The gillnets selectivity of <i>Citharinus citharus</i> (Pisces: Citharinidae), <i>Distichodus rostratus</i> (Pisces: Distichodontidae), <i>Hydrocynus forskalii</i> (Pisces: Characidae) and <i>Synodontis membranaceus</i> (Pisces: Mochokidae)

Abstract

Studies on selectivity of gillnets multi-mesh for four fish species Citharinus citharus, Synodontis membranaceus, Distichodus rostratus and Hydrocynus forskalii in Lake Kainji North-West Nigeria were conducted. A total of 383 fish were selected during the experimental fishing. The master selectivity curve was determined for four species that had at least 16 samples per net type. The length used for probability estimation was the standard length (mm) of the fish caught. The master selectivity curves of the four gillnet types used for the four most dominant species caught (Citharinus citharus, Synodontis membranaceus) were skewed distribution and (Distichodus rostratus and Hydrocynus forskalii) had two peaks. The minimum selection length for these species caught was not the same for each of the four gillnet type. The gillnet had a narrower selection range that skewed to the left or right, a higher modal and median length showed larger individual species being entangled in the net. In contrast, strong selectivity was characteristic of species, which tend to ‘wedge' in gillnets. Whereas smaller stretched mesh size (Particularly 50.8 and 63.5mm) and even the larger sizes of 76.2 and 88.9mm gillnets caught significant numbers of illegal sized fish.


Keywords: Citharinus citharus, Synodontis membranaceus, Distichodus rostratus, Hydrocynus forskalii, gillnet selectivity, Lake Kainji.


Nigerian Journal of Fisheries Vol. 5 (1) 2008: pp. 49-62