Essential fatty acid (EFA) requirements vary qualitatively and quantitatively with both species and during ontogeny of fish, with early developmental stages and broodstock being critical periods. Environment and/or trophic level are major factors, with freshwater/diadromous species generally requiring C18 polyunsaturated fatty acids (PUFA) whereas marine fish have a strict requirement for long-chain PUFA, eicosapentaenoic, docosahexaenoic and arachidonic acids. Other than marine fish larvae, defining precise quantitative or semi-quantitative EFA requirements in fish have received less attention in recent years. However, the changes to feed formulations being forced upon the aquaculture industry by the pressing need for sustainable development, namely the replacement of marine fish meal and oils with plant-derived products, have reintroduced EFA into the research agenda. It is particularly important to note that the physiological requirements of the fish to prevent deficiency pathologies and produce optimal growth may not parallel the requirements for maintaining nutritional quality. For instance, salmonids can be successfully cultured on vegetable oils devoid of long-chain n-3 PUFA but not without potentially compromising their health benefits to the human consumer. Solving this problem will require detailed knowledge of the biochemical and molecular basis of EFA requirements and metabolism.
Aquafeed ingredients are global commodities used in livestock, poultry and companion animal feeds. Cost and availability are ditated less by demand from the aquafeed sector than by demand from other animal feed sectors and global production of grains and oilseeds. The exceptions are fishmeal and fish oil; use patterns have shifted over the past two decades resulting in nearly exclusive use of these products in aquafeeds. Supplies of fishmeal and oil are finite, making it necessary for the aquafeed sector to seek alternative ingredients from plant sources whose global production is sufficient to supply the needs of aquafeeds for the foreseeable future. Significant progress has been made over the past decade in reducing levels of fishmeal in commercial feeds for farmed fish. Despite these advances, the quantity of fishmeal used by the aquafeed sector has increased as aquaculture production has expanded. Thus, further reduction in percentages of fishmeal in aquafeeds will be necessary. For some species of farmed fish, continued reduction in fishmeal and fish oil levels is likely; complete replacement of fishmeal has been achieved in research studies. However, complete replacement of fishmeal in feeds for marine species is more difficult and will require further research efforts to attain.
The gastrointestinal (GI) tract of an animal consists of a very complex and dynamic microbial ecosystem that is very important from a nutritional, physiological and pathological point of view. A wide range of microbes derived from the surrounding aquatic environment, soil/sediment and feed are found to colonize in the GI tract of fish. Among the microbial groups, bacteria (aerobic, facultative anaerobic and obligate aneraobic forms) are the principal colonizers in the GI tract of fish, and in some fish, yeasts are also reported. The common bacterial colonizers in the GI tract of freshwater and marine fish include Vibrio, Aeromonas, Flavobacterium, Plesiomonas, Pseudomonas, Enterobacteriaceae, Micrococcus, Acinetobacter, Clostridium, Fusarium and Bacteroides, which may vary from species to species as well as environmental conditions. Besides, several unknown bacteria belonging to Mycoplasma, Arthrobacter, Brochothrix, Jeotgailbacillus, Ochrobactrum, Psychrobacter and Sejongia species in the GI tract of different fish species have now been identified successfully using culture-independent techniques. Gnotobiotic and conventional studies indicate the involvement of GI microbiota in fish nutrition, epithelial development, immunity as well as disease outbreak. This review also highlights the need for manipulating the gut microbiota with useful beneficial microbes through probiotic, prebiotic and synbiotic concepts for better fish health management.
The innate immune system of fish is considered to be the first line of defence against a broad spectrum of pathogens and is more important for fish as compared with mammals. Lysozyme level or activity is an important index of innate immunity of fish and is ubiquitous in its distribution among living organisms. It is well documented that fish lysozyme possess lytic activity against both Gram-positive bacteria and Gram-negative bacteria. It is also known to be opsonic in nature and activates the complement system and phagocytes. It is present in mucus, lymphoid tissue, plasma and other body fluids of freshwater and marine fish. It is also expressed in a wide variety of tissues. Lysozyme activity has been shown to vary depending on the sex, age and size, season, water temperature, pH, toxicants, infections and degree of stressors. Here, we review our current understanding of different types of lysozyme and their expression and its role in fish innate immune system.
Restriction or ban on antibiotic administration in aquaculture encourages the development of environment‐friendly feed additives as immunostimulants. Short‐chain fatty acids ( SCFA s) and their salts are ‘Generally Regarded as Safe’ and are often used as antimicrobials in the livestock feed industry. Formate, acetate, propionate, butyrate and their salts are among the most studied SCFA s in aquaculture. These SCFA s affect the host performance as well as physiological response upon three ways: either through effects of the feeds that are being administered, through effects on the gastrointestinal tract of the animal or through direct effects on metabolism. To date, most of the available data are focused on the effects of SCFA s on growth performance and feed utilization. Despite extensive research studies on the effects of the different type of SCFA s and their salts on growth performance and feed utilization, the effects of these feed additives on the health of aquatic organisms have only been receiving attention recently. The results of the studies demonstrated beneficial effects of SCFA s as promising feed additives in aquaculture. The present review article summarizes and discusses the topic of dietary administration of SCFA s and their salts in aquaculture with a closer look at the recent findings regarding the effects of SCFA s on growth performance and health status of fish and shellfish. Furthermore, this review identifies the gaps of existing knowledge regarding the roles of SCFA s in the growth and health status of aquatic animals and suggests research areas that merit further investigations.
This review presents an overview of antinutritive factors (ANFs) relevant for fish nutrition. The sources of ANFs and the possibilities of reducing the impact of ANFs are briefly mentioned. Proteinase inhibitors, lectins, saponins and oligosaccharides are given a more thorough presentation regarding mechanisms of action and the state of knowledge regarding effects on gut function in fish and upper safe dietary levels. Thereafter, selected results from recent works addressing the involvement of T cells and proteinase-activated receptors in soybean-induced enteritis are summarized. Our conclusions are as follows: we are only beginning to understand effects of ANFs in fish; strengthening of the knowledge base is urgently needed to understand the effects and to find the means to overcome or modify these effects; interactions between the effects of ANFs appear to be very important; the microbiota may modify the effects of ANFs; not only salmonids are affected; not only soybeans contain ANFs of biological importance in fish; and with increased knowledge, we can develop better diets for optimal nutrition, health and economy in aquaculture.
Despite the recent progress in the production of inert diets for fish larvae, feeding of most species of interest for aquaculture still relies on live feeds during the early life stages. Independently of their nutritional value, live feeds are easily detected and captured, due to their swimming movements in the water column, and highly digestible, given their lower nutrient concentration (water content>80%). The present paper reviews the main types of live feeds used in aquaculture, their advantages and pitfalls, with a special emphasis on their nutritional value and the extent to which this can be manipulated. The most commonly used live feeds in aquaculture are rotifers (Brachionus sp.) and brine shrimp (Artemia sp.), due to the existence of standardized cost-effective protocols for their mass production. However, both rotifers and Artemia have nutritional deficiencies for marine species, particularly in essential n-3 highly unsaturated fatty acids (HUFA, e.g., docosahexaenoic acid and eicosapentaenoic acid). Enrichment of these live feeds with HUFA-rich lipid emulsions may lead to an excess dietary lipid and sub-optimal dietary protein content for fish larvae. In addition, rotifers and Artemia are likely to have sub-optimal dietary levels of some amino acids, vitamins and minerals, at least for some species. Several species of microalgae are also used in larviculture. These are used as feed for other live feeds, but mostly in the `green water' technique in fish larval rearing, with putative beneficial effects on feeding behaviour, digestive function, nutritional value, water quality and microflora. Copepods and other natural zooplankton organisms have also been used as live feeds, normally with considerably better results in terms of larval survival rates, growth and quality, when compared with rotifers and Artemia. Nonetheless, technical difficulties in mass-producing these organisms are still a constraint to their routine use. Improvements in inert microdiets will likely lead to a progressive substitution of live feeds. However, complete substitution is probably years away for most species, at least for the first days of feeding.
Similar to other industries, aquaculture constantly requires new techniques to increase production yields. Modern technologies and different scientific fields, such as biotechnology and microbiology, provide important tools that could lead to a higher quality and a greater quantity of products. New feeding practices in farming typically play an important role in aquaculture, and the addition of various additives to a balanced feed formula to achieve better growth is a common practice of many fish and shrimp feed manufacturers and farmers. As ‘bio‐friendly agents’, immunostimulants, such as biological factors, probiotics and vitamins, can be introduced into the culture environment to control and kill pathogenic bacteria, as well as to promote growth of the cultured organisms. In addition, immunostimulants are non‐pathogenic and non‐toxic and do not produce undesirable side effects when administered to aquatic organisms. In this review, we summarize previous studies performed with both traditional immunostimulants and the most promising new generation of immunostimulants, such as polysaccharides, nutrients, oligosaccharides, herbs, microorganisms, prebiotics and different biological factors. This review primarily focuses on their protective efficacies and on what is known concerning their effects on the immune systems of aquatic organisms when delivered in vivo .
Over the years, aquaculture has shown increasing development in terms of production. However, due to intensive farming practices, infectious diseases represent the main problem in fish farms, causing heavy economic losses. The use of antibiotics for controlling diseases is widely criticized for its negative impact, including selection of antibiotic‐resistant bacterial strains, immunosuppression, environmental pollution and accumulation of chemical residues in fish tissues. On the other hand, though vaccination is the most effective prophylactic method of preventing disease outbreaks, the development of effective formulations is often hindered by high production costs and the antigenic heterogeneity of the microbial strains. Recently, there has been increased interest in the possibility of using medicinal herbs as immunostimulants, capable of enhancing immune responses and disease resistance of cultured fish. Plant‐derived products seem to represent a promising source of bioactive molecules, being at the same time readily available, inexpensive and biocompatible. The aim of this article is to provide an overview of recent research dealing with the use of medicinal plants in aquaculture. Special attention is given to the information about the effects of plant extracts/products on fish growth, haematological profiles, immune responses and resistance to infectious diseases.
Considering the costs of feed costs (nearly 60% of production cost), nutrition, feeding and feed utilization are among the most important factors in commercial aquaculture. During the last decade, administration of functional feed additives has been practiced for enhancing nutrient digestibility and digestive enzyme activities of cultured fish and shellfish. Traditionally, antibiotics were used for boosting growth performance and nutrient digestibility in commercial aquaculture. However, emergence of resistance pathogens and possible risk to human health resulted in limitation or prohibition of prophylactic administration of antibiotics. Recently, there was increasing attentions towards dietary administration of functional feed additives that include probiotics, prebiotics and synbiotics for elevation of digestive enzyme activity and nutrient digestibility. The results of those studies revealed contradictory effects of different pro‐, pre‐ or synbiotics on various fish species. It seems that the effects are species specific and related to modulation of the intestinal microbiota. In view of this issue, the present review provides a comprehensive sight on the effects of different pro‐, pre‐ and synbiotics on digestive enzyme activity and nutrient digestibility in different species with special focus on the mode of action. In addition, the present review highlighted the gaps of existing knowledge as well as suggesting the subjects which needs additional studies.
Tilapia are the second most farmed fish worldwide and their production has quadrupled over the past decade due to ease of aquaculture, marketability and stable market prices. Tilapia aquaculture must adopt sustainable practices (such as polyculture) for continuing increased production and improved sustainability. This article reviews tilapia polyculture around the world and discusses its benefits, strategies and practices. Tilapia polyculture improves feed utilization, enhances water quality, increases total yield and profit. Further investment will increase these gains. Research on tilapia polyculture in China was also summarized and addressed that polyculture in semi‐intensive systems was a way of improving sustainability for tilapia aquaculture.
In this study, we documented the changes in the intestinal bacterial community at four stages in Litopenaeus vannamei: 14 days postlarvae (L14) and 1-, 2- and 3-month old juveniles (J1, J2, J3), using 454 pyrosequencing techniques. The intestinal bacterial community was dominated by three bacterial phyla, Proteobacteria, Bacteroidetes and Actinobacteria at all stages. However, the relative abundance and bacterial lineages varied at the family level. The intestinal bacterial community of L14 and J1 was similar, with dominant members belonging to the Comamonadaceae of Betaproteobacteria. Conversely, bacterial members affiliated to Flavobacteriaceae of Bacteroidetes were dominant in J2 and Vibrionaceae of Gammaproteobacteria was dominant in J3. The abundance of Microbacteriaceae of Actinobacteria also fluctuated during the four stages. Bacterial members of Flavobacteriaceae and Rhodobacteraceae (Alphaproteobacteria) were present through all growth stages, and likely form the intestinal core microbiome of L. vannamei. However, they varied at the operational taxonomic unit (OTU) level through the growth stages. The intestinal bacterial community of pond-rearing shrimp included the three main bacterial phyla identified above, and an additional group, Mycoplasmataceae of Mollicutes. Our results demonstrate that the intestinal bacterial community of L. vannamei was highly dynamic during the growth stages. Bacterial members belonging to Commamonadaceae dominated in the earlier growth stage of shrimp, possibly influenced by feeding with Artemia nauplii, but there was a shift to Flavobacteriaceae in the mid and Vibrionaceae in the late growth stages.
The aim of this study was to illustrate the effects of dietary loquat leaf extract ( LLE ) on the expression of some intestinal cytokines as well as serum innate immune parameters in common carp ( Cyprinus carpio ) fingerlings. The fish were fed with experimental diets supplemented with 0 (control), 0.25% (0.25 LLE ), 0.5% (0.5 LLE ) and 1% (1 LLE ) LLE over a 7‐week period. At the end of the trial, the serum lysozyme (Lys) activity, ACH 50, total Ig as well as the expression of IL 1B , IL 8 , TNF ‐alpha , LYZ and TGF ‐ β in intestine were evaluated. The results showed that administration of 0.5% or 1% LLE significantly increased serum total Ig. However, in case of serum Lys activity significant elevation was observed just in fish fed 0.5% LLE . Also, supplementation of diet with LLE significantly increased ACH 50 compared to the control group, regardless of inclusion levels. Gene expression studies revealed upregulation of TNF ‐alpha , IL 1B , IL 8 and LYZ in intestine of fish fed LLE . However, the effects varied dependent on LLE levels and the tested immune related gene. Also, in case of TGF ‐ β significant downregulation was observed just in 1% LLE treatment. In conclusion, dietary LLE supplementation significantly upregulated immune related genes in intestine and improves innate immune responses. Altogether, LLE can be recommended as fish immunostimulant in early stage of carp culture.
Optimising the amino acid supply in tune with the requirements and improving protein utilization for body protein growth with limited impacts on the environment in terms of nutrient loads is a generic imperative in all animal production systems. With the continued high annual growth rate reported for global aquaculture, our commitments should be to make sure that this growth is indeed reflected in provision of protein of high biological value for humans. The limited availability of fish meal has led to some concerted efforts in fish meal replacement, analysing all possible physiological or metabolic consequences. The rising costs of plant feedstuffs make it necessary to strengthen our basic knowledge on amino acid availability and utilization. Regulation of muscle protein accretion has great significance with strong practical implications. In fish, despite low muscle protein synthesis rates, the efficiency of protein deposition appears to be high. Exploratory studies on amino acid flux, inter-organ distribution and particularly of muscle protein synthesis, growth and degradation and the underlying mechanisms as affected by dietary factors are warranted. Research on specific signalling pathways involved in protein synthesis and degradation have been initiated in order to elucidate the reasons for high dietary protein/amino acid supply required and their utilization.
This study investigated the effects of different prebiotics, including galactooligosaccharide ( GOS ), fructooligosaccharide ( FOS ) and inulin ( INL ), on skin mucosal immune parameters, humoral immune responses as well as performance of common carp ( Cyprinus carpio ). Two hundred and forty specimens (13.85 ± 0.85 g) were stocked in 12 fibreglass tanks assigned into three treatments and a control group. The experimental diets were formulated to have equal level (2%) of the prebiotics. At the end of the feeding trial, the highest skin mucus lysozyme activities and total immunoglobulin (total Ig) were observed in GOS ‐fed group ( P < 0.05). However, skin mucus protease activity showed no significant difference among different dietary groups ( P < 0.05). Blood respiratory burst activity was significantly increased in all prebiotic‐fed fish compared to the control group ( P < 0.05); the highest activity was observed in GOS treatment. Furthermore, evaluation of humoral immune response revealed that feeding with GOS ‐supplemented diet significantly increased lysozyme and alternative complement ( ACH 50) activity as well as total Ig compared to the control and other prebiotic groups. While no significant difference was observed between FOS and INL groups, common carps fed GOS ‐supplemented displayed improved ( P < 0.05) growth performance, including final weight, weight gain, specific growth rate ( SGR ) and feed conversion ratio ( FCR ), compared to the control treatment. These results revealed that different prebiotics modulate carp growth and immune response in different manner, and GOS seems to be the most suitable prebiotic.
Responses to anaesthesia with essential oil ( EO ) of Aloysia triphylla (135 and 180 mg L −1 ) and tricaine methanesulfonate ( MS 222) (150 and 300 mg L −1 ) were assessed in silver catfish. Exposure to the anaesthetics elicited a stress response in the species. In the case of MS 222, it was displayed as a release of cortisol into bloodstream, elevation in hematocrit and plasma ion loss. The EO presented cortisol‐blocking properties, but increased haematocrit and disturbances of hydromineral balance were observed. Liver antioxidant/oxidant status of EO and MS 222‐anaesthetized silver catfish was also estimated. The synthetic anaesthetic induced lipoperoxidation, notwithstanding increased catalase contents, whereas the naturally occurring product was capable of preventing the formation of lipid peroxides, possibly due to combined actions of catalase and glutathione‐S‐transferase. Anaesthetic efficacy was also tested via induction and recovery times. Overall, the promising results obtained for the physiological parameters of the EO ‐treated fish counterbalanced the slight prolonged induction time observed for 180 mg L −1 . As for 135 mg L −1 , both induction and recovery times were lengthy; despite that, the EO was able to promote oxidative protection and mitigate stress. None of the MS 222 concentrations prompted such responses concomitantly.
Organic salts may improvement the animal performance, increasing the efficiency of nutrient utilization and modifying the intestinal microbiota. This study aimed to evaluate the effects of sodium butyrate and sodium propionate supplementation at different levels of dietary inclusions in the growth of Litopenaeus vannamei . In total, seven diets were evaluated: a control diet (without supplementation) and three diets from each sodium salt, propionate and butyrate, in concentrations of 0.5%, 1% and 2%. We used 21 tanks of 6000 L stocked with 150 shrimps (2.53 ± 0.03 g). The shrimps fed diets supplemented with propionate and butyrate, in all concentrations, increased their final weight. The feed efficiency, nitrogen retention, protein efficiency rate, survival and yield of shrimps fed the diet containing 2% butyrate were higher in comparison with control treatment. The shrimps supplemented with butyrate also showed lower counts of Vibrio sp. in the intestine. The shrimps fed the diet supplemented with butyrate and propionate also showed higher values of serum agglutination titre. Thus, it is possible to conclude that dietary supplementation with propionate and butyrate in different dietary concentrations modify the intestinal microbiota and improves the growth of L. vannamei .
A 20‐week feeding trial was conducted to measure growth, nutrient utilization and faecal/gut bacterial counts in triplicate groups of red hybrid tilapia, O reochromis sp., when fed diets supplemented with 0.5% organic acids blend ( OAB ), 1.0% OAB , 0.5% oxytetracycline ( OTC ) or a control diet (no additives). At the end of the feeding trial, tilapia were challenged with S treptococcus agalactiae for 22 days. Fish fed the OTC diet had significantly higher ( P 0.05). Phosphorus, dry matter and ash digestibility were significantly higher in the 1.0% OAB diet than the control diet. Fish fed the OAB diets had significantly lower colony‐forming units of adherent gut bacteria compared to the control or OTC treatments while those fed the 1.0% OAB diet had the lowest total faecal bacterial counts. Tilapia fed the 0.5% OTC or OAB diet had significantly higher resistance to S . agalactiae than those fed the control diet. This study indicates that dietary organic acids can potentially replace OTC as a growth promoter and antimicrobial in tilapia feeds.
This study was conducted to investigate graded levels of dietary zinc on the growth, flesh quality, and the relationship between flesh quality and muscle antioxidant status in young grass carp ( C tenopharyngodon idella V al.). Per cent weight gain ( PWG ), special growth rate ( SGR ), feed intake ( FI ), feed conversion ratio ( FCR ), anti‐hydroxy radical ( AHR ), superoxide dismutase ( SOD ), catalase ( CAT ), glutathione reducase ( GR ) activities and glutathione ( GSH ) content were significantly increased with increasing levels of Zn up to a point, and thereafter declined ( P < 0.05). Serum zinc, alkaline phosphatase ( AKP ), muscle anti‐superoxide anion ( ASA ), glutathione peroxidase ( GP x), glutathione‐ S ‐transferase ( GST ) activities and collagen content were significantly enhanced with dietary zinc levels up to a point ( P < 0.05), beyond which it plateaued. Cooking loss, shear force and malondialdehyde ( MDA ) were significantly reduced with increasing level of zinc up to a point, and thereafter increased ( P < 0.05). The pH value significantly increased with the increasing zinc levels, whereas the trend of protein carbonyl content was opposite. Flesh quality was positively related to the antioxidant enzymes activities in muscle of young grass carp. These results indicated that optimum zinc could improve growth, and improve flesh quality partly through improving muscle antioxidant status of young grass carp.
The bioflocs technology ( BFT ) for shrimp production has been proposed as a sustainable practice capable of reducing environmental impacts and preventing pathogen introduction. The microbial community associated with BFT not only detoxifies nutrients, but also can improve feed utilization and animal growth. Biofloc system contains abundant number of bacteria of which cell wall consists of various components such as bacterial lipopolysaccharide, peptidoglycan and β‐1, 3‐glucans, and is known as stimulating nonspecific immune activity of shrimp. Bioflocs, therefore, are assumed to enhance shrimp immunity because they consume the bioflocs as additional food source. Although there are benefits for having an in situ microbial community in BFT systems, better understanding on these microorganisms, in particular molecular level, is needed. A fourteen‐day culture trial was conducted with postlarvae of L itopenaeus vannamei in the presence and absence of bioflocs. To determine mRNA expression levels of shrimp, we selected six genes (prophenoloxidase1, prophenoloxidase2, prophenoloxidase activation enzyme, serine proteinase1, masquerade‐like proteinase, and ras‐related nuclear protein) which are involved in a series of responses known as the prophenoloxidase (proPO) cascade, one of the major innate immune responses in crustaceans. Significant differences in shrimp survival and final body weights were found between the clear water and in the biofloc treatments. m RNA expression levels were significantly higher in the biofloc treatment than the clear water control. These results suggest that the presence of bioflocs in the culture medium gives positive effect on growth and immune‐related genes expression in L .vannamei postlarvae.