Dietary n−3 LC-PUFA requirements in silvery-black porgy juveniles (Sparidentex hasta)

Abstract

Abstract To determine the effects of n − 3 long chain polyunsaturated fatty acids (n − 3 LC-PUFAs) in juvenile silvery-black porgy ( Sparidentex hasta ), an eight-week feeding trial was conducted using five isonitrogenous and isolipidic semi-purified diets containing graded levels of n − 3 LC-PUFAs (0.1, 0.6, 1.2, 1.9 and 4.2%). Specific growth rate, body weight gain (WG) and feed conversion ratio (FCR) improved by increasing the dietary LC-PUFA content from 0.1% to 1.2%, and remained stable at higher n − 3 LC-PUFA levels. Apparent digestibility of nutrients did not change among different groups; however, fish fed 0.1% n − 3 LC-PUFAs showed the lowest lipid and protein retention values. The whole body and liver fatty acid profiles were correlated with the fatty acid profile of diets, especially for total monounsaturated fatty acids, DHA, EPA, ARA/EPA, DHA/EPA and n − 3/n − 6 ratios. Hemoglobin content and hemolytic and bactericidal activities were highest in fish fed 1.2% n − 3 LC-PUFAs. Fish fed 0.1% n − 3 LC-PUFAs had the highest hepatosomatic index, a change in the liver fatty acid profile, an increase in plasma cholesterol, triglyceride, low density lipoprotein, very low density lipoprotein and alkaline phosphatase concentrations; as well as a decrease in plasma glucose, which indicated signs of n − 3 LC-PUFA deficiency in this group. The broken-line regression method using FCR and WG data allowed us to estimate that the minimum nutritional requirement for n − 3 LC-PUFAs in silvery black porgy juveniles was between 0.6 and 0.8% in diets containing 15% lipids. Statements of relevance Silvery-black porgy ( Sparidentex hasta , Valenciennes 1830) is a commercially valuable carnivorous fish species in Oman Sea and Persian Gulf region for supporting marine aquaculture activities. Thus, the aim of present study was to provide insight into the nutritional requirements of silvery-black porgy, by evaluating the effects of dietary n − 3 LC-PUFA levels on growth performance, feed utilization, body composition and health indices in silvery-black porgy juveniles.