Effect of periphyton technology on the growth performance and fecundity of Nile tilapia, Oreochromis niloticus (Linnaeus, 1758) cultured in earthen ponds
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Aquaculture plays a big role in eliminating poverty and malnutrition. However, the current pond-based systems rely on the supply of large amounts of low-quality commercial feeds that limit aquaculture productivity and have the potential to cause environmental problems such as eutrophication in the receiving waters. Poor brood stock productivity remains a major constraint in aquaculture growth. Early sexual maturation of O.niloticus before it attains market size results to stunted growth affecting its productivity. The present study was therefore guided by the following specific objectives: i) To determine the effect of periphyton technology (PPT) on the growth performance indicators of O. niloticus reared in earthen ponds ii) To determine the effect of PPT on the fecundity of O. niloticusiii) To determine the effect of PPT on plankton diversity and abundance iv) To determine the effect of PPT on pond water quality parameters. The research was done at Kenya Marine and Fisheries Research Institute (KMFRI), Sang’oro.Six earthen ponds used for the study were limedat a rate of 4 g.m-2 and filled with water one week after liming. The ponds were fertilized using chicken manure. Two treatments, i.e., PPT-and control-ponds, were evaluated in the study and triplicated. The PPT ponds were fitted with 2-m long eucalyptus poles of 5 cm diameter at 50 cm interval with the inclusion of molasses as carbon source. The control ponds were not treated. Tilapia fish (mean weight, 12.35±0.15g) were stocked in all ponds at a density of 3fish/m2, and fed on a commercial diet with 20 % crude protein (CP) twice daily at 3 % body weight. 30 fish were sampled weekly from each pond for growth, and 10 fish were sampled bi-weekly for the determination of fecundity. Water samples were collected from the ponds to determine plankton abundance and diversity. Selected physicochemical water parameters were monitored in situ weekly using multi-parameter meter. Total ammonia nitrogen (TAN) was measured in a laboratory using standard procedures. R software version 3.2.1 was used to conduct statistical analysis. The effects of PPT on growth performance, fecundity of O. niloticus, water quality parameters, plankton diversity and abundance were analyzed using independent t-test. The PPT-ponds registered significantly higher mean weight (150.69 ± 0.99 g), SGR (2.75 ± 0.01), and lower FCR (1.29 ± 0.01),than the control ponds: Mean weight (99.23 ± 0.96 g), SGR (2.29 ± 0.00), and FCR (1.58 ± 0.01).There was significantly higher fecundity in the PPT-ponds (2.28 ± 0.09 g) than control (1.74 ± 0.06 g.fish-1) with prolific spawning behavior starting earlier in the fourth week in control pond (fish mean weight, 29.19 ± 0.26) but delayed to the eighth week in the PPT-ponds with fish having a mean weight of 81.37 ± 0.51. PPT-ponds had a higher phytoplankton and zooplankton diversity index of 3.19 and 3.42, respectively, compared to 2.57 and 2.34, respectively, in control-ponds. There was a significantly higher zooplankton mean abundance in the PPT-ponds (2771.83 ± 313.11)than in control (262.67 ± 16.78). The control-ponds recorded significantly higher concentrations of nitrite (0.07 ± 0.01 mg.L-1), ammonia (0.21 ± 0.03 mg.L-1) and ammonium (0.20 ± 0.04 mg.L-1)compared to PPT-ponds: nitrite (0.02 ± 0.01 mg.L-1), ammonia (0.06 ± 0.01 mg.L-1), and ammonium(0.02 ± 0.01 mg.L-1). This study demonstrated that PPT is a quality natural fish feed that can be used with supplemental feed to replace the costly commercial fish feeds. PPT also has a high potential of improving the water quality of the culture system, thereby providing the ideal conditions for maximum growth of fish. The present study recommends the adoption of PPT in replacing the costly commercial fish feeds used in tilapia culture. Further studies are recommended to explore other substrates for installing PPT in ponds.