Observations on the Nile Perch (Lates niloticus) in the Sudan
- 1 The damming of the Blue Nile at Sennar resulted in an increase in the numbers of Lates in the pools immediately below it. There was no trustworthy evidence of any corresponding decrease elsewhere on the river.
- 2 This fish is extremely variable in form in Sudan rivers, and study by a competent taxonomist appears desirable.
- 3 Sexual maturity appears to be reached at a live-weight of about 7 lb. (3.2 kg.): indications of possible habits and rhythms of spawning are noted.
- 4 The spawning season at Sennar corresponds to the peak of the angling season. It lasts from December till April, with maximum in February and March.
- 5 The ova are described: rough counts indicated approximately 3000 ova per gram of ovary, and 26 grams of ovary per kilo live-weight.
- 6 The sexes were taken in very equal proportions throughout the season. The average weight for females exceeded that of males by nearly 9 lb. No male over 35 lb. occurred, but females of over 100 lb. were taken.
- 7 The condition factor is considered for both sexes at various stages of sexual condition. A wide range of variation suggests heterogeneity in the population.
- 8 The fishing season varies considerably up and down the Nile. This is thought to be due, not to a migration, but to seasonal concentrations of the local populations of Lates into limited reaches where conditions favour better oxygenation. The probable effects of climatic rhythms at Assuan, Khartoum, and Sennar upon this process are discussed in the light of the imperfect records available.