Growth performance of Nile tilapia, Oreochromis niloticus (Linn.) in relation to provision of substrate and supplementary feeding, and grown in brackishwater ponds

The present study attempts to assess the effects of periphyton and supplementary feeding with commercial pelleted feeds on the growth performance of juvenile Nile tilapia, Oreochromis niloticus (mean body weight 1.49g) grown in inland brackish groundwater ponds for 90 days. Three treatments (with bamboo substrate grown with periphyton; with supplementary feeding without bamboo substrate; control – neither bamboo substrate nor supplementary feeding) were tested in duplicate in brackish water ponds. Irrespective of the treatments, all ponds were fertilized with cowdung at 7500 kg•ha^-1•yr^-1. Increase in the growth of fish reared in ponds provided with substrate was significant (P 0.05), about 31 and 56% higher than those in supplementary feeding and control ponds respectively. Length-weight relationship (W=cL^n) also showed higher exponential value (n) of length in substrate ponds (n=3.1) compared to other treatment ponds. Among the water quality parameters tested, the calcium content, turbidity, NH4-N, NO2-N, net primary productivity, phytoplankton, chlorophyll a and epilithic periphyton density were significantly (P 0.05) lower in substrate ponds compared to other treatment ponds; no significant differences in other water quality parameters were observed among all the treatment ponds. Significantly (P 0.05) higher values of periphyton biomass were observed at a depth of 50 cm, while autotrophic index remained lower at this depth in substrate ponds. Sediment chemistry indicated significantly (P 0.05) higher values for alkalinity, NO3-N, organic matter and benthos in supplementary feeding ponds compared to other treatment ponds Fish grown in ponds provided with additional substrate had significantly (P 0.05) higher values of digestive enzyme activity (protease, amylase and cellulolytic). High accumulation of muscle protein, muscle glycogen and higher values of viscero-somatic index and hepato-somatic index were also observed in fish grown in substrate ponds as compared to others. Results of the present study clearly suggest that provision of bamboo substrate colonized with periphyton could significantly enhance the growth and yield of Nile tilapia grown in brackish groundwater ponds. The presence of periphyton in culture ponds is thus useful to enhance growth of fish low in the food web such as the tilapia species.