II. THE AQUATIC ANIMAL SPECIES INTRODUCED OR TRANSLOCATED IN ZAMBIA

(outside their natural distribution range)

The control of these introductions was among the most important point in the terms of reference. Visits to several fish farms, crayfish farms and institutions known or supposed to have introduced aquatic animal species, were organized for the consultant on arrival in Zambia by the staff of ALCOM and the Department of Fisheries, Zambia. Information obtained during these trips led to other visits. Before departure and after returning to Belgium, the consultant checked historical papers on transport of fish during the period 1945 – 1960, and interviewed Dr A.F. De Bont (Leuven, Belgium). In Zambia, very useful information on the earliest fish introductions was obtained from Mr Mubamba of the Fisheries Department, Chilanga.

II a. Survey of introduced and translocated species

Fishes

Astatoreochromis alluaudi

Bagrus meridionalis

Boulengerochromis microlepis (Kuhe, Kupi)

Ctenopharyngodon idellus (Grass Carp)

Cyprinus carpio (Carp)

Gambusia affinis (Top minnow; mosquito fish)

Limnothrissa miodon (Kapenta)

Labeo altivelis

Lepomis cyanellus (green sunfish)

Lepomis macrochinus (bluegill)

Micropterus dolomieui (small-mouthed bass)

Micropterus punctulatus (spotted Bass)

Tilapia andersonii (three-spotted bream)

Natural distribution : Upper (and Middle) Zambezi system. Introduced into the Lake Tanganyika system :

Tilapia aurea

Tilapia macrochir (Greenheaded Bream)

Tilapia mortimeri (or T. mossambica mortimeri)

1950 :

From Middle Zambezi to Chilanga fish ponds; no records available, but this species was in the '50s also transported to Elizabethville from Chilanga, under the name of T. mossambica and from there even into the Lufira system, Zaïre basin; checked by consultant in 1959–61 in Southern Zaïre. Note : Probably hybridized at Chilanga with T. andersonii; the purity of the present strain at Chilanga and at AMI farm does not seem certain any more.

1991:

From Kariba to Chilanga

Tilapia nilotica

Tilapia rendalli

Natural all over Zambia (in all river systems) but Luapula - Mweru strain imported from Elizabethville to Chilanga in 1948, and then probably further spread throughout Zambia.

Tilapia sparrmanii

Introduced (?) or natural in lake Chila, Lake Tanganyika system; observed in catches of local fishermen in lake Chila and in Uningi pans; the presence of T. sparrmanii in the lake Tanganyika system was up to now not known; as fishes have been introduced into lake Chila, import is most probable.

Tinca vulgaris (Tench)

Onchorhynchus mykiss (rainbow trout)

Serranochromis robustus or S. thumbergii

Aquarium fishes

Poecilia reticulata (Peters, 1859) (Guppy)

• Found in streams near Kitwe around 1980; no further information
• Mentioned by De Moor & Bruton (1988) as possibly establishing permanent population in Kafue swamp.

Xiphophorus helleri (Swordtail)

• Imported at Chilanga, period unknown; still present in some ponds and in some ornamental ponds in Botanical Gardens in September, 1992.
• Both species also present in fish ponds at Freshnet Kariba Farm, Kariba system (Sept. 1992); so escape into lake Kariba possible and highly probable, but survival in the lake rather improbable.

Crustaceans

Procambarus clarkii (crayfish)

Cherax albidus (Yabbie crayfish)
Cherax quadricarinatus

Macrobachium rosenbergi

Limnocaridina tanganicae (Tanganyika shrimp)

Freshwater Clams (Spathopsis wahlbergi or S. Petersi)

Introduced during 1980 from Kariba to Chilanga; still surviving in fish ponds in 1992.

II b. Comments on the different introductions and translocations

In the survey published by R. Welcomme (1984) only five fish species were mentioned as having been introduced in Zambia. The present survey updates this list to 21 fish species, 4 species of crustaceans and 1 species of molluscus. These introductions can be grouped into different categories :

1) The early introductions during the 1940s – 1950s

1940s : Gambusia - Mosquito fish
1942 : Onchorhynchus - Rainbow trout
1945 : Micropterus punctulatus - Spotted bass
1946 : Tinca vulgaris - Tench
1946 : Cyprinus carpio - Carp
1946 : Leopomis macrochirus - Bluegill
1947 : Micropterus dolomieui - Smallmouthed bass

Comments: These introductions took place during a period when general knowledge on African fishes was still very poor. Fisheries officers knew only a little about European fishes, and almost nothing about African fishes. Introductions were based on scanty information about introduction of fishes from North America to Europe and vice versa, and on the recent introduction of exotics into Southern Africa — an area, however, with a much cooler climate than Zambia.

Apparently no quarantine or other measures were ever taken, and these introductions certainly do not meet the present EIFAC recommendations. Fortunately, these early introductions do not seem to have been successful and apparently have left no traces.

2) The first tilapia transports (1945–1950)

Few records are available but fishes were exchanged with other countries. Some Tilapia rendalli from Luapula-Mweru were transported by train from Elizabethville to Chilanga in 1948. In 1949–50 some transport of fishes inside Zambia to Chilanga took place; probably the Tilapia macrochir strain of Luapula was sent to Chilanga, and the Tilapia mortimeri from Middle Zambezi was also introduced in Chilanga. However, no written or published information is available for the latter transports and no traces are found in rivers and ponds. It should be noted that in Zambia very few or no exotic tilapia were translocated, and government services started very early to work with local species. As such the policy of the Zambian Fisheries Department was exemplary.

Comments : By 1945–50 it was believed that tilapia were almost miracle fishes, and they spread widely in Africa; so that many criss-cross transports of these fishes had taken place. It was believed that they could not do any harm as tilapia were natural everywhere. But their biology and natural distribution were still poorly known at that time, so many cases of transport of tilapia species occurred outside their natural range.

From his 30 years of experience, the consultant believes that tilapia in Africa are to be considered as “soft exotics” with only minor or no harmful effects to the ecosystem. Their diet is strictly phytophagous or microphytophagous; they are not even zooplankton-feeders, and of all species known, none has even the slightest tendency toward predating on eggs or preying on juveniles of other fishes. Futhermore, in almost every African aquatic system, there are already one or two ecotypes of tilapia naturally present.

The plant-eating tilapia (subgenus Coptodon; species T. zillii, T. rendalli), and the microphagous female mouth-breeding tilapia (Subgenus Oreochromis; species T. nilotica, T. aurea, T. macrochir, T. mossambica) are indeed composed of one or more series of allopatric (or vicariant) species which are rather closely related to one another and which occupy in different areas almost the same or very similar niches. Therefore translocations of tilapia species inside Africa to other faunistic areas where other related tilapia species are present, will mostly have only the following reduced effects:

• Competition for food and for breeding sites with the local vicariant tilapia species; this can lead to a shift in relative numbers of the tilapia species in competition (like recently in the Kafue flats where T. nilotica replaced T. andersonii -- see Annex VII; or formerly the introduction of T. macrochir in Lake Kariba which was not successful.)

• Natural hybridizations, which occur quite often.

In general, these effects are rather harmless for the total aquatic environment, and for the other fish species, especially in larger hydrological systems with a rather important number of fish species utilizing the total aquatic resources in a balanced way. In small water bodies, which can only sustain a reduced number of fish species, this can lead to the disappearance of the introduced or the local species.

One negative side-effect of tilapia transports can be -- and certainly was so before 1960 -- that the species purity was always assumed, but some juvenile Haplochromis fishes may have been transported at the same time. These Haplochromine fishes predate on the eggs and fry of other fish species, and as such can be a major threat to the local fish farmer. The disappearance of Barbus luhondo from Lake Luhondo (Rwanda) occurred a few years after the introduction of Tilapia niliotica in that lake (1927), an introduction that also contained many Haplochromis as impurities (see Devos, Snoeks & Thys V.D. Audenaerde, 1990). There are no records of similar “mixed” transports, but fish ponds at Mwekera station contained many Haplochromis besides the tilapia. Therefore the species purity of all tilapia transports should be checked by competent officers.

3) The second and third wave of tilapia transports

• 1959–1962 : The introduction of Tilapia macrochir fry into lake Kariba.
• From 1980 on : distribution of the Chilanga strain of Tilapia andersonii all over Zambia, also in Luapula, Mweru, and Rukwa and in Tanganyika basins.
• Possible transport of Tilapia mortimeri (as T. mossambica) inside Zambia.
• Possible transport of Tilapia sparrmanii to Uningi Pans and lake Chila.

Comments : The introduction of T. macrochir into lake Kariba was the result of a thorough investigation into the ecological niches of the lake and their biological occupancy. The absence of T. macrochir from the Middle Zambezi was due to the specific ecologic conditions in the sand-bank-river area of the Middle Zambezi, which is however within the natural range of Tilapia macrochir; and thus this introduction, strictly speaking, cannot be considered as an introduction. As the transformation into lake Kariba of the Middle Zambezi constituted a major change in ecology for this area, all species, as well as T. macrochir, had more or less to adapt to the changed environment.

The transport of T. andersonii throughout Zambia was the result of comparative investigations with FAO assistance during the late 70s and early 80s on the tilapia that could best be used for aquaculture in Zambia. The decision to carry out these experiments and to promote T. andersonii are among the most valuable decisions and actions taken by FAO and the Fisheries Department of Zambia. As T. andersonii is a local species, it cannot strictly speaking be considered as an exotic. Unfortunately the species purity of the distributed strain does not seem guaranteed, and some hybridization with T. mortimeri may have occurred as this species was also introduced in Chilanga. But apparently in recent years it was also overlooked that T. andersonii did not occur naturally outside the Zambezi drainage area. Therefore it is regretted that T. andersonii was imported into the lake Rukwa system without any previous examination of its possible impact on T. rukwaensis, the local endemic species. This situation calls for a follow-up.

T. andersonii constitutes an exotic fauna element for Luapula-Mweru, and the Tanganyika system. The ecology of the lacustrine habitats of lake Tanganyika however is so different from the fluvial habitat that it is hard to imagine that T. andersonii could successfully adapt to the lacustrine Tanganyika habitat. However a follow-up would do no harm.

But the distribution of T. andersonii in fish farms of the Luapula-Mweru area is a rather unfortunate decision; in this area T. andersonii comes into competition with the Luapula strain of T. macrochir, a strain that now supports successful fisheries in the Mweru, Bangwelu and Mweru-Wantipa areas. Therefore, all further transport of T. andersonii in this area should be stopped, and if possible this species should in that area be replaced by the local T. macrochir for aquaculture.

4) The introductions into Lake Kariba and Lake Itezhi-tezhi

Both introductions into lake Kariba were the results of through preliminary scientific investigations, and could also benefit from data derived and experience gained from the introduction of the Ndakala into lake Kivu (1954–60). They can be considered as models for preliminary research, decision-making, execution and follow-up for introductions.

The fact that Stolothrissa (and Limnocaridina?) did not survive successfully, is however a permanent warning that even the best scientific preparation and evaluation cannot always predict the exact consequences of an introduction. This is also proven by the dispersal of the rather vulnerable Limnothrissa downstream of the Zambezi through spillway and rapids till the Cahora Bassa dam and probably farther downstream.

The recent introduction into lake Iteshiteshi of Limnothrissa is more hazardous but without noticeable environmental dangers: If successful, it can support an important fisheries in a new and young and rather important dam lake : further spread downstream would only bring these fishes through the Kafue river into the Lower Zambezi area where they are already present in lake Cahora Bassa.

5) Some introduction of aquatic animals during the latest decennia by the Fisheries Department of Zambia.

Although these introductions probably occurred with the best of intentions, it seems nevertheless that they occurred without any serious preliminary planning and more or less as a result of some chance encounters or suggestions. EIFAC criteria were most probably not followed.

The Göttingen strain of Tilapia nilotica, of which 52 specimens were imported in 1991, was already reduced from 52 to ± 20 fishes in 1992 and no follow-up programme existed. The fishes were kept in small concrete ponds which were not suitable for successful survival.

For this tilapia introduction, see also the remarks on “Soft exotics” under II-b-2, pp 7.

The other introductions, however, should be considered as “hard exotics” or non-autochthonous species which have no closely related equivalent or vicariant in the aquatic system concerned, and which therefore after introduction have to create their own new niche in between and against the existing species. The outcome of this niche-shifting and competition is generally very difficult to predict accurately, and ecological distress may occur. Therefore such introductions need considerable preliminary research before any recommendations or conclusions are arrived at. For none of the introductions discussed below was such research done.

Of the introduced grass carp, only nine specimens survived in 1992, and no programme was mentioned for these specimens, they were just kept in ponds at Chilanga.

The specimens of Boulengerochromis all disappeared in a flood, but no attempt was even made to check any survival, which is fortunately very improbable, especially as the river downstream of Mwekera is somewhat polluted by mining activities. It seems fortunate that this predator did not survive.

Only the carp introduction was followed by a further reduced dispersal to Mwekera and to Misamfu, but is now subject to artificial spawning for further distribution.

The arguments used for carp reproduction and dispersion seem to be:

• Carp is a fast grower and a good food converter; it exploits in ponds a food niche different from tilapia.

• When escaping into natural waters, carp is only a minor danger to local fish fauna as it will almost never reproduce in African waters; when it does so, its eggs sticking to the aquatic vegetation will be severely predated by the indigenous fishes.

Presently Mwekera and Misamfu aim at ± 1 000 000 carp seedlings a year. Mwekera has already produced some 3–400.000 seedlings; the first induced spawnings took place in Misamfu. So by the end of 1992 a massive spread of carp in rural ponds is to be expected.

The arguments for and against carp introduction and dispersal in Africa have been published many times (see Welcomme, 1984, De Moor & Bruton, 1988).

The consultant is personally not in favour of the dispersal of carp in tropical Africa, certainly not in the rural environment, because of the dangers (exposed in many technical papers) it poses to natural and indigenous fishes.

The Fisheries Department, however, has to take urgent decisions about the present spawning programmes -- whether to let them go on or stop them immediately. If these programmes and actions are not stopped, it will become very difficult to prevent a massive spread of carp in the Copperbelt and the North-Eastern provinces of the country, areas belonging to the Zambezi and Zaïre-drainage systems, two of the largest river systems in Africa.

Some consultation concerning a common policy with neigbouring countries would be very useful. Presently Zimbabwe and Malawi prescribe the eradication of carp. FAO and ALCOM can play an important role in harmonizing fisheries and aquaculture decisions and policies between these countries. It must be evident that government policy on carp has to be the same for private farmers, companies, and rural farmers.

6) Fish introductions realized by larger companies and by commercial farmers:

These introductions always took place without the necessary authorisation by the Department of Fisheries, and without notice being given to the department.

Large commercial companies and commercial farmers enjoy easy access to information on aquaculture outside Africa and elsewhere in the world, and this information is generally much better than their knowledge on African fishes. The techniques for commercial aquaculture of these exotic species are well-known through published literature which is easily accessible.

It seems evident, therefore, that while local rural fish farmers accept without comment the fish species distributed by Fisheries Department Officers, commercial farmers first turn to exotic species.

However, the experiences at Kafue Fisheries Estate demonstrate that, if some permanent selection is applied, the local species, T. andersonii, can give results as good as or even better than exotic species.

According to the Fisheries Act, an exotic species can be imported only if permission is given by the Director of the Fisheries Department. However, during the last decennia, all imports of exotic fish and aquatic animals occurred on the basis of permission given by the Ministry of Commerce and Industry; these permits were generally delivered without consulting or even giving notice to the Fisheries Department.

Such imports were clearly based only on arguments of economic expectation by the farmers, and no biological arguments (such as EIFAC rules) were taken into consideration.

The roles and responsibilities of the Fisheries Department in Zambia therefore have to be made clear to all border authorities. The Ministry of Commerce and Industry and customs authorities must be told to prevent further introductions without any biological control or evaluation.

The introduction of Tilapia nilotica seems to have reached by 1992 a point of no return. The species has already established a permanent population in the Kafue flats, and is also present in lake Kariba (see map Annex VII).

As stated before (see II b 2), in these places T. nilotica will come into competition with T. andersonii, T. macrochir and T. mortimeri, and it is hard to predict the outcome. Most probably these species will co-exist in variable numbers. There are however more and more demands, especially on the Zimbabwean side of Lake Kariba, for imports of T. nilotica and for the use of this species in cage culture. As T. nilotica is presently widespread in the tropical world, being even now the Tilapia species most commonly used in aquaculture, and as considerable research and development has been done on this species, now available under a large number of strains, it may be useful to start some comparative tests between T. andersonii and some T. nilotica strains. These tests could be the basis for the decision to go further with T. nilotica or to continue with T. andersonii.

With regard to the introduction of grass carp and carp, the Government of Zambia has to take a quick decision whether to continue the spread of carp or prohibit and eradicate it. A common policy for SADC countries seems necessary.

7) Introduction of crustaceans by private farmers

Introduced freshwater crayfishes constitute a totally new element of African and local fauna. Reason: such species were not present in Africa, where their ecological niche was (partly) exploited by freshwater crabs which mostly feed on dead animal material. It should be noticed that detritus-feeders and especially hard tissue detritus-feeders, are almost absent from African waters. These freshwater crayfish can thus be considered as occupying non-utilized food niches, and as such could be considered as a valuable addition. However their digging habits present another danger (see the experience in Kenya), and their uncontrolled spread only enhances this danger.

The theory that crayfish and barbel (Clarias) are not compatible, and that Clarias will in nature eliminate crayfish, evidently does not stand. In small ponds where fish cannot hide, encounters between crayfish and Clarias will be frequent and can result in elimination of the crayfish. But in a natural environment where fish can hide more easily and there are less frequent encounters, the crayfish can easily survive. Specimens of Macrobrachium rosenbergii, which escaped as larvae from cages or ponds near lake Kariba, grow very well into adults in the presence of Clarias and other fishes. The Macrobrachium species however do not reproduce in fresh water. The other introduced species, Procambarus clarkii, and the two Cherax species, do reproduce in fresh waters. At this moment these species are useful only to one aquaculturist. The exact food niche they occupy and their impact on ecology and fauna is not clear at this moment. A control of escape possibilities seems indicated.

It should be mentioned here that—just as for the former category of introductions (see § 6 above)-— these crustaceans were introduced without the knowledge and the permission of the Fisheries Department.

8) Aquarium escapes or introduction of aquarium fishes

Year ? : Lebistes maculatus (or Poecilia reticulata, see p 6): Guppy
Year ? : Xiphophorus helleri : Sword tail

These can be considered merely as aquarium curiosities; their habit of slow swimming near the surface makes them a good target for all small predators, and they seem to survive only in decorative ponds without predators. They cannot possibly be considered as having a serious environmental impact on Zambian waters.