STUDIES ON NILE TILAPIA (OREOCHROMIS NILOTICUS) MALE PRODUCTION AND THEIR SUSCEPTIBILITY TO BACTERIAL AND FUNGAL INFECTIONS | ||
| Veterinary Medical Journal (Giza) | ||
| Volume 39, Issue 3, July 1991, Pages 763-774 PDF (7.78 M) | ||
| DOI: 10.21608/vmjg.1991.379214 | ||
| Authors | ||
| A.F. BADRAN* 1; M.A.K. DANASOURY2 | ||
| 1Dept. of Avian and Aquatic Medicine, Fac. of Vet. Med., Suez Canal University. | ||
| 2Dept. of Animal and Fish Production, Fac. of Agriculture, Suez Canal University. | ||
| Abstract | ||
| Monosex culture of tilapia has long been recognised as one of the most satisfactory solution to over population (Brown and Van Someren, 1953). Many workers (Hickling 1967, Pruginin 1967, Shell 1967 and Bardach et al., 1972) have observed that male tilapia grow at a faster rate than females in culture, and Fryer and Iles (1972) confirmed this to be true of certain wild fish. Male tilapia can be obtained by: (1) sorting of tilapia fingerlings according to sexual characters and this method is wasteful in terms of the female fish are discarded, as well as being laborious and time consuming, (2) sex modification. by irradiation, chemical castration and sex reversal. The best method for sex reversal is feeding of methyltestosterone or ethyltestosterone during the first weeks of life (Guerrero 1976). Epidermis and mucous layer of fish provide the first line of defence against infection by potential environmental pathogens and are involved in the basic processes of locomotion, osmoregulation and mechanical protection. Changes in the structure of the fish epidermis (reducing the numbers of goblet cells and consequently mucous secreation) are associated with the age, sex and state of maturity (Pottinger and Pickering, 1985). These changes disturb the equilibrium between the forces favoring parasitic invasion and the forces resisting colonization. Therefore, the incidence of skin parasites as S. diclina type 1 (Richards and Pickering, 1978 and Willoughby, 1978) and Protozoan flagellate Ichthyobodo (Robertson, 1979) is greater in sexually mature fish compared with immature fish sampled at the same time from the same body of water. Moreover, sexually mature males are more readily infected by a variety of ectoparasites and fungal pathogens than are mature females or immature fish of either sex (White 1975, Richards and Pickering 1978 and Pickering and Christie 1980). This work was conducted to explain the relation between Nile tilapia males produced by hormonal treatment and their susceptibility to skin parasite infections (one bacterial, F. columnaris, and one fungal, S. diclina,). | ||
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