Manipulation of ovulation time in the yellowtail flounder, Limanda ferruginea storer using photothermal cues and gonadotropin hormone releasing hormone analogue (GnRH-a) administration

Lush, Pauline Lynn (2005) Manipulation of ovulation time in the yellowtail flounder, Limanda ferruginea storer using photothermal cues and gonadotropin hormone releasing hormone analogue (GnRH-a) administration. Masters thesis, Memorial University of Newfoundland.

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Abstract

The yellowtail flounder (Limanda ferruginea) once considered a prime candidate for aquaculture, were photothermally manipulated in an attempt to advance the ovulation time of females of this species. The success of these techniques would be highly beneficial to the broodstock management of yellowtail flounder. -- Two groups of female yellowtail flounder were held under compressed photothermal environmental laboratory conditions as an attempt to advance ovulation and spawning time. One group was administered a controlled release gonadotropin hormone-releasing hormone analogue (GnRH-a) in February, the other group was administered a sham pellet in an identical manner. A third group of fish was held under ambient photoperiod and temperature conditions. The experiment ran for two years using a different group of animals for each year. In year two, a sub-group (five females) of the ambient control fish was given a GnRH-a pellet in February. In year one a total of 6 females were used in each of the photothermally advanced group. In year two this number was increased to twelve in both photothermally treated groups. -- Throughout annual reproductive development the degree of advancement of the females was monitored using both ovarian cannulation and plasma steroids (estradiol-17P and testosterone) analysis. No significant advancement was noted in either of the photothermal manipulated groups in the oocyte diameters obtained through the cannulation or in steroid levels. -- Advanced spawning in the group photothermally manipulated and administered the GnRH-a pellet (PP-GnRH-a) was noted in March in both year one and two. The photothermally manipulated group receiving the sham pellet (PP-Sham) did not spawn in advance of the ambient control group. Egg quality parameters, based on egg viability, fertilization and hatch rates, for the PP-GnRH-a group were excellent and were significantly higher than the PP-Sham group for viability and fertilization. Egg quality for the PP-GnRH-a group was not significantly different from the ambient group of females. The PP-Sham and control group both spawned in June, which is the expected ambient spawning time for yellowtail flounder in captive conditions. A single female from the ambient group administered the GnRH-a pellet in February spawned, however egg and larval quality was extremely poor, and larvae produced from this female did not survive for more than one day post hatch. -- Further investigation is required to determine an appropriate way to advance ovulation in the yellowtail flounder using environmental cues, and to improve on general broodstock husbandry of this species.

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