The Radiosensitivity of Nile Tilapia (Oreochromis Niloticus) Fingerlings

Abstract

The Nile Tilapia (Oreochromis niloticus), a very popular fish commercially in the Philippines, was studied to determine its radiosensitivity and to see its potential as a biological indicator in aquatic ecosystems. Nile Tilapia was seen to be radiosensitive. The fish were exposed to gamma-irradiation and chromosomal aberrations were induced. The various types of aberrations seen were chromatid gaps, chromosome gaps, chromatid fragments, dicentric rings, fusions, despiralizations and translocations. Among the aberrations observed, dicentric rings, fusions and chromosome gaps were strongly correlated with dosage, with only the dicentric rings increasing steadily with increasing dosage. In the course of the study, the lethal dosage50 for Nile Tilapia within 18 days was determined and it was observed at 2.0 krad. The modal chromosome number was also established at 2n=44 with karyotype exhibiting 22 pairs of acrocentric chromosomes with 2 pairs of marker chromosomes present.