Effects of dietary n‐3 LC‐PUFA on the growth performance, gonad development, fatty acid profile, transcription of related genes and intestinal microflora in adult sea urchin ( Strongylocentrotus intermedius )

A study was conducted to investigate the effects of dietary n-3 LC-PUFA on the growth performance, fatty acid profile, transcription of related genes and intestinal microflora in adult sea urchin (Strongylocentrotus intermedius). Kelp (Laminaria japonica) and four formulated feeds with graded levels of n-3 LC-PUFA (0%, 0.5%, 0.8% and 1.0% dry diet) were prepared as the experimental diets. Each diet was randomly allocated to ten adult sea urchin individuals. The feeding period lasted for 90 days. Results showed that gonadosomatic index (GSI) of adult S. intermedius fed formulated feeds was significantly higher than that fed kelp (p < 0.05), while weight gain rate (WGR) showed no significance between kelp and feed groups (p > 0.05). Neither WGR nor GSI showed significant differences among the four feed treatments (p > 0.05). Notably, ARA and EPA in the gonads of S. intermedius fed the feeds devoid of n-3 LC-PUFA were comparable to that fed the feeds with 0.5% n-3 LC-PUFA (p > 0.05). Transcription of Elovl4 and Δ5-desaturase in the intestine and gonad significantly decreased as dietary n-3 LC-PUFA increased (p < 0.05). Proteobacteria and Bacteroidetes (phylum level) and Psychromonas and Sulfurimonas (genus level) were the most abundant bacteria species in the intestine of S. intermedius. The abundance of Sulfurimonas was comparable in the S. intermedius fed kelp and the feed with 0% n-3 LC-PUFA, which was significantly higher than that fed the other formulated feeds (p < 0.05). These results indicated that S. intermedius seems to have a low requirement for n-3 LC-PUFA to sustain its normal growth and gonad development. The increased transcription of rate-limiting enzymes (Elovl4 and Δ5-desaturase) could be responsible for the considerable amounts of EPA and ARA in the gonads of S. intermedius when fed feeds without LC-PUFA. The intestinal microflora were affected to a certain extent by the die categories and the n-3 LC-PUFA in the formulated feeds. It is speculated that some unknown bacteria in the genus of Sulfurimonas could participate in the synthesis of LC-PUFA.