Somatic Growth Parameters of Black Sea Bivalvia Mollusks—Cerasoderma glaucum (Bruguiere, 1789), Mytilus galloprovincialis (Lamark, 1789), and Mytilaster lineatus (Gmelin, 1791) in Summer (Azov–Black Sea Basin)

The results of a comparative analysis of morphophysiological and biochemical indices of somatic growth for three Black Sea bivalve mollusks living in shallow waters near the Kerch Strait—cockle Cerastoderma glaucum (Bruguiere, 1789), mussel Mytilus galloprovincialis (Lamark, 1789), and Mytilaster lineatus (Gmelin, 1791)—are presented. Lengths from 15 to 20 mm are studied. The size–weight dependence is estimated as very high according to the Chaddock scale for C. glaucum, with the correlation coefficient R = 0.97, and it was high for M. galloprovincialis (R = 0.73) and M. lineatus (R = 0.86). Linear regression models between total mussel mass and soft tissue mass illustrated a large proportion of explained variance, with determination coefficients from 0.70 to 0.87. Based on the values of total RNA content and the RNA/DNA growth index in C. glaucum and M. galloprovincialis, it is shown that the level of synthesis of protein structures of somatic tissues in the juveniles of these species is estimated as average; in M. lineatus it is high. The species specificity of somatic growth between species of different families is noted: the level of tissue biosynthesis is 2.3 times higher in M. lineatus (Mytilidae) than in C. glaucum (Cardiidae).