Refining Ammonia Treatments for Control of Prymnesium parvum in Striped Bass Fingerling Production Ponds

Texas state fish hatcheries use un‐ionized ammonia nitrogen (NH 3 ‐N) treatments of 0.14–0.25 mg/L to control Prymnesium parvum in production ponds for phase‐1 Striped Bass Morone saxatilis based on a published ammonia tolerance for 4‐ to 6‐d‐old Sunshine Bass (female White Bass M. chrysops × male Striped Bass M. saxatilis ). Because fingerling production has been inconsistent and the treatments require frequent reapplications to maintain control of P. parvum , we conducted this study to answer two questions: (1) are the treatments developed for Sunshine Bass appropriate for Striped Bass culture, and (2) can the maximum treatments be increased as the fish grow. Striped Bass (4, 10, 20, and 28 d old) were exposed to NH 3 ‐N concentrations up to 1.2 mg/L for 96 h. Ammonia concentrations and fish mortalities were monitored at 24‐h intervals, their relationship modeled using logistic regression, and ammonia concentrations that 90% of the fish survived during the various exposure periods (maximum treatments) were estimated. The 4‐ to 6‐d‐old Striped Bass survived ammonia concentrations similar to those of Sunshine Bass of the same age‐group. The 20‐d‐old fish were the least tolerant of NH 3 ‐N, followed by 4‐d‐old fish and then 10‐d‐old fish. The 28‐d‐old fish was the most tolerant of ammonia toxicity. The maximum treatment varied with fish age. Thus, the current practice of treating for concentrations between 0.14 and 0.25 mg NH 3 ‐N/L throughout production of phase‐1 fish is inappropriate. Treating with 0.14‐ to 0.25‐mg NH 3 ‐N/L can be suitable for culture of Striped Bass fry and fingerlings, except for fish in the 22–24‐d age range. The upper limit of concentration may be increased up to 0.37 and 0.40 mg NH 3 ‐N/L for 10‐ to 12‐d‐old and 28‐ to 30‐d‐old Striped Bass, respectively. However, the concentration must be lowered to 0.1 mg NH 3 ‐N/L for 22‐ to 24‐d‐old Striped Bass.