Use of Aluminum Sulfate to Reduce pH and Increase Survival in Fingerling Striped Bass Production Ponds Fertilized with Nitrogen and Phosphorus

Abstract

AbstractPrevious studies revealed inorganic nitrogen (300 μg/L) and phosphorus (30 μg/L) additions thrice weekly is effective in controlling the density of Prymnesium parvum, a flagellated haptophytic golden alga with ichthyotoxicity in fish culture ponds. However, increased pH resulting from this treatment is also toxic to fry and fingerlings of Striped Bass Morone saxatilis. We evaluated the efficacy of aluminum sulfate (alum) in lowering pH in ponds fertilized for P. parvum control. The effects of alum on dissolved N and P concentrations, as well as the efficacy of this fertilization treatment for P. parvum control, were also examined. Striped Bass fingerlings (27.93 mm total length) were raised for 42 d in 10 plastic‐lined ponds (0.1 ha) fertilized for P. parvum control. Five ponds received alum applications at a rate of 1 mg/L for each 1 mg/L phenolphthalein alkalinity when afternoon pH was ≥9.0. The remaining five ponds served as controls and received no alum. Among alum ponds, morning pH was reduced by an average of 1.2 units and afternoon pH by an average of 0.8 units compared with controls. However, the alum treatment did not maintain afternoon pH below 9.0. Alum reduced concentrations of total P, soluble reactive P, total Kjeldahl N, nitrite + nitrate N, and total N but not ammonium N. The fertilization regimen was not as aggressive in controlling P. parvum in alum ponds as it was in control ponds, which may be attributed to N and P removal by alum. Striped Bass production was poor in all ponds, probably because of high pH. Future studies should investigate higher alum treatment rates (e.g., phenolphthalein alkalinity : alum = 1:1.5 or 1:2) along with modification of the timing or frequency of fertilization.