EFFECTS OF FISH MEAL LEVELS ON GROWTH AND IMMUNITY OF BLACK CARP (MYLOPHARYNGODON PICEUS) IN DIFFERENT CULTURE DENSITIES

To study the effects of fishmeal level and stocking density on the growth and immunity of juvenile black carp, a two-factor design of fishmeal level (10%, 20%) × culture density (50, 100, 200 tails/box) was applied. The young black carp (2.50±0.02) g were divided into 6 groups of L₅₀, L₁₀₀, L₂₀₀, H₅₀, H₁₀₀ and H₂₀₀ with 3 replicates in each group using reservoir cages (1.5 m×1.5 m×1.5 m). In the early stage of experiment (week 8), the weight gain rate of black carp increased at first and then decreased with the increase of the stocking density, and the weight gain rate of the H₂₀₀ group was higher than that of the L₂₀₀ group (P>0.05), while it was significantly lower than that of the L₂₀₀ group in the later stage (week 16) (P<0.05). The survival rate of the L₂₀₀ group was lower than that of the L₅₀ group (P>0.05). The stocking density and fishmeal levels showed an interactive effect on the survival rate and the weight gain rate (P<0.05). In the early stage, levels of lysozyme (LSZ) and serum glucose (GLU) of the low-fishmeal group decreased firstly and then increased with the increase of density, and intestinal secretory immunoglobulin A (S-IgA) increased. The levels of LSZ, complement 4 (C4), immunoglobulin M (IgM), S-IgA and cortisol (COR) of the H₂₀₀ group were higher than those of the L₂₀₀ group, while the GLU of the H₂₀₀ group was lower than that of the L₂₀₀ group (P>0.05). In the later stage, the level of C4 in the high and low fishmeal groups decreased at first and then increased with the increase of density (P>0.05). In the H₂₀₀ group, the IgM and COR levels were higher than those of the L₂₀₀ group, and the level of GLU was lower than that of the L₂₀₀ group (P>0.05). In summary, high-density culture negatively regulate the growth performance, body’s immunity and anti-stress ability. The increased fishmeal level reversed the effects of high-density culture on growth performance, the immunity and anti-stress ability in the early stage. However, in the later stage, the increased fishmeal level only reduce high-density culture-mediated the survival rate without rescuing the growth performance and immune function.