Reproduction, age and growth of Tilapia zillii (Cichlidae) in Oued Righ wetland (southeast Algeria)
The aim of this study is to contribute to a better understanding of Tilapia zillii (Cichlidae) biology in the Saharan wetland of Oued Righ (south-eastern Algeria). Eight seasonal sampling campaigns have been conducted between October 2011 and September 2012 for a total of 813 specimens, including 230 males, 329 females and 254 individuals of indeterminate sex. Reproduction of T. zillii was investigated by considering the reproductive cycle, sex distribution and length at first maturity. Seasonal sex distribution was in favour of females during all seasons. The values of the gonadosomatic (GSI) and hepatosomatic (HSI) indexes of females and males indicated a single reproduction period from April to July. The length at first maturity (Lm50) was 9.9 cm for females and 9.7 cm for males. The condition factor K indicated a good condition of the individuals that is reflected by an accumulation of reserves. The age was determined by two methods: the Bhattacharya’s indirect method (1967) and a direct method, which was based on scale reading on 155 individuals with size from 6.4 to 19.9 cm. Monitoring scale marginal elongation over a year identified the formation period of the stop growth ring, which occurs in winter. These data allowed to determine the spawning period and to estimate the ages of T. zillii.