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The rearing of fish in intensive systems reduces their immunity leading to eruption of diseases, consequently prompting the use of antibiotics. Antibiotics are currently used in cultured fish globally to treat/prevent diseases. On the one hand, antibiotics used in aquaculture help to improve fish health by killing or inhibiting pathogenic bacteria proliferation. However, on the other hand, they cause multiple side effects. To date, information on systemic effects of antibiotics in cultured fish is scattered and their potential human health risk remains elusive. This review critically analyses and discusses the available information in the literature on the positive and negative effects of antibiotics in cultured fish and their potential human health risk via fish consumption. The review found 44 different antibiotics dominated by oxytetracycline were studied in various fish species worldwide. Antibiotics used in global aquaculture either decrease or increase fish growth and survival rates. They induce oxidative stress, which affect antioxidant and detoxification responses and cause host–microbiota dysbiosis. These changes compromise the fish immunity system, which ultimately lead to cellular damage. The toxicities generated inhibit the fish aerobic glycolysis, suppress lipogenesis and fatty acid β‐oxidation while increase energy demand by initiating gluconeogenesis and anaerobic glycolysis. Consumption of fish treated with antibiotics causes human health risk. Future studies are required on agents to restore dysfunctions induced by antibiotics in cultured fish, while attempts to limit their utilisation in aquaculture production are underway. [Correction added on 21 November 2020, after first online publication: The abstract has been amended to clarify the scope of the review.]

The use of antibiotics for anti-infection and growth promotion has caused the overuse of antibiotics in aquaculture. However, the benefit or risk of the long-term use of antibiotics on fish growth or health has not been fully addressed. In the present study, zebrafish were fed with sulfamethoxazole (SMX) or oxytetracycline (OTC) at the therapeutic concentrations (100 and 80 mg/kg body weight per day, respectively) for 6 weeks to mimic the long-term use of antibiotics. The digestive enzyme activities were higher in both antibiotic treatments, and higher oxygen consumption rate was found in OTC treated group. As a result, SMX increased the weight gain of zebrafish, and OTC treatment did not show significant prompting effect on growth. The mortality was higher in SMX or OTC treated group on 2nd-4th day after exposure to Aeromonas hydrophila. Lower alkaline phosphatase (AKP) and acid phosphatase (ACP) activities were found in OTC treated group, while higher malondialdehyde (MDA) content was found in the intestine of both SMX and OTC treated zebrafish. Furthermore, feeding OTC decreased the intestinal microbial richness. This study revealed that long-term use of legal aquaculture concentrations of antibiotics caused systemic adverse effects on fish gut health; stringent policy for use of antibiotics in fish is urgent.

Key points In a cold environment, mammals increase their food intake while fish decrease or stop feeding. However, the physiological value of fasting during cold resistance in fish is currently unknown. Fasting for more than 48 h enhanced acute cold resistance in zebrafish, which correlated with lipid catabolism and cell damage attenuation. Lipid catabolism and autophagy were necessary for cold resistance in fish and the inhibition of mitochondrial fatty acid β‐oxidation or autophagy weakened the fasting‐induced cold resistance. Repression of mechanistic target of rapamycin (mTOR) signalling pathway by rapamycin largely mimicked the beneficial effects of fasting in promoting cold resistance, suggesting mTOR signalling may be involved in the fasting‐induced cold resistance in fish. Our study demonstrates that fasting may be a protective strategy for fish to survive under cold stress. Abstract In cold environments, most homeothermic animals increase their food intake to supply more energy to maintain body temperature, whereas most poikilothermic animals such as fishes decrease or even stop feeding under cold stress. However, the physiological value of fasting during cold resistance in poikilotherms has not been explained. Here, we show that moderate fasting largely enhanced cold resistance in fish. By using pharmacological (fenofibrate, mildronate, chloroquine and rapamycin) and nutritional approaches (fatty acids diets and amino acids diets) in wild‐type or specific gene knock‐out zebrafish models (carnitine palmitoyltransferase‐1b‐deficient strain, CPT1b−/−, or autophagy‐related protein 12‐deficient strain, ATG12−/−), we verified that fasting‐stimulated lipid catabolism and autophagy played essential roles in the improved cold resistance. Moreover, suppression of the mechanistic target of rapamycin (mTOR) pathway by using rapamycin mostly mimicked the beneficial effects of fasting in promoting cold resistance as either the physiological phenotype or transcriptomic pattern. However, these beneficial effects were largely reduced when the mTOR pathway was activated through high dietary leucine supplementation. We conclude that fasting helps fish to resist cold stress by modulating lipid catabolism and autophagy, which correlates with the mTOR signalling pathway. Therefore, fasting can act as a protective strategy of fish in resisting coldness.

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Unaffordability of commercial feeds to semi-intensive Nile tilapia, Oreochromis niloticus farmers has led to reliance on supplemental feeding and fertilization for nutrition of their fish without a scientific basis. This study compared the growth, survival, condition factor and yield performance of O.niloticus fed on mixed ingredients (MI) and rice bran alone (RB) diets reared in fertilized earthen ponds in small scale farmers’ ponds. The study also determined phytoplankton composition, biomass and abundance in the experimental ponds. Quadruplicate ponds were stocked with O. niloticus and African sharptooth catfish, Clarias gariepinus at a stocking ratio of 1:3. The initial mean weights of O. niloticus and C. gariepinus were 14.62 ± 0.61 and 20.34 ± 1.44 g respectively. The fish were fed on MI and RB diets with protein content of 184.74 and 126.06 g kg−1 respectively for 270 days. The results showed that growth performance, survival rate and condition factor of O.niloticus were not affected by either feeding with MI or RB diet (p > 0.05). Moreover, there were no significant differences obtained in phytoplankton biomass and abundance in O.niloticus ponds fed on the two diets (p > 0.05). Furthermore, feeding O.niloticus either on MI or RB diet did not affect the net and gross fish yields (p > 0.05). The study revealed that the use of either MI or RB diet does not significantly affect the performance of O.niloticus cultured in semi-intensive earthen ponds where natural food organisms are an integral part of the culture system. Rice bran could be used for semi-intensive culture of O.niloticus in fertilized ponds to boost the production based on its availability and low cost.