Combined effects of surface area of periphyton substrates and stocking density on growth performance, health status, and immune response of Nile tilapia (Oreochromis niloticus) produced in cages

摘要

A 4-month feeding trial was conducted to investigate the effect of surface area of periphyton substrates (PS) and stocking density (SD) of juvenile Nile tilapia, Oreochromis niloticus, on growth, major blood constituents, and some immunity biomarkers. Six treatments (T1-T6) were established in 18 floating cages (1 m(3) water each) fixed in an earthen pond for growing tilapia (1.12 +/- 0.10 g), in a 2 x 3 factorial design experiment (2 SD x 3 PS). For T1, T2, and T3, fish were stocked at a rate of 70 m(-3) with 1, 2, or 3 PS units (area: 0.7, 1.4, and 2.0 m(2), respectively). For T4-T6, fish were stocked at 90 m(-3), also with 1, 2, or 3 PS units. All fish were fed a 20% crude protein supplemental diet. The best growth rates, feed efficiency, body composition, immune response, and overall health status were attained for T2 group with 70 fish m(-3) in the presence of 2 PS units (1.4 m(2)) followed by T5 with 90 fish m(-3) plus 2 PS. Stocking density affected albumin while periphyton substrates impacted cholesterol, triglycerides, and alanine aminotransferase levels in fish serum. Meanwhile, total proteins and glucose-6-phosphate dehydrogenase were not significantly affected. Serum immunoglobulin (IgM and IgG) values were relatively higher in fish reared at 70 m(-3) than at 90 fish m(-3) indicating better immunity response. Periphyton biomass (dry matter, DM and ash-free DM) was lower in T2, than in other treatments, whereas periphyton populations belonged mainly to Chlorophyta (52-75%), Cyanobacteria (17-23%), and Charophyta (4-21%). Accordingly, the present study suggests that 70 fish m(-3) and 2 PS units (surface area of 1.4 m(2)) would be an optimal combination for the best growth, health status, and immunity response of juvenile Nile tilapia reared in periphyton-based cage system.