Abstract
In Eriocheir sinensis aquaculture, crabs feeding an artificial diet without steroid hormones available in ice-fresh fish or snails show delayed ovarian maturation and a delay in listing. Icariin (ICA), a safe monomer compound derived from plant, can effectively promote oestradiol (E2) synthesis and ovarian development in mammals, but its use on crustaceans has not been reported. We investigated the effects of ICA on oestrogen synthesis, vitellogenesis, and oocyte development in Chinese mitten crabs fed one of four diets containing 0, 50, 100, and 200 mg/kg ICA, respectively, for eight weeks. Results showed that vitellogenin contents, gonadosomatic indexes, and oocyte volumes in ICA50 and ICA 100 crabs were significantly higher than those in the control. The highest up-regulated expression of Vitellogenin (VTG) in hepatopancreases and ovaries were detected in ICA100 crabs. Haemolymph E2 contents were also significantly increased in ICA100 crabs. Enzyme-linked immunosorbent assay and western blot analysis indicated that the increase in E2 concentrations was attributable to an elevation in aromatase protein levels in ovaries through the cyclic adenosine monophosphate/ protein kinase A/ cAMP response element binding protein pathway. These findings suggest that ICA could serve as a natural additive to resolve the problem of delayed ovarian maturation of crabs raised in ponds.
Highlights
The Chinese mitten crab, Eriocheir sinensis, is a commercially important cultured freshwater species with a huge consumer market in China
There was no significant difference in gonadosomatic indexes (GSIs) (GSI ∼2.33%) of crabs fed with ICA200 diets compared to that in the CON group (P > 0.05)
Significant increases in GSI were found in crabs fed with ICA50 (GSI ∼3.81%) and ICA100 (GSI ∼4.65%) diets compared to those in the CON group (GSI ∼2.02%), but crabs fed with ICA200 (GSI ∼2.33%) did not show any difference in GSI compared with those in the CON group
Summary
The Chinese mitten crab, Eriocheir sinensis, is a commercially important cultured freshwater species with a huge consumer market in China. Consumers prefer to consume crabs during traditional holidays such as the Mid-Autumn Festival and the National Day, which generally fall in September or October During this same period, harvested crabs fed an artificial diet show poor ovarian development and delayed ovarian maturation, which is characterized by lower gonadosomatic index (GSI) and less vitellin (Vn) deposition in ovaries (Wu et al, 2010). This leads to a delay in listing, and lower prices for these crabs in contrast to those fed with a traditional diet of ice-fresh fish and snails. We chose the critical period before listing (form early August to early October) to carry out this study to find a functional feed additive that can promote ovarian development in E. sinensis for use in the crab aquaculture industry
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