Skip to main content
ARS Home » Southeast Area » Stoneville, Mississippi » Warmwater Aquaculture Research Unit » Research » Research Project #431147

Research Project: Improved Reproduction in Foodfish (Catfish and Largemouth Bass), Baitfish, and Ornamentals Using a New Spawning Aid (GnRH IIa)

Location: Warmwater Aquaculture Research Unit

Project Number: 6066-31000-012-19-R
Project Type: Reimbursable Cooperative Agreement

Start Date: Jun 1, 2016
End Date: Aug 31, 2018

Objective:
Spawning aids have been used by the aquaculture industry to improve fry production for many years as a large number of aquaculture species do not reproduce readily under captive conditions (GnRH IIa (D-Arg6-Pro9-NHet) has garnered recent interest as an alternative GnRH subtype which offers increased biological activity and reliability in channel catfish compared to mGnRH Ia and sGnRH IIIa. Researchers at four institutions will collaborate to evaluate the efficacy, reliability, safety, and mode of action of GnRH IIa in a range of species encompassing foodfish, baitfish and ornamentals. Efficacy of varying doses of cGnRH IIa on successful ovulation or spermiation will be evaluated by measuring parameters including latency time, fecundity, fertilization, hatching success, egg and larval morphometrics, testis size, sperm fluidity, volume, density and motility. Animal safety will be quantified by the percentage of broodstock surviving post hormone administration. A more in depth evaluation will occur in catfish by gross and histopathological examinations of female channel catfish induced to ovulate with GnRH IIa. The endocrine actions of GnRH IIa on catfish ovarian tissues will be compared to those of mGnRH Ia and sGnRH IIIa. Ultimately this investigation will help to assess the viability of cGnRH IIa as spawning aid for a wide variety of fish species. In addition, the activities listed have been designed to support an INAD application for GnRH IIa. The USDA co-PI will be in charge of refining the dose needed to induce ovulation in female channel catfish, determining the effect of GnRHII implants in blue catfish male on testis and sperm characteristics.

Approach:
ub-objective 3a. Determine dosage efficacy and animal safety determination of a two dose injection (priming/induction) of GnRH IIa in female catfish. Previous works established the effectiveness of GnRH IIa to induce ovulation in female channel catfish (Quiniou et al;, 2014) and also determined that there was no apparent ill effect on broodfish or fry of GnRH IIa compared to mGnRH Ia and sGnRH IIIa (overall mortality). We propose to refine the dosages and determine the smallest efficacious dose needed to induce ovulation of channel catfish. We will also conduct a spawning trial that focus on fish safety aspects of the compound by gross and histopathological examinations of female channel catfish induced to ovulate with GnRH IIa. A first study will be divided into three independent, weekly trials over the course of the spawning season (Early; Mid; Late) with 40 gravid females preselected based on phenotypic characters (rounded belly and redness of papilla) per trial. Twenty females will be injected with the usual priming and resolving doses used in catfish (20µg/kg and 80µg/kg) and 20 with 1/4 doses (5µg/kg and 20µg/kg). The quarter dose was chosen based on ovulation results from a previously conducted trial in which female channel catfish were injected with 1/4; 1/10; 1/20 and 1/50 doses. A second study will be conducted in which 16 channel catfish females fish injected with the regular dose (20µg/kg and 80µg/kg), 3 times (60µg/kg and 240µg/kg) and 5 times (100 µg/kg and 400µg/kg) the dose of GnRH IIa and 8 control females injected with physiological saline will be used to determine the effect of GnRH IIa on the fish health. The fish will be maintained in bags till the stripping then in a raceway. Fish (n=24) will be sacrificed at day 3 after the second GnRH IIa injection. A blind coelomic cavity inspection will be conducted and gross organ evaluation followed by the removal and fixation of tissue/organs (10% neutral buffered formalin). Various tissues will be examined histologically by an experienced specialist for signs of inflammation, infectious disease, vascular disease, toxic insult, metabolic derangement, and neoplastic proliferation. If consistent abnormal alterations in tissues are present, changes will be fully described. Sub-objective 3c. Evaluation on GnRH IIa implants on maturation of testis in Blue catfish male Compared to channel catfish for which nearly all males show well developed testis by year 2, only about 1/3 blue catfish male exhibit well devloped testis by year 5. mGnRH Ia implants have been used to successfully improve gonad maturation in both male and female fish. GnRH IIa implants have also been shown to be successful at inducing vitellogenesis. We would like to determine if a continuous delivery of GnRH IIa using implants could enhance development of testes in male blue catfish. Forty-five 4 year old blue males weighting approximately 2 kg will be implanted intraperitoneally in late March-early April with Alzet osmotic micropumps model 2004 containing either PBS (control), 100 micrograms or 500 micrograms of GnRHIIa. The 2004 model has a constant delivery rate of 0.25µl/hr for 4 weeks.