Effect of pH on the growth performance and survival rate of Clarias gariepinus fry

Abstract

The growth performance and survival rate of Clarias gariepinus fry subjected to various pH treatments was investigated. The tests were conducted in plastic baths of 3.5 litre capacity filled to 2 litre mark with freshly prepared experimental solution and labelled according to pH requirements for the test. Each bath was stocked with forty (40) fry of body length between 6.90mm and 7.03mm. They were exposed to the experimental solution for a period of fourteen (14) days for growth estimation. For survival rate, the test organisms were examined at 2hour intervals for probable death. The fry were fed during the time of this study using shell free Artemia, normally used as starter food at the onset of exogenous feeding. The length, measured as tip of the snout to the end of the caudal fin, was determined prior to stocking and at 2days interval, for the period of study. Every 24 hours the medium was checked for any change in pH and adjusted if any. The temperature of the culture media was averagely constant (26.5oc) and dissolved oxygen content remained approximately 6.0mg/l. Within 48hrs, average increase in length of between 0.16mm and 2.28mm was recorded in pH 5,6,7,8,and 9. There was no surviving fry on day 2 in pH 2,3,10,11 and 12 i.e. 100% mortality 24 hrs of stocking while pH4 recorded total mortality after 192hrs. Percentage survival in the other pH varied between 99.7% (in pH7 and pH8) and 51.67% (in PH5). Optimal growth of 92.03% was recorded in PH 7 while the median lethal pH (ML50pH) is 4.3 and 9.2 for acidic and alkaline treatment respectively. Results from this study shows that reduced pH condition has a depressing effect on the growth rate of Clarias gariepinus fry. This suggests the need for constant monitoring of pH changes in water especially in fish farming operations.