BREEDING BEHAVIOUR OF THE MPASA, OPSARIDIUM MICROLEPIS (GUNTHER) (PISCES:CYPRINIDAE), IN LAKE MALAWI

SUMMARY

Observations on the breeding behaviour of mpasa, a commercially valuable cyprinid endemic to Lake Malawi, were conducted in the Bua and North Rukuru Rivers. The spawning run takes place over an extended period during and after the rains, with an apparent peak in breeding activity in May-June. Spawning occurs over a gravel substratum, often in very shallow water, during the night and early morning. Sanjika, a close relative of the mpasa, spawns in a similar manner in the same habitat. The male guards a territory about 1,5-2 m wide, patrolling in a regular figure of eight manner until joined by the female, who initiates the spawning act in the centre of the territory. The eggs filter down through the interstices in the gravel and the developing fry remain in the gravel until the yolk sac is absorbed. Juveniles remain in the river for several months and then remain close inshore near the river mouth until their second year. North Rukuru mpasa usually reach maturity in their third year from 280 mm total length, but Bua fish are much larger, suggesting that the rivers have separate stocks. Ovaries of North Rukuru River-caught fish contained from 1 381 eggs in a fish of 190 mm total length to 22 077 in a 555 mm fish. Mpasa's dependence on clean gravel for spawning has important implications for the future survival of the fish and fisheries. The spawning reaches in the Bua are protected within Nkhotatoka Game Reserve and hence do not suffer from siltation as a result of deforestation and agriculture. The catchments of other rivers sustaining large runs of mpasa are also lightly populated and very hilly. The Luweya River, however, is threatened by forestry development. Continued protection of the river catchments is important for the future survival of the species.

KEY WORDS:

• Opsaridim microlepis
• mpasa
• sanjika
• Lake Malawi
• river migrations
• spawning
• maturity
• fecundity
• catchment protection.