Effects of sand sediment and vertical surfaces (AquaMats TM) on production, water quality, and microbial ecology in an intensive Litopenaeus vannamei culture system

Growth and production of Pacific white shrimp ( Litopenaeus vannamei) was examined along with water quality, and general indicators of microbial activity in replicate intensive tank cultures with no sediment, sand sediment, and sand sediment together with additional vertical surfaces (sand/mat). All treatments received similar feed and fertilizer input. Initial linear shrimp growth rates was relatively high (1.65 g/week) in all treatments. A reduction in growth rates was seen in the no-sediment and sand treatments, while linear growth continued longer in the sand/mat treatment. Shrimp weight, survival and production was significantly greater in the sand/mat treatment than in the sand and no-sediment treatments. While the latter two treatments yielded similar production, the no-sediment treatment required weekly additions of soda ash during the last month of the 104-day season to maintain a minimum pH of 7.0. Significantly higher pH, in conjunction with lower phytoplankton biomass and ammonia in the sand/mat treatment than in the sand treatment suggests greater carbon fixation by the attached algal community of the sand/mat treatment. This is further supported by similar carbon mineralization rates in all treatments as roughly indicated by water respiration rates in conjunction with greater sludge accumulation in the sand/mat treatment. Phyto and bacterioplankton levels were significantly lower in the sand/mat treatment than in the other treatments. Ammonia, nitrate and sludge accumulation were similar in the no-sediment and sand tanks. The sand/mat treatment had significantly greater nitrite than the other treatments. Water column nitrification rates were similar in the sand and no-sediment treatments and significantly greater in the sand/mat treatment, suggesting that nutrient cycling rates may be greater in this treatment. From a production standpoint, the primary difference in the no-sediment and sand treatments was the need for proactive management of pH in the no-sediment tanks. The quantity of vertical surface area addition tested in the sand/mat treatment of this study yielded higher shrimp production in conjunction with significant differences in water quality and indicators of general activity, suggesting that this relatively high level of vertical surface addition may significantly affect aquaculture production systems.