Practical Management of Fish Seeds (Fry and Fingerling)

In fish life history, egg(fertilized) Larva fry fingerling sub- adult/juvenile adult. The larval stage ends when it fills up its air bladder with air, begins swimming in a fish-like manner and starts to eat external food that it becomes to fry. In addition to needing all the essential requirements of the larva e.g. adequate O2, suitable temperature, removal of waste matter etc, the fry also requires external food which should be adequate both qualitatively and quantitatively. The early fry may still have a part of the yolk left and can draw on it for sustenance from 1-4days depending on the species. The fry spends this period and learns to find its own food. Fry are said to require a more precise and careful nursing to ensure their survival and proper growth. Authors have remarked that lack of suitable food caused high fry mortality. Fingerling is bigger than fry e.g. 5-10cm and it is the stage that is usually stocked. Management of these developmental stages is based on their fragility and difference in sizes in terms of their habitats, stocking density, feeding and control of their infections and diseases. These stages are crucial because there cannot be harvest without recruitment. Hence, these stages are called fish seed or recruits. Fry are nursed in small earthen ponds which vary from 100-200m2 for about 3-4 weeks to attain fingerling stage. Fingerlings are reared rather than nursed in bigger earthen ponds. The pond is usually prepared to have a standing crop of rotifers and must be checked to exclude cyclopoid copepods which are natural enemies of fry. Food is crucial for growth which must be observed daily. Fry have two sources of food during the initial stage – yolk and external food to ensure better survival. Maintain these. It is part of the management that mixing of different age groups of same species should be avoided and it is advisable to use a monoculture of fishseed. The most commonly provided artificial feed is finely ground and sieved through 100-150µm mesh called starter food. After two weeks, the size of feed particles is increased. Cutting the grasses on the dyke and throwing them around the shallow part of pond helps to increase natural food production in the pond. After about one month, the young fingerling have to be removed from the small nursing pond and stock in a large pond. The artificial feeding continues but the size of food changes due to changes in the size of mouth. It is necessary to thin out the stock in order to provide sufficient space, O2, food to the fast growing fingerling. Enemies of these stages must be managed too. These enemies change with the age of the fish. These are categorized as (i) enemies of fry (ii) enemies of advanced fry and (iii) of fingerlings. Identify these enemies and treat adequately. For example enemies of fry include carnivorous Cyclops, insect and insect larvae (e.g. dragonfly), which predate largely on the fry. It has been stated that Cyclops are responsible for the highest mortality of fry at this stage next only to that caused by hunger. The advanced fry is less prone to predation by Cyclops since it is more agile and its skin in thicker and stronger. It is the insect larvae that pose greater danger at this stage followed by hunger if there is acute food shortage. O2 deficiency may kill in heavily manured ponds. Abrupt changes in temperature and extreme cold may exterminate the fry population. Enemies of the fingerling – Besides hunger, O2 deficiency, sudden change in temperature, white spot disease caused by Ichthyophthirius, Trichodina and gill worm infections could exterminate the entire stock within a brief period in fingerling ponds. Infection of a pond with any protozoan or bacteria or fungus can be diagnosed through certain indicative signs such as: (i)swimming of fry/fingerling in large school near the surface (ii) their accumulation below the water inlet (iii) the occurrence of dark specimens (iv) sudden occurrence of dead fish on the surface. It should pointed out that fish that die because of parasitic infection usually float on the surface while those that die due to dietary factors often remain at the bottom.