The effect of a commercial bacterial supplement on the high-density culturing of Litopenaeus vannamei with a low-protein diet in an outdoor tank system and no water exchange

The effect of adding a commercial bacterial supplement to shrimp growout facilities was studied with respect to shrimp yield and water quality parameters. Shrimp (Litopenaeus vannamei) were grown in 12 10.5-m(2) outdoor tanks with no water exchange. Each tank was stocked with juvenile L. vannamei (average weight, 1.69 g) at a density of 40/m(2). The shrimp were fed with a 21% protein diet. Six randomly assigned tanks were treated with the bacterial supplement, which was added five times per week, throughout the test period. The other six shrimp tanks, which did not receive the bacterial supplement, served as controls. The test lasted 14 weeks, at which point the shrimp from all the tanks were harvested. Water quality parameters were tested daily or weekly. Sludge slurries were examined at harvest time. There were no significant differences in the water and sludge parameters between the untreated shrimp tanks and those tanks that were treated with the commercial bacterial supplement. The harvested shrimp were weighed and counted to calculate shrimp survival, mean final weight and feed conversion ratio (FCR). The untreated and bacterially treated shrimp tanks had mean survival rate of 91 and 93%, mean final weight of 12.17 and 11.69 g, and a FCR of 2.15 and 2.19, respectively. There was no significant difference in these values between the treated and untreated tanks. The addition of the bacterial supplement showed no improvement either in water and sediment quality or in shrimp yield over the untreated tanks. It appears that the natural microbial flora in the shrimp tanks was sufficient to maintain high water quality, and support the growth and survival of the shrimp, thus fulfilling the task intended for the bacterial supplement. Therefore, there was no need for such an outside bacterial intervention. (C) 2000 Elsevier Science B.V. All rights reserved.