Supplementation of organic acids and algae extracts in the diet of red drum Sciaenops ocellatus: immunological impacts
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2016 John Wiley & Sons Ltd The evaluation of a wide variety of immunostimulatory compounds in the diet of cultured fish has received heightened attention in recent years. However, two organic acids, polyhydroxybutyrate (PHB) and potassium diformate (KDF), have been researched to only a limited extent with aquatic species but have been shown to have various positive effects on terrestrial animals. Two algae extracts, carrageenan and alginic acid, also have been shown to elicit immunostimulation in some fish. Therefore, this study was conducted with red drum, Sciaenops ocellatus, as a model marine species to study the effects of organic acids and algae extracts as feed supplements by evaluating several humoral and cellular immune responses. A 7-week feeding trial was conducted with disease-free juvenile red drum (average initial wt. 2.60.2g). Semipurified diets were formulated to be isocaloric and contain 40% crude protein. Based on previous studies with other fish species, experimental diets were produced by supplementing the basal diet with KDF at 0.6%, PHB at 2%, alginic acid at 1% or carrageenan at 0.5% by weight in place of cellulose. Fish were stocked into 110-L aquaria operated as a recirculating system with each diet assigned to three replicate aquaria containing 15fish. At the end of 7weeks, weight gain and feed efficiency were significantly (P<0.0001) reduced in fish feed PHB compared to the basal diet and both algae extracts. The greatest phagocytic activity was found in fish fed the diet containing PHB. Total immunoglobulin level was higher in fish fed the diet supplemented with carrageenan. Goblet cell proliferation was greatest in the posterior end of the gastrointestinal tract but not different among dietary treatments. Organic acids and algae extracts evaluated in this study produced variable immunological responses in red drum with carrageenan showing the greatest potential as an immunostimulant.
