Effects of dietary n-3HUFA on different growth stages of the white shrimp, Litopenaeus vannamei: Growth, haematological characteristics, enzyme activities and fatty acid profiles

This study investigated the effects of n-3 high unsaturated fatty acid (n-3HUFA) levels on the growth performance, antioxidant enzyme activities and fatty acid profiles of both subadult and adult Litopenaeus vannamei (L. vannamei). Seven iso-nitrogenous and iso-lipidic diets were used, containing n-3HUFA concentrations of 1.6 (control), 4.8, 7.4, 13.9, 23.9, 29.2 and 34.4 g/kg, respectively. Two 8-week feeding trials were conducted to determine the dietary n-3HUFA requirements of L. vannamei with an initial body weight of 4.25 +/- 0.00 g (subadults) and 8.50 +/- 0.01 g (adults). The results showed that the dietary n-3HUFA level significantly affected the weight gain rate (WGR), specific growth rate, the feed conversion ratio and the hepatosomatic index (HSI) (p < 0.05), but did not significantly affect the survival rate (p > 0.05). At appropriate level, dietary n-3HUFA improved growth performance and HSI of both subadult and adult L. vannamei. Both subadults and adults showed significant differences in body composition (p < 0.05), except for moisture and crude ash (p > 0.05). Cholesterol and low-density lipoprotein significantly decreased with increasing dietary n-3HUFA both in subadults and adults (p < 0.05); however, triglyceride showed no significant change (p > 0.05). High-density lipoprotein (HDL) in subadults was significantly affected by dietary n-3HUFA (p < 0.05), but followed no apparent regularity; HDL significantly changed in adults and showed an upward trend followed by a downward trend (p < 0.05). There was no significant effect on aspartate transaminase (AST) activity in subadults, but AST in adults and alanine transaminase (ALT) in subadults and adults were significantly affected (p < 0.05). Dietary n-3HUFA significantly affected serum polyphend oxidase, malic dehydrogenase, alkaline phosphatase, superoxide dismutase and sodium-potassium adenosine triphosphatase enzyme activities in gills (p < 0.05). The fatty acid composition of the shrimp tissue was associated with the fatty acid composition of the diet. Dietary n-3HUFA supplementation significantly improved the contents of tissue n-ary sumation HUFA and n-3HUFA, increased the n-3/n-6 ratio in the tail muscle and decreased the contents of tissue polyunsaturated fatty acid and saturated fatty acid (p < 0.05). Based on the WGR, the broken-line equations indicated that the optimum requirements of dietary n-3HUFA were determined to be 9.0 and 5.1 g/kg for subadult and adult L. vannamei, respectively.