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Modified Wednesday, December 22, 2004

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Use of Human Chorionic Gonadotropin in June sucker

The June Sucker (Chasmisties liorus) is an endangered species endemic to Utah Lake. The June Sucker was a critical food fish for the early settlers in Utah. Unique features of the June Sucker include a subterminal mouth, smooth lips, and a cleft bottom lip with almost parallel sides to the wide gap. June Suckers are often confused with the more abundant Utah Sucker (Catostomus ardens), but upon closer examination the Utah sucker has a small wedge shaped gap and rough lips on the ventral mouth.

Propagation and population augmentation is part of the June Sucker recovery plan. The Fisheries Experiment Station (FES) Logan, Utah has constructed an interim facility to hold June Sucker for research and brood stock (see Ichthyogram Volume 2, #3). The Utah Division of Wildlife Resources plans to build a permanent facility to house these and other endangered fish. In 1991, the construction of the June Sucker interim facility was completed and the first year group of June Suckers (1989 year class) was transferred in from Utah State University (USU). The fish from USU had been hatched from eggs collected during the June Sucker spawn on the Provo river.

Currently, the FES facility has five year classes, three of which have shown signs of spawning preparation each Spring, yet few females ripen. Necropsies of natural mortality in May, June, July and even into August have shown developed ovaries in the females. A prominent sign of staging in the female June Sucker is an enlarged vent. Male June Suckers develop tubercles on their caudal fins, caudal peduncle, but mostly on their anal fin.

Fish reproductive timing is regulated by a neurohormonal mechanism in which environmental stimuli and genetically imprinted cycles trigger the release of gonadotropin-releasing hormone (GnRH) or gonadotropin-release inhibiting factor GRIF from the hypothalamus. The GnRH released from the hypothalamus triggers the pituitary to release gonadotropic hormones. The gonadotropic hormones cause the maturation of gametes in the gonads through progesterone or testosterone. In females prostaglandin controls the rupture of the follicle and expulsion of the eggs. Hormonal specificity among vertebrates is low, the ratios of hormones is the greatest difference. The use of pituitary extracts, or gonadotropin from one species can effect the reproductive cycle of another species. The use of human chorionic gonadotropin (HCG) has long been know to induce spawning in many breeds of fish. HCG is extracted from a placenta or can be synthetically produced. HCG can be dried and stored for extended periods of time. HCG is not registered for use in fish by Food and Drug Administration.

In a preliminary research trial in June of 1998 five female June Sucker received an 800 IU(international units) per pound of body weight intraperitoneal injection of Human Chorionic Gonadotropin (HCG). Seven male June Suckers received a 400 IU/lb IP injection of HCG. For this trial the fish most likely to have mature gametes were chosen. Females were chosen by size and amount of swelling around the vent. Males were chosen by size. One day after injection, none of the five females gave eggs but three of the seven males gave increased volumes of milt. Four days after the injection two of the five females gave a small quantity of eggs (<200). The fish that were unaffected by the first injection (3 females, 4 males) received a second injection of HCG. Due to the limited amount of HCG obtained, only half of the original dose was administered. Five days later, no eggs or milt were collected. On a side note, one of the fish which had never been injected gave over 5,000 eggs and one fish that had given eggs five days earlier gave another small lot. The participating June Suckers showed no side effects from the drugs, but experienced additional handling stress.

The results of the limited trial showed a tolerance for HCG but little/no favorable effects from the injection. Possible reasons for the failure include: timing of the injection, additional stress on the fish, dose too low, and other hormones may be limiting. The timing of the injection (June 15) was chosen to correspond with dates that ripe females had been found in previous years. Necropsies done on natural mortality showed developed ovaries in all dead females from these year classes. The necropsies have continued to show developed ovaries into August. The natural spawn takes place in late May or early June.

The inability to spawn may also be related to stress. The June Sucker were evaluated the first part of May for deformities as part of a feed trial. The deformity index evaluation induces a lot of handling stress.

Successful spawning has been achieved in many species using HCG in a variety of dosages (Opuszynski K and Shireman J, 1995). In similar trials, Grass Carp were not successfully spawned on HCG alone but were successful when HCG was used in conjunction with carp pituitary extracts (Opuszynski K and Shireman J, 1995). In another trial Grass Carp were successfully spawned on high concentrations of HCG (Opuszynski K and Shireman J, 1995).

Further trials utilizing three modifications to these methods are being considered: higher doses of HCG, varied timing, and a follow up injection of carp pituitary extracts. White Sucker (Catostomus commersoni) have been successfully spawned using 1,000 IU/KG IM injections for four consecutive days. The use of this method may prove successful in the June Sucker. Injecting some fish each week through May, June, and July may show that 800 IU/KG is adequate if the timing is right. A third trial in which the HCG injection is followed by an injection of carp pituitary extracts should be tried.

Thanks go out to the USFWS for help on this project.

Ludwig, G. M. 1997. Inducing Spawning in Captive White Sucker, (Catostomus commersoni), and Spotted Sucker, (Minytrema melanops). Journal of Applied Aquaculture, Vol. 7(3):7-17.

Opuszynski, K and Shireman, J. V. 1995. Herbivorous Fishes Culture and Use for Weed Management. CRC Press, Ann Arbor, Michigan