A preliminary study on the response of mangrove mud crab (Scylla serrata) to different feed types under drivein cage culture system

Abstract

The populations in coastal areas in east Africa have increased dramatically in the last decades, resulting in increased pressure on coastal resources. The examples are declining fish catches, deteriorating conditions of coral reefs and reduction of mangroves forests. The objective of the study was to asses the potential of grow-out Aquaculture of mud crabs Scylla serrata, as an alternative livelihood for resource-poor coastal communities. Growth rate and survival of mud crabs (S. serrata) cultured in individual drive-in cages (30 x 30 x 30 cm) located in the mangrove forests dominated by Rhizophora mucronata were evaluated. The effect of feed (Terebralia pallustris - gastropod meat, fish offal and mixture of the 2) was determined in a completely randomised design. Feeding was done at 10% body weight at incoming tide throughout the experimental period of 120 days. Monthly sampling was employed and total weight (g), cheliped length (cm), carapace length (cm) and width (cm) were measured. The study aimed at establishing the growth rate, moulting and mortality of crabs fed using locally available feeds. A total of 180 drive-in cages were used for the experiment giving 60 replicates for each treatment. Drive-in cages were built with "fitos" and grouped in sets of 10 for easy management. Crab seed stock of 50 - 380 g for the experiment were bought from artisanal fishermen. Application of ANOVA and post-hoc test revealed that crabs fed with mixed feed had significantly higher % growth (47.9%) compared to fish offal (33.4%) but were similar to gastropod meat (43.2%) p < 0.05. Growth rate was significantly affected by feed type, where higher values were recorded in mixed feed diets (gastropod meat and fish offal, 1.29 g/day) compared to the individual feeds (0.96 and 0.97 g/day for fish offal and gastropods meat respectively. There was no significant difference in growth of monosex crabs female (0.996 - 1.55 g/day) and males (0.893 -1.01 g/day) p = 0.373.