Salinity range related to sperm motility and propagation response in some tilapiine. In：R.S.V. Pullin, T. Bhukaswan, K. Tonguthai and J.L. Maclean (eds.)

Abstract

Tilapiine is known to be euryhaline fish. In recent years, both 0. niloticus and 0. aureus are tried to be cultured in sea water, while on the contrast, the feasibility of breeding 0. mossambicus in sea water is well known. This paper is to investigate the feasible salinity range for reproduction of these three tilapia species. Results indicate 0. mossambicus is able to breed throughout 0-33 ppt while 0. niloticus and 0. aureus are able to spawn in sea water although the hatching rate is found only in 0-20 ppt, comparatively lower than that for 0. mossambicus. Except for Salmonidae, freshwater fishes are divided into two types according to the salinity range able for expressing their sperm motility. Firstly, sperms of stenohaline fishes such as Cyprinidae, Cobitidae, and Siluridae show motility under a narrow salt concentration from 0 to 150 mM NaCl. Secondly, sperms of euryhaline fishes such as Cyprinodontidae, Gasterostaidae, Cottidae, and Osmeridae show motility under a much wide range from 0 to 350 mM NaC1, i.e. 2/3 diluted sea water. It is of high interest and significance that among the so-called euryhaline tilapia O. mossambicus, like the euryhaline fishes, shows sperm motility under 0-350 mM NaC1 (0-20 ppt salinity) while O. niloticus and 0. aureus partially like the stenohaline fishes, only under 0-100 mM (0-5 ppt salinity). The following conclusion can be made: 1. 0. niloticus, 0. aureus and 0. mossambicus all belong to cichlid which are euryhaline fish. However, it is found that the former two species differ much from the latter one by their sperm motility. 0. niloticus and 0. aureus are actually stenohaline, showing sperm motility in NaCl and KC1 only up to 150 mM and a salinity up to 5 ppt. There are some interesting relationships between these two and other stenohaline fish such as Cyprinida. Sperm motility may be considered as a criterion for further classification. 2. 0. niloticus and O. aureus are able to reproduce within the salinity range of 0-20 ppt. Because of their adaptability to salinity, they can live in a wider salinity range. However, if the sperm motility of these two is considered, the possibility of expanding the salinity range for reproduction, at least to that of 0. mossambicus, is difficult. Nevertheless, cross breeding with O. mossambicus or T. zillii is worthy of further investigation.