Acute Responses to Salinity for Sunshine Bass and Palmetto Bass

Abstract

Differences in salinity tolerance and osmoregulatory performance between sunshine bass (white bass Morone chrysops ♀ × striped bass M. saxatilis ♂) and palmetto bass (striped bass ♀ × white bass ♂) were evaluated by using direct-transfer toxicity testing and monitoring of plasma osmolality during salinity elevation. The 24-h LC50 (concentration lethal for 50% of test animals) for sunshine bass was a salinity of 27.9‰ with a 95% lower and upper confidence interval (CI) of 24.5‰ to 36.2‰. The 24-h LC50 for palmetto bass was 28.0‰ with a 95% CI of 26.2‰ to 30.8‰. Test temperatures during this interval ranged from 19.6°C to 21.7°C, and the LC50 values for both crosses did not differ significantly. Differences in osmoregulatory performance were determined by sampling blood plasma osmolality (mmol/kg) during a stepwise elevation in salinity from freshwater to 52‰. Plasma osmolality of sunshine bass was significantly higher at 11‰, but osmolality of palmetto bass was higher at 41‰ and 52‰. Sunshine bass maintained baseline plasma osmolality through 41‰, whereas palmetto bass could only maintain baseline osmolality through 31‰. Although both crosses have similar tolerance to increasing salinity in terms of survival, sunshine bass appear to tolerate osmoregulatory stress better than palmetto bass, based on blood plasma osmoregulation.