Presently investigation on induced breeding are mainly carried out at the Fish Breeding Station at Százhalombatta. Research work has also been initiated at Szarvas recently. The percentage of successful induced breeding in common carp and in other carps is being further improved. The erratic results are correlated with either bad weather or bad condition of the spawner. Therefore, research efforts are directed to increase the percentage of success of induced breeding and the main investigations on this problem are carried out at the warm water hatchery at Százhalombatta, which is fully equipped with facilities needed for such studies. Use of 17B Progesteron and LH-RH is being investigated at Százhalombatta in inducing carps to breed.
3.1.1 Preservation of Sex Products
Experiments are being carried out at Szarvas on freezing common carp sperm in liquid nitrogen and using such frozen sperm for breeding. Sperms stored for five months have yielded about 20 percent fertility. Attempts should also be made to preserve either fertilized or unfertilized eggs in liquid nitrogen with a suitable medium mixed with the egg fluid obtained after homogenizing the eggs and centrifuging them (see para. 5.1.4.2). These studies will help in carrying out the off season fertilization and incubation of the eggs.
Very valuable information has been collected at Százhalombatta on the total time required at different temperatures of water for maturation/stripping after hypophysation. The best result is obtained at 205–215 hoursgrades (i.e., the amount of total temperature needed for ovulation by summing up temperatures measured every hour after pituitary treatment) for grass carp, 210–220 hoursgrades for silver carp, 235–245 hoursgrades for bighead and 240–260 hoursgrades for common carp, whereas water temperature between 21 and 24°C is the optimal for grass carp and silver carp, 22 to 25°C for bighead carp and 22 to 24°C for common carp (Horváth, MS.).
Very interesting work is being carried out at Százhalombatta in order to increase the number of breeding cycles annually so as to obtain the eggs throughout the year. Common carp spawning four times within 16 months has been achieved. It appears by manipulating the temperature of the water and providing proper food that, with suitable environment and food, the carps complete their sexual cycle in 2–3 months time. Thus, it seems possible that these fishes can spawn four times a year if given suitable conditions. So will the Chinese carps. Results obtained in natural conditions in India are where the same individuals of Indian and Chinese carps have been bred with hypophysation twice a year, once just after the onset of the monsoon and a second time just before the close of the monsoon. In Malaysia, Chinese carps are bred throughout the year. Year-round fish breeding is highly feasible and needs serious attention, not only to increase the seed production potential but also to fully utilize the staff/facilities available with a highly sophisticated hatchery. Further, investigation is essential to learn the effect of temperature on the production of primary oocyte, whether this is absolutely controlled genotypically or can be modified phenotypically especially by influencing temperature. If this is so, then it is also necessary to know the optimum temperature needed to increase the number of primary oocytes formation and thus eventually to increase the fecundity of the fish.
The nutritional requirements of female fish of common carp is being investigated at Százhalombatta, where it has been shown clearly that there is a considerable difference in feed requirement before and after ovulation. Also it has been shown that, once vitellogenesis is completed, the feeds rich in starches and lipoids result in fattening of the fish, which leads to unsuccessful hypophysation. However, such feeds favour oogenesis. This needs further elaboration in other species.
Due to the development of numerous predatory copepods in the nursery ponds, their is a low survival rate of early fry of common carp and Chinese carp. Investigations have been carried out with organophosphate insecticides, e.g., Flibol E and Ditrifon, and it has been found out that 1 ppm of this kills the predatory copepods, insects and other crustaceans, whereas the fish fry and their food, i.e., Rotatoria are not killed. This is used most commonly now in major hatcheries and improves the survival of the fry considerably.
