Water quality control in shrimp culture by integrated culture with the microalga, Spirulina platensis

Abstract

This study was an evaluation of using Spirulina platensis for water quality control in shrimp culture tanks. This was including the physiological study of Spirulina nutrient uptake kinetics at different salinity under laboratory condition, the use of semi-continuous harvesting to remove the excess algal biomass from the shrimp aquariums and the evaluation of nitrogen and phosphorus removal in the Spirulina-shrimp culture system under outdoor condition.It was found that high salinity (15 and 30 psu) had strong affect to nitrogen uptake rate in both ammonium and nitrate forms but salinity seemed to have more affect to nitrate uptake than ammonium uptake. The half-saturation concentration (K[subscript m]) and maximum uptake rate (V[subscript max]) of ammonium uptake by Spirulina in various salinities (0, 15, and 30 psu) were 5.470, 4.544, 3.717 mg NH[subscript 4]-N L[superscript -1] for K[subscript m] and 0.320, 0.200, 0.120 mg NH[subscript 4]-N mg Chl-a[superscript -1] h[superscript -1] for V[subscript max], respectively. In addition, the K[subscript m] and V[subscript max] constants of nitrate uptake by Spirulina in various salinities (0, 15, and 30 psu) were 16.444, 5.342, 6.293 mg NO[subscript 3]-N L[superscript -1] for K[subscript m] and 0.732, 0.313, 0.206 mg-NO[subscript 3]-N mgChl-a[superscript -1] h[superscript -1] for V[subscript max], respectively.In the second experiment, S. platensis was co-cultured with black tiger shrimp (Penaeus monodon) for water quality control. Two experimental trials were performed in order to evaluated the effects of: (1) three Spirulina trial conditions on inorganic nitrogen concentrations at one shrimp density. Spirulina trial conditions included: absent, non-harvested and semi-continuous harvesting, and (2) two shrimp densities on inorganic nitrogen concentrations, with and without Spirulina. The results showed that semi-continuous harvesting of Spirulina at one shrimp density resulted in significantly reduced (P<0.05) inorganic nitrogen concentrations (NH[subscript 4][superscript +], NO[subscript 2][superscript -] and NO[subscript 3][superscript -]). With non-harvested Spirulina, considerable variability occurred with nitrogen concentrations. The factorial evaluation of shrimp density versus presence and absence of Spirulina resulted in greatly reduced nitrogenous compounds with Spirulina present regardless of shrimp density, and only moderately increased nitrogen with greater shrimp density. Without Spirulina, all nitrogen compounds were substantially elevated and shrimp survived was significantly reduced at high shrimp density.The closed shrimp culture system in the last experiment consisted of three treatments i.e., shrimp culture without Spirulina (control), shrimp culture with Spirulina harvest (treatment 1) and shrimp culture with Spirulina harvest and shelter (treatment 2) and was conducted in 480 L fiberglass tanks located outdoor. The results demonstrated that feed contributed about 51-53% nitrogen and 56-60%phosphorus of total nutrients input to the system. Major outputs of nutrients were accounted as dissolved in water fraction which ranged between 6-37% for nitrogen and 30-35% for phosphorus of the total inputs. Harvest of Spirulina in treatment 1 removed 4.8% of nitrogen and 8.3% of phosphorus from the culture system. Moreover, other sessile algae contaminated during the experiment also had a significant portion of nutrient removal from the tank, up to 6-11% of nitrogen and 8% of phosphorus removal. Shelter in the treatment 2 significantly increased survival rate of shrimp but decreased growth of Spirulina due to shading of the shelter