Effects of Dietary Animal Protein Source Composition on the Growth Performance, Intestinal Health, and Protein Metabolism of Largemouth Bass (Micropterus salmoides)

Abstract

Terrestrial animal protein sources contain less antinutritional factors, high protein content, and functional factors, which are beneficial to fish health. Among them, poultry byproduct meal (containing 65%-73% protein rich in vitamins) and porcine meat meal (containing 45%-60% protein and high contents of proline and glycine) are the most widely used meals in aquatic compound feeds, and are important fish meal replacement sources. As a carnivorous fish species, largemouth bass (Micropterus salmoides) is highly dependent on dietary fish meal, and the level of fish meal added in its commercial feeds is up to 50%. However, the rising price of fish meal increases the farming cost of M. salmoides. Therefore, it is necessary to identify a suitable alternative protein source to reduce the amount of dietary fish meal and the feed cost. Therefore, seven compound feeds (D1-D7) were prepared in this study. The added ratios of fish meal/poultry byproduct meal/porcine meat meal were as follows: 45.0/22.6/0, 37.1/22.6/8.0, 28.8/22.6/16.0, 45.0/14.5/8.0, 45.0/5.3/16.0, 41.6/18.0/8.0, and 37.0/13.8/16.0. Juvenile M. salmoides (initial body weight ~55 g) were fed the above diets for 60 days with five replicates in each group. The effects of the animal protein source combination on the growth performance, tissue biochemical indices, muscle texture characteristics, liver protein metabolism, and intestinal inflammatory factor-related gene expression were evaluated. The water temperature during the feeding trial was 27.4-32.3 ℃ and the ammonia nitrogen concentration was 0.1-0.2 mg/L. After the feeding experiment, three fish were randomly selected from each cage to collect the serum, liver, intestinal tract, muscle, and other samples, which were then stored at -80 ℃. In addition, three fish were randomly selected from each cage to determine their morphological indices. At the same time, two fish were selected from each cage to determine the muscle texture characteristics and the whole fish proximate composition. Physiological and biochemical indices of serum and liver tissues, albumin, urea nitrogen (BUN), total amino acid (T-AA), alanine aminotransferase (ALT), aspartate aminotransferase, total protein (TP), and blood ammonia (SA) levels), were determined using commercial kits, and the texture characteristics of muscle were determined by using a texture analyzer. The moisture, crude fat, crude protein, and ash contents of whole fish and muscle were determined by atmospheric drying, Soxhlet extraction, Kjeldahl nitrogen determination, and Muffle furnace incineration, respectively. Real-time quantitative PCR was used to determine the expression levels of genes related to liver protein metabolism and the intestinal inflammatory response. All test data were expressed as the mean±standard error, and multiple comparisons were made by the Tukey test, with P 0.05). The whole-body crude protein content in the D3 group was significantly higher than that in the D1 group, and the crude lipid level in the D3 group was significantly lower than that in the D6 group (P 0.05). The serum T-AA content of fish in the D3 group was significantly higher than that in the D1 and D4 groups (P 0.05). In terms of muscle quality, the muscle hardness, adhesion, and mastication in the D3 group were significantly lower than those in the D4 and D6 groups, respectively (P 0.05). In addition, the mRNA expression levels of intestinal il-10 and liver tor, s6k1, akt, and pi3k in the D3 group were upregulated, and were significantly higher than those in the D7 group (P < 0.05). The mRNA expression levels of il-1β and il-6 in the intestines and 4ebp-1 in the liver of the D3 group were significantly lower than those of the D1 group (P < 0.05). These results indicated that combined use of 28.8% fish meal, 16.0% porcine meat meal, and 22.6% poultry byproduct meal had the best growth promotion effect on M. salmoides, and was able to improve liver protein synthesis and maintain intestinal health. The results of this study provided technical support for reducing the dependence of M. salmoides compound feed on fish meal.

Keywords

• micropterus salmoides
• animal protein source
• growth performance
• protein synthesis
• intestinal health