Effects of dietary protein level and source on the growth and survival of two genetic lines of specific pathogen free Pacific white shrimp, Penaeus vannamei
An eight week trial compared the performances of two genetic lines of Penaeus vannamei, T line and G line, fed with different levels and sources of dietary protein. Both lines were originated from the same founder populations but had gone through genetic selection targeting different breeding goals for more than four generations. T line was bred for fast growth and Taura syndrome viral disease resistance, and G line was bred for fast growth and production yield under super high density. Five dietary treatments were employed: two commercial diets and three semipurified diets (A, B, and C) The semipurified diets were formulated at similar levels of digestible energy. Diet A contained 35% crude protein (CP) from marine meals (fish, 15% and squid, 15% Diet C contained 35% CP from a reduced marine protein level from fish (11.5% and squid meals (11.5% Diet B contained only 20% CP but had the same level of marine protein as diet C. The two commercial shrimp feeds, containing 35% and 40% protein, served as reference diets. Three replicate tanks per dietary treatment were used. Each tank was stocked with 50 tagged shrimp (25 each of T line and G line) and 100 untagged shrimp, with average initial weight (IWT) of 10.4 g, at a density of 107/m2. Diet significantly affected shrimp growth (p 0.0001) but did not interact with shrimp line. Shrimp fed either diet A or diet C grew over 25% faster than those fed diet B or either of the two commercial diets. Diets A and C yielded similar growth (0.30 to 0.33 g/day) and survival rates (83 to 93% to a harvest size of over 29 g per shrimp, suggesting that the soy protein isolate that replaced part of the marine protein in diet C can serve as a good alternative protein source. Growth rates of the two shrimp lines were similar regardless of dietary protein levels or sources, but dietary plant protein level did interact with shrimp line when the measure was survival: T line survived better than G line on average when fed diet B, a nutritionally inferior diet containing 20% protein and no plant protein, but not when fed diet C, containing 35% protein, 15% of which was of plant origin (soybean) Microsatellite marker analyses quantified the genetic relationship of the two lines and confirmed that they were the most closely related of the lines derived from the same founding stock. This preliminary study provided information that will be useful for further studies of the relationship between dietary nutrition and genetics and for exploration of the potential of genetic selection for improving the efficiency of plant protein use in shrimp.