Development of models of threshold and efficient algal densities for larval and juvenile tilapia Oreochromis niloticus on raw Spirulina

Abstract

Different densities of 14Carbon ( 14C) labeled Spirulina platensis were fed to larval and juvenile tilapia Oreochromis niloticus with a body weight of 10 mg, 20 mg, 200 mg, 700 mg, 1000 mg, and 1800 mg at a constant temperature of 25 °C during 1-h feeding period. Ingestion rate (IR, μgC/fish/h), assimilation rate (AR, μgC/fish/h), and clearance rate (CR, mL/fish/hour, an indicator exhibiting the fish water filtration effort) of Spirulina were investigated by monitoring the fate of the 14C labeled food. Quadratic regression models were developed for evaluation of ingestion and assimilation of raw Spirulina by larval and juvenile tilapia of different sizes under various algal densities. We estimated the threshold density (TD, mg/L) of Spirulina for tilapia of each size to sustain the basic metabolism when AR calculated from the models initially matched their respective values of resting carbon consumption requirement for respiration. The relationship between TD and body weight (BW, mg) could be expressed as TD = 26.937 W − 0.248 ( R 2 = 0.936). We estimated the efficient density (ED, mg/L) for the fish of each size to assimilate Spirulina without ‘surplus’ feeding of suspended raw Spirulina when AR calculated from the models reached their respective maxima. The relationship between ED and body weight (BW, mg) could be expressed as ED = 220.03 BW − 0.203 ( R 2 = 0.901). Larval and juvenile tilapia seem to utilize Spirulina in a feeding strategy of controlling the net intake and requirement of energy by conditioning the clearance rate on algal suspension at various densities of Spirulina. This feeding strategy becomes more effective with the development of the buccopharyngeal filter feeding apparatus. Only in an artificial ecological system, e.g. CERAS may provide sufficient densities of Spirulina for early larval tilapia without the soundly developed buccopharyngeal filter feeding apparatus to sustain the basic metabolism.