Evaluation of High Stocking Densities on the Water Quality and Growth Performance of Pacific White Shrimp Litopenaeus vannamei Reared in a Mixotrophic Biofloc Nursery System
Ghasem Mohammadi, Mohammad Seddiq Mortazavi, M. Hafezieh
Abstract
The present study aimed to explore the effects of intensive culture densities on the water quality and growth performance of the Pacific white shrimp Litopenaeus vannamei reared in a mixotrophic biofloc system (heterotrophic/chemoautotrophic) at three stocking rates of 5,000, 4,000, and 3,000 PL/m3 (namely G5000, G4000, and G3000, respectively) for 21 days. At the end of the study, the mean values of water temperature, dissolved oxygen, dissolved oxygen saturation level, pH, oxidation-reduction potential, free carbon dioxide, alkalinity, total ammonia nitrogen (TAN), nitrite-nitrogen (NO2-N), nitrate-nitrogen, and settleable solids did not substantially differ among study groups ( <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" id="M1"> <a:mi>p</a:mi> <a:mo>></a:mo> <a:mn>0.05</a:mn> </a:math> ). In addition, the highest mean levels of TAN and NO2-N recorded were 1.27 mg/l (G4000) and 9.23 mg/l (G3000), respectively. The results of growth performance revealed that final body weight, weight gain, weekly growth rate, and specific growth rate were not affected by the studied densities ( <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" id="M2"> <c:mi>p</c:mi> <c:mo>></c:mo> <c:mn>0.05</c:mn> </c:math> ). Although no significant differences were observed ( <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" id="M3"> <e:mi>p</e:mi> <e:mo>></e:mo> <e:mn>0.05</e:mn> </e:math> ), the G3000 treatment exhibited the highest survival rate (80.66% ± 8.56%), followed by G4000 (75.05% ± 0.31%) and G5000 (71.63% ± 2.11%). However, the shrimp yield was meaningfully higher for G5000 treatment (1.72 ± 0.0.09 kg/m3, 0.69 ± 0.03 kg/m2) compared with G3000 group (1.27 ± 0.0.12 kg/m3, 0.48 ± 0.04 kg/m2) ( <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" id="M4"> <g:mi>p</g:mi> <g:mo><</g:mo> <g:mn>0.05</g:mn> </g:math> ). Our results indicate L. vannamei can be reared at intensive nursery densities of up to 5,000 PL/m3 (2,000 PL/m2) until reaching 0.5 g without significant retardation in water quality, growth, and survival.