Feeding ecology of Lagocephalus spadiceus in the Beibu Gulf by high-throughput sequencing and stable isotope analyses

The demersal fish populations constitute a valuable commercial resource in the Beibu Gulf, northern South China. However, our understanding of the ontogenetic dietary shifts of fish, particularly Lagocephalus spadiceus, which is the most widely distributed fish in the northern South China Sea, is lacking. Therefore, we conducted a study using high-throughput sequencing and stable isotope analyses to examine the diet of L. spadiceus. The individuals were collected during 2 bottom trawl surveys in April and August 2022. The length distribution showed that small L. spadiceus was more abundant in shallow water, whereas large fish were generally found in offshore water. High-throughput sequencing indicated that L. spadiceus mainly fed on crustaceans and fish. Ontogenetic changes in diet composition and stable isotope values were also observed. As L. spadiceus grew, they started preying on larger individuals, specifically fish. The 15N enrichment in large fish supported to small fish supports these findings. The trophic niche indicated a segregation between individuals in shallow waters (mostly small fish) and offshore waters (mostly large fish), which helps in reducing the competition within the species. The L. spadiceus occupied the role of mid-predator (trophic level ~ 3.66) and increased with body length and water depth. Consequently, both high-throughput sequencing and stable isotope analyses provided evidence of intraspecific dietary variation and trophic niche partitioning of L. spadiceus in the Beibu Gulf, South China Sea.