Relationship Between Body Size, Growth Rate, and Maximal Enzyme Activities in the Brine Shrimp, Artemia franciscana

Activity-body size relationships for eight enzymes (citrate synthase, CS; lactate dehydrogenase, LDH; pyruvate kinase, PK; alanine aminotransferase, ala AT; aspartate aminotransferase, asp AT; glutamate dehydrogenase, GDH; glucose-6-phosphate dehydrogenase, G6Pdh; and nucleoside diphosphate kinase, NDPK) were examined in the brine shrimp, Artemia franciscana. The animals were fed on the alga Dunaliella salina, which was provided in three concentrations representing a 25-fold range. Enzyme activities per animal (Y) were regressed against body size (M, expressed as dry mass or protein) in the form of the allometric equation, log Y = log a + b log M, where a and b are fitted constants. For all enzymes considered, the value of the scaling exponent (b) was significantly higher when dry mass was used, as a body size index, than when protein mass was used. Therefore, the index of body size chosen can influence the exponent obtained in allometric studies. Although specific growth rates of different cultures varied greatly, no significant differences in scaling relationships were found between cultures for any enzyme. For many enzymes, growth rate may not be a source of variation in scaling relationships. Unlike the other enzymes examined, the log-transformed NDPK activity versus log-transformed mass was not linear; NDPK activity reached a plateau. Variation in NDPK scaling relationships with growth may provide a means to predict growth rate in Artemia.