________ is the method to ensure the supply of pure fish seed in desired quantities throughout the year.

 Reason: The practice of growing four to five fish species in a single fish pond is known as composite fish culture. In such systems, these species are selected so that there does not exist any competition for food among them having different types of food habits. E.g. catlas are surface feeders, rohus feed in the middle zone of the pond, mrigals and common carps are bottom feeders and grass carps feed on the weeds. These species when together can use all the food in the pond without competing with one another. This increases the fish yield from the pond. One problem with such composite fish culture is that many of these fish breed only during monsoon. Even if fish seed is collected from the wild, it can be mixed with that of other species as well. So, a major problem in fish farming is the lack of availability of good quality seed. To overcome this problem, ways have been worked out to breed these fish in ponds using hormonal stimulation. This has ensured the supply of pure fish seed in desired quantities. Change in food habits will not work as already the fishes selected for composite farming have different food habits. Therefore, improving their feed will also not help in getting pure fish seed. Satellites and echo-sounders are used to locate large school of fish in the open sea.