THE GONAD MORPHOLOGY AND MATURATION IN ARCTIC CALANUS SPECIES

Gonad morphology and maturation of the dominant Arctic copepod species Calanus glacialis and C. hyperboreus were studied using a combination of observations on whole animals (''whole-body analysis'') and histol ogical sections to describe basic reproductive processes. The comparis on with C. finmarchicus shows that the internal organisation of the go nads is the same in the Calanus species: from the dorsally laying ovar y, two anterior diverticula extent into the head region and two poster ior diverticula extend into the abdomen. In the diverticula, the oocyt es increase in size and development stage in a dorso-ventral direction . There were no physiological differences between the oocytes in the d iverticula and oviducts in any of the three species. During gonad deve lopment, the morphological modifications of the gonads mainly refer to an increase in number, developmental stage and size of the oocytes bo th in diverticula and oviducts. During spawning the most ventral layer of oocytes is released, and then the adjacent dorsal layer begins fin al maturation. Thus, the final maturation processes occur simultaneous ly as it is essential to produce clutches. (C) 1998 Elsevier Science B .V. All rights reserved.