VPP 322: Aquatic Animal Diseases, Health Care and Management (1+1)

CARE OF EGG AND HATCHLINGS

• The commercial ornamental fish culture and the associated management and bulk fish production have three phases, viz., nursery phase, rearing phase and production phase.

Nursery phase

• In ornamental fishes, the fertilized eggs hatch out either as embryos as in the case of angel fish or as tender spawn as in the case of goldfish, koi carp, fighter and tetra. In cichilds like oscar, auratus and blue morph etc, the fertilized eggs are uniquely collected by the mother fish in the buccal cavity for incubation. The hatched out youngones come out as fry from the mouth of the parent and are protected by the parent’s for a few days. The nursery tanks may be of rectangular structure of 12x6x1 m size and are used foe effective management of the growth, and survival microscopic organism such as phytoplankton and zooplankton as starter feed. The growth and survival of the spawn and fry depend largely on the occurrence of such food organisms.
• Uniform sized fishes should be stocked in the nursery tank at a time, at a density of 500 per m². The period of rearing normally would be 15 days. The spawn and fry are also fed with finely sieved mixture of rice bran and oilcake at 1:1. A survival rate of 40% could be obtained during the nursery phase of rearing. Microscopic organism such as diatoms, green algae and zooplankton like cladocerans (Daphnia sp., Moina sp.), rotatorians (Branchionus sp.) and copepods serve as ideal food to the hatchlings.

Feeding schedule of spawn for 15 days of rearing

Period after stocking (Days)	Blind feeding frequency
1-5	4 times
6-14	8 times

If the spawn are to be harvested on the 15^th day, they must be starved to condition them

• Besides the naturally occurring planktonic food organisms, supplementary feed may also be broadcasted on the water surface in the morning hours. The feed may also be soaked in water to get a thick paste which is kept in plastic pots and suspended in the aquaria. The survival rate of the fry could be enhanced considerably by treating with antibiotics and vitamin B12 supplementation. Among the micronutrients, yeast and vitamin B-complex have been found to increase the growth of the spawn in their order. As the hatchlings grow, their feeding habit normally changes and the fry would start feeding on plant and animal matter. Therefore, artificial feeding is essential to stimulate the growth of the fry. During this period, at least partial water change should be done to maintain the dissolved oxygen content of the water, besides minimizing the accumulation of the toxic substances and gases.

Rearing phase

• After 15 - 20 days of nursery, the fry are transferred to a cement rearing tank of size 25x12x1 m and the fry are reared here for about 60 days till they become marketable sized fingerlings (4x10 cm). The rearing tank must be devoid of fish predators such as frogs, snakes, turtles, etc. The fry are fed with the grower mash to enhance their growth. A stocking density of 150/m² can be followed. Protein rich feed components such as silkworm pupae, soybean, cowpea, fish meal, chopped beef liver, redworm and tubifex should be supplied depending on their availability. Artificial feed mixture consisting of 40% protein is also suitable for optimum growth of the fish. Antibiotics such as Romat and tetracycline may be mixed with the feed at the rate of 100 mg/kg of feed to give disease resistance and to safeguard the fingerlings from the attack of parents. The feed ration may be increased from 1-3% of the total weight of the fry or fingerlings gradually. The growth of the fry may be assessed periodically by measuring their length and weight with the help of velon screen net once in every month.

Production or stocking tank

• Though production tank is not strictly for ornamental fish culture practices, such type of tanks are required to raise all kinds of broodfish. Special care in feeding and disease management are a prerequisite for rearing ornamental fishes in tanks. Larger fishes such as goldfish, koi carp, red tail shark, oscar and angel fishes are raised in production tanks only. Some of the management measures followed in rearing tanks should also be adopted in these production tanks. However, the stocking density in this type of rearing system is largely decided according to expected yield and rearing time. A production tank of 50x10x1.5 m or 1.5 m² water area would be preferable. The fish production of the stocking pond is more related to the natural productivity of the pond as well as other management practices such as fertilization, supplementary feeding, stocking density, species combination, etc. In order to obtain maximum fish yield, the production pond should be stocked with young fish at an optimal level. The stocking density suitable for a production pond could be calculated The most basic formula for calculating stocking density is the total biomass of fish divided by the available space.