Incidence of conjoined twins in tilapia after thermal shock induction of polyploidy


Correspondence: J A Hargreaves, Department of Wildlife and Fisheries, Mississippi State University, Box 9690, Mississippi State, MS 39762, USA


Conjoined twins (polyembryonic fish) were observed in batches of blue tilapia Oreochromis aureus (Steindachner) and Nile tilapia O. niloticus (L.) embryos incubated at 28 °C. Heat shock (41.8 °C) treatment of fertilized eggs for 3–4 min applied between 4 min and 27 min after fertilization increased the twinning rate by three or four times over that of unshocked eggs. Two basic morphological variations – ventrally or laterally conjoined twins – were observed. Twins did not survive beyond 21 days after hatching. The proportion of twins in heat-shocked egg batches of both species combined ranged from 0.32% to 0.40%.