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 threetreatment groups based on body weight and diameter of the largest clutch of oocytes present. Treatmentsadministered were an intramuscular implant of one of two gonadotropin releasing hormone analogues (DAla6,Pro9-NHEt)-LHRH ethylamide (LHRHa, 150 g) and salmon gonadotropin releasing hormone analogue(sGnRHa, 150 g, OvaplantR), or a saline injection (control). Over a period of 20 days, 12 of 14 implanted andone control fish ovulated. There was no significant variation between egg volumes and percent fertilization(P0.4968) of implant-treated and naturally ovulating females; however, significant variation did exist forthe estimated number of hatched larvae among treatments (P=0.0169). Non-spermiating captive wildcaughtAtlantic cod males (n=11 Georges Bank) were divided into two treatment groups (OvaplantR andsaline control) based on body weight. Large volumes of milt with high motility and spermatocrits wereobtained from each of five OvaplantR-treated males starting 6 days post-implant. Over a 27 day period, eachof six control males produced milt at least once, but in small volumes with variable motility and lowspermatocrits. Milt volumes of the OvaplantR-treated males were higher than naturally spermiating males(P=0.0002), but had similar motilities and spermatocrits (P0.0462). These results demonstrate theeffectiveness of GnRHa implants in inducing ovulation and spermiation in Atlantic cod broodstock withoutadversely affecting gamete quality.1. IntroductionA general decline in Atlantic cod (Gadus morhua) stocks andcontinuous, high consumer demand has stimulated the developmentof 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 fromconsiderable 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(Bjrnsson et al., 2007) and post-harvest fillet quality (Esaiassen et al.,2008). Additionally, several studies were conducted to understand thereproductive biology of captive cod and control of the reproductivecycle to meet the increasing demand for juveniles for aquaculture(Rakitin et al., 1999; Norberg et al., 2004; Skjraasen et al., 2006).Atlantic cod spawn volitionally in captivity and the onset ofspawning is regulated by photoperiod (Norberg et al., 2004; Hansenet al., 2001). Depending on stock origin and age, females ovulate 320times during a 1660 d spawning period, and the initiation ofspawning varies among individuals within the same stock (Kjesbu,1989; Trippel, 1998). In males, spermiation lasts for a period of severalmonths (Rakitin et al., 1999), but initiation and duration amongindividuals also varies within a stock. The variation in ovulation andspermiation onset can prolong and stagger volitional spawningamong individuals and increase costs associated with live feedproduction during the labor-intensive phase of larviculture. In otherfish species, ovulation has been synchronized and milt volume hasbeen increased by administering exogenous hormones such asanalogues of gonadotropin releasing hormone (GnRH; Zohar andMylonas, 2001). The purpose of this study was to investigate theeffectiveness of GnRHa implants on the induction of ovulation andspermiation in Atlantic cod.2. Materials and methods2.1. Broodstock collection and maintenanceAtlantic cod were collected from the northeast peak of Georges Bank(4142Nlatitude, 6667Wlongitude) in September andOctober 2006and transported to the St. Andrews Biological Station (SABS),St. Andrews, New Brunswick, Canada (45 N latitude; 67Wlongitude)for spawning in winter 2007. Broodstock were tagged with PassiveIntegrated Transponders (PIT, Sokymat, Switzerland) prior to spawning.All broodstock were maintained in 15 m3 tanks with ambient watertemperature and photoperiod and fed to satiation on a diet of northernshortfin squid (Illex illecebrosus) and Atlantic mackerel (Scomberscombrus) with vitamin and mineral supplement twice weekly. Fishwere not fed for the duration of the study (03 January to 14 February).Prior to handling, tankwater levelswere reduced by approximately 50%and metomidate hydrochloride (Aquacalm, Syndel LaboratoriesLtd., Qualicum Beach, BC, Canada) was added at 2 ppm concentrationto sedate broodstock and prevent egg loss from ovulating females.Individuals were anaesthetized with 20 mg/l tricaine methane sulphonate(MS-222; Finquel; Argent Laboratories, Redmond, WA, USA)during handling unless eggs were freely extruded. Body weight wasrecorded (100 g) prior to treatment application. At the onset ofexperimentation, temperatures were raised to, and held at, 6 C in three15 m3 tanks two experimental