E.A. Huisman
Organization for Improvement of Inland Fisheries (OVB),
Nieuwegein, The Netherlands, and
Department of Fish Culture and Inland Fisheries, Agriculture University,
Wageningen, The Netherlands
Ladies and Gentlemen, dear Colleagues,
Starting my introduction to this Workshop I should like to add to the officially addressed welcome, my gratitude to all of you for coming here and to many of you for submitting review and experience papers as guidelines for our discussions.
In my opinion it is worthwhile to stress that at this very moment we are representing 16 different countries of which 14 are member countries of EIFAC. I think that this is a clear illustration of the very need for and interest in this phase of fish culture. And at the same time it lays a claim on us to do the very best we can in all our activities during the next few days.
In this Workshop we are dealing with the mass rearing of fry and fingerlings of fresh water fishes as a logical consequence and follow-up of the “Workshop on Controlled Reproduction of Cultivated Fishes” of EIFAC, held in Hamburg, 1973.
For a fish culture industry the necessity of a dependable supply of fry, either produced or caught, is quite obvious. For many species fry can be obtained using more or less controlled reproduction methods as was dealt with extensively during the already mentioned 1973 EIFAC Workshop. However, quite an important part of fish culture still relies on the supply of fry by catch from the wild, as for example eel (Anguilla ssp), milkfish (Chanos chanos), mullet (Mugil ssp), catfishes (Clarias ssp), etc. This supply from the wild can fluctuate considerably. For instance in Taiwan the catch of milkfish frv in 1967 amounted to 28 000 000 and in 1970 to 207 000 000 (Chen, 1976). In the Central African Empire only 50–60% of the available fish ponds were in operation in 1975 mainly due to the absence of an adequate fry and fingerling supply (Miller, 1975). Eel production in Japan dropped considerably after 1969 correlated with a strong decline in the catch of elvers (Japan Fisheries Society, 1975).
But also pond or hatchery produced fry can be scarce. In some regions this might be structural by lack of adequate fry producing capacity as was pointed out recently by Dwivendi (1979) for India. However, also in Europe temporary market shortages do occur for fingerlings of carp (Cyprinus carpio), pike (Esox lucius), pike perch (Stizostedion lucioperca) and others, due to unfavourable weather conditions and/or disease outbreaks.
Woynarovich (1975) very clearly pointed out that the controlled reproduction of fishes has been, is, and will be of increasing importance for a dependable and continuous (even out-of-season) supply of fry for aquaculture industry. This is the first link in the whole chain of fish production but the rearing of fry to fingerling stage may be regarded as a just as important second link in this process.
The terms “fry” and “fingerlings” are rather easily used, but it should be kept in mind very clearly that most fishes have to increase their weight by a thousand or even a few thousand times just to grow from fry, starting with the first exogenous feeding, to fingerling size. This is particularly true for most of the fishes considered in this Workshop. It implies that we are dealing with that phase in fish culture in which the relative weight development of these fishes is much larger than during the fattening of the fish in the next phases of fish culture. This combines with the fact that the period of this so-called nursing is very short in relation to the following fattening period. So, our Workshop deals with husbandry methods of organisms at extremely high growth rates.
Results achieved in our institutes with cyprinid fishes (Huisman, 1974, 1979) and with an African catfish (Hogendoorn, 1979) indicate, that during the first days after yolk sac absorption specific growth rates up to 100% of body weight per day are quite common. This implies that the food ration during the first days of nursing has to be several times (depending on the nature of the feed) the total biomass of the fish per day.
In studying the literature concerning nursery operations and fry rearing experiments, it is striking how often low growth rates - in fact too low relative to the growth potential - are reported. This is not only true for experiments carried out in artificial environments using artificial diets but also for the proven control diet (Appelbaum, 1977; Kossmann, 1970; Meske and Pfeffer, 1978; Schlumpberger et al., 1976). It indicates most probably that either the quantity of feeding is inadequate or that the quality of the husbandry techniques is rather poor.
Apart from quantitative aspects of feeding, qualitative aspects may be of equal or even more importance. It is well known that nutritional requirements depend among other factors on the size of the fish and it would be even native to assume that a thousandfold increase in weight during the initial growth phases should not change these requirements.
On first sight it may be considered economically irrelevant or even impossible to use different feeds during such a short nursery period. But in not doing so, we may have traced a reason why fish fry reared in ponds usually outgrow the hatchery reared ones fed on artificial diets, even when the best known methods are used.
Although in ponds a great variety of food (organisms) may be present, pond management still has to be carefully directed towards the particular phase of the life cycle of the fish fry cultivated. Experimental results of pike perch propagation indicate that the final production of fingerlings largely depends on the availability of suitable, tiny food organisms during the very early days of exogenous feeding. This means it depends on the pond filling time, ambient temperature, etc.
Selective feeding not only in respect of the size but also of the species of the prey may be of great importance especially when the fry are small.
Apart from these and other nutritional and aqua-zootechnical nursery aspects, the production of fry and fingerlings can be strongly hampered by infestations of pathogens. Outbreaks of diseases are most critical in the very sensitive young stages of fish. It is well known that infections with specific viruses are detrimental just for the younger fish stages as for instance Infections Pancreatic Necrosis (I.P.N.), Channel Catfish Virus Disease (C.C.V.D.) and Pike Fry Rhabdovirus Disease (P.F.R.D.), while bigger fishes are far less or not at all susceptible, although they might be infected (carriers). Praxis directed research in the basic principles of the immune response development during the early life stages of fish is highly required.
The examples mentioned thusfar can easily be extended to others - and I am sure they will during this Workshop. This illustrates that in rearing of fry and fingerlings from the zootechnical point of view one deals with an organism in a very susceptible and crucial stage of its life cycle.
On the other hand the objectives of this phase of fish culture are very challenging. In general two objectives can be distinguished i.e. the production of a half-product for use in fish culture (cyprinids, trout, etc.), and the production of an end-product for (re)stocking purposes (pike, coregonids, etc.) as a tool in fisheries management. An intermediate position is taken by the production of for instance fingerlings of Pacific salmonids (Oncorhynchus ssp) for ocean ranching, which is rapidly expanding and is expected to increase total salmon production with 30% in the next 5 or 6 years (FAO Fisheries Statistical Yearbook 1976).
Whatever the objectives will be, the development of methods for a safe and dependable mass rearing of fry and fingerlings can be regarded as an important link between reproduction of fish on the one hand and fish culture and fisheries management on the other.
It is my sincere hope that this Workshop may contribute largely to this crucial phase in fish culture to enhance the safe supply of fry and fingerlings of fresh water fish.
REFERENCES
Appelbaum, S., 1977 Geeigneter Ersatz für Lebendnahrung von Karpfenbrut. Arch. Fisch. Wiss., 28, 31–43.
Chen, T.P., 1976 Aquaculture practices in Taiwan. Norwich, Page Bros LTD.
Dwivendi, S.N., 1979 The seed suppliers. Fish Farm Int., 5, 8–11.
Japan Fisheries Association., 1975 Fish farming in Japan. Tokyo, Japan Fisheries Association Publ., 44 pp.
Hogendoorn, H., 1979 Controlled propagation of the African catfish, Clarias lazera (C. & V.). III. Rearing of fry. Aquaculture (submitted).
Huisman, E.A., 1974 A study on optimal rearing conditions for carp (Cyprinus carpio L.). (In Dutch, with English summary). Thesis State Agriculture University, Wageningen, 95 pp.
Huisman, E.A., 1979 The culture of grass carp (Ctenopharyngodon idella Val.) under artificial conditions. In: Halver, J.E. and K. Tiews (Ed.): Finfish Nutrition and Fish feed technology 1: 491–500, Heenemann GmbH & Co., Berlin.
Kossmann, H., 1970 Versuch zur Erhöhung der Zuwachsleistung von Karpfen in Teichwirtschaften durch gezielte Bruterzeugung in Warmwasser. 1. Mitteilung. Die Anzucht von vorgestreckter Karpfenbrut im Warmwasserhaus. Fischwirt, 20, 255–263.
Meske, Ch. and E. Pfeffer., 1978 Growth experiments with carp and grass carp. Arch. Hydrobiol. Beih., 11, 98–107
Miller, J.W., 1975 Review and evaluation of rural fish culture extension in the Central African Republic. A final report subjected to the Director of the UNDP/FAO project “Vulgarisation de la Pisciculture”, CAF/72/002, 50 pp.
Schlumpberger, W., K. Anwand and R. Mende., 1976 Erfahrungen bei der Brutaufzucht von Amurkarpfen (Ctenopharyngodon idella, Val.) und Silberkarpfen (Hypophthalmichthys mollitrix, Val.) mit verschiedenen Trockenfuttermitteln. Ztschr. Binnenfisch. DDR., 23, 164–174.
Woynarovich, E., 1975 The role of induced breeding in fish culture development. In: Workshop on controlled reproduction of cultivated fishes. EIFAC Techn. paper 25, 18–24.
