Length -weight relationship and condition factor in the Polyculture of Clarias and Tilapia in concrete tanks

Abstract

The experiment was conducted to determine the length weight relationship and condition factor of Clariasgariepinus and Oreochromisniloticus in five different stocking combinations for a period of twelve weeks from 17th July – 9th October, 2009. A total of 1,509 juveniles of C. gariepinus with
average weight of 24.88g and average length of 14.52cm, and 2,991 juveniles of O. niloticus with average weight of 24.90g and average length of 10.93cm were stocked at 30 fish/m2 in clarias:tilapia ratios of 0:1, 1:0, 1:2, 1:4, and 1:6. The fish were fed at 3% body weight per day (BWD) over a period of 84 days. The monoculture of the two species (Treatments 1 and 2) yielded the lowest growth indices (WG, %WG and SGR), while the performance of clarias at each of the three polyculture systems were higher than those of tilapia. For clarias Treatment 5 (1:6) had the maximum length (17.92±0.37cm) while the monoculture recorded the minimum of 16.60±0.29. The monoculture of tilapia gave the lowest length gain (4.83±0.41cm) while the highest (11.60±0.51cm) for tilapia was recorded in Treatment 4 (1:4). From the regression parameters and the associated statistics (r and SE) for the validation of the models, it is evident that there was a strong positive relationship between length and weight. Even though the relationship was curvilinear there were still higher percentages of regression coefficient in all the treatments and between the species. The SE was also low in all the treatments which further validated the log
transformed models. Therefore, the models are valid for estimating weight of the fishes from the length measurements without necessarily measuring the weight. Stocking ratio of 1:6 should be encouraged for better growth performance.

Keywords: Polyculture, length – weight, condition factor, clarias, tilapia, juveniles.