REPRODUCTION IN THE EAST AFRICAN LUNG-FISH PROTOPTERUS AETHIOPICUS HECKEL

Authors


*British Museum (Nat. Hist.), London, S.W.T.

SUMMARY

  • 1Four occupied nests, which differ in form and environment, of P. aethiopicus are described from Lake Victoria. These constitute the first definite records of the nests of this species. Evidence is adduced which strengthens the possibility that certain structures previously thought by other authors to be nests were in fact those of lung-fishes.
  • 2The oxygen content of one nest was determined and found to be low, probably never exceeding 3 p.p.m. During the breeding periods studied, the modal day water temperature was 23oC. and the temperature range 17-8o to 25-0oC. The least diurnal temperature variation was 0–5o and the greatest 3–6oC.
  • 3From one nest over 5,000 larvae were recovered and from another (incompletely sampled) more than 2,000. Some broods showed a distinct fractioning into several ontogenetic stages. It is concluded that fractioning is attributable to slight initial differences in the time of fertilization and reinforced by individual variation in developmental rates. The scanty data available suggest that more than one female spawns in a nest.
  • 4Larval P. aethiopicus begin air-breathing when they have reached a length of 23 to 25 mm. It seems probable that whilst the larvae remain in the nest they are not dependent on aerial respiration.
  • 5In its external features, the embryology of P. aethiopicus closely resembles that of P. annectens. Slight differences in ontogeny are discussed. The ova, embryos and larvae of P. aethiopicus are larger than those of P. annectens, and have a slower- developmental rate. Also, the larvae attain a larger size before the yolk is fully resorbed.
  • 6At ca 23oC. young P. aethiopicus remain in the nest for fifty to fifty-five days. Pre-hatching development takes about fifteen days; thereafter the young grow to a length of ca 35 mm. in forty days.
  • 7Post larval P. aethiopicus live actively in the matted papyrus roots and the root systems of swamp grasses. There is no evidence to support an earlier idea that they pass the first year of life in a quiescent condition.
  • 8The external gills are ciliated. Data relating to the development and subsequent necrosis of these gills is reviewed and summarized.
  • 9The breeding cycles of P. aethiopicus in Lake Victoria are imperfectly known. Observations made on ovarian conditions indicate a peak breeding season from November to April. Occupied nests were found in this period, and in September. This latter nest suggests that spawning may also occur during unseasonal. wet periods.

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