Interdemic variation in haematocrit and lactate dehydrogenase in the African cyprinid Barbus neumayeri

This study evaluated whether the African cyprinid Barbus neumayeri from Rwembaita Swamp (low‐oxygen) and Njuguta River (high‐oxygen) in the Kibale National Park, Uganda differed in traits related to aerobic and anaerobic metabolic potential. Haematocrit was measured as an index of blood oxygen‐carrying capacity, and tissue activities and isozyme composition of lactate dehydrogenase (LDH) were measured as indices of tissue anaerobic capacity. To address whether site‐dependent differences were acute responses v . longer‐term adjustments to environmental conditions, these variables were measured in fish sampled shortly after collection and after laboratory maintenance under well‐aerated conditions. In fish sampled in the field, those from the low‐oxygen site had significantly higher haematocrit, but this difference disappeared after long‐term laboratory maintenance. In contrast, fish from the low‐oxygen site had higher liver LDH activities than fish from the high‐oxygen site, and this difference persisted during laboratory maintenance. Polymorphism was detected at both the LDH‐A and LDH‐B loci, and genotype frequencies for LDH‐B differed significantly between collection sites. These results demonstrate physiological, biochemical and genetic differences in B. neumayeri from habitats differing in dissolved oxygen availability and suggest both acute and long‐term responses to local environmental conditions.