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The aim of this study was to assess – for the first time – the occurrence and distribution of microplastics (MPs) in the gastrointestinal tracts (GITs) of a marine commercial fish species (Micropogonias furnieri) from the Bahía Blanca Estuary (BBE) in Argentina, and to evaluate fish potential associated stress. In order to do this, juveniles were sampled using artisanal fishing arts at two sampling locations. Basic measurements of individual fish were taken (total length, total weight, weight of the liver) and GITs were subsequently removed, digested with 30% H2O2 for 5 days at 60°C, filtered on Whatman paper and then dried. Samples were observed with a stereomicroscope, and it was demonstrated that 100% of the individuals contained microplastic particles in their GITs. In total, 241 microplastic particles were removed from the GITs of all fish. They were categorized as fibers (60.8%), pellets (28.9%), fragments (8.6%) and laminas (1.4%), and they ranged in size from 0.98 to > 5 mm. The average number of particles per fish was higher than that reported in previous global marine studies. Moreover, a positive correlation between the number of MPs per fish and hepatosomatic index was found, suggesting a probable stress in their health condition. These findings provide the first and southernmost evidence of microplastic contamination in biota from the Argentinean sea, which is found in the South Atlantic sea.

Protein accretion in some fish species is affected by dietary lipids, starch and their interactions, but this aspect of nutrition is largely unknown in largemouth bass (LMB). Therefore, we designed six experimental diets with three starch levels (5%, 10%, and 15%; dry matter basis) and two lipid levels (10% and 12.5%; dry matter basis) to evaluate the effects of dietary starch and lipid levels on the protein retention, growth, feed utilization, and liver histology of LMB. There were three tanks (18 fish per tank, ~ 4.85 g per fish) per dietary treatment group and the trial lasted for 8 weeks. Fish were fed to apparent satiation twice daily. Results indicated that increasing the dietary starch level from 5 to 15% reduced (P < 0.05) absolute feed intake (AFI; − 9.0%, − 15% and − 14% on days 14–28, 28–42, and 42–56, respectively) and weight gains (− 4.4% and − 6.5% on days 42 and 56, respectively) of LMB. Increasing the dietary lipid level from 10 to 12.5% reduced (P < 0.05) AFI (− 9.7%, − 11.7% and − 11.9% on days 14–28, 28–42; and 42–56, respectively), weight gains (− 4.2%, − 5.9% and − 6.9% on days 28, 42 and 56, respectively), and survival rate (by a 5.6% unit) of LMB. The retention of dietary protein and some amino acids in the body was affected by dietary starch or lipid levels and their interactions. The viscerosomatic index (VSI), hepatosomatic index (HSI), and intraperitoneal fat ratio (IPFR) increased with increasing the dietary starch level from 5 to 15%. Compared with 10% lipids, 12.5% lipids in diets increased IPFR but had no effect on VSI or HSI. The concentrations of glucose in serum increased with increasing the dietary starch level from 5 to 15% at 4 to 24 h after feeding, with the effect of dietary lipids being time-dependent. Compared with a 5%-starch diet, fish fed a diet with 10%- or 15%-starch exhibited an enlarged and pale liver with excessive glycogen. Based on these findings, we recommend dietary lipid and starch levels to be 10% and < 10%, respectively, for juvenile LMB to maximize the retention of dietary protein in their bodies.

High-fat diet (HFD) usually induces oxidative stress and astaxanthin is regarded as an excellent anti-oxidant. An 8-week feeding trial was conducted to investigate the effects of dietary astaxanthin supplementation on growth performance, lipid metabolism, antioxidant ability, and immune response of juvenile largemouth bass (Micropterus salmoides) fed HFD. Four diets were formulated: the control diet (10.87% lipid, C), high-fat diet (18.08% lipid, HF), and HF diet supplemented with 75 and 150 mg kg−1 astaxanthin (HFA1 and HFA2, respectively). Dietary supplementation of astaxanthin improved the growth of fish fed HFD, also decreased hepatosomatic index and intraperitoneal fat ratio of fish fed HFD, while having no effect on body fat. Malondialdehyde content and superoxide dismutase activity were increased in fish fed HFD, astaxanthin supplementation in HFD decreased the oxidative stress of fish. The supplementation of astaxanthin in HFD also reduced the mRNA levels of Caspase 3, Caspase 9, BAD, and IL15. These results suggested that dietary astaxanthin supplementation in HFD improved the growth performance, antioxidant ability and immune response of largemouth bass.

The present study was conducted to investigate the effects of high dietary lipid levels on growth, metabolism, antioxidant capacity, and immune responses of largemouth bass. Fish (initial body weight 13.38 ± 0.11 g) were fed three isonitrogenous semi-purified diets containing 5%, 10%, and 20% lipid, respectively. The results indicated that fish fed 10% lipid diet showed significantly better final body weight, specific growth rate (SGR), protein efficiency ratio (PER), and feed conversion ratio (FCR) compared with that fed 5% lipid diet. Meanwhile, fish fed 20% lipid diet had a significantly higher viscera ratio (VR), hepatosomatic index (HSI), intraperitoneal fat ratio (IPF), and liver lipid content than those fed the other diets. Higher alanine aminotransferase (ALT) and aspartate transaminase (AST) activities, total cholesterol (TC), triglyceride (TG), free fatty acids (FFA), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C) contents, and LDL-C/HDL-C value in plasma were recorded in fish fed 20% lipid diet, while higher insulin contents were obtained in fish fed 5% lipid diet. In addition, the highest carnitine palmitoyltransferase I (CPT1), AMP-activated protein kinase (AMPK), fructose-1,6-bisphosphatase (FBPase), and phosphoenolpyruvate carboxykinase (PEPCK) activities in the liver were also observed in fish fed 20% lipid diet. However, fish fed 20% lipid diet had a significantly lower superoxide dismutase (SOD) and catalase (CAT) activities and higher MDA contents in liver than those fed the other diets. The higher nitric oxide (NO) contents and inducible nitric oxide synthase (iNOS) activity in liver were recorded in fish fed 10% lipid diet. Moreover, the alkaline phosphatase (ALP), inducible nitric oxide synthase (iNOS) and lysozyme activities, and nitric oxide (NO) contents in plasma were higher in fish fed the 10% diets than the other groups. In conclusion, high dietary lipid levels could suppress growth performance and liver anti-oxidative capacity, and reduce immune responses of largemouth bass.

Background Global trend of the introduction of high levels of relatively cheap carbohydrates to reduce the amount of costly protein in the aquatic animal feed production has affected the aquaculture of an economically important cyprinid fish, blunt snout bream ( Megalobrama amblycephala ). This dietary shift has resulted in increased prevalence of metabolic disorders, often causing economic losses. High dietary intake of carbohydrates, associated with obesity, is one of the major causes of non-alcoholic fatty liver disease (NAFLD) in humans. Results We have conducted an eight-week feeding trial to better understand how a high-carbohydrate diet (HCBD) affects the liver health in this fish. Hepatosomatic index and lipid content were significantly ( P  < 0.05) higher in the HCBD group. Histology results also suggested pathological changes in the livers of HCBD group, with excessive lipid accumulation and indication of liver damage. Metabolomics and serum biochemistry analyses showed that a number of metabolites indicative of liver damage were increased in the HCBD group. This group also exhibited low levels of betaine, which is a metabolite crucial for maintaining the healthy liver functions. Transcriptomic and qPCR analyses indicated that HCBD had a strong impact on the expression of a large number of genes associated with the NAFLD and insulin signalling pathways, which may lead to the development of insulin resistance in hepatocytes, pathological liver changes, and eventually the NAFLD. Conclusions Transcriptomics, metabolomics and histology results all indicate early symptoms of liver damage. However whether these would actually lead to the development of NAFLD after a longer period of time, remains inconclusive. Additionally, a very high number of upregulated genes in the HCBD group associated with several neurodegenerative diseases is a strong indication of neurodegenerative changes caused by the high-carbohydrate diet in blunt snout bream. This suggests that fish might present a good model to study neurodegenerative changes associated with high-carbohydrate diet in humans.

Gracilaria gracilis and Nannochloropsis oceanica, single or blended, were tested in European seabass (Dicentrarchus labrax) diets. A control (CTRL) diet was compared with experimental diets including either 8% G. gracilis (GRA8), 8% N. oceanica (NAN8), or a blend of 4% of each alga (NAN4GRA4). After 106 days of feeding, growth, nutrient utilization, antioxidant defense, immunological status, and end-product quality were evaluated. All fish exhibited similar feed intake (1.4–1.5%), body weight, growth, and feed conversion ratio (1.6). Dietary inclusion N. oceanica did not affect digestible N intake and gain. Fish fed GRA8 had the lowest digestible N and energy intake (P < 0.05), and simultaneously the highest nitrogen retention efficiency and energy retention efficiency, resulting in a N and energy gain similar to all other treatments. All fish had well-preserved intestinal morphology; feeding NAN8 resulted in a significant increase in neutral goblet cells compared with GRA8. Fish fed the algal diets had significantly lower (P < 0.05) hepatosomatic index (1.7–1.8 vs 2.1) and plasma triglyceride levels than CTRL, but whole body composition remained similar among treatments. The liver total antioxidant capacity of fish fed NAN8 was significantly higher than that of fish fed GRA8 but did not differ significantly from the CTRL group. NAN4GRA4 resulted in lower values of total glutathione, glutathione peroxidase, and alternative complement. N. oceanica decreased fillet springiness; however, with NAN4GRA4, the muscle fillet became less resilient. G. gracilis and N. oceanica biomass, either used single (8%) or blended (4% each), can be valuable natural ingredients for partial replacement of fish meal in European seabass diets.

Photoperiod represents light manipulation to advance or delay reproduction in Siamese fighting fish (Betta splendens Regan, 1910). This study aimed to evaluate different photoperiod regimes against ovarian maturity of fish by examining morphoanatomical indexes. The female Siamese fighting fish underwent different photoperiod regimes, for 45 days, i.e. P1 (10h light, 14h dark), P2 (14h light, 10h dark), and P3 (ambient light as control). Morphoanatomical indexes were accessed through gonadosomatic index (GSI), hepatosomatic index (HSI), and viscerosomatic index (VSI), being corelated With vitellogenesis. Vitellogenesis was analyzed through ovarian histology preparations. Results showed that GSI, HSI, and VSI were statistically significantly different in P2 (38.25%, 24.61%, 34.93%). P1 (25.48%, 18.23%, 22.53%) and P3 (15.92%, 12.55%, 15.71%) were not different. These photoperiod regimes affected female morphoanatomical indexes. GSI, HSI, and VSI increased comparably with vitellogenesis. HSI and VSI promoted GSI at a high-level.

The ridgetail white prawn Exopalaemon carinicauda has the potential to be used as a model organism in crustacean research because it has a transparent body, available draft genome, and short life cycle. However, their ovarian development pattern remains unclear under laboratory culture conditions. This study investigated the changes of ovarian external feature, ovarian histology, gonadosomatic index (GSI), and hepatosomatic index (HSI), as well as the expression and localization of vitellogenin in the ovary and the hepatopancreas during the first ovarian development cycle of E. carinicauda under laboratory-reared condition. The results demonstrated that (1) the first ovarian development cycle of E. carinicauda could be divided into 5 different stages in which the ovary changes its color from white to yellow during the vitellogenesis process in parallel with increasing GSI. (2) After pubertal molt, most females reached ovarian stage II while the females reached stage V after premating molt. (3) During the ovarian development, GSI increased smoothly and HSI relatively stable during the period of stages I to IV, while GSI increased but HSI decreased significantly from stages IV to V. (4) In situ hybridization (ISH) revealed that EcVg was slightly expressed in the oocyte cytoplasm of previtellogenic oocytes. The positive signal was mainly detected in hepatopancreatic fibrillar cells, and a strong signal was found in the hepatopancreas at stage IV. Moreover, the expression level of EcVg -mRNA in the hepatopancreas is stage-specific, and the hepatopancreas contributes majority of vitellin precursor protein to support the ovarian development of E. carinicauda .

A moderate surplus of the one carbon (1C) nutrients methionine, folic acid, vitamin B6 and B12 above dietary recommendations for Atlantic salmon has shown to improve growth and reduce hepatosomatic index in the on-growing saltwater period when fed throughout smoltification. Metabolic properties and molecular mechanisms determining the improved growth are unexplored. Here, we investigate metabolic and transcriptional signatures in skeletal muscle taken before and after smoltification to acquire deeper insight into pathways and possible nutrient–gene interactions. A control feed (Ctrl) or 1C nutrient surplus feed (1C+) were fed to Atlantic salmon 6 weeks prior to smoltification until 3 months after saltwater transfer. Both metabolic and gene expression signatures revealed significant 1C nutrient-dependent changes already at pre-smolt, but differences intensified when analysing post-smolt muscle. Transcriptional differences revealed lower expression of genes related to translation, growth and amino acid metabolisation in post-smolt muscle when fed additional 1C nutrients. The 1C+ group showed less free amino acid and putrescine levels, and higher methionine and glutathione amounts in muscle. For Ctrl muscle, the overall metabolic profile suggests a lower amino acid utilisation for protein synthesis, and increased methionine metabolisation in polyamine and redox homoeostasis, whereas transcription changes are indicative of compensatory growth regulation at local tissue level. These findings point to fine-tuned nutrient–gene interactions fundamental for improved growth capacity through better amino acid utilisation for protein accretion when salmon was fed additional 1C nutrients throughout smoltification. It also highlights potential nutritional programming strategies on improved post-smolt growth through 1C+ supplementation before and throughout smoltification.

Reproduction in many organisms can be disrupted by changes to the physical environment, such as those predicted to occur during climate change. Marine organisms face the dual climate change threats of increasing temperature and ocean acidification, yet no studies have examined the potential interactive effects of these stressors on reproduction in marine fishes. We used a long-term experiment to test the interactive effects of increased temperature and CO2 on the reproductive performance of the anemonefish, Amphiprion melanopus. Adult breeding pairs were kept for 10 months at three temperatures (28.5°C [+0.0°C], 30.0°C [+1.5°C] and 31.5°C [+3.0°C]) cross-factored with three CO2 levels (a current-day control [417 μatm] and moderate [644 μatm] and high [1134 μatm]) treatments consistent with the range of CO2 projections for the year 2100. We recorded each egg clutch produced during the breeding season, the number of eggs laid per clutch, average egg size, fertilization success, survival to hatching, hatchling length, and yolk provisioning. Adult body condition, hepatosomatic index, gonadosomatic index, and plasma 17β-estradiol concentrations were measured at the end of the breeding season to determine the effect of prolonged exposure to increased temperature and elevated CO2 on adults, and to examine potential physiological mechanisms for changes in reproduction. Temperature had by far the stronger influence on reproduction, with clear declines in reproduction occurring in the +1.5°C treatment and ceasing altogether in the +3.0°C treatment. In contrast, CO2 had a minimal effect on the majority of reproductive traits measured, but caused a decline in offspring quality in combination with elevated temperature. We detected no significant effect of temperature or CO2 on adult body condition or hepatosomatic index. Elevated temperature had a significant negative effect on plasma 17β-estradiol concentrations, suggesting that declines in reproduction with increasing temperature were due to the thermal sensitivity of reproductive hormones rather than a reduction in energy available for reproduction. Our results show that elevated temperature exerts a stronger influence than high CO2 on reproduction in A. melanopus. Understanding how these two environmental variables interact to affect the reproductive performance of marine organisms will be important for predicting the future impacts of climate change.