Reproductive biology of farmed lumpfishCyclopterus lumpus: Gonadal development and associated profiles of selected endocrine factors

Abstract

AbstractThe demand for lumpfish (Cyclopterus lumpus) as a cleaner fish for the Atlantic salmon industry to battle sea lice infestations results in an increased interest of juvenile production in aquaculture. For successful control of the lumpfish reproduction, it is crucial to adequately understand its reproductive biology. Female and male lumpfish were sampled four times during a 24-week experiment where gonadal development in relation to endocrine factors was studied. Histologically, we identified and described ten oogenic and four spermatogenic stages during gamete development. The female gamete stages were grouped into ovarian development stages to simplify categorization of ovarian development. The ovarian development and the associated endocrine factors were typical for fish with group-synchronous ovarian organization, and from our histological observations it is possible that lumpfish females release up to four batches of eggs in one spawning season. During early stages of testis development, spermatogenic cells were observed in cysts. The cystic spermatogenesis and the distribution of spermatogonial cysts through the germinal compartment indicated an unrestricted spermatogonial distribution type. Despite its variance, the expression of genesgnrh2andgnrh3in the brain of lumpfish decreased in females and increased in males during gonadal development. Gonadal development was also associated with increasing trends of gene expression in gonadotropin receptors, vitellogenin receptors, steroidogenic enzymes, and blood plasma concentrations of sex steroids. The genesfshr, lhr, vtgr, cyp19a1and the sex steroid E2 increased up to oocyte maturation and decreased at ovulation, while GSI, T and 11-KT increased up to ovulation. Whilefshrandlhrpeaked at spermatocyte stage and decreased later,cyp17a1, T and 11-KT increased up to the spermatid stage and decreased at the spermatozoa stage in males. Our findings improve the current understanding on lumpfish reproductive biology and suggest future research directions.