Full Length Research Paper

Acute and chronic toxicity of pawpaw (Carica papaya) seed powder to adult Nile tilapia (Oreochromis niloticus Linne 1757)

Ezekiel O. Ayotunde* and Benedict O. Ofem

Department of Fisheries, Faculty of Agriculture, Cross River University of Technology, P.M.B. 102, Obubra Campus, Calabar, Nigeria.

*Corresponding author. E-mail: eoayotunde@yahoo.co.uk. Tel: 08059791815.

Accepted 25 February, 2008

This experiment determined the toxicity of pawpaw seed powder to adult tilapia, Oreochromis niloticus, the most cultivable fish species in Africa. The 96 h static bioassay experiment was conducted to determine the median lethal concentration (LC₅₀) for adult Nile tilapia, to pawpaw seed, Carica papaya. Two hundred live, and apparently healthy O. niloticus measuring 11.5 - 14.6 cm total length and 65.6 - 112.4 g were used for the experiment. Eighteen (75 x 45 x 45 cm) glass tanks of 121.5 litres capacity each were filled with 50 litres aerated unchlorinated well water. The toxicant was introduced at different concentrations in triplicate per treatment. The 96-h LC₅₀ of pawpaw seed powder to adult tilapia is 4.2 mg/l with 95% confidence limit of 31.86 – 93.81 mg/l and the maximum admissible toxicant concentrations ranges between 0.042 - 0.42 mg/l, while the total mortality occurred in the concentration of 8 mg/l within 24 h exposure period. Toxic reaction exhibited by the fish includes erratic movement, air gulping, loss of reflex, discolouration, molting, loss of scale, and haemorrhage. The pathologic lesion of gill, skin, liver and kidney includes different level of degeneration of cells, lamellar hyperemia, hyperthrophy of gill arch, shrinkages and dermal erosion and necrosis of skin, while hyperplasia, disarrangement of hepatic cell, necrosis and vacuolation occurred in liver and kidney of adult tilapia O. niloticus. Damages became severe with increasing concentration of C. papaya to fish and time of exposure. There was no significant changes in the water quality during the experiment; the result obtained before the test, during the test and after the test were found close to the water quality parameters of the control. Results of the tests provided baseline information and established safe limits of using C. Papaya seed powder as an antifertility agent in controlling excessive breeding of tilapia in fish farm.

Key words: Toxicity, pawpaw seed, tilapia (Oreochromis niloticus) adults, tolerance limit, histology, haematology.