Induction of diploid
gynogenesis in southern flounder (Paralichthys lethostigma) with
homologous and heterologous sperm
J.A. Luckenbach, J. Godwin, H.V. Daniels, J.M.
Beasley, C.V. Sullivan, R.J. Borski-2004
Aquaculture, 237(1-4): 499-516
Abstract:
Effective methods for induction of diploid
gynogenesis in North American flounder of the genus Paralichthys are
needed to initiate monosex culture, which will allow growers to take
advantage of the more rapid growth and larger size attained by females. To
test methods for inducing diploid gynogenesis in southern flounder (Paralichthys
lethostigma) using homologous sperm, four treatments, named for their
expected outcome, were employed: haploid, diploid, triploid, and gynogenetic
diploid. Diploid gynogenesis was induced by activating egg development with
UV-irradiated flounder sperm (70 J/cm2) for 3–4 min in
seawater, and then subjecting the eggs to cold shock in 0–2 °C seawater
for 45–50 min. Cold shock was used to prevent extrusion of the second
polar body. Control treatments omitted one or more of these steps to
separately assess the effectiveness of UV irradiation and cold shock. Larvae
were observed for physical abnormalities and then histologically processed
for ploidy determination. Haploid larvae exhibited abnormal external
morphology while diploid, gynogenetic diploid, and triploid larvae showed
normal morphologies. Cross-sectional areas of erythrocyte nuclei were
measured for larvae in each treatment group and significant differences were
found. Nuclear areas for treatment groups corresponded to predicted ploidy
(triploid>diploid>haploid) and did not differ between normal diploid
controls and gynogenetic diploids. These results suggest that the procedures
of sperm irradiation and egg cold shock successfully generated gynogenetic
diploids. Due to the low volumes of semen produced by male flounder, and to
eliminate any potential genetic contribution by homologous sperm, activation
of flounder eggs with heterologous sperm was also investigated. Induction of
diploid gynogenesis was successful when flounder eggs were fertilized with
irradiated (50 J/cm2) sperm from striped mullet (Mugil
cephalus), and then cold shocked. This work provides procedures for
induction of diploid gynogenesis in southern flounder using homologous and
heterologous sperm, and validates a method for verification of ploidy in
larval fish.
(Department of Zoology, North Carolina State
University, Box 7617, Raleigh, NC 27695, USA, e-mail of R.J. Borski: russell_borski@ncsu.edu)