Physico-chemical water parameters variation in the floating cages of snappers (Lutjanus peru and L. guttatus) farmed in tropical sea

The water column in a fish farm was sampled at three depth layers to determine large and short term changes in water quality. The overall goal of this study was to determine the variation of nutrient concentrations in the water column in open-ocean floating cages with cultures of Lutjanus peru (Pacific red snapper) and L. guttatus (spotted rose snapper). Nutrient concentration (ammonia-N, nitrite-N, nitrate-N, and phosphate) were evaluated every fifteen days in the water column at three stations (cages) and two depths; likewise, several water quality parameters were analyzed daily (water temperature, salinity, dissolved oxygen and Secchi disk). Analyses of water in general showed that no significant differences existed between the monthly concentration of nutrients from the control stations and depths. Nitrate was the nutrient with the highest concentration (2.83 to 3.56 mg/L); however, these values were relatively low and normal for these waters. The results show that when working with fish densities of 2500 to 3500 fish/cage and small quantities of food (60 ton/year) no impact is made on the water column quality in the floating cages culture system.