Sex reversal in Nile tilapia: Is it possible to produce all male stocks through immersion in androgens?

摘要

One of the primary tilapia species cultured around the world is the Nile tilapia (Oreochromis niloticus). Usually, monosex male stocks of Nile tilapia are desirable, because cultivation of mixed sex tilapia leads to overcrowding of the tanks and consequently poor growth rates. The negative effects of mixed sex culture are related to some reproductive biology characteristics of the Nile tilapia. We will briefly explain some of these, to help you to understand why monosex male stocks are preferable.In this species, males and females can reach sexual maturation approximately 3-5 months after hatching and fish weighing between 20-40 g are usually ready to spawn. Males and females can spawn throughout the year in water temperatures above 23 deg C. Females can spawn at every 20-40 days intervals and each one can produce between 4-8 eggs per gram of body weight. So, a female weighing 30 g could generate, every 40 days, 120-240 new alevins. In addition, females incubate the eggs orally, which substantially increase the survival of the offspring (Figure 1 A-D). Females may keep the alevins in their mouths up to 15 days post hatching, releasing them when they are able to swim and feed by themselves. During this period females do not eat and therefore have poor growth. New offspring released into the tank will increase competition for space, water quality, and food. Taking into account that the grow-out period of Nile tilapia is between 6 to 12 months, it is quite easy to realize why mixed sex culture isundesirable. Culture of all male stocks eliminates these negative aspects. Males also grow faster than females, inasmuch as males do not need to allocate any of their energy reserves for the production of eggs.