Influence of conspecific contact upon blood sex steroid levels and the dynamics of ovarian development in female red-bellied tilapia, Tilapia zillii

摘要

Provision of visual and chemical (pheromonal) contact with adjacent conspecific males (following a period of deprivation) significantly increased circulating levels of serum testosterone (P<0.05) but not 17beta-oestradiol in a group of female red-bellied tilapia held in individually-partitioned recirculating aquaria. Male contact also resulted in a significant increase (P<0.05) in the relative proportions of stage 4 (cortical alveolar) and stage 5 (early vitellogenic) oocytes in the ovary. Visual/chemical contact with a male appeared to induce the recruitment of a cohort of pre-vitellogenic oocytes into vitellogenic growth. It is concluded that the degree of contact between male and female tilapia is likely to be a crucial factor in the determination of the inter-spawn interval and is, therefore, an important consideration for successful broodstock management.