SECTION II: CULTIVATED SPECIES (contd.)

5 CONCLUSIONS AND RECOMMENDATIONS

In Africa, there has been an awakening or rather a revival of interest during recent years to introduce exotics and non-endemics, particularly for the development of aquaculture from a subsistence level activity to a commercial-scale operation. This is because all the developing countries are in need of increasing their food production in order to increase the protein-calorie intake of their people (FAO, 1975). It seems, therefore, that more introductions will take place in the near future.

There is no reason why exotics and non-endemics should not be imported provided that when an introduction is proposed, the necessity for the introduction and its merits is clearly established and no decision to stock must be taken until all aspects of the case, including the history of previous introductions of similar nature elsewhere in the world, have been taken into consideration (Hora and Pillay, 1962; Jackson, 1960). Once an introduction is recommended, controlled experiments must be conducted to assess their influence on the local fauna (Hora and Pillay, 1962). This means that whenever possible, trial introduction sites should be confined to closed water systems of manageable size that will permit close surveillance of predator establishment or otherwise and efficiency. This precaution is also important to facilitate early eradication of the species introduced should it show signs of becoming a pest (James and Fouler, 1970). This is because once it has escaped into the local streams, it tends eventually to spread over a wide area and unless the species cannot withstand competition with the local fish fauna and is soon eliminated, a fish introduction cannot be undone or repaired as with a chemical accident. It is a permanent thing and its impact on the local fish goes on throughout time (WHO, 1973). Under these circumstances a decision to introduce an exotic or non-endemic fish should not be taken lightly.

In this connexion, I would like to point out to the members of this Symposium the necessity of establishing an Advisory Committee for fish introductions into Africa so that any African country interested in introducing any species should seek the help and opinion of this Committee, whether or not there exist within the area any fish species of high biological or aesthetic interest, or which may be rare or endangered, that may be threatened by such introductions.

With respect to the species which have already been introduced into Africa, it is recommended that:

1. handicaps in trout transplantation to higher altitudes should find a solution

2. carp culture should be encouraged but its transplantation into natural waters should be prevented

3. great care should be exercised in the introduction of Gambusia affinis into new ecosystems; endemic T. nilotica should be used as a larvivore

4. introduction and cultivation of shellfishes in Africa should be encouraged

5. the production of 100% males of Tilapia spp. through hybridization with non-endemics should be popularized

6. pond culture of Clarias lazera, Heterotis niloticus should be encouraged and a solution for the difficulties to obtain natural spawning in ponds of the latter should be found

7. unsuccessful introductions should be eradicated.

6 ACKNOWLEDGEMENTS

My grateful thanks due to Dr. Z.H. Shehadeh, Technical Secretary, CIFA Symposium on Aquaculture in Africa for inviting me to write on this subject and to Dr. Y.B. Abu Gideiri, Head of Zoology Department, University of Khartoum, for reading the manuscript and useful suggestions.

For all the information obtained on the subject, through personal communication, I am indebted to the following scientists:

Ardill, U.D. (Mauritius), Atir, D.D. (Nigeria), Agr. Senior Fisheries Officer (The Gambia), Bard, J. (Centre Technique Forestier Tropical), Bishai, H.M. (Egypt), Cuerden, C. (FAO Fisheries Branch Library), Elloit, O.O. (Nigeria), Gay, W. (Zambia), Hogendoorn, H. (Cameroon), Ibrahim, K.H. (Tanzania), Kanyike, E.S. (Uganda), Lessent, P. (Centre Technique Forestier Tropical), Meskal, F.H. (Ethiopia), Ngaram A. (Tchad), Nasfi, H.F. (Tunisia), Vieyra, A.R. (Ivory Coast), and Vincke, M. (Central African Republic).

7 REFERENCES

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APPENDIX I
Principal exotic and non-endemic cultivable species deliberately introduced into Africa

APPENDIX II
Cultivable species deliberately introduced by the African countries

OBSERVATIONS ON THE INTRODUCTION OF Tilapia andersonii (Castelnau) INTO TANZANIA FROM ZAMBIA

by

R. Lema, B. Giadom and K.H. Ibrahim,
Freshwater Fisheries Institute, Nyegezi,
P.B. 1213, Mwanza, Tanzania

Abstract

Aquaculture in Tanzania, mostly practised with a few species of tilapia, is faced with the common problem of excessive breeding leading to overcrowding and stunted growth. The report that Tilapia andersonii (Castelnau) matured in ponds in Zambia in 12–15 months time and that the species bred only once a year gave the idea that this species would probably fare better in Tanzania. Hence in 1968 an experimental consignment was introduced into Tanzania from Zambia and experiments carried out at the experimental fish farm at Malya. Results indicated that T. andersonii adapted to local conditions, matured and bred in three to five months time and in growth, survival and production etc. behaved in no way different from other species of tilapia available locally.

Resumé

En Tanzanie, l'aquiculture, qui consiste essentiellement en l'élevage de quelques espèces de tilapia, se heurte au problème courant d'une prolificité excessive conduisant au surpeuplement et au rabourgissement. Comme il a été rendu compte que, dans les étangs de Zambie, Tilapia andersonii (Castelnau) parvient à maturité sexuelle au bout de 12 à 15 mois et ne se reproduit qu'une fois par an, on a pensé qu'il serait probablement plus aisé d'engraisser cette espèce en Tanzanie. Aussi, en 1968, une livraison expérimentale en provenance de la Zambie a-t-elle été introduite en Tanzanie et des expériences ont elles été effectuées à la station expérimentale de pisciculture de Malya. Les résultats ont montré qu'après adaptation aux conditions locales, T. andersonii parvient à maturité et se reproduit au bout de 3 à 5 mois et que sa croissance, sa survie et sa productivité ne diffèrent en rien de celles des autres espèces de tilapia trouvées sur place.

1. INTRODUCTION

Subsequent to the initiation of systematic pond culture in the forties with several species of tilapia, aquaculture has been faced with several problems. After an initial explosive growth of aquaculture in Africa, further progress and development came to a standstill or suffered a serious setback (Bard, 1962; Lemasson and Bard, 1964; Meschkat, 1967). Early maturation and repeated breeding of tilapia under tropical pond conditions, leading to overcrowding in ponds, are considered to be the major factors that led to the present impass in fish culture development. However, various techniques such as mono-sex culture, use of predators in tilapia ponds, use of sterile or mono-sex hybrids, use of better and fast-growing species, etc., have been suggested by several workers and investigations carried out on these lines.

The present status of aquaculture in Tanzania (Gould, 1951; Ibrahim and Lema, 1974a, 1974b; Ibrahim et al., 1974; Ibrahim, 1975; Matthes, 1974) is in no way different from the conditions mentioned above. Among the species cultivated in ponds in Tanzania, Tilapia esculenta, T. rendalli, T. zillii, T. nilotica, T. pangani, T. rukwensis, etc., respond in a similar manner regarding growth maturation and breeding. Hence it was felt that a fast-growing species would be more suitable for culture. At this time the report that T. andersonii matured in ponds in Zambia in 12–15 months time and that the species bred only once in a year (Maar et al., 1966; Meecham, 1962; Meschkat, 1967) gave the idea that probably this species could fare better in Tanzania. Thus an experimental consignment of T. andersonii was introduced into Tanzania from Zambia in 1968 (Anon., 1971; Ibrahim and Lema, 1974b).

2. MATERIALS AND METHODS

The main purpose of the experiments was to (1) find out the utility of T. andersonii for pond culture in Tanzania and (2) determine whether this species behaved differently from other local tilapias, particularly regarding maturation and breeding.

In July 1968 an air consignment of 100 fingerlings of T. andersonii (average length of 100 mm and 56.6 g weight) under oxygen packing was brought to Mwanza and stocked in a specially prepared pond of 0.08 hectar area at the small experimental fish farm at Malya, about 125 km from Mwanza (Fig. 1). The fish were fed daily on rice sweepings obtained locally, at a rate approximately equal to the weight of fish stocked. By November 1968, or in about four months time, specimens with an average length of 189 mm and 188.8 g weight bred, and fry were available.

A total of 500 fry of T. andersonii produced locally from the first brood and of an average weight of 14 g were stocked in a prepared pond of 0.08 hectar area on 14 March 1969 to study growth and breeding. Feeding was as before with rice sweepings. The fish were sampled in 15 to 20 days and growth recorded. At the end of 142 days the pond was harvested by repeated netting followed by draining of the pond. A similar experiment was conducted with another set of T. andersonii fry of average weight 8.15 g. In this case 500 fry were stocked on 23 June 1971 in another 0.08 hectar pond and observations made as in previous experiments.

3. RESULTS AND DISCUSSION

In the first experiment T. andersonii attained a size of about 120 g in about two months time and 170 g in four months time. In 142 days T. andersonii started breeding as evidenced by the presence of eggs and larvae in the mouth of several females. When the experiment was terminated, the survival among the 500 stocked was 61 percent. The growth pattern is presented in Figs. 2 and 3.

In the experiment initiated on 23 June 1971, fry of 8.2 g average weight attained an average weight of 88 g in five months. However, very early breeding was recorded when the average weight of the fish was only about 47 g or about three months after stocking.

These preliminary experiments indicate that the original stock imported, as well as the progeny produced locally, matured and bred in less than five months time under local conditions. Thus T. andersonii, under local conditions in Tanzania behaved similarly to local species with regard to maturation and breeding. Differences in temperature and other ecological factors between Zambia and Tanzania could be responsible for this type of differential behaviour.

However, T. andersonii, a reportedly plankton feeder, could adapt to local conditions in Tanzanian waters and could be a welcome addition to the locally available cultivable species.

4. REFERENCES

Bard, J., 1962 Fish breeding techniques developed in Africa and their practical results. U.N., E/Conf., 39/C/290, 4 p.

Gould, R.E., 1951 Progress of fish farming in Tanganyika. Fisheries Series Pamphlet No. 2, 1951

Ibrahim, K.H., 1975 Progress and present status of aquaculture in Tanzania. FAO Symp. on Aquaculture in Africa, 1975

Ibrahim, K.H., and R. Lema, 1974a Growth rates of T. esculenta Graham and T. zillii (Gervais) under cultivation in ponds at Nyegezi, Tanzania. Proc.Symp.Aquat.Resour, of East and Central Africa, Kampala, 1974. Afr.J.Trop.Hydrobiol.Fish., (in press)

Ibrahim, K.H., and R. Lema, 1974b Hybridization between T. zillii (Gervais) × T. andersonii (Cast.) at the Freshwater Fisheries Institute, Nyegezi, Tanzania. Proc.Symp.Aquat.Resour. East and Central Africa, Kampala, 1974. Afr.J.Trop.Hydrobiol.Fish., (in press)

Ibrahim, K.H., T. Nozawa and R. Lema, 1974 Preliminary observations on cage culture of T. esculenta and T. zillii in Lake Victoria waters and the Freshwater Fisheries Institute, Nyegezi, Tanzania. Proc.Symp.Aquat.Resour.East and Central Africa, Kampala, 1974. Afr.J.Trop.Hydrobiol.Fish., (in press)

¹ Lemasson, J., and J. Bard, 1974 Bilan de la pisciculture dans neuf états d'Afrique Tropicale. Centre Technique Forestier Tropical, 32 p.

Maar, A., M.A.E. Mortimer and I.V.D. Lingen, 1966 Fish Culture in Central East Africa. FAO, Rome, 1966

Matthes, H., 1974 Coastal and estuarine aquaculture. Proc.Conf.Marine Resources Development, Dar-Es-Salaam, 1974

Meecham, K., 1962 Report on Fish Farming in Africa. Internal report to the Government of Ghana, 5 p. (unpublished MS.)

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Anon., 1971 Experiments on T. andersonii. Internal report to the Ministry of Natural Resources and Tourism, Tanzania

¹ Not consulted in original

Fig. 1. A view of the experimental fish farm at Malya where Tilapia andersonii (Cast.) was introduced.

Fig. 2. Growth rate of T. andersonii in experimental fish ponds at Malya.

Fig. 3. Growth rate of T. andersonii at the experimental fish farm at Malya.