Temperature and oxygen requirements of early life stages of the endangered spined loach, Cobitis taenia L. (Teleostei, Cobitidae) with implications for the management of natural populations

The responses of early life stages of Cobitis taenia to various temperatures and oxygen levels revealed the species to be warm-mesothermic and comparatively resistant against low oxygen concentrations. Lower and upper lethal temperatures were 12.1 and 30.8 degreesC, respectively. As estimated from the combined final size (CFS, the number of healthy survivors multiplied by their mean length), temperatures of 14.0, 15.8, 28.4 and 30.3 degreesC were suboptimal, while temperatures of 17.8-26.1 degreesC represented the optimum range. At 21.9 +/- 1.0 degreesC, oxygen concentrations of 0.9 to 1.8 mg l(-1) were lethal; those of 2.1 and 2.2 mg l(-1) suboptimal and those of 3.2 to 7.8 mg l(-1) optimal. Regarding body size, the optimum range for both, temperature and oxygen concentration, was narrower than for CFS, while it was broader if reflected by the survival rate. The most critical period concerning temperature was prior to hatching. Under low oxygen concentration, the main mortality occurred until the middle of the free embryonic phase. The early life stages of spined loach express early hatching as well as morphological (external gills, rich skin vascularisation in the dorsal fin) and behavioural (ventilation by movements of body and pectoral fins) adaptations to low oxygen supply. These adaptations are related to an evolutionary binding of spined loach to a microbabitat with frequent oxygen depletions, as it was former postulated on the base of behavioural studies. The necessity of high temperature for development binds the spined loach to warm microhabitats for reproduction. Therefore, the availability of a suited microhabitat for the early life stages with warm water becomes a key requirement for the successful maintenance of populations of C. taenia. This specialisation has to be considered in conservation measures for the Europe-wide endangered species.