The effect of migration distance and timing on metabolic enzyme activity in an anadromous clupeid, the American shad (Alosa sapidissima)

The American shad (Alosa sapidissima) is a common anadromous fish species w ith ecological and economic importance on the east coast of North America. This iteroparous species undergoes an energetically costly upriver spawning migration in spring. To evaluate metabolic changes associated with this mi gration, we assessed the maximum activity of five metabolic enzymes (citrat e synthase (CS), phosphofructokinase (PFK). lactate dehydrogenase (LDH), be ta-hydroxyacyl coenzyme A dehydrogenase (HOAD), alanine aminotransferase (G PT)) in liver, red muscle and white muscle during upstream migration in two successive years in the Connecticut River. For aerobic capacity (CS), glyc olytic capacity (LDH) and utilization of stored lipid and protein energy (H OAD and GPT), there is a general pattern of increasing activity with a subs equent decline at the most upriver sites. Red muscle CS activity increased by as much as 40% during the migration while white muscle CS activity was 1 20% higher in the river than in the ocean. In contrast, muscle anaerobic ca pacity, indicated by PFK, was low as fish entered the river and then increa sed 5-fold at the most upriver sites. White muscle HOAD increased similar t o 30% while red muscle HOAD and muscle GPT increased as much as 60%. There were interannual and sex-associated differences in enzyme activity during u pstream migration and through time at a single location. In some cases inte rannual differences can be larger than those seen during upriver migration as in the case of red muscle CS where sampling years differed by 125%. Thes e interannual differences may be a result of differing river conditions tha t affect migratory effort. We have demonstrated that American shad use tiss ue and sex-specific regulation of enzyme activity during migration and we s uggest that American shad metabolically acclimate to upstream migration.