Fish oil replacement with tallow and emulsifier in diet for olive flounder, Paralichthys olivaceus

Abstract

In Chapter I, the supplementary effect of an emulsifier mixture (polyoxyethylene (20) sorbitan monolaurate and distilled monoglycerides) was investigated on feed utilization, growth performance and immunity of olive flounder (Paralichthys olivaceus), replacing fish oil with beef tallow. A fish oil containing diet was considered as a positive control (PC) and a diet containing beef tallow replacing fish oil was considered as a negative control (TW). Two other diets (EM01 and EM02) were prepared by adding 0.01% and 0.02% emulsifier into TW diet. After eight weeks of a feeding trial, growth performance and feed utilization were significantly higher in fish fed EM01, EM02 or PC diets compared to those fed TW diet. Dry matter digestibility was higher in EM01 and EM02 diets than that in TW diet and comparable to PC diet. Lipid digestibility was significantly higher in PC diet compared to that in TW diet. Liver EPA and DHA levels were lower, and oleic acid level was higher in fish fed diets containing tallow compared to PC group. Significantly increased aspartate aminotransferase and triglyceride levels were observed in TW group. Dietary emulsifier restored the reduced performance of olive flounder fed diets containing tallow instead of fish oil. The optimum inclusion level of the emulsifier could be approximately 0.02% when beef tallow was included in diets. Chapter 2, effects of graded levels of arachidonic acid (ARA) in a low fish meal diet were evaluated on growth, feed utilization and immunity of olive flounder at suboptimal temperature (15.2±1.2 ˚C) season. Six low fish meal diets (30% fish meal and 30% plant protein blend) were formulated with graded levels of ARA. A control diet was formulated incorporating 3% fish oil and 5.1% soybean oil without ARA (ARA0.0). Five different levels ARA were added replacing soybean oil to contain 0.3, 0.6, 0.9, 1.2 and 1.5% ARA (ARA0.3, ARA0.6, ARA0.9, ARA1.2 and ARA1.5) respectively. Triplicate groups of fish (88.24 ±0.06 g) were distributed into 18 polyvinyl circular tanks (215 L) with 24 fish per tank and fed one of the experimental diets for nine weeks. Significantly improved growth performance was shown in ARA0.6 group. Liver C18:2n-6 was significantly reduced and liver ARA content significantly increased with its increase in diets. Nitroblue tetrazolium activity was significantly higher in ARA0.6 and the highest super oxide dismutase (SOD) and myeloperoxidase (MPO) levels were observed in ARA0.9 treatment. Immunoglobulin and lysozyme activity were significantly improved in ARA0.3 group. Antiprotease activity was increased with ARA0.6 and ARA0.9 diets. ARA0.3 diet fed fish showed lower liver lipid content compared to ARA0.0 group. These results indicates that the supplementation of 0.3-0.9% ARA might improve the growth, immune and hematological parameters of olive flounder.