Trans-omics analyses revealed differences in hormonal and nutritional status between wild and cultured female Japanese eel (Anguilla japonica)

Abstract

Long-term stock decline in the Japanese eel (Anguilla japonica) is a serious issue. To reduce natural resource utilization in Japan, artificial hormonal induction of maturation and fertilization in the Japanese eel has been intensively studied. Recent experiment on feminized (by feeding a commercial diet containing estradiol-17β for first half year) cultured eels have shown ovulation problem, which is seldom observed in captured wild eels. In this study, we tried to investigate causes of ovulation problem frequently seen in cultured eels by comparative trans-omics analyses.The omics data showed low growth hormone and luteinizing hormone transcription levels in the brain and low sex hormone–binding globulin transcription levels in the liver of the cultured eels. In addition, we found high accumulation of glucose-6-phosphate and, maltose in the cultured eel liver. We also found that docosahexaenoic (DHA) acid, eicosapentaenoic acid (EPA) and arachidonic acid (ARA) ratios in cultured eels were quite different from wild eels.The data suggested that ovulation problem is due to prolonged intake of a high-carbohydrate diet and/or unbalanced DHA/EPA/ARA ratios in diet.

Feeding habitat and silvering stage affect lipid content and fatty acid composition of European eel Anguilla anguilla tissues

“…These essential FAs promote oocyte growth (da Silva et al ., 2016) in anguillid eels, as well as reproductive success and broodstock growth in the context of aquaculture (Furuita et al ., 2007). Furthermore, a diet devoid of optimal DHA/EPA/ARA ratios has been suggested to alter gamete production and quality in A. anguilla (Baeza et al ., 2014; Butts et al ., 2015) and to cause ovulation issues in cultured A. japonica (Higuchi et al ., 2019). We observed decreases in EPA proportions in liver and muscle tissue with advancing stage, while those of DHA decreased only in muscle tissues and those of ARA were conserved across stages I, II and III.…”