Spawning technology of parent fish of cultured turbot

Turbot is found in coastal waters from the Mediterranean to Norway. Turbot is a valuable farmed fish in Europe. Turbot culture has developed continuously in the past 10 years. The production of turbot culture increased from 150t in 1985 to 3700 t in 1998. In the Atlantic coastal waters, turbot reproduces naturally in summer, but it may reproduce all year round by artificially controlling the light cycle and water temperature, or only by controlling the light cycle.

Turbot spawned in batches and spawned as many as 10 times during the breeding period. Under the condition of reception, turbot does not release eggs even if it ovulates naturally, so it needs to squeeze the eggs by hand. Moreover, due to the irregular ovulation of females in reception, the onset of spawning between females is not synchronized, and ovulation can not be predicted. The reproductive period of female fish will be lengthened sooner or later, which deviates from the intensive production requirements.

In order to ensure an adequate supply of fish eggs, production enterprises generally stock a large number of parent fish. In order to solve this problem, that is, to shorten the breeding period and increase the number of ovulatory females, French experts carried out as early as 1995 the implantation of gonadotropin-releasing hormone analogues to induce female turbot spawning. Synchronous research on promoting female spawning of turbot was reported in the recent Journal of Aquaculture published in the Netherlands in 2000. This paper briefly introduces the main results of this study, which can be used as a reference for domestic turbot seedling breeding enterprises.

Method of inducing labor

Parent fish cultivation: all the female fish used in this study came from a commercial fish farm on the Atlantic coast of France, the French turbot company. The study was divided into two experiments. The first experiment was carried out from April to June 1995. In order to reproduce early, 24 female fish were cultured under artificial light cycle, 12 in the control group and 12 in the treatment group, with an average weight of 4.4 ±0.7 kg. In the second experiment, from June to August 1995, 51 female fish were cultured under the condition of natural light cycle, 20 in the control group and 31 in the treatment group, with an average weight of 5.0 ±0.7 kg. In the two experiments, the stocking density of female fish was 8kg / m3. The culture water temperature of female fish is 14 ±1 ℃. At the beginning of spawning, the water temperature is lowered, and the water temperature is maintained at 12 ℃ throughout the spawning period to prevent overcooked fish eggs.

Treatment of labor induction: the continuous release granules used contain 75 micrograms of gonadotropin-releasing hormone analogues (luteinizing hormone-releasing hormone analogues). The implanted site is the back muscle at a dose of about 25 micrograms per kilogram of body weight.

Comparison of ovulation rate of female fish: in the first experiment, there was no significant difference in ovulation rate between the treatment group and the control group, that is, the percentage of ovulation females, but in the second experiment, the ovulation rate of female fish in the treatment group reached 100%. Compared with 47% in the control group.

Comparison of ovulation synchronization: in the first experiment, in the treatment group, between the first spawning female and the latest spawning female, the start time of ovulation was 15 days, while in the control group, it was 54 days. In the second experiment, the delay in the treatment group was 28 days, while that in the control group was more than 70 days. In the first experiment, the whole spawning period of the treatment group lasted for 4 weeks. In the second experiment, the examination was stopped before the final ovulation. However, the whole spawning period of the treatment group did not seem to exceed 6 weeks. The spawning period of the control group was at least 8-9 weeks (the first experiment) and 13-14 weeks (the second experiment). In the two experiments, the average spawning duration of the treated individuals (16 days) was significantly shorter than that of the control group (26-35 days). In the two experiments, there was no significant difference in the number of ovulation per female between the treatment group and the control group. However, the ovulation rhythm of the treatment group was faster than that of the control group. the average ovulation interval of the control group was 2.5-2.8 days, while that of the treatment group was 1.6-1.8 days.

Comparison of egg collection of female fish: during the whole spawning period, there was no significant difference in the total egg collection per female between the treatment group and the control group, but the average egg collection per time in the treatment group (214 ml) was significantly higher than that in the control group (144 ml). During the whole breeding period, in the first experiment and the second experiment, the total number of eggs collected in the control group was 7 million (12) and 5 million (20), respectively, and that in the treatment group was 23 million (12) and 58 million (31), respectively.

Comparison of hatching rate of fish eggs: there was no significant difference in fish egg size between the treatment group and the control group. In production, the fertilization rate of the treatment group (74.7%-77.2%, average 76.6%) was significantly lower than that of the control group (88.2%-92%, average 89.5%). However, there was no difference in hatching rate. Hormone treatment seems to have an effect on egg quality, at least at the stage of fertilization. The dose of hormones used in this study can be reduced, presumably not to weaken the effect of ovulation induction, but help to improve the quality of eggs.

From an economic point of view, the application of gonadotropin-releasing hormone implantation technology is expected to reduce the stock of parent fish by 2030%. In conventional production, 56% of female fish ovulate during the breeding season, and the rest are either unable to spawn or ovulate too late. Using the hormone granules, the percentage of ovulatory females may be increased to 90%.