Growth performance, morphometric traits and gonad development of induced reciprocal diploid and triploid hybrids between the mud loach (Misgurnus mizolepis Günther) and cyprinid loach (Misgurnus anguillicaudatus Cantor)

Two species of loach, the mud loach (Misgurnus mizolepis Günther) and the cyprinid loach (M. anguillicaudatus Cantor), are commercially important in Korea both for food and ceremonial purposes. The mud loach has superior potential for aquaculture in terms of growth, whereas the cyprinid loach has a more desirable body shape and colour. This study was conducted to produce reciprocal diploid and triploid hybrids and to evaluate their potential benefits in culture by examining growth performance, morphometrics and gonad development. Reciprocal diploid and triploid hybridization was performed by artificial insemination without or with the induction of triploidy. The successful formation of diploid or triploid karyogamy was verified by flow cytometric analysis. Body weights of induced reciprocal diploid hybrids were intermediate between those of the two parental species, i.e. hybrids were heavier than cyprinid loach but lighter than mud loach. In contrast, the growth performance of triploid hybrids was similar to that of their corresponding maternal parents. Diploid hybrids showed intermediate morphometric traits between the two species; however, the body proportions of triploid hybrids were more similar to those of the maternal species than the paternal species. Histological analyses indicated that reciprocal diploid hybrids of both sexes were able to reach maturity, as evidenced by the presence of mature oocytes or spermatozoa in the gonad tissues. However, triploid hybrids showed stringent sterility at the gonadic level; the sizes of ovaries and testes were much smaller, and gonad development was abnormal and significantly retarded.