Effects of Salmon Gonadotropin-Releasing Hormone Analog (GnRHa) on Reproductive Success and Egg Size in Rainbow Trout and Brook Trout

Abstract

Rainbow Trout Oncorhynchus mykiss were treated with a 100- or 25-μg/kg dose of salmon gonadotropin-releasing hormone analog (sGnRHa) that was emulsified in Freund's incomplete adjuvant (FIA). Controls were treated with a mixture of FIA and physiological saline. Latency (number of days from the first injection to the date of detected ovulation) was significantly shortened in treated groups compared with the control group. Egg weight, eyeing rate, and hatching rate were significantly reduced in treated groups; mortality after the eyed stage was significantly higher in treated groups. The relationship between latency and the eyeing rate or hatching rate was positive, but the relationship between latency and mortality after the eyed stage was negative. Brook Trout Salvelinus fontinalis were treated with a single injection of sGnRHa–FIA at 12.5 μg/kg, double acute injections of sGnRHa at 12.5 μg/kg administered 3 d apart, or a single acute injection of sGnRHa at 50 μg/kg. Controls were injected with FIA and physiological saline. Latency was significantly shortened in treated groups except the group that received the single acute injection of 50 μg/kg. Egg weight and alevin weight were significantly lower in treated groups. Egg mortality after the eyed stage was significantly higher in the double-injected group than in the 12.5-μg/kg sGnRHa–FIA group and the control group. Latency had a negative relationship with the eyeing rate and hatching rate. This result for Brook Trout is opposite that observed for Rainbow Trout. Latency and mortality after the eyed stage were not correlated. It is evident that the experimental designs currently used in salmonid research should be updated to determine reliable means of avoiding egg mortality, particularly in Rainbow Trout, after GnRHa treatment.

Received March 27, 2013; accepted May 18, 2013

ACKNOWLEDGMENTS

This work was supported by the following projects: CENAKVA CZ.1.05/2.1.00/01.0024, GAJU 074/2013/Z, and Ověření technologie hormonální synchronizace umělého výtěru jikernaček lososovitých ryb CZ.1.25/3.4.00/10.00314. Experiments were conducted at the trout farm Rybářství Litomyšl Ltd., Czech Republic (49°53′3.104′′N, 16°17′9.362′′E). We thank the hatchery management of Rybářství Litomyšl Ltd., especially Mirek Fabianek and Petr Trnka, for their excellent help. We also thank the Lucidus Consultancy for providing English correction.