Hormonal induction of ovulation and spermiation in Atlantic cod (Gadus morhua)

Captive, wild-caught female Atlantic cod, Gadus morhua, from Georges Bank (n=19) were divided into three

treatment groups based on body weight and diameter of the largest clutch of oocytes present. Treatments

administered were an intramuscular implant of one of two gonadotropin releasing hormone analogues —(DAla6,

Pro9-NHEt)-LHRH ethylamide (LHRHa, 150 μg) and salmon gonadotropin releasing hormone analogue

(sGnRHa, 150 μg, OvaplantR), or a saline injection (control). Over a period of 20 days, 12 of 14 implanted and

one control fish ovulated. There was no significant variation between egg volumes and percent fertilization

(P≥0.4968) of implant-treated and naturally ovulating females; however, significant variation did exist for

the estimated number of hatched larvae among treatments (P=0.0169). Non-spermiating captive wildcaught

Atlantic cod males (n=11 Georges Bank) were divided into two treatment groups (OvaplantR and saline control) based on body weight. Large volumes of milt with high motility and spermatocrits were

obtained from each of five OvaplantR-treated males starting 6 days post-implant. Over a 27 day period, each

of six control males produced milt at least once, but in small volumes with variable motility and low

spermatocrits. Milt volumes of the OvaplantR-treated males were higher than naturally spermiating males

(P=0.0002), but had similar motilities and spermatocrits (P≥0.0462). These results demonstrate the

effectiveness of GnRHa implants in inducing ovulation and spermiation in Atlantic cod broodstock without

adversely affecting gamete quality.

1. Introduction

A general decline in Atlantic cod (Gadus morhua) stocks and

continuous, high consumer demand has stimulated the development

of cod aquaculture in several countries, including Canada, Iceland,

Ireland, Norway and the United States (Rosenlund and Skretting,

2006). The development of this industry has benefited from

considerable research in areas such as larviculture (Foss et al.,

2006), genetics (Kolstad et al., 2006), fish health (Bricknell et al.,

2006), nutrition (Hansen et al., 2007), juvenile and adult growth

(Bj?rnsson et al., 2007) and post-harvest fillet quality (Esaiassen et al.,

2008). Additionally, several studies were conducted to understand the

reproductive biology of captive cod and control of the reproductive

cycle to meet the increasing demand for juveniles for aquaculture