Abstract
In recent years, largemouth bass have become one of the most commonly aquacultured species in China, however, its low survival rate during larval weaning has always been a bottleneck that has restricted industrial development. Understanding the changes in liver metabolism and intestinal microflora during the weaning of largemouth bass larvae can help to design better weaning strategies and improve survival. In this study, liver mRNA and intestinal microflora 16S rRNA genes were analyzed using high-throughput sequencing at the pre, mid, and post weaning stages [15, 30, 45 days post hatching; total length (cm) were 2.21 ± 0.12, 3.45 ± 0.21, 5.29 ± 0.33, respectively]. The transcriptome results revealed that the genes with increased expression were related to amino acid metabolism in the pre-weaning stage, but they were related to fatty acid metabolism in the post-weaning stage. A similar phenomenon was observed in the intestinal microflora where the dominant microbe Proteobacteria (relative abundance 56.32%) in the pre-weaning stage was gradually replaced by Firmicutes (relative abundance 62.81%) by the post-weaning stage. In addition, the three most important digestive enzymes (trypsin, lipase, and amylase) in the intestine were significantly decreased during the mid-weaning stage (P < 0.05), which was also true for some genes crucial to immune pathways in the liver. Overall, these findings showed that weaning in largemouth bass can cause changes in liver metabolism and intestinal microbial communities, which has improved our understanding of fish adaptation to changes in food sources during weaning.
Highlights
While the global demand for aquatic products strongly increased over the last 20 years, fisheries resources have sharply declined due to overfishing, prompting the aquaculture industry to rapidly increase its production, making it the fastest growing sector in the animal production field (FAO, 2018)
The expression of genes related to fatty acid metabolism pathways significantly increased during the weaning process, while the expression of genes related to amino acid metabolism decreased (Figure 2)
In the mid-weaning period, the palatability of artificial compound feed was inferior to animal bait such as Chironomus plumosus, and we found that the big fish had already eaten the little fish
Summary
While the global demand for aquatic products strongly increased over the last 20 years, fisheries resources have sharply declined due to overfishing, prompting the aquaculture industry to rapidly increase its production, making it the fastest growing sector in the animal production field (FAO, 2018). Many fishes have difficulty transitioning from live prey to formulated diets (weaning) as they mature through their larval stages, a transition that has consistently proven to be a major bottleneck in fish farming (Rønnestad et al, 2013; Sun et al, 2015). Weaning of Largemouth Bass is the process of gradually replacing live prey with artificial feed in fish larvae. Weaning has been investigated in a variety of fishes, with a focus on the effects of the co-feeding method, start time, and duration of weaning on growth performance and survival of larvae. The success rate of weaning can be affected by the nutrient composition of formula feeds (Gisbert and Mozanzadeh, 2019)
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