The effects of Geno hot spring cyanobacteria on growth, survival and morphology of gill tissue in killifish Aphanius dispar in normal and long term thermal stress environments

A killifish species Aphanius ginaonis occurs in Geno hot spring is one of the unique fish species that could successfully survive and acclimated to the high temperature of hot springs. In this study, we investigated the effects of Geno's cyanobacteria extracts on growth, survival and morphology of gill tissue in Aphanius dispar exposed to normal temperature and long-term thermal stress. For this purpose, 228 fish divided in four treatments including control (25°C), thermal (40-37°C), cyanobacteria control and cyanobacteria thermal. Our results showed significant affects of prolonged thermal stress in all growth parameters of A. dispar. At the end of the experiment at day 44, most of the growth parameters significantly decreased compared to the control group. The results showed that growth factors, including specific growth rate (SGR), weight gain (WG) and food conversion rate (FCR) in the control and the control – cyanobacteria groups were significantly higher than those of thermal and thermal- cyanobacteria treatments (p<0.05). The survival rate of fish in control and control - cyanobacteria treatments was 100%, whereas survival rate significantly reduced in thermal and thermal - cyanobacteria treatments (p<0.05). Fish kept at 37-40 °C showed changes in gill tissue included blood congestion of primary lamellae and shortened secondary lamellae. In normal temperature, cyanobacteria caused blood congestion of primary lamellae, but in thermal stress, severe pathological changes observed. The conclusion can be drawn that at the thermal environment of hot spring, cyanobacteria extracted from Geno hot spring reduced the physiological functions of fish and could not modulate thermal tolerance in Aphanius fish.