| Popis: |
Pacific white shrimp Penaeus vannamei, as one of the most productive and economically valuable shrimp species in the world, have many favorable characteristics, such as a short growth cycle, strong adaptability and disease resistance, and a low nutritional demand. They are omnivorous animals whose diet mainly consists of animal-derived food. Conventional feed used in their culture contains fishmeal as the main protein source. Feed costs account for 40%~60% of their production costs. Therefore, breeding P. vannamei strains without demand for fishmeal would be an effective way to address the issues of fishmeal shortage and high feed costs. Improving utilization efficiency for diets without fishmeal is key to breeding such P. vannamei strains. In this study, genetic parameters for feed efficiency traits (feed efficiency ratio, feed intake, and weight gain) and genotype by environment interaction were evaluated using two diets, one without fishmeal (38% protein) and one with 25% fishmeal (42% protein).Thirty families of P. vannamei were selected for a 40-day feeding experiment. A total of 900 shrimp (30 animals per family) were selected. Fifteen animals per family were fed a zero-fishmeal diet, and the other 15 animals were fed a high fishmeal diet. The feed intake and body weight of all animals were measured for calculating the feed efficiency ratio and weight gain. The variance components for these traits were estimated using a univariate model and an average information restricted maximum likelihood algorithm, and genetic (phenotypic) correlations between traits were estimated using bivariate analysis.The results showed that shrimp fed a high fishmeal diet exhibited a significantly higher mean weight gain (62.00%) and feed efficiency ratio (124.00%) than those fed a zero-fishmeal diet, which had a mean weight gain of 23.50% and feed efficiency ratio of 49.40%. There was a small difference in the mean feed intake between shrimp fed a high fishmeal diet (7.09 g) and those fed a zero-fishmeal diet (7.28 g).The heritability estimates for feed intake of shrimp fed zero- and high fishmeal diets were 0.699 ±0.155 and 0.556±0.139, respectively. For weight gain, the heritability estimates of shrimp fed zero- and high fishmeal diets were 0.458±0.140 and 0.667±0.146, respectively, which were high. However, the differences between diets and between traits were not statistically significant (P > 0.05). The heritability estimates for feed efficiency ratio of shrimp fed zero- and high fishmeal diets were 0.186 ±0.098 and 0.341±0.110, respectively, which were low to medium. The differences in feed efficiency ratio between diets was not statistically significant (P > 0.05). All the above heritability estimates were overestimated, to some extent, because common environmental effects were not estimated. Therefore, there was not much genetic variation in feed efficiency ratio in shrimp fed a zero-fishmeal diet, suggesting limited potential in selection breeding of this trait.Regardless of diet, genetic correlations among feed intake, weight gain, and feed efficiency ratio were moderate to high (0.580±0.188 to 0.945±0.040). Genetic correlations between diets were 0.580± 0.171 and 0.676±0.155 for feed intake and weight gain, respectively, indicating that these two traits had moderate genotype by diet interactions. The genetic correlation between diets was only 0.299±0.304 for feed efficiency ratio, which indicates a serious genotype by diet interaction. According to the above results, use of a zero-fishmeal diet is not good for the culture and breeding of P. vannamei. In the future, fishmeal content in the diet may be appropriately increased, and genetic parameters and potential feed efficiency traits should be evaluated in low fishmeal diets. |
