Preliminary Studies On Use Of Raphia Palm (Raphia Hookeri) Pulp To Harvest Fish And Possible Effects On Fish Production In The Niger Delta Area, Nigeria

Abstract

Four hundred and eighty (480), six week old hatchery bred Holland Clarias gariepinus post fingerlings were used to test the toxicity of the pulp from Raphia hookeri fruit on fish. The fingerlings were randomly distributed in tens into forty-eight (48) glass tanks measuring 24in x 12in x 12in. Length and weight of fingerlings in each tank were measured to the nearest centimetre and gram. The study was in two parts. In the first run of experiment, twenty-four (24) of the tanks were randomly arranged into eight (8) treatments of three replicates each and labelled 0A-C to 7A-C. Varying concentrations of ether extract (1ml/l to 7ml/l) of R. hookeri pulp was added to each of the treatment tanks according to their corresponding serial numbers. Treatment 0A-C which served as control, contained only distilled water. Tanks were observed for the lethal concentration and time taken for half the number of fingerlings in each treatment to die (LC 50). In the second run of experiment, the remaining twenty-four (24) tanks were similarly grouped into eight treatments of eight treatments of three replicates and labelled 0a-c to 7a-c respectively. Graded concentrations of untreated R. hookeri pulp solution (1g/l to 7g/l) were also added to the treatment tanks according to the corresponding serial number of the glass tanks. The fingerlings in each tank were monitored for eight hours, for mortality and time for half the sample fingerlings in each treatment to die (LC 50). Results of the study revealed that the ether extract from the pulp of R. hookeri fruit had no effect on the fingerlings whether small or big, or at high or low concentrations. The untreated pulp solution on the other hand, was highly toxic to the fingerlings even at concentrations as low as 1g/l of the solution. The study revealed that the smaller fishes were more susceptible to the effect of the toxin. This was shown in the bigger samples taking a longer time to die, compared to the smaller samples, when exposed to the same concentration of pulp solution from the R. hookeri fruit. The pH of the water was raised from pH 6.8 to between pH 11.9 and 12.9 by serially adding from 1 – 7 g/l of the pulp solution to the water. These values were beyond the alkaline death point hence the mortalities recorded. Mortality was observed to be higher and faster when fingerlings were exposed to higher concentrations of the pulp solution. The ether extract not causing any mortality during the period of study, may be due to the effect of heat, which may have denatured the toxin in the process of extraction. This study has shown that R. hookeri pulp is toxic to fish and can be used to harvest fish. When properly boiled before eating, the toxin becomes denatured and harmless when consumed. The method is however not recommend, because of its none selective action. It kills both adults and juveniles, thus affecting sustainable fish production.

Keywords: Raphia hookeri, fish, pH, lethal concentration, mortality.