View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Aquatic Commons SPONSORS Hydrobiologists from East, Central and West Africa with substantial support from other African countries, Fishery Scientists in the United States, Canada, U.K., Europe, Soviet Union and Israel. OBSERVATIONS EDITOR SIZE ON BOTTO Dr. J. Okedi, Director, E.A.F.F.R.O., Jinja, Uganda. WITH EMPHASI: EDITORIAL BOARD Mr. M. Abolarin, Co-Manager, Kainji Lake Professor W.B. Banage, Makelere Univer­ Project, Lagos, Nigeria. sity, Kampala, Uganda. ALMO J. CORDONE Al UNDP(SF)/ FAO Lake Vici Mr. J. Kambona, Chief Fisheries Officer, Mr. R.E. Morris, Director, E.A.M.F.R.O., Freshwater Fisheries Resel Dar es Salaam, Tanzania. Zanzibar. Mr. J. Mubanga, Director, Fisheries Division, Dr. T. Petr, Senior Lecturer in Hydrobiology, Chilanga, Zambia.. Makerere University, Kaflpala, Uganda. Dr. L. Obeng, Director, Institute of Aquatic Professor Mohamed Hyder, University of Biology, Achimota, Ghana. Nairobi, Kenya. Mr. N. Odero, Director ofFisheries, Nairobi, Professor, A. F. De Bont, Universite de Kenya. Kinshasa, Kinshasa XI, Republique Demo­ Mr. S.N. Semakula, Chief Fisheries Officer, cratique du Zaire Entebbe, Uganda. PROGRAMME The African Jout-nal of Tropical Hydrobiology and Fisheries will only accept original and well supported ideas on techniques, methodology and research findings from scientists, fishery officers,. fishery economists and sociologists. The Journal will therefore strengthen the African lesearch scientist by making research material available and also increasing the awareness and utility of aquatic resources. Its quality will conform to International standards, and will be published in English and French. MANUSCRIPT ADDRESS Manuscripts should be addressed to E.A.F.F. R.O., East African Freshwater Fisheries, Research Organisation, East African Community, Box 343, Jinja, Uganda. REPRINTS The Lake Victoria Fishe Authors will receive 60 reprints frce of charge. Extra reprints may be procured on cost. ject and the East A PUBLISHER Fisheries Research Orga East African LiteratllIc Bureau. P.O. Box 30022. Nairobi. Kenya. on a co-operative explora ing survey of Lake Vic1 ISSUES objectives of this progran The Journal consists of one volume a year, consisting of two issues with approximately tain the relative abundan eighty pages each. of the major commerci evaluate bottom trawlin~ SUBSCRIPTION fishing technique. The j Annual subscription within East Africa Sh. 35. Outside East Africa. East African Sh. 70, bottom trawling survey h US $ IO,(Xl 1968, and terminated in F A .a ._,,~ .. ;' OBSERVATIONS ON THE BIOLOGY OF NOTHOBRANCHIUS GUENTHERI (PFEFFER) (CYPRINODONTIDAE), AN ANNUAL FISH FROM THE COASTAL REGION OF EAST AFRICA R. G. BAILEY Formerly: Fisheries Laboratory, Central Agricultural Research Centre, !/onga, Kilosa, Tanzania Nothobranchius guntheri is found in seasonal pools and streams in the coastal region of Tanzania. A population recurring annually in a pond near Kilosa has been studied. Growth in length was rapid and maximum mean lengths were attained within 11-12 and 7-8 weeks of hatching by males and females respectively. Males grew larger and exhibited wider variation in length than females. N. guentheri shows clear sexual dichro­ matism. No significant inequality in the sex ratio was found. Females with ripe eggs were found 7-8 weeks after hatching. Spawning continued throughout adult life and fecundity increased markedly with increasing length. In laboratory aquaria, aggressiveness between adult males was noted and females were actively driven on to the substratu~ preparatory to spawning. The diet of the fish pond consisted chiefly of aquatic and terrestrial insects, of which midge larvae and pupae were the most common. N. guentheri is exploited by man in the aquarist trade and for the bio­ logical control of mosquitoes. An extended redescription of the species is appended which includes N. melanospilus (Pfeffer) as a synonym. Present address: Departmenc of Zoology. Chelsea College, University of London, England Nothobranchius belongs to the remarkable one or more of three stages during its norma group of cyprinodont genera known as embryonic development (PETERS 1963, 'annual fishes', which typically inhabit small WOURMS 1964). bodies of water subject to periodic drying The data presented in the following out. At such times hatched fish die and the account were obtained from occasional population survives in the egg form. The studies of a population of Nothobranchius latter is drought resistant and capable of occurring annually in a pond situated in long term survival. Provided with a tough the fields of the Agricultural Research chorion, it is able to lenghten its development Centre at Ilonga, near Kilosa in Tanzania, time by undergoing a period of diapause at East Africa. During the period from 1963- c 34 R. G. BAILEY 65, several other collections of the same minimum of 21°C on 23 June. The mean Table J. Sample species were made in the Kilosa~Kimamba value for the period was 25°C. j -indeterrninat( area and near Bagamoyo on the coast. The Ilonga Pond was larger and deeper An examination of these collections together than other successful collecting sites examined Date with material in the British Museum, Natural by the author. These included isolated pools History Section provided a specific identifica­ and sluggish streams. All were seasonal in tion and led to a recent redescription (BAILEY nature, shallow and muddy, agreeing well 1963 1969) of the species Nothobranchius guentheri with ROWE'S (1958) description ofcollecting March-May (Pfeffer) 1893. As in other members of the sites around Dar es Salaam. VANDER­ 1965 31 March genus, N. guentheri exhibits clear sexual PLANK (1941) reports that N. taen;opygus 7 April dichromatism. The adult male is very in central Tanzania inhabits seasonal polls 14 April colourful with a preponderance of red, but is absent from nearby streams and 28 April whereas the female is bluish-grey with a rivers. 12 May scattering of dark spots. In the light of 26 May 9 June further study and recent publications by THE POPULATION OF NOTHOBRAN­ 23 June others, an extended redescription of the CHIUS GUENTH.aRI 7 July species is appended. 21 July First reported in Ilonga Pond by field 4 August staff retting kenaf, 70-80 specimens were 18 August THE ILONGA POND caught during the period from March to Excavated for the purpose of retting the May 1963. Compared with subsequent years GROWTH fibrous bark of kenaf and jute, the pond the pond appeared to support a smaller The mean, was in the form of a broad trough approxi­ population of larger fish (Table I). of the total lei mately 5 m in width and 20 m long. It filled In 1964, N. guentheri recurred. A sample (Table~1 annually during the rains to a maximum taken in May provided a large number of dates growth curv central dep'th of 1.25 m, becoming consider­ small fish, among which very few males Ilonga Pond ably shallower at either end. In 1965, the were found. This may have been due to an e~ only year for which a record was kept, water unequal sex ratio or to a spatial separation absence of chosen as the I began to accumulate in early February and of the sexes in the pond. ROWE (1958) has of the growth the pond completely filled on 5 March observed the latter phenomenon in large i day which fa following a heavy overnight rain of 6.7 cm. ponds. entry of water A high water level remained throughout No longer used for fibre processing, the attained its n March and April but dropped visibly from pond supported a large population. of the middle of May onwards. On 18 August N. guentheri in 1965. Regular samples were a maximum depth of only 10 cm was recorded removed from 31 March until the pond dried Growth in /en~ and within one week the pond had fully up. Fishing was by means of a small mos­ This was ra dried out. quito-net seine (3 m X I m), thrown into the in both sexes Throughout the seven months of its water by two operators on the bank. Samp­ By the end of1 existence in 1965 the pond was extremely ling was confined to the shallow ends of the had virtually muddy. Secchi disc readings in June gave pond until the level fell. Only rarely were length, wherei values of 15-18 cm. In the same month the more than two hauls required to make an at a declining: pH of the water was 7.5. Water temperature adequate catch. A mean number of 128 fish On all samPi was measured at forthnightly intervals from per sample was recorded. The sample data exhibited a 31 March until 20 August, usually between are presented in Table I. No other species females, the 11.00-14.00 hours. A temperature maximum of fish were found in the pond during the old populati, of 30°C was recorded on 28 April and a investigations. reached the OBSERVATIONS ON THE BIOLOGY OF NOTHOBRANCHIUS GUENTHERI 35 June. The mean Table 1. Sample data from Ilonga Pond for 1963 and 1965. Total lengths are given in mm; m-male, f-female, 25°C. i-indeterminate, X-mean, s-standard devialion. lrger and deeper ng sites examined Lengths ed isolated pools Date Total % sex ratio - male -female nos. m f i X s range X s range were seasonal in I --- ly, agreeing well 1963 ltion ofcollecting March-May 60 40 60 - 51 9.5 34-68 46 7.3 34---63 am. VANDER­ 1965 31 March 81 25 .t N. taeniopygus 27 48 22 1.7 19-25 20 1.1 18-22 7 April 128 40 40 20 25 1.9 21-30 23 1.7 20--27 ts seasonal polls 14 April 47 64 36 - 28 1.9 24-34 26 2.0 22-31 Jy streams and 28 April 173 53 47 - 31 1.6 25-39 29 1.5 24-34 12 May 153 52 48 - 33 3.2 29--44 29 1.8 25-37 26 May 144 48 52 - 34 2.1 31-42 29 2.3 23-38 9 June 131 47 53 - 35 2.4 30--41 30 2.2 26-35 NOTHOBRAN- 23 June 133 49 51 - 34 2.5 28--43 30 2.0 26-36 7 July 117 39 61 - 34 3.6 28--44 29 2.1 25-36 21 July 108 40 60 - 32 2.7 28-38 29 2.1 26-34 Pond by field 4 August 131 53 47 - 34 4.1 29-56 29 2.0 26-37 18 August 140 50 50 - 34 4.7 28-60 29 2.3 26-39 specimens were I from March to mbsequent years GROWTH and 63 mm for males and females respecti­ ,port a smaller vely.