Fishing for Dagaa with 5 mm and 10 mm mesh nets: A comparison of length-frequencies and biological characteristics

Abstract

Two mesh sizes (5 and 10 mm) usually used to harvest Rastrineobola argentea in Lake Victoria were assessed from April to September 2001 to determine their suitability. It was observed that 13.2% of fish caught in 5 mm and 11.2% caught in 10 mm for April, May, June and July were of a size below maturity (44 mm standard length, [SL]). Mean size of fish caught with the 5 mm mesh was 46.8 ± 1.2 mm and that of fish caught with the 10 mm mesh was 46.8 ± 0.5 mm (SL). Catches per unit effort (CPUE) from the two meshes were not significantly different, with Haplochromis laparogramma (50.1%) dominating the catch followed by R. argentea (48.9%). Juveniles of Nile Perch, Brycinus jacksonii, Brycinus sadleri, and Barbus spp. (0.9%) were caught in small numbers. About half of the females matured at 43.5 mm and the males at 46.6 mm SL. Fish caught with the 5 mm mesh had on average 1050 ± 400 eggs and those caught with the 10 mm mesh had 918 ± 281 eggs, but the difference was not significant. However, a significant difference was noted between non-infected fish (1050 ± 400 eggs) and fish infected by the cestode Ligula intestinalis (663 ± 316 eggs). Given the absence of differences in key parameters under investigation between the fish caught with the 5 and 10 mm mesh sizes, the two meshes can be used interchangeably.

Keywords:

• net mesh size
• Lake Victoria
• Ligula intestinalis

Acknowledgements

The authors would like to thank Dr. Martin Van der Knaap, the Coordinator for Lake Victoria Fisheries Research Project (LVFRP) which provided the funds for this research. Thanks are also extended to Professor P. O. J. Bwathondi of Tanzania Fisheries Research Institute (TAFIRI) and to Mr. E. F. B. Katunzi the TAFIRI Mwanza Centre Director, for permitting the use of the necessary laboratory equipment at the Mwanza centre and for their continued support as immediate supervisors of this work.