorexic genes (cart and prlh) and growth inhibiting somatostatin (sst), which was further verified through both in vitro brain culture and individual feeding test. These results revealed modulated regulation of the stress-feeding-growth cascade in L. maculatus under thermo-saline changes, which may regulate feeding behavior and ultimately control growth. These findings may provide vital guidance for the development of fast-growing L. maculatus in diverse thermo-saline environments like seawater cages, freshwater ponds, or even alkaline waters.

Fish models to explore epigenetic determinants of hypoxia-tolerance

The occurrence of environmental hypoxia in freshwater and marine aquatic systems has increased over the last century and is predicted to further increase with climate change. As members of the largest extant vertebrate group, freshwater fishes, and to a much lesser extent marine fishes, are vulnerable to increased occurrence of hypoxia. This is important as fishes render important ecosystem services and have important cultural and economic roles. Evolutionarily successful, fishes have adapted to diverse aquatic freshwater and marine habitats with different oxygen conditions. While some fishes exhibit genetic adaptions to tolerate hypoxia and even anoxia, others are limited to oxygen-rich habitats. Recent advances in molecular epigenetics have shown that some epigenetic machinery, especially histone- and DNA demethylases, is directly dependent on oxygen and modulates important transcription-regulating epigenetic marks in the process. At the post-transcriptional level, hypoxia has been shown to affect non-coding microRNA abundance. Together, this evidence adds a new molecular epigenetic basis to study hypoxia tolerance in fishes. Here, we review the documented and predicted changes in environmental hypoxia in aquatic systems and discuss the diversity and comparative physiology of hypoxia tolerance in fishes, including molecular and physiological adaptations. We then discuss how recent mechanistic advances in environmental epigenetics can inform future work probing the role of oxygen-dependent epigenetic marks in shaping organismal hypoxia-tolerance in fishes with a focus on within- and between-species variation, acclimation, inter- and multigenerational plasticity, and multiple climate-change stressors. We conclude by describing the translational potential of this approach for conservation physiology, ecotoxicology, and aquaculture.

Study of feed intake rate as a physiological biomarker in Nile Tilapia, Oreochromis niloticus (Linnaeus 1758) under Chlorpyrifos and Cypermethrin exposure

Chlorpyrifos and cypermethrin are the two most extensively applied insecticides in agricultural areas across the world and are found to contaminate adjacent water bodies, posing risks to non-target aquatic organisms, including fish. Aquaculture is primarily concerned with the feeding and growth of fish. This study evaluated the effects of sub-lethal concentrations of chlorpyrifos and cypermethrin on the physiological biomarker 'feed intake rate' of Oreochromis niloticus through 96 h static renewal bioassays. The fish were fed a formulated diet containing 30 % crude protein at 5 % of their body weight per day. The feed intake rate calculation was based on the outcome of 6 h feeding of fish carried out in glass aquariums. Uneaten diets (leftovers) were carefully collected and dried, and the weight of the uneaten diets was subtracted from the total amount of dry feed delivered to determine the actual feed intake rate. In the present study, the actual feed intake rates in O. niloticus exposed to chlorpyrifos and cypermethrin varied from 3.06 ± 0.02 to 3.92 ± 0.02 g/100 g BW/d and from 3.32 ± 0.02 to 4.02 ± 0.01 g/100 g BW/d, respectively. Feeding rates and growth of O. niloticus decreased in all sub-lethal concentrations of both test pesticides when compared to the control. Even at a sub-lethal concentration of 5 μg/L chlorpyrifos and 0.5 μg/L cypermethrin, O. niloticus lost its appetite. It can be concluded that chlorpyrifos and cypermethrin even in low concentrations (μg/L) in aquatic media can affect the feed intake rate and growth in fish.

The potential effects of corn cob biochar on mitigating pendimethalin-induced toxicity in Nile tilapia (Oreochromis niloticus): Effects on hematological, biochemical, antioxidant-immune parameters, and histopathological alterations

This study aims to examine the restorative impact of corn cob biochar (CCB) on pendimethalin (PMD)-induced toxicity in Oreochromis niloticus. Fish were divided into four groups: the first control group without treatment, the second group (CCB) exposed to 10 g CCB/L, the third group (PDM) exposed to 0.355 mg PDM/L, and the fourth group (PDM+ CCB) receiving both 0.355 mg PDM/L and 10 g CCB/L for 30 days. PDM exposure resulted in behavioral alterations, low survival rate (73.33 %), hematological and biochemical impairments, increased oxidative stress, suppressed immunity, and histopathological damage in gill, liver, and brain tissues. Co-treatment with CCB significantly alleviated these effects, as evidenced by improved survival rate (88.88 %), hematological, biochemical, and antioxidant-immune parameters and reduced histopathological alterations. In conclusion, CCB demonstrated a promising potential to mitigate PDM-induced toxicity in O. niloticus by enhancing physiological, biochemical, and histological resilience.

Environmental toxicology of microplastic particles on fish: A review

The increase in plastic debris and its environmental impact has been a major concern for scientists. Physical destruction, chemical reactions, and microbial activity can degrade plastic waste into particles smaller than 5 mm, known as microplastics (MPs). MPs may eventually enter aquatic ecosystems through surface runoff. The accumulation of MPs in aquatic environments poses a potential threat to finfish, shellfish, and the ecological balance. This study investigated the effect of MP exposure on freshwater and marine fish. MPs could cause significant harm to fish, including physical damage, death, inflammation, oxidative stress, disruption of cell signalling and cellular biochemical processes, immune system suppression, genetic damage, and reduction in fish growth and reproduction rates. The activation of the detoxification system of fish exposed to MPs may be associated with the toxicity of MPs and chemical additives to plastic polymers. Furthermore, MPs can enhance the bioavailability of other xenobiotics, allowing these harmful substances to more easily enter and accumulate in fish. Accumulation of MPs and associated chemicals in fish can have adverse effects on the fish and humans who consume them, with these toxic substances magnifying as they move up the food chain. Changes in migration and reproduction patterns and disruptions in predator-prey relationships in fish exposed to MPs can significantly affect ecological dynamics. These interconnected changes can lead to cascading effects throughout aquatic ecosystems. Thus, implementing solutions like reducing plastic production, enhancing recycling efforts, using biodegradable materials, and improving waste management is essential to minimize plastic waste and its environmental impact.

A simple inland culture system provides insights into ascidian post-embryonic developmental physiology

Maintenance and breeding of experimental organisms are fundamental to life sciences, but both initial and running costs, and hands-on zootechnical demands can be challenging for many laboratories. Here, we first aimed to further develop a simple protocol for reliable inland culture of tunicate model species of the Ciona genus. We cultured both Ciona robusta and Ciona intestinalis in controlled experimental conditions, with a focus on dietary variables, and quantified growth and maturation parameters. From statistical analysis of these standardized datasets, we gained insights into the post-embryonic developmental physiology of Ciona and inferred an improved diet and culturing conditions for sexual maturation. We showed that body length is a critical determinant of both somatic and sexual maturation, which suggests the existence of systemic control mechanisms of resource allocation towards somatic growth or maturation and supports applying size selection as a predictor of reproductive fitness in our inland culture to keep the healthiest animals at low density in the system. In the end, we successfully established a new protocol, including size selection, to promote both sperm and egg production. Our protocol using small tanks will empower researchers to initiate inland Ciona cultures with low costs and reduced space constraints.

Using a blend of oilseed meals in the diets of Nile tilapia (Oreochromis niloticus): effects on the growth performance, feed utilization, intestinal health, growth, and metabolic-related genes

In this study, Nile tilapia were fed a blend of oilseed meals (BOM) that includes cottonseed meal (CSM), linseed meal (LSM), sesame meal (SSM), and sunflower meal (SFM) at a ratio of 1 CSM: 1 LSM: 1 SSM: 1 SFM. Six diets were formulated where the first diet included FM and SBM as protein sources and considered the positive control diet (FM). Another five FM-free diets were formulated, where SBM was substituted with BOM and included at 0, 100, 200, 300, and 400 g/kg diet. After 90 days, the FBW, WG, and PER were markedly increased while FCR decreased by FM-based diet and BOM at 0, 100, or 200 g/kg compared to fish-fed BOM at 300, and 400 g/kg (P < 0.05). The groups treated with BOM at 100-200 g/kg demonstrated considerable impairments, followed by those treated with BOM at 300 g/kg. Furthermore, fish given BOM at 400 g/kg had significantly less intestinal histological characteristics than the other groups. The relative expression of the IGF-1, GHR1, FABP, and CCK genes were downregulated in tilapia-fed BOM at 200, 300, and 400 g/kg compared to fish-fed FM-based diet (P < 0.05). The relative cost of feed per kg fish gain showed 4.42, 7.11, 8.14, 10.32, and 8.10% reduction rates in fish-fed SBM, or BOM at 100, 200, 300, and 400 g/kg. In conclusion, dietary BOM can be incorporated in Nile tilapia diets at up to 200 g/kg without affecting growth performance or feed utilisation. High inclusion levels (300 and 400 g/kg) may impair growth performance and feed utilisation by disrupting intestinal histological characteristics and reducing expression of growth and metabolic genes (GHR1, IGF-1, FABP, and CCK) in the liver.

Buspirone administration: Influence on growth, spawning, immune response, and stress in female goldfish (Carassius auratus)

The current study evaluated the impact of buspirone supplementation on the growth, physiology, stress response, spawning, and immunity in female goldfish (Carassius auratus). For this purpose, buspirone was dissolved in absolute methanol and sprayed onto the feed to create four experimental groups: B0 (control), B25 (25 mg kg-1), B50 (50 mg kg-1), and B100 (100 mg kg-1). Fish were fed their respective diets for 56 days and subjected to stress using the air exposure method at the end of the experiment. Growth performance analysis revealed that fish in the B100 group exhibited significantly higher final weight, weight gain, specific growth rate, and average daily gain than the other groups (P < 0.05). Plasma stress response indicated that cortisol levels were significantly lower in the B100 group after stress exposure, accompanied by a simultaneous decrease in glucose levels. The mucus stress response also showed lower cortisol and glucose levels in the B100 group compared to the other groups. Immunological analysis revealed significant increases in total protein, albumin, complement C3 and C4, and immunoglobulin M concentrations in both plasma and mucus of the B100 group (P < 0.05). Reproductive performance showed a notable enhancement in the number of eggs, fertilization rate, hatching rate, and survival rate in the B100 group compared to other groups (P < 0.05). Buspirone at higher concentrations, positively impacted various physiological aspects of goldfish, including growth, stress, immune activity, and reproductive performance. The significant improvements observed in growth parameters, cortisol levels, immunological markers, and reproductive outcomes suggest the potential of buspirone supplementation as a beneficial strategy in aquaculture practices.

Comparative Analysis of Growth Performance, Morphological Development, and Physiological Condition in Three Romanian Cyprinus carpio Varieties and Koi: Implications for Aquaculture

This study investigates the influence of internal factors on growth dynamics in four Cyprinus carpio varieties, three Romanian strains (Frăsinet, Ineu, and Podu Iloaiei) and the Koi variety. Fish were measured for total length, maximum height, and weight at four ontogenic stages, namely 7 days post-hatch, 3 months (0+), 18 months old (1+), and 36 months (2+). Weight Gain (WG), Specific Growth Rate (SGR), Relative Growth Rate (RGR), Fulton's condition factor, and the profile index were calculated and analyzed. Results revealed significant intervariety differences in growth performance and physiological condition across life stages. At the 2+ stage, Podu Iloaiei exhibited the highest WG (849.73 ± 4.09 g), while Koi showed the lowest (403.99 ± 14.21 g). Koi demonstrated a unique growth pattern, with the highest SGR (0.18 ± 0.00% day-1) and RGR (0.98 ± 0.05 g day-1) at the 2+ stage. Fulton's condition factor varied markedly, with Frăsinet showing the highest value at 7 days post-hatch (149.57 ± 17.485) and Koi the lowest at the 1+ stage (0.63 ± 0.011). The profile index decreased with age in all varieties, with Podu Iloaiei showing the most dramatic change from 4.22 ± 0.149 at 7 days to 2.18 ± 0.004 at 2+. These findings highlight the complex interplay between genetic and developmental factors in carp varieties, offering new insights for tailored breeding programs and aquaculture practices.

Effect of hypoxia in the post-hatching development of the salmon (Salmo salar L.) spinal cord

Introduction

Hypoxia has a teratogenic effect on the fish during embryonic development. Nevertheless, the effects on the larval stage are not yet known. Therefore, the aim of this study was to assess the effects of hypoxia on the number of neurons and their apoptotic rate in the spinal cord of Salmo salar alevins after hatching.

Methods

We used a total of 400 alevins, establishing both hypoxia and control (normoxia) groups (n = 8), considering post-hatching days 1, 3, 5, and 7, each with 50 individuals. Transversal sections of 50 μm thickness were cut from the alevin body. We performed cresyl-violet staining and counted the spinal cord neurons. Also, immunohistochemistry for HIF-1α and caspase-3 were used. For statistical analysis ANOVA one-way and Tukey's Test were used.

Results

HIF-1α was expressed in spinal neurons in both the hypoxic and normoxic groups, with the former being significantly higher. Both the hypoxic and normoxic groups evidenced the process of neuronal apoptosis, with the hypoxic groups demonstrating a higher significance. The number of neurons in the spinal cord was significantly lower in the hypoxic group.

Discussion

We found that when oxygen levels in the aquatic environment were low in Salmo salar farming alevins post-hatch, the number of spinal neurons dropped by half. These results contribute to increasing our knowledge of the biological development of salmon, in particular the genesis of the spinal cord, and the effects of hypoxic conditions on the development of this structure of the nervous system.

A non-microcystin-producing Microcystis wesenbergii strain alters fish food intake by disturbing neuro-endocrine appetite regulation

Cyanobacterial harmful algal blooms (cHABs) are pervasive sources of stress resulting in neurotoxicity in fish. A member of the widely distributed Microcystis genus of bloom-forming cyanobacteria, Microcystis wesenbergii can be found in many freshwater lakes, including Dianchi Lake (China), where it has become one of the dominant contributors to the lake's recurrent blooms. However, unlike its more well-known counterpart M. aeruginosa, the effects of dense non-microcystin-containing M. wesenbergii blooms are seldom studied. The disturbance of appetite regulation and feeding behaviour can have downstream effects on the growth of teleost fish, posing a significant challenge to aquaculture and conservation efforts. Here we examined the effects of M. wesenbergii blooms on the food intake of Acrossocheilus yunnanensis, a native cyprinid in southern China. This fish species has disappeared in Dianchi Lake, and its reintroduction might be negatively affected by the presence of this newly-dominant Microcystis species. We co-cultured juvenile A. yunnanensis with a non-microcystin-producing strain of M. wesenbergii at initial densities between 5 × 104 and 1 × 106 cells/mL and monitored fish feeding behaviour and changes in neurotransmitter and hormone protein levels. High-density M. wesenbergii cultures increased the feeding rate of co-cultured fish, elevating concentrations of appetite-stimulating signalling molecules (Agouti-related protein and γ-aminobutyric acid), while decreasing inhibitory ones (POMC). These changes coincided with histopathological alterations and reduced somatic indices in brain and intestinal tissues. Given this potential for detrimental effects and dysregulation of food intake, further studies are necessary to determine the impacts of chronic exposure of M. wesenbergii in wild fish.

Unraveling stress resilience: Insights from adaptations to extreme environments by Astyanax mexicanus cavefish

Extreme environmental conditions have profound impacts on shaping the evolutionary trajectory of organisms. Exposure to these conditions elicits stress responses, that can trigger phenotypic changes in novel directions. The Mexican Tetra, Astyanax mexicanus, is an excellent model for understanding evolutionary mechanisms in response to extreme or new environments. This fish species consists of two morphs; the classical surface-dwelling fish and the blind cave-dwellers that inhabit dark and biodiversity-reduced ecosystems. In this review, we explore the specific stressors present in cave environments and examine the diverse adaptive strategies employed by cave populations to not only survive but thrive as successful colonizers. By analyzing the evolutionary responses of A. mexicanus, we gain valuable insights into the genetic, physiological, and behavioral adaptations that enable organisms to flourish under challenging environmental conditions.

The effects of environmental changes on the endocrine regulation of feeding in fishes

Fishes are exposed to natural and anthropogenic changes in their environment, which can have major effects on their behaviour and their physiology, including feeding behaviour, food intake and digestive processes. These alterations are owing to the direct action of environmental physico-chemical parameters (i.e. temperature, pH, turbidity) on feeding physiology but can also be a consequence of variations in food availability. Food intake is ultimately regulated by feeding centres of the brain, which receive and process information from endocrine signals from both brain and peripheral tissues such as the gastrointestinal tract. These endocrine signals stimulate or inhibit food intake, and interact with each other to maintain energy homeostasis. Changes in environmental conditions might change feeding habits and rates, thus affecting levels of energy stores, and the expression of endocrine appetite regulators. This review provides an overview of how environmental changes and food availability could affect feeding and these endocrine networks in fishes. This article is part of the theme issue 'Endocrine responses to environmental variation: conceptual approaches and recent developments'.

Identification of Insulin-like Growth Factor (IGF) Family Genes in the Golden Pompano, Trachinotus ovatus: Molecular Cloning, Characterization and Gene Expression

Insulin-like growth factors (IGFs) are hormones that primarily stimulate and regulate animal physiological processes. In this study, we cloned and identified the open reading frame (ORF) cDNA sequences of IGF family genes: the insulin-like growth factor 1 (IGF1), insulin-like growth factor 2 (IGF2), and insulin-like growth factor 3 (IGF3). We found that IGF1, IGF2, and IGF3 have a total length of 558, 648, and 585 base pairs (bp), which encoded a predicted protein with 185, 215, and 194 amino acids (aa), respectively. Multiple sequences and phylogenetic tree analysis showed that the mature golden pompano IGFs had been conserved and showed high similarities with other teleosts. The tissue distribution experiment showed that IGF1 and IGF2 mRNA levels were highly expressed in the liver of female and male fish. In contrast, IGF3 was highly expressed in the gonads and livers of male and female fish, suggesting a high influence on fish reproduction. The effect of fasting showed that IGF1 and mRNA expression had no significant difference in the liver but significantly decreased after long-term (7 days) fasting in the muscles and started to recover after refeeding. IGF2 mRNA expression showed no significant difference in the liver but had a significant difference in muscles for short-term (2 days) and long-term fasting, which started to recover after refeeding, suggesting muscles are more susceptible to both short-term and long-term fasting. In vitro incubation of 17β-estradiol (E2) was observed to decrease the IGF1 and IGF3 mRNA expression level in a dose- (0.1, 1, and 10 μM) and time- (3, 6, and 12 h) dependent manner. In addition, E2 had no effect on IGF2 mRNA expression levels in a time- and dose-dependent manner. The effect of 17α-methyltestosterone (MT) in vitro incubation was observed to significantly increase the IGF3 mRNA expression level in a time- and dose-dependent manner. MT had no effect on IGF2 mRNA but was observed to decrease the IGF1 mRNA expression in the liver. Taken together, these data indicate that E2 and MT may either increase or decrease IGF expression in fish; this study provides basic knowledge and understanding of the expression and regulation of IGF family genes in relation to the nutritional status, somatic growth, and reproductive endocrinology of golden pompano for aquaculture development.

Ecosystem-based fishery enhancement through pen culture of Indian major carp Labeo catla in a tropical floodplain wetland of North Eastern Region, India, during COVID pandemic

The present study was conducted with the objective of developing ecologically and economically feasible pen culture protocols for Labeo catla as an alternate income source for wetland fishers in the context of the COVID-19 pandemic. Yearlings of L. catla (12.33 ± 1.99 cm mean total length and 26.05 ± 6.57 g mean weight) were reared in HDPE pens (500 m2 area each) at three different stocking densities of 3 (SD3), 6 (SD6) and 9 (SD9) no. m-2 in triplicates. Fishes were fed with floating pelleted feed containing 28% crude protein and 5% crude lipid two times daily at 1.5-3% of body weight. During the culture period, fish grew from 26.05 ± 6.57 to 434.61 ± 30.63 g, 306.13 ± 10.68 g and 221.13 ± 14.92 g, respectively, at stocking densities of 3, 6 and 9 no. m-2 respectively. Weight gain percentage and specific growth rate declined with increase in stocking density. Gross fish yield increased with increase in stocking density and was highest at SD9 (657.92 ± 53.55 kg pen-1), while net fish yield increased initially from SD3 to SD6 (594.31 ± 29.72 kg pen-1) and then declined with further increase in stocking density. Important water quality parameters influencing fish growth were measured, and significant difference (p > 0.05) was not observed between treatments (inside pens) and reference site (outside pen at 10-m distance). Weight gain was positively correlated (p < 0.05) to water temperature (r = 0.989) and total phosphorus (r = 0.81). Benefit cost ratio and net return was highest at SD3 (1.61; US $518.88, respectively). Stocking density of 3 no. m-2 can be considered economically feasible for table fish production of L. catla in pens. Post pen culture, monthly income of fishers increased by 10.76-179.11%, with a mean increase of 90.57%, compared to the period of first COVID-19 wave in India. The present findings can provide an impetus for effective utilization of pen enclosures for income generation and livelihood enhancement of small-scale wetland fishers during pandemic.

Tissue-specific transcriptional response of post-larval clownfish to ocean warming

Anthropogenically driven climate change is predicted to increase average sea surface temperatures, as well as the frequency and intensity of marine heatwaves in the future. This increasing temperature is predicted to have a range of negative physiological impacts on multiple life-stages of coral reef fish. Nevertheless, studies of early-life stages remain limited, and tissue-specific transcriptomic studies of post-larval coral reef fish are yet to be conducted. Here, in an aquaria-based study we investigate the tissue-specific (brain, liver, muscle, and digestive tract) transcriptomic response of post-larval (20 dph) Amphiprion ocellaris to temperatures associated with future climate change (+3 °C). Additionally, we utilized metatranscriptomic sequencing to investigate how the microbiome of the digestive tract changes at +3 °C. Our results show that the transcriptional response to elevated temperatures is highly tissue-specific, as the number of differentially expressed genes (DEGs) and gene functions varied amongst the brain (102), liver (1785), digestive tract (380), and muscle (447). All tissues displayed DEGs associated with thermal stress, as 23 heat-shock protein genes were upregulated in all tissues. Our results indicate that post-larval clownfish may experience liver fibrosis-like symptoms at +3 °C as genes associated with extracellular matrix structure, oxidative stress, inflammation, glucose transport, and metabolism were all upregulated. We also observe a shift in the digestive tract microbiome community structure, as Vibrio sp. replace Escherichia coli as the dominant bacteria. This shift is coupled with the dysregulation of various genes involved in immune response in the digestive tract. Overall, this study highlights post-larval clownfish will display tissue-specific transcriptomic responses to future increases in temperature, with many potentially harmful pathways activated at +3 °C.