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The replacement of fish oil with plant oils is a common practice in aquaculture to compensate for the shortage of fish oil supply and has been thoroughly studied. However, because the experimental conditions vary in many aspects, the results are usually inconsistent quantitatively. Therefore, a meta‐analysis was conducted based on a dataset containing 328 articles to systematically model the influence of plant oils on the main aquaculture fish. In addition to demonstrating the species‐specific dose‐dependent impact of plant oils on fish growth, feed utilization efficiency, lipid deposition and health parameters, we have also investigated the role of other factors in this process. We found that the adverse effects caused by plant oils worsen as the experimental duration extends for Atlantic salmon, while Gilthead seabream and European seabass gradually adapt to the change. Further, water temperature could be a decisive factor for Rainbow trout, and early adaptation to plant oils would be helpful for Gilthead seabream. Moreover, sufficient fishmeal supply could alleviate the adverse effects caused by plant oils for most species, but for Gilthead seabream and European seabass, the growth suppression effect of plant oil was larger when fed high‐fishmeal diets. Besides, by comprehensively considering the effects of plant oils, we matched the potential optimal plant oil for each fish species. Our article quantitatively modelled the adverse effects of replacing fish oil with plant oils, investigated the influences of assistant factors and offered a panorama of the research status with emphasis on potential breakthrough orientations. [ABSTRACT FROM AUTHOR]

The price of fishmeal (FM) has been increasing continuously due to the expansion of the gap between its stable production and rising demand. Therefore, plant protein sources are widely applied in the aquaculture industry to accomplish the protein requirement of farmed fish species. However, the massive number of results produced under various experimental conditions appended challenges for comprehensive summarization and comparison of the effects of plant protein sources on carnivorous fish species. Thus, a systemic review and meta‐analysis were conducted to compare the impacts of various plant protein sources on growth, feed utilization efficiencies, blood lipid, and liver health of representative carnivorous species. Supported by the data from 256 articles, our results indicated that Atlantic salmon, African catfish, Black seabass, and Hybrid striped bass were better at utilizing plant protein sources than Grouper and Japanese seabass. Cottonseed and lupin proteins were promising protein alternatives, while rapeseed showed significant growth suppression effects for these carnivorous fish species. Besides, deep processing methods such as fermentation and enzymolysis alleviated undesirable consequences effectively when less than half of FM was replaced by plant protein sources. Moreover, the optimal plant protein sources are discussed for each fish species. Overall, this article depicts the impact patterns of major plant protein sources on carnivorous farmed fish species and lays a solid foundation for further investigation on mechanisms for improving plant protein utilization. [ABSTRACT FROM AUTHOR]

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.] [ABSTRACT FROM AUTHOR]

Key points: The pparab subtype in zebrafish is much more highly expressed in tissues with high oxidative activity than pparaa.The pparab deficiency in zebrafish reduces fatty acid β‐oxidation both in liver and muscle, illustrating its functional homology as a mammalian peroxisome proliferator‐activated receptor α (PPARα).pparab deficiency promotes metabolic reprogramming by increasing glucose utilization and inhibiting amino acid breakdown.The present study brings new insights into the comprehensive regulatory roles of PPARα in the cellular fuel selection and provides a valuable animal model for PPARα studies from a viewpoint of comparative physiology. Dysfunction of lipid metabolism is involved in the pathogenesis of several chronic metabolic diseases. Peroxisome proliferator‐activated receptor α (PPARα) is essential for normal metabolic homeostasis and, in particular, for the regulation of fatty acid β‐oxidation (FAO). However, little is known about its regulation roles in systemic nutrient metabolism. To explore the underlying modulation role of PPARα in metabolic homeostasis, we generated a pparab‐knockout zebrafish (Danio rerio) model. The pparab mutants demonstrated lower expression of key enzymes involved in FAO, as well as lower mitochondrial and peroxisomal FAO in tissues, which was associated with lipid accumulation in liver and visceral mass. Conversely, glucose utilization was higher because they demonstrated lower blood glucose and tissue glycogen concentrations, as well as activation of the phosphoinositide 3‐kinase/AKT pathway. In addition, pparab‐deficient zebrafish demonstrated activation of AKT/mammalian target of rapamycin signalling and higher protein content, implying greater protein synthesis and/or lower amino acid breakdown. These data clearly revealed that pparab deletion reduces FAO but increases glucose utilization and protein deposition to maintain energy homeostasis. The present study provides new insights into the comprehensive regulatory role of PPARα in systemic energy metabolism in fish, and this pparab‐deficient zebrafish also constitutes a valuable model for investigating the functions of PPARα in mammals from comparative physiology aspects. Key points: The pparab subtype in zebrafish is much more highly expressed in tissues with high oxidative activity than pparaa.The pparab deficiency in zebrafish reduces fatty acid β‐oxidation both in liver and muscle, illustrating its functional homology as a mammalian peroxisome proliferator‐activated receptor α (PPARα).pparab deficiency promotes metabolic reprogramming by increasing glucose utilization and inhibiting amino acid breakdown.The present study brings new insights into the comprehensive regulatory roles of PPARα in the cellular fuel selection and provides a valuable animal model for PPARα studies from a viewpoint of comparative physiology. [ABSTRACT FROM AUTHOR]

L‐carnitine is a multi‐functional nutrient which plays a leading role in fatty acid metabolism in mammals and other eukaryotes. Its main physiological function is to promote fatty acid β‐oxidation to produce energy, which reduces body fat content and improves body weight without affecting moisture content in whole body and muscle. In recent years, its dietary supplementation in aquaculture nutrition has been studied in different cultured species. It has been proved that L‐carnitine can improve growth and increase lipid utilization rate in some aquatic animals. However, such beneficial effects of dietary L‐carnitine are limited or absent in other species. The reasons for the conflicting results obtained on L‐carnitine functions in aquatic animals need to be elucidated. This review explores comprehensively the different physiological functions of L‐carnitine in various aquatic animals. In the end, research strategies are provided to elucidate the existing conflicts on dietary L‐carnitine application in aquaculture nutrition in order to promote its utilization in aquatic feed industry. [ABSTRACT FROM AUTHOR]

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. 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. 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 FROM AUTHOR]

In this study, we explored the function of arachidonic acid (ARA) in adipogenesis in the grass carp ( Ctenopharyngodon idellus) using in vivo and in vitro models. An 8-week feeding trial was performed using three isonitrogenous and isoenergetic purified diets: ARA-free, ARA, and ARA + acetylsalicylic acid [ASA, a cyclooxygenase (COX) inhibitor]. Fish were sampled after 4 and 8 weeks of feeding. Results showed that ARA-fed fish had a significantly lower intraperitoneal fat index (IPFI) and smaller adipocytes; these decreases were reversed by ASA after 8 weeks of feeding. Nevertheless, at week 4, the IPFI and adipocyte size were higher in the ARA group, and they were comparable to those of fish fed ARA + ASA. To further investigate the influence of ARA on adipocyte differentiation, confluent pre-adipocytes of grass carp were incubated with ARA for 3 days. This in vitro experiment demonstrated that ARA promoted adipogenesis in a dose-dependent manner. Pre-treatment with the lipoxygenase (LOX) inhibitor nordihydroguaiaretic acid attenuated the pro-adipogenic function of ARA. However, after treatment with ARA for 8 days, adipocytes had a lower lipid content than cells treated with oleic acid, and ASA could suppress this effect. We thus revealed the dual function of ARA in adipogenesis in grass carp. The LOX pathway may play a key role in pro-adipogenesis after short-term treatment with ARA, whereas the COX pathway is possibly responsible for the inhibition of adipogenesis after long-term treatment. [ABSTRACT FROM AUTHOR]

Natural selection endows animals with the abilities to store lipid when food is abundant and to synthesize lipid when it is limited. However, the relevant adaptive strategy of lipid metabolism has not been clearly elucidated in fish. This study examined the systemic metabolic strategies of Nile tilapia to maintain lipid homeostasis when fed with low- or high-fat diets. Three diets with different lipid contents (1%, 7%, and 13%) were formulated and fed to tilapias for 10 weeks. At the end of the feeding trial, the growth rate, hepatic somatic index, and the triglyceride (TG) contents of serum, liver, muscle, and adipose tissue were comparable among three groups, whereas the total body lipid contents and the mass of adipose tissue increased with the increased dietary lipid levels. Overall quantitative PCR, western blotting and transcriptomic assays indicated that the liver was the primary responding organ to low-fat (LF) diet feeding, and the elevated glycolysis and accelerated biosynthesis of fatty acids (FA) in the liver is likely to be the main strategies of tilapia toward LF intake. In contrast, excess ingested lipid was preferentially stored in adipose tissue through increasing the capability of FA uptake and TG synthesis. Increasing numbers, but not enlarging size, of adipocytes may be the main strategy of Nile tilapia responding to continuous high-fat (HF) diet feeding. This is the first study illuminating the systemic adaptation of lipid metabolism responding to LF or HF diet in fish, and our results shed new light on fish physiology. [ABSTRACT FROM AUTHOR]