Production of functional sperm from in vitro-cultured premeiotic spermatogonia in a marine fish

In vitro production of functional gametes can revolutionize reproduction by reducing generation intervals and accelerating genetic breeding in aquaculture, especially in fish with relatively long generations. Nevertheless, functional sperm production from in vitro-cultured spermatogonia remains a challenge in most aquaculture fish. In this study, we isolated and characterized premeiotic spermatogonia from marine four-eyed sleepers (Bostrychus sinensis), which are prone to ovotesticular or sterile testicular development, and induced the differentiation of the spermatogonia into flagellated sperm in a three-dimensional (3D) culture system. Artificial insemination indicated that the in vitro-derived sperm were capable of fertilizing mature oocytes to develop into normal larvae. Furthermore, melatonin significantly promoted spermatogonia proliferation and differentiation through the ERK1/2 signaling pathway, and thus increased the efficiency in functional sperm production. The 3D culture system and resulting functional sperm hold great promise for improving the genetic breeding of aquaculture fish.

Reproductive biology and annual reproductive cycles of two sympatric lineages of Bostrychus sinensis with a natural habitat on southeastern coast of China

The two phylogeographic lineages [South China Sea (SCS) lineage and East China Sea (ESC) lineage] of the four-eyed sleeper (Bostrychus sinensis) occur sympatrically along the southeastern coast of China, where there is a small percentage of hybrids in a natural habitat. To assess the mechanism responsible for the incomplete reproductive isolation between the SCS and ECS lineages of four-eyed sleeper, there was sampling of individuals from the Yueqing Bay from November 2018 to November 2019 to determine whether there are differences in characteristics of the reproductive cycles and reproductive biology. The two lineages varied in reproductive seasonality, body size and shape, and egg number. The SCS lineage spawned annually between May and August, with the absolute fecundity (AF) of the SCS lineage being 9960 to 39,517 eggs per female, and there was positive allometric growth of this species. The ECS lineage spawned annually between June and July, with females producing 4064 to 10,370 eggs per fish and individuals having an isometric growth pattern. Preliminary results indicated that there was partial overlap in the spawning season between the two lineages in the sympatric region, which may not be a primary factor in the incomplete reproductive isolation. Furthermore, the lineage differences in fecundity and body shape and size may lead to variation in mate choice and reproductive strategy. The results from this study provide insight into the biology, reproductive strategies, and speciation of the four-eyed sleepers.