Beneficial roles of feed additives as immunostimulants in aquaculture: a review

Signiﬁcant efforts should be devoted to reducingwaste outputs from aquaculture operations in orderto lower the environmental impacts of aquaculturein many parts of the world. Since most aquaculturewastes are ultimately from dietary origin, reductionof waste outputs should ﬁrst be through improve-ments of diet formulation and feeding strategies.The ﬁrst step in the production of feeds producingless solid waste is to eliminate poorly digestibleingredients (such as whole grain or grain by-products used as binders and ﬁllers in the feedformulae) and to use highly digestible ingredientswith good binding properties. Further reduction ofsolid waste can then be achieved through carefulselection of the ingredients to improve apparentdigestibility and the nutrient balance of the feed.Nitrogen waste outputs can be reduced through thereduction of the digestible protein to digestibleenergy (DP/DE) ratio of the diet. Phosphorus wasteoutputs can be reduced through careful selection ofthe ingredients and optimization of the digestiblephosphorus content of the diet to meet therequirement of the ﬁsh but avoid greatly exceedingthis required level. Finally, feeding practices thatminimize feed wastage should be adopted since feedwastage can have a very signiﬁcant impact onwaste outputs from ﬁsh culture operations.Keywords: aquaculture, waste, feed, feedingIntroductionOvert the past decade, the environmental impacts ofaquaculture operations have become a matter ofconcern for the public, the various levels ofgovernment and the aquaculture producers them-selves. Minimizing environmental impacts is there-fore a key factor in insuring long-term sustainabilityof the aquaculture industry.Containment and collection of wastes, both solidand dissolved, is very difﬁcult and costly inaquaculture, as the wastes are rapidly dispersedinto the surrounding waters. The release of solidwastes, phosphorus (P) and nitrogen (N) fromaquaculture operations may have signiﬁcant eutro-phication effects on receiving waterbodies andassociated ecosystems (Persson 1991). P wasteoutputs are a greater concern in freshwater sinceP is generally the most limiting factor for plant(algae) in that environment. N waste outputs aregenerally a greater concern in the marine environ-ment for the same reason (Persson 1991). Solidwastes (faecal material and wasted feed) settling tothe sediment can have an impact on the benthicecosystem of inland and marine waters (Gowen,Weston & Ervik 1991). Degradation of organicwaste by bacteria and other organisms leads to theconsumption of oxygen (O

A review of diet formulation strategies and feeding systems to reduce excretory and feed wastes in aquaculture.

Taurine: a critical nutrient for future fish feeds

Publisher Summary Diet formulation and manufacture are exercises in compromise between the ideal and the practical. The perfect feed formulation that meets the nutritional needs of an animal or fish must always be modified to be less than ideal so that it can be manufactured. Diet formulation and manufacture are not independent activities. When feeds are formulated, the pelleting characteristics of mixtures are just as important as the nutritional content of the mixture. Production diets must be economical to manufacture, ship, store, and deliver to the fish. Pellets must remain intact in water until fish consume them. This ensures adequate intake of nutrients that might otherwise leach out of the pellets and minimize water pollution caused by disintegrating pellets. Thus, the way in which feed ingredients are chosen, prepared, combined, and processed is influenced by many factors, and compromise between the ideal and the practical is a necessity requiring a solid foundation of knowledge and experience. Rising concerns about the effects of fish farming on the aquatic environment, coupled with concerns about the dependence of fish feeds on fish meal produced from fully utilized or over-utilized wild fish stocks, have also influenced fish feed formulation and manufacture.

Diet Formulation and Manufacture

The use of antibiotics in the feeds of cultured aquatic animals to mitigate infectious diseases or to boost growth performance is commonly practised. In recent years, the prophylactic use of antibiotics has been criticized which eventually led to their ban in animal production by many countries. In view of the current restrictions on antibiotic use, there is a critical need to evaluate alternatives. One potential substitute for antibiotic growth promoters in aquafeeds is organic acids and/or their respective salts. The use of dietary organic acids in the culture of aquatic animals has been the focus of much research and commercial interest recently. This review provides a comprehensive compilation of the current knowledge on the use of organic acids in aquafeeds, with emphasis on its impacts on growth, nutrient utilization, mineral availability, gut microbiota and disease resistance. Many studies have reported that some organic acids can significantly enhance the growth performance and health status of fish. Contradictory results have also been reported, which seems to depend on the aquatic animal species, type and concentrations of organic acids and the culture conditions used. Recent research indicating the beneficial impact of dietary organic acids on shrimp growth and health is highlighted. Possible mechanisms of action of these functional feed additives are discussed. Strategies for enhancing the effectiveness of dietary organic acids are given. This review aims to contribute to the sustainability of global aquaculture production by providing a viable alternative to harmful antibiotics, thereby meeting the growing consumer demand for antibiotic-free seafood products.

The utilization and mode of action of organic acids in the feeds of cultured aquatic animals

Juvenile rainbow trout Oncorhynchus mykiss (Walbaum) were fed six low-phosphorus (P) diets supplemented with two different sizes of ground fish bone-meals (fine, 68 μm or less; coarse, 250–425 μm) and a coarse bone-meal diet containing four levels of citric acid (0, 4, 8 or 16 g kg−1 diet) to investigate the effects of pH and bone particle size on P bioavailability The basal diet provided 34 g P kg−1 and bone-meal increased P contents to 54–60 g P kg−1 Coarse bone-meal diets supplemented with 0, 4, 8 or 16 g kg−1 of citric acid had pH values of 60, 57, 54 and 50, respectively Weight gain and whole-body water, protein and lipid contents were not influenced by bone-meal supplementation Supplementing the basal diet with both coarse and fine bone-meal significantly increased whole-body ash content Fish fed no bone-meal were hypophosphataemic compared with fish fed with either fine or coarse bone-meals Phosphorus in fine bone-meal had higher availability than P in coarse bone-meal Bone-meal supplementation significantly decreased whole-body manganese content from 89 μg g−1 in fish fed no bone-meal to 23 and 45 μg g−1 in fish fed with fine and coarse bone-meals, respectively The concentration of magnesium increased but zinc concentration was not affected by bone-meal supplements Citric acid increased whole-body ash content but the influence of citric acid on the body P content was not significant (P = 007) Dietary acidification by citric acid significantly increased whole-body iron in a linear fashion The bioavailability of dietary P can be improved by fine grinding the bone in fish meals

Ruohonen

Papers

Supplemental citric acid and particle size of fish bone‐meal influence the availability of minerals in rainbow trout Oncorhynchus mykiss (Walbaum)