In general, there is a relationship between growth and reproduction, and gonads are known to be important organs for growth, but direct evidence for their role is lacking. Here, using a fish model, we report direct evidence that gonads are endocrine organs equal to the pituitary in controlling body growth. Gonadal loss of function, gain of function, and rescue of growth were investigated in tilapia. Gonadectomy experiments were carried out in juvenile males and females. Gonadectomy significantly retarded growth compared with controls; however, this retardation was rescued by the implantation of extirpated gonads. Because gonads express growth hormone, it is possible that gonads control body growth through the secretion of growth hormone and/or other endocrine factors. We propose that gonads are integral players in the dynamic regulation of growth in teleosts.

In tilapia, growth during critical periods of the life cycle varies at different ages of development and is influenced by sexual maturation. The mechanisms controlling gametogenesis and how growth affects this process are poorly understood. This study indicates that tilapia exhibit a sexually dimorphic growth pattern in which males grow faster and bigger than females. During critical periods of development growth patterns of tilapia vary between males and females as they increase in age and sexual maturation. In this study interactions between growth and reproductive development were examined by monitoring and comparing growth rates and reproductive histology. Female growth rate peaked at the very early stages of reproductive development during the cortical alveolar stages and male growth rate peaked after complete sexual maturation during spermiogenesis. The accumulation of cortical alveoli in the oocyte in females and spermiogenesis in males was determined to be the critical developmental periods of tilapia effecting growth rates.

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