Effects of temperature on food intake and the expression of appetite regulators in three Characidae fish: The black-skirted tetra (Gymnocorymbus ternetzi), neon tetra (Paracheirodon innesi) and Mexican cavefish (Astyanax mexicanus)

The Characidae family of fish is composed of commercially important species for which little is known about the regulation of feeding. Fish are ectotherms so that their body temperature fluctuates with the temperature of the surrounding water. Changes in water temperature can thus have major effects on the physiology of fish, in particular their feeding. The mechanisms by which appetite is influenced by changes in temperatures in fish remain unclear. In this study, we examined the effects of temperature on feeding behavior, food intake and the expression of appetite regulators in three characid fish (black tetra, neon tetra and cavefish) by submitting them to four different temperatures for 2 weeks (20°C, 24°C, 28°C, 32°C). In all species, food intake increased with increasing temperature. In neon and black tetras, increasing temperatures decreased expressions of orexin and leptin and increased that of cocaine and amphetamine regulated transcript (CART). In cavefish, temperature had no effect on brain orexin, leptin or CART. In all three species, higher temperatures induced increases in intestine expression of cholecystokinin (CCK), but no effects were seen for intestine ghrelin and peptide YY expressions. Our results show that temperature affects feeding in Characidae fish and induces species-specific changes in the expression of appetite regulators.

Fluorescent protein transgenesis has varied effects on behaviour and cold tolerance in a tropical fish (Gymnocorymbus ternetzi): implications for risk assessment

Fluorescent protein (FP) transgenesis is used in the ornamental aquarium trade to produce new colour morphs in tropical fish. Understanding whether such genetic modification could alter ability to survive temperate waters, or interactions with native fish, should such fish be released to natural systems is critical in developing policy on their commercial use. We examined the competitive foraging ability and cold tolerance of unrelated pet-trade sourced adult green FP transgenic tetra and non-transgenic white tetra (Gymnocorymbus ternetzi), as well as white non-transgenic and green FP transgenic juvenile progeny of these groups. FP transgenesis did not affect the foraging success or aggressive behaviour in either adult or juvenile fish, indicating FP transgenesis may not influence potential hazards through this pathway. During a cold temperature tolerance trial, adult green tetras had greatly diminished cold tolerance relative to unrelated adult white fish, while sibling juvenile offspring of these groups had intermediate cold tolerance between adult fish groups that were not affected by FP transgenesis. This data suggests background genetics, rearing history and/or life stage may play larger roles in cold tolerance than FP transgenesis in this species. Unexpectedly, both adult and juvenile white tetras were 3.8 times more likely to take refuge in shelters when temperature declined than green tetras. These data indicate FP transgenic fish may pose equal or lesser risk than non-transgenic fish, should they be released to natural environments. Results also demonstrate that unrelated pet-trade sourced fish may not always be appropriate models for examining effects of FP transgenesis.

Cold temperature tolerance of albino rainbow shark (Epalzeorhynchos frenatum), a tropical fish with transgenic application in the ornamental aquarium trade

Application of fluorescent protein transgenesis has commercial use for the ornamental aquarium trade by creating new colour phenotypes in various species. To determine the potential for transgenic ornamental aquarium fish to overwinter in Canada, the minimum temperature tolerance of albino rainbow shark (Epalzeorhynchos frenatum (Fowler, 1934)) was estimated to complement a previous study examining cold tolerance of zebrafish (Danio rerio (Hamilton, 1822)), black tetra (Gymnocorymbus ternetzi (Boulenger, 1895)), and tiger barb (Puntius tetrazona (Bleeker, 1855)). Rainbow shark had higher low temperature tolerance limits (LD50 = 10.7 ± 0.1 °C) than surveyed winter water temperatures in Canada. There was a significant negative correlation between condition factor and temperature at loss of equilibrium, suggesting fish with lower social status may be more susceptible to cold temperature than dominant fish. These results indicate transgenic E. frenatum are not expected to persist over winter in Canadian waters.