Under intensive culture conditions, fish are subject to increased stress owing to environmental (water quality and hypoxia) and health conditions (parasites and infectious diseases). All these factors have negative impacts on fish well-being and overall performance, with consequent economic losses. Though good management practices contribute to reduce stressor effects, stress susceptibility is always high under crowded conditions. Adequate nutrition is essential to avoid deficiency signs, maintain adequate animal performance and sustain normal health. Further, it is becoming evident that diets overfortified with specific nutrients [amino acids, essential fatty acids (FAs), vitamins or minerals] at levels above requirement may improve health condition and disease resistance. Diet supplements are also being evaluated for their antioxidant potential, as fish are potentially at risk of peroxidative attack because of the large quantities of highly unsaturated FAs in both fish tissues and diets. Functional constituents other than essential nutrients (such as probiotics, prebiotics and immunostimulants) are also currently being considered in fish nutrition aiming to improve fish growth and/or feed efficiency, health status, stress tolerance and resistance to diseases. Such products are becoming more and more important for reducing antibiotic utilization in aquafarms, as these have environmental impacts, may accumulate in animal tissues and increase bacterial resistance. This study reviews knowledge of the effect of diet nutrients on health, welfare and improvement of disease resistance in fish.

Nutrition and health of aquaculture fish.

Utilisation of dietary carbohydrates in farmed fishes: New insights on influencing factors, biological limitations and future strategies

Effect of dietary lipid levels on growth, feed utilization, body composition and serum metabolites of meagre (Argyrosomus regius) juveniles

World food fish production has increased significantly during the past decades. As fisheries captures stagnate the additional production of fisheries products needs to be fulfilled by aquaculture production. This puts an enormous pressure on the use of fishmeal (FM) and fish oil (FO) for inclusion in aquafeeds with the consequent increase in price of these commodities with demand. The use of fisheries by-products in aquafeeds is also environmentally unsustainable. Thus, reducing aquafeeds dependency on FM and FO is of the utmost importance and it is a priority for the sustainable development of aquaculture, particularly for carnivorous species. Overall, reducing half of the FM and FO in carnivorous fish diets is relatively simple. However, further reductions are more complicated without affecting growth performance and animal health. Further, FO is nowadays the only commercial source of essential fatty acids for marine fish; thus it is at risk of becoming a bottleneck for the growth of marine fish production. Thus, it is mandatory to pursue efforts to replace FM and FO in aquafeeds and to develop strategies that minimize the impacts of FO reduction in the diet and on fish fillet quality. The alternative aquafeeds (low in FM and FO) must also ensure good fish health and a resultant final product that is nutritionally adequate, safe to eat and well accepted by consumers. This chapter provides a comprehensive review of feedstuffs used in aquafeeds, indicating potential advantages and inconveniences of their use. Overall, there is potential for significant sparing of FM and FO in carnivorous fish diets during the grow-out phase without affecting fish performance. However, more research is required to evaluate the effects of simultaneous replacement of FM and FO in the diet, as well as aspects related to immunological status, oxidative status, and health and disease resistance of animals fed these alternative diets.

Replacing fishmeal and fish oil in industrial aquafeeds for carnivorous fish

Temperature and dietary carbohydrate level effects on performance and metabolic utilisation of diets in European sea bass (Dicentrarchus labrax) juveniles

In this study, two growth trials were conducted to evaluate the effect of dietary protein and lipid levels on growth and feed utilization of white sea bream (Diplodus sargus) juveniles. For the first trial, five diets were formulated to contain 120 g kg−1 lipid and increasing levels of protein, ranging from 400 to 600 g kg−1. Two additional diets were formulated with 400 and 600 g kg−1 protein and 180 g kg−1 lipids. The diets were fed to apparent visual satiety to duplicate groups of fish with a mean weight of 1.5 g for 10 weeks. For the second growth trial, four diets were formulated to contain 120 g kg−1 lipid and 380–520 g kg−1 protein. Two additional diets were formulated with 380 and 520 g kg−1 protein and 180 g kg−1 lipids. The diets were fed to apparent visual satiety to triplicate groups of fish with a mean weight of 41 g for 12 weeks. At the end of both trials, there were no growth differences among groups independent of the dietary protein content. In the first trial, growth was negatively correlated to dietary lipid levels. No significant differences of feed intake were detected among groups in both trials, but a direct correlation between feed efficiency and dietary protein level was observed. Protein efficiency ratio and nitrogen (N) retention (% N intake) significantly decreased with the increase of dietary protein levels. In both trials, energy retention (% energy intake) was highest in groups fed on diets with the highest protein-to-energy (P/E) ratio. At the end of both trials, no significant differences in whole-body composition were observed among groups. Specific activity of enzymes involved in amino acid catabolism [aspartate aminotransferase (AST), alanine aminotransferase (ALT) and glutamate dehydrogenase (GDH)] showed no significant differences with dietary protein level in both trials. Nevertheless, in the first trial, a significantly lower GDH activity was observed in fish fed with higher dietary lipid levels. No differences were found for specific activity of the lipogenic enzymes, fatty aid synthetase and glucose-6-phosphate dehydrogenase, in the second trial. Results of this study indicate that a diet with a protein level of 380–420 g kg−1 and a P/E ratio of 20 g protein MJ−1 satisfies the growth requirements of D. sargus juveniles. Also, within the range tested, no evidence of protein sparing by dietary lipids seems to occur.

Effect of dietary protein and lipid levels on growth and feed utilization of white sea bream (Diplodus sargus) juveniles

Growth performance and metabolic utilization of diets with different protein:carbohydrate ratios by white sea bream (Diplodus sargus, L.) juveniles

A trial was undertaken to estimate the protein requirement of white sea bream (Diplodus sargus). Five fish meal-based diets were formulated to contain graded levels of protein (from 60 to 490 g kg⁻¹). Each diet was assigned to triplicate groups of 25 fish with a mean individual body weight of 22 g. Fish fed the 60 g kg⁻¹ protein diet lost weight during the trial, while growth improved in the other groups as dietary protein level increased up to 270-370 g kg⁻¹. Feed efficiency improved as dietary protein level increased. Maximum protein efficiency ratio (PER) was observed with the 17% protein diet. N retention (NR) (% N intake) was not different among groups fed diets with 17% protein and above. Ammonia excretion (g kg⁻¹ABW day⁻¹) increased as dietary protein level increased, while no differences in urea excretion were noted. An exponential model was used to adjust specific growth rate and NR (g kg⁻¹ day⁻¹) to dietary protein level. Based on that model, dietary protein required for maximum retention was 330 g kg⁻¹, while for maximum growth it was 270 g kg⁻¹. On a wet weight basis, there were no differences in whole body composition of fish-fed diets with 170 g kg⁻¹ protein and above, except for the protein content, which was lower in group fed the 170 g kg⁻¹ protein diet than the 490 g kg⁻¹ protein diet. Specific activities of hepatic amino acid catabolism enzymes (glutamate dehydrogenase, alanine aminotransferase and aspartate aminotransferase) increased as dietary protein levels increased. There were no differences among groups in fatty acid synthetase and malyc enzyme but 6-phosphate dehydrogenase (G6PDH) was significantly lower in fish fed the 60 g kg⁻¹ protein diet than the 170 and 490 g kg⁻¹ protein diets.

Dietary protein requirement of white sea bream (Diplodus sargus) juveniles

.— A 8-wk trial was performed with white sea bream, Diplodus sargus, juveniles (17.3 g initial weight) to evaluate the effect of dietary lipid levels on growth performance and whole-body composition. Six experimental diets were formulated to be isoproteic (45% protein) and to contain from 9 to 24% dietary lipid levels (dry matter basis). Fish meal and fish oil were used as the main protein and lipid sources, respectively. At the end of the trial, there were no significant differences (P > 0.05) among groups in fish performance or in whole-body composition. From the results of this trial, it is concluded that, within the range of values tested, increasing dietary lipid levels above 9% has no advantage as it does not promote growth or spare protein for growth purposes.

R. Sá

Papers

Effect of dietary protein and lipid levels on growth and feed utilization of white sea bream (Diplodus sargus) juveniles

Growth performance and metabolic utilization of diets with different protein:carbohydrate ratios by white sea bream (Diplodus sargus, L.) juveniles

Dietary protein requirement of white sea bream (Diplodus sargus) juveniles

Dietary Lipid Utilization by White Sea Bream (Diplodus sargus) Juveniles