Relating the slot size regulation to the sizes of Nile perch maws for trade

Abstract

Fish maw refers to swim bladder extracted from fish and processed in fresh/dry form. The maws had for long been regarded as a waste of Nile perch processing however, maws have become the most profitable product of the Nile Perch. In Uganda, the size of the Nile perch fish accepted for harvest is determined by the total length of fish. However, maw traders determine the value of fish maws based on its weight. This drove the need for studying the relationship between the sizes of fish and maws in order to determine the right size of maws that should be traded basing on the slot limits sizes of fish that is allowed for harvest to ensure sustainability of the fishery. The study comprised of 150 Nile perch fish obtained randomly from fishers at Bugonga landing site on Lake Victoria. Measurements of fish weights were done using a weighing scale and the weights of maws were measured using an electronic weighing scale while length of fish and maws were measured using a tape measure. Seven maws from fish measuring 50 cm TL and 4 maws from fish measuring 85 cm TL were processed into dry maws after which, each of the maws were measured separately for their weight The findings of the study revealed a high positive relationship between weight of fish and length of fish (R2 = 0.95; p= 0.05;). The same relationship trend was observed between length of maws and the length of fish (R2 = 0.81; p=0.05). Similarly, a positive relationship was also observed between weight of maws and the length of fish (R2 = 0.91; p=0.05), the same relationship was observed between weight and length of maw (R2 = 0.77; p= 0.05). The mean weight and length of fresh Nile perch maws from minimum slot limit size were 171.4 mm and 34g, respectively whereas mean length and weight of fresh maws from maximum slot size were 260.5 mm and 130.25g, respectively. The mean weight of dry maws from minimum slot limit size was 7.57g whereas the mean weight of dry maws from maximum slot limit was 29.5g. Based on the slot limit sizes regulation of the Nile perch fishery, the acceptable minimum size of maws that can be sustainably traded in is 34g and 170mm for fresh maws and 8g for dry maws. To protect large female tilapia that are important in population regeneration, the maximum size of fresh maws that can be sustainably traded in should not exceed 260.5 mm or 130g while dry maws should not weigh more than 30g.