Zeolite as a major control factor of water quality problems arising from stocking density of European sea bass (Dicentrarchus labrax) juveniles

Improperly managed ammonia levels alter growth, survival and creates unfavorable conditions on fish health in production systems. This experiment was designed to determine the impact of natural zeolite on removing ammonia from water, growth enhancement and survival rate of European seabass, Dicentrarchus labrax juvenile. D. labrax with initial body weight of 4.5±0.06 g fish-1 were stocked at three different densities, namely 1kg m-3 (low density), 2 kg m-3 (medium density) and 3 kg m-3 (high density) with three levels of zeolite (5, 7.5 and 10 ppt) and a control group (without zeolite) forming twelve treatments for 120 days in winter season. Thus, 24 hapas with an average area 0.5 m3 were fixed in twelve concrete ponds (4x8x1.5 m) to form two replicates for each treatment. The results revealed that water quality parameters improved significantly (p < 0.05) with increasing zeolite level controlling the negative impact of densities on pH and dissolved oxygen which improved from 7.05 and 4.8 mg L-1 to 8.0 and 6.35 mg L-1 respectively. Ammonia removal efficiency significantly (p < 0.05) improved with increasing zeolite level with all density levels. The best ammonia removal rate (76.60%) was obtained at Z10 treatment (71.2±0.445) with low density. Fish survival rate was significantly (p < 0.05) high among treatments, the best survival rate obtained was at low density with high zeolite level (94%), while the lowest (76%) obtained was at high density with Z0 (control) treatment. Growth performance was significantly (p < 0.05) higher at Z10 for all densities when compared with Z0, Z5 and Z7.5 treatments. Despite of the negative effect of stocking density, feed conversion ratio (FCR), protein efficiency ratio (PER) and protein productive value (PPV) showed significant (p < 0.05) improvement with increasing zeolite level. However, significant (p < 0.05) increase of body protein was observed, while fat and ash content decreased with increasing zeolite that diminished the adverse effect of increased density. The present study highlights the important role of zeolite (Z10) level in improving water quality, ammonia removal rate, growth performance and survival rate in stocking juveniles of European seabass.