Abstract
Organisms exposed to sub-zero temperatures are at risk of freezing damage. Fingerling channel catfish, Ictalurus punctatus, hybrid catfish (channel catfish female×blue catfish, Ictalurus furcatus, male), channel catfish transgenic for the goldfish glutamate decarboxylase 65 gene driven by the carp β-actin promoter (βA-GAD65), and channel catfish transgenic for the catfish growth hormone gene driven by the antifreeze protein promoter (AFP-ccGH) were compared for survival at different temperatures (9.0°C, 6.0°C, 3.0°C, 1.0°C, 0.5°C, 0°C, and −0.5°C) at different salinities (0ppt, 2.5ppt, 5ppt, and 7.5ppt). The two transgenes were of interest as growth hormone not only affects growth, but also affects osmoregulation, and GAD65 construct could alter gonadotropin with the potential consequence that GnRH affects growth hormone production. Survival was 98–100% for all genetic groups at all salinities between 0°C and 9.0°C. However, large differences were observed at −0.5°C. At 0ppt salinity, 100% of AFP-ccGH transgenic (T) fingerlings survived, but survival of all other genetic groups was 0–2%. Raising salinity to 2.5ppt at sub-zero temperature had a strong positive impact on survival as survival rates of AFP-ccGH (T), AFP-ccGH control (C), channel catfish, βA-GAD65 (T), βA-GAD65 (C) and hybrid catfish were 100, 100, 98, 76, 100 and 18%, respectively. Increasing salinity further to 5ppt decreased overall survival, although it was still higher than at 0ppt. Survival rankings were altered, with means for βA-GAD65 (T), βA-GAD65 (C), AFP-ccGH (T), AFP-ccGH (C), channel catfish and hybrid catfish of 69, 0, 15, 22, 0 and 0%, respectively. Mortality was 100% in all genetic groups at −0.5°C and 7.5ppt demonstrating significant interaction between temperature and salinity. Negative heterosis was observed for the hybrids at low temperature at the respective salinities.
We believe that this topic has not been previously addressed. These pleiotropic effects have never been described in GH transgenic or GAD transgenic fish and have relevance for aquaculture/natural resource management for future climate change as well as management and genetic management today.
It is the first paper to evaluate the survival of hybrids under freezing, very important for countries that are suffering from freezing weather.
•We transferred two different constructs, AFP-ccGH and βA-GAD65 to channel catfish.•Different genetic groups were compared for survival at different concentrations of salinities, and low temperatures.•Massive mortality occurred for most genotypes at - 0.5 oC and 0 ppt salinity except for AFP-ccGH transgenic catfish.•Survival of all genetic groups was very high at - 0.5 oC and 2.5 ppt salinity.