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ABSTRACT
The hybrid red tilapia, Oreochromis niloticus x O. mossambicus, is utilized in semi-intensive fish culture practices in Northeastrn Brazil, and this paper reports on the reproductive behaviour and gonadal development of this hybrid. Mature males and females of hybrid red tilapia were observed under laboratory conditions during their reproductive phase, to verify behaviour related to dominance during agonistic interactions, nest building, courtship, mate selection, mating and parental care. Histological examinations of ovaries and testes were carried out in different developmental stages to identify maturity stages and to determine the gonadosomatic index, fecundity and type of spawning. Aggression and dominance exhibited by males during agonistic interactions are influenced by their body size. The gonadosomatic indices of males show positive correlations with their dominance level. Large and aggressive males in possession of spawning sites were preferred by females during mate selection. The ovaries showed immature (phase I and II), initial maturing (phase II and III), final maturing (phase IV and V), mature (phase I to V) and partially spent stages. The testes showed immature, maturing, mature and partially spent stages during development. Ovaries of mature females presented synchronic oocyte development indicating multiple spawning, with mean batch fecundity of 1.213 mature oocytes. Parental care was exhibited by the pair after mating and males were more aggressive than females during egg and larval protection. Effective participation on the part of females during parental care phase resulted in higher survival rate of larvae.
Keywords: Reproduction, agonistic interactions, gonadosomatic index, parental care, hybrid red tilapia
INTRODUCTION
The cichlid fishes have a wide geographical distribution and they are distributed in Africa, South and Central America, Southeastern part of North America (South of Texas and México), Madagascar, India, Sri Lanka, Syria, Israel and Iran (Kullander, 1998). The family Cichlidae comprises of 1600 valid species. Tilapia is the common name given for nearly a hundred species of cichlid fish, which inhabit a variety of fresh water habitats. Breeding of tilapia adapted to temperate climates and saline environments was designed to exploit the ease of producing inter-specific hybrids among tilapias. Triploids have been produced in Oreochromis niloticus, O. mossambicus and O. aureus, and tetraploids have been induced in Oreochromis niloticus and O. mossambicus. In the case of polyploid hybrids, it is expected...