Milt characteristics of diploid and triploid Atlantic cod (Gadus morhuaL.)

Abstract

The work compares the characteristics of milt produced by diploid and triploid Atlantic cod in terms of sperm motility, density, DNA content, seminal-fluid composition and the ability of sperm to fertilize the eggs. The mean track velocity (VCL) was higher in the sperm of diploid than in the triploid males at 20 s post-activation (p.a.; 124.04 ± 6.91 vs. 113.32 ± 6.32 μm s−1), but not at 40 s p.a. No differences between ploidies were observed for the remaining sperm-motility descriptors as for spermatozoa density, spermatocrit or seminal fluid's variables like pH, osmolarity, Cl−, Na+, Ca2+ and K+ concentration. Triploid males produced aneuploid sperm cells (average 1.46n, range 1.2–1.6n) and the larvae generated from artificial crossings with diploid females showed abnormal morphology and did not survive to exogenous feeding. Plasma concentration of 11-ketotestosterone in sexually mature diploid and triploid males was similar (5.35 ± 1.54 vs. 4.82 ± 1.15 ng mL−1) and no differences were found in the ability of males of both ploidies to induce spawning when held in tanks with diploid females. The paper provides evidence of gametic sterility of triploid males and examines the use of triploid fish as a management option to address the issues of genetic containment of farmed cod alongside measures for securing present fish-farming technologies.