METABOLIC ENZYME-ACTIVITIES IN ATLANTIC SALMON (SALMO-SALAR L.) EMBRYOS RESPOND MORE TO CHRONIC CHANGES IN OXYGEN AVAILABILITY THAN TO ENVIRONMENTAL-TEMPERATURE

Chronic exposure to an increased temperature (e.g., 10 degrees C as co mpared to 5 degrees C) and to a different oxygen tension can dramatica lly affect muscle cellularity in Atlantic salmon embryos at a developm ental stage close to hatching. Maximal activities of enzymes of aerobi c and anaerobic metabolism have been shown to vary with temperature an d growth rates in fish but only limited data are available for embryon ic fish. In order to obtain data on Atlantic salmon embryos and to be able to compare temperature and oxygen effects, the maximal activities of lactate dehydrogenase (LDH) and cytochrome c oxidase (CCO) were de termined in body tissue containing mainly muscle as measures of anaero bic and aerobic metabolism, respectively. Temperatures of 5 and 10 deg rees C, different O-2 tensions (50% normoxic, normoxic, 150% normoxic) , and growth within (chorionated) or without (dechorionated) the egg c apsule were chosen as environmental conditions. Temperature affected C CO activities and thus the CCO/LDH ratio in dechorionated but not in c horionated embryos (5 < 10 degrees C) and had no effect on LDH activit ies. However, changes in oxygen availability had an effect on all para meters measured. Tissue protein concentration increased after dechorio nation but no temperature effect was found. Both LDH and CCO activitie s undergo complex responses to oxygen availability depending on incuba tion temperature. There thus appeared to be an interaction of temperat ure and oxygen availability with regard to maximum activities of key e nzymes of the aerobic and anaerobic metabolism in the salmon embryos.