Comparison of egg and offspring size of karyologically identified spined loach, Cobitis taenia L., and hybrid triploid Cobitis females (Pisces, Cobitidae)

The aim of this study was to determine and compare for the first time the size of eggs laid by C. taenia (2n=48) and its naturally occurring triploid (3n=74) hybrid females and the total length of offspring of these females obtained from experimental crosses, in the period from hatch to 22 days post hatch. The eggs laid by triploid females had an average diameter of 1.18mmand were significantly larger than the eggs spawned by C. taenia females, which averaged 0.93 mm in diameter. The size of the triploid female eggs was associated with their level of ploidy. Similarly, the average total length of triploid female progeny from one to ten days post hatch was statistically significantly higher than the average total length of C. taenia offspring in the same period of life. After two weeks, the offspring of diploid and triploid females reached average total lengths of 13.27 mm and 13.60 mm, respectively, which was not a significant difference. The possible causes of triploid Cobitis female domination in diploid-polyploid populations in terms of egg size and other traits associated with polyploid functioning was also investigated.