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Home , Kenya Colony, Northern Rhodesia, Tanganyika (territory)

WAIg No. 38 for January, 1957 PISCA TOR

A NOTE ON EELS (ANGUILLA SPP.) By WINIFRED E. FROST Freshwater Biological Association, Ferry House, Ambleside, England

N 1955 and 1956 Mr. P. I. R. Maclaren, Fisheries Officer for Northern Rhodesia, wrote I to me about some eels, Anguilla spp., which he had collected from the Zambesi river system, and in September 1956 he sent me six specimens from his collection which I received in December. We had intended to discuss his finds when he came to England on leave in 1957, but his untimely and tragic death in October 1956, from an attack by a crocodile, prevented such a discussion. In view of this, the following account of eels collected by the late Mr Maclaren is given so that his findings may be recorded.

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I , IS 8 : Q.= Z . V1CTCRIA INDIAN FAL.S. 'V < ' - OCEAN. N. .._ 201 2 30 1'12,000,000 0 KNOWN OCCURRENCE OF EELS. • SITE OF EELS MENTIONED IN I XT. X PROBABLE BARRIERS. TO EELS. 1 I 2000,000 2$ 28' 30' 32 Sketch Map made by P. I. R. Mac aren showing localities where eels are known to occur in the Zambesi River system. i•-= • 314

PISCATOR No. 38 for January, 1957

I do not know the total number of eels that Maclaren collected in the Zambesi river system from 1954 to 1956 but he first mentioned them in a letter of November 1955 in which he enquired about methods of identifying his captures. The classic work for this purpose is Ege's (1939) "Revision of the genus Anguilla". The characters by which Ege separates all the known species of eel include colour, dentition and certain body proportions, in particular that of the "distance between verticals through anus and origin of dorsal fin in percentage of the total length". In 1948 Dr. Ege made me a key, based on this ano-dorsal fin length character and the colour of the fish, by which to separate the four species of eels he records from African fresh waters : namely Anguilla nebulosa labiata Peters, the mottled long-finned eel; A. marmorata Quoy and Gaimard, a mottled eel; A. mossambica Peters, the plain long-finned eel and A. bicolor bicolor McClelland, the plain short-finned eel. As this key is given in my paper on the eels of Kenya (1955) I sent a copy of this publication to Mr. Maclaren who then made the body measurements requisite for establishing the fin-length character ("D" in the table below) on nine specimens of his collection and sent the data obtained, together with notes on coloration, that on them I might identify his eels. Later he sent me four of these specimens and also one eel and the head of another which he himself had not examined, which I received December 31, 1956. All these had been preserved in formalin. Thus there are measurements and colour data on ten eels. The information on which the eels have been identified is given in the table. Although these eels from the Zambesi have been identified, it is believed correctly, on colour and one morphometric character only, it should be noted that Ege (1939) gives other length characters, together with dentition, for separating the four African species of Anguilla.

Place and date Length Weight Values Basis of my of capture cm. kg. Colour Sex for D Species identification Lunsemfwa River 146.0 8.70 mottled ? 12.6 A. nebulosa labiata Maclaren's data only February 1956 147.3 8.70 mottled ? 12.1 A. nebulosa labiata Maclaren's data only 142.2 7.65 mottled fem. 13.8 A. nebulosa labiata Maclaren's data 134.6 6.75 mottled fem. 13.2 A. nebulosa labiata and also the 153.6 10.12 mottled fem. 13.7 A. nebulosa labiata specimens themselves 139.7 6.20 mottled ? 12.7 A. nebulosa labiata Maclaren's data only Lunsemfwa River 140.5 7.70 mottled fem. 13.6 A. nebulosa labiata No data from 1954 One head only — mottled — — Possibly A. nebu- Maclaren, losa labiata identifications because mottled made on specimens only Lunsemfwa River 127.0 — mottled 18.4 A. marmorata (? Maclaren's data see text) •:11 February 1955 158.0 — unmottled — Not identifiable C\Talille for "D" insufficient data too high for A.n. labiata, the other mottled species Lower Zambesi 97.0 — unrnottled — 14.1 A. mossambica (? Maclaren's data River (Chipepo) see text) only Angust 1955 95.5 mottled fem. 12.2 A. nebulosa labiata No data from Maclaren (?) identification on specimen only No. 38 for January, 1957 PISCATOR

The table shows that the identity and distribution of eels which Mr. Maclaren found in the Zambesi river system is as follows: — LUNSEMFWA RIVER. Anguilla nebulosa labiata (the mottled long-finned eel). Seven whole specimens) and one head, possibly this species. Anguilla marmorata (?) (a mottled eel). One specimen. I query this because Ege (1939) records only a single specimen of this species from the African mainland, and recent enquiries about the identity of this specimen made by Dr. K. H. Barnard of the South African Museum indicate that it was not in fact A. marmorata (in litt). LOWER ZAMBESI RIVER (CHIPEPO). (Maclaren sites Chipepo as 28° 50' E. 16° 45' S.) Anguilla nebulosa labiata. One specimen. Anguilla mossambica (the plain long-finned eel). One specimen, identified on Maclaren's data of "unmottled" and "D=14.1", but correspondence and time and place of capture suggest this fish may be the same specimen (95.5 cm) as that examined by me and identified, because mottled, as A.n. labiata. This confusion questions the record of A. mossambica. In a letter of February 22, 1956, Maclaren noted that the eels from the Liemfwa river (a tributary of the Luangwa which itself runs into the Zambesi) were taken above the Power Station Falls "by the grid at the end of the canal leading to the intake of a hydro-electric station and so were presumably going downstream. To get to this river young eels would have to surmount a series of cascades totally 250 feet". In his first letter (Nov. 1955) about his captures at the Power Station he remarks: "I think it physically impossible for any fish to get up the falls and rapids which would point to the fact that the species [A.n. labiata] is not katadromous". This last suggestion is challenged by the capture, in January and February 1956. of two elvers,* which I identified as A.n. labiata, in the Mzinga Creek, Dar-es-Salaam, Tanganyika, 200 yards above high water mark. This find suggests that it is highly probable that the adult A.n. labiata descends to the sea to breed and thus we may assume that the large A.n. labiata of the Lunsemfwa River arose from elvers which entered the Zambesi river and which either as eNers or eels were able to negotiate the obstacles to their upstream migration. That eels are widely distributed in the Zambesi river system is apparent from the figure, a sketch map drawn for me by Mr. Maclaren to show "the river systems which are known to have eels". He comments that "there are no definite records above Victoria Falls and do not know the Southern Rhodesian tributaries of the Zambesi". The localities shown on the map refer primarily to the presence of eels not to any particular species. The records noted above of A.n. labiata based on the eels collected by Mr. Maclaren are the only records of this species from the Zambesi river system in Northern Rhodesia, the other locality in this watershed from which A.n. labiata has been recorded is Tette in Portuguese East Africa (Ege 1939) for which country there is also one other record, the Licuare River, Boror. It may be mentioned that of the three other species which Ege records from East and South Africa (see above) there is no record of A. mossambica from the Zambesi system and A. bicolor bicolor has been noted from one locality only in this region, the Licuare River, in Boror, Portuguese East Africa. Mr. Maclaren's collections of eels have added appreciably to our knowledge of the distribution of Anguilla in African freshwaters. Records of eels (and elvers) from African waters are most welcome since not only do they extend our knowledge of the distribution of Anguilla spp. but they throw light on the biology of eels of Africa about which so little is known. References. Ege, V (1939). "A revision of the genus Anguilla Shaw, a systematic, phylogenetic and geographical study." Dana Report No. 16, 1-256. Frost, W. E. (1955). "Observations on the biology of eels (Anguilla spp.) of Kenya Colony, East Africa." Col. Off. Fish. Pub. No. 6, 1954, 1-28. * These two elvers, sent to me by Mr. G. J. Lockley, Fisheries Officer, Tanganyika Territory, are the first elvers of A.n. labiata to be found. A note to this effect has been sent to "Nature".