Effects of Grading Frequency on Growth, Intra−Cohort Cannibalism and Economic Benefits of African Catfish (Clarias Gariepinus, Burchell, 1822)
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Date
2024-10
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Kenyatta University
Abstract
The profitability of C. gariepinus still suffers from poor growth performance, low
survival and high cases of cannibalism. Attempt that aims at increasing economic
benefits must therefore target strategies that decouple link between catfish culture
with poor growth survival and cannibalism. This study determined the effects of in pond grading frequency on the growth performance, cannibalism and economic
benefits of C. gariepinus in tank culture system. Three treatments designated as G0
(no grading), G2 (grading every 2 weeks) and G4 (grading every four weeks) in a
completely randomized design (CRD) was applied in triplicate. The tanks were
stocked with 200 fingerlings each. Sampling was conducted weekly to measure length
and weight of fish. Mortalities were recorded and dead fish observed under dissecting
microscope to ascertain that it is due to cannibalism. An enterprise budget was
conducted to determine the economic benefits of grading frequency. The highest
weight gain was reported in fish graded every two weeks (50.8 12.42 g), followed
by those graded every 4 weeks (41.59 10.27 g), while the lowest weight gain was
recorded in fish that were not graded (control) (35.63 10.02 g). Specific growth rate
(SGR) was significantly (P < 0.01) highest in fish that were graded every two weeks
(8.95 0.08 %day−1) followed by fish graded every four weeks (8.59 0.06 %day−1)
while no grading treatment produced the lowest SGR (8.81 0.27b %day−1). There
were significant difference in FCR among treatment (F =13.423, df = 2, P < 0.001),
where the lowest FCR also occurred in treatment that were graded every two week
(1.21 ± 0.13) followed by those graded every four week (1.42 ± 0.24) and lowest in
the no grading treatment (1.81 ± 0.23). Changes in fish heterogeneity was observed
after day 42 and continued until day 60. The size variation was significantly affected
by grading frequency. The mean TL of fish graded every 2 weeks was the highest,
followed by grading every four weeks and finally the no grading treatment was the
lowest. Fish size heterogeneity (CV% and skewness) was consistently the highest in
C. gariepinus in no grading treatment followed by fish where grading was done every
four weeks while it was lowest in treatment where grading was done every two weeks.
Mortality owing to cannibalism was affected by grading frequency where highest
cannibalism mortality occurred in C. gariepinus where there was no grading followed
by grading every four weeks and intermediate at grading frequency every four weeks.
Meanwhile other mortality by other causes such as such as wounds and suffocation in
fish did not differ with grading frequency. Highest total fish yield, net returns above
TVC and TC was obtained in treatment where grading was done every 2 weeks. The
enterprise budget analysis of grading frequency in the present study indicated that it
is economically feasible to culture C. gariepinus when grading was done every four
weeks but the best economic returns occur when the grading frequency is done every
two weeks.
Description
A Thesis Submitted in Partial Fulfilment of the Requirements for the Award of the Degree of Master of Science (Fisheries Sciences) in the School of Pure and Applied Sciences of Kenyatta University October, 2024