Belonesox Research Articles

Lower lethal temperatures for fourteen non-native fishes in Florida

The most important factor affecting the potential range of 14 non-native fishes in Florida appears to be their lack of tolerance to low temperatures. In this study, temperatures associated with reduction in feeding, cessation of feeding, loss of equilibrium and death were identified by decreasing water temperature 1°C day−1. Fishes tested and their mean lower lethal temperatures were: Astronotus ocellatus (12.9°C), Belonesox belizanus (9.7°C), Cichlasoma bimaculatum (8.9°C), C. cyanoguttatum (5.0°C), C. meeki (10.3°C), C. octofasciatum (8.0°C), C. trimaculatum (10.9°C), Clarias batrachus (9.8°C), Hemichromis bimaculatus (9.5°C), Hypostomus sp. (11.2°C), Tilapia aurea (6.2°C), T. mariae (11.2°C), T. melanotheron (10.3°C) and T. mossambica (9.5°C). These data indicate that temperature is less limiting for these fishes in Florida than was previously recognized.

Visual pigments in a fish exposed to different light-environments.

THE poeciliid Belonesox belizanus Kner has a mixture of two visual pigments in its retina. One of these is based on vitamin A1 (λmax = 498 mµ), the other on vitamin A2 (λmax = 521 mµ)1,2. Like the cyprinids Scardinius3 and Notemigonus2 the proportions of these pigments in the retina vary throughout the year, there being more of the vitamin A2-based pigment in the winter and less in summer2. As in Notemigonus4, there is considerable variation of retinal visual pigment composition among individuals of Belonesox caught at the same time and in the same place (Bridges, C. D. B., unpublished observations).