Reproduction of the stone loach, Barbatula barbatula (L.) in Estonia

Reproduction of the stone loach was investigated in two rivers of northwestern Estonia (Vääna and Maidla, 59 degrees N). Loaches in the Vääna River were slow growing and males prevailed among older fish; in the Maidla River loaches were fast growing and females dominated among older fish. Reproduction indices (age at maturation, duration of the spawning season, number of egg batches, fecundity, oocyte diameter, annual dynamics of gonadosomatic index and oocyte diameter) of comparably sized loach of Vääna and Maidla were similar and intermediate between more southern and more northern populations. Female investment in offspring (measured as the volume of spawned eggs) in Estonia was close to that in England; however, energy was invested in a smaller number of larger eggs (larvae). Our results confirm earlier data on the remarkable variation of life history patterns of the stone loach and indicate clinal variation of several reproduction indices along a north-south axis.