Influence of Conspecific Contact Upon Blood Sex Steroid Levels and the Dynamics of Ovarian Development in Female Red-Bellied Tilapia, Tilapia zillii

ABSTRACT 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) in a group of female red-bellied tilapia, Tilapia zillii, 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. Results suggest 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.

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