Semi-intensive aquaculture of giant freshwater prawn, Macrobrachium rosenbergii (de Man) in Sri Lanka is limited mainly due to unavailabilty of suitable commercial feeds. At present, the widely used commecial feed is poultry feed starter-I, which is of low nutritive value. Present study was therefore carried out to develop a suitable feed using currently unutilized material as the protein source namely, cattle intestines disacrded from slaughter houses, mussel meat discarded after removing shells for lime and poultry industries, and trash fish discarded at landing sites.Post-larvae of M. rosenbergii having an initial weight of 44-78 mg were stocked in glass tanks measuring 60 cm x 30 cm x 30 cm at a stocking density of 50 individuals per tank and fed with formulated experimental feeds and the poultry feed starter-I as the control diet. Feeding experiments were carried out in triplicate in two culture cycles of 90 days each.Specific growth rates of post-larvae when fed with experimental feeds formulated with mussel, trash fish and cattle intestines as the protein source were 2.08, 2.07 and 2.03 in the first culture cycle and 2.25, 2.27 and 2.33 in the second culture cycle respectively. These were significantly higher than those observed when fed with the control diet which were 1.36 and 1.39 in the first and second culture cycles respectively (p < 0.05). Higher specific growth rates resulted in significantly higher weight gains in post-larvae fed with experimental feeds (458-898 mg) than in those fed with the control diet (217-318 mg) (p<0.05). Survival rates of post-larvae fed with experimental feeds (42-52%) were significantly higher than those of the post-larvae fed with the control diet (16-24%) whereas food conversion ratios of the former (2.47-3.22) were significantly lower than those of the latter (4.90-5.02) (p < 0.05).Present study indicates that lower amounts of feeds formulated using mussel meat, trash fish or cattle intestines as the protein source yield better growth and 18 K.W.R.R. Amaraweera et al. / Sri Lanka J. Aquat. Sci. 18 (2013): 17-26 © Sri Lanka Association for Fisheries and Aquatic Resources survival rates of M. rosenbergii post-larvae than the currently used poultry feed starter-I. Since discarded material are used as the protein source, the cost of feed will also be low resulting in high profits.

The present study was carried out from May 2001 to August 2001 to investigate the diversity, distribution and environmental interactions of mangrove crabs in the Kadolkele mangrove ecosystem associated with the Negombo estuary in the west coast of Sri Lanka. The data on diversity and abundance of crabs, salinity, pH, organic carbon content, moisture and temperature of the soil, ambient air temperature and floral species of mangrove were collected from three 10 m x 50 m belt transects laid perpendicular to the shore. Of the six species of crabs found in the study area, five were identified up to species level. They were Episesarma versicolor, Sesarma smithii, Sesarma guttatum, Metopograpsus thukuhar and Metopograpsus messor. This is the first record of Metopograpsus thukuhar and Sesarma guttatum in Sri Lanka. Diversity of crabs decreased with the increasing distance from the lagoon but the number of crabs present did not vary significantly (p > 0.05). The distribution of the crabs varied with the increasing distance from the lagoon. S. smithii and M. messor were distributed throughout the 50 m distance while M. thukuhar and the unidentified species were restricted to 0-20 m and 0-10 m from the lagoon respectively. E. versicolor and S. guttatum were found towards the landward side (25-50 m). The distribution of S. smithii showed a positive correlation (p < 0.05) with the soil salinity and soil moisture content while M. thukuhar, S. guttatum and E. versicolor showed negative correlations (p < 0.05). All species except E. versicolor showed a positive correlation with soil organic carbon content (p < 0.05). M. thukuhar showed a negative correlation with soil pH while S. guttatum and S. smithii showed a positive correlation (p < 0.05). M. thukuhar and unidentified juvenile crabs were found restricted to Rhizophora/Bruguiera zone, while E. versicolor and S. guttatum were confined to the Avicennia /Lumnitzera zone.

Ahslrnct : Sonie aspects of reproductive biology of the mud crab, Scylln serrnta in the Negonlbo estuary were studied by screening bi-weekly samples over a period of one year. The study revealed that the size of the female crab at first maturity was 12 cm and the estimated pre-spawning and post-spawning fecundities were around 3 and 1.5 nlillion respectively. The ova mature at the size of about 3001im and are found in three batches indicating a partial spawning behaviour. Spawning occurs in two seasons, April and August. The sex ratio was uneven in most size groups and in most months of the year. About 85% of the comn~ercial catches comprise immature females.

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The present study was carried out during the period from May to July 2014 to assess the vegetation pattern and to estimate biomass of the mangroves in Irakkandy Lagoon, Trincomalee. Five belt-transects of 10 m in width were laid perpendicular to the shoreline. Data were collected on tree diameter at breast height (dbh) and tree height from each sub-plot (100 m 2 ) in belt transects using standard methods. Above ground biomass, basal area and relative density of the mangroves were also estimated. Diversity and evenness of each sub-plot was calculated using Shannon-Wiener diversity index and Pielou's evenness index respectively. Results revealed that the study site is composed of 5 true mangrove species and highest density was recorded for Avicennia marina (414 trees/ha, 700 saplings/ha, 2354 seedlings/ha), followed by Lumnitzera racemosa, Excoecaria agallocha, Rhizophora apiculata and Heritiera littoralis. The greatest mangrove diversity (1.28) was observed in subplot 1 of transect 2. The least mangrove diversity (0) was found in transect 5. There is a significant difference among transects concerning the diversity and evenness (P<0.05). The results showed that Avicennia marina was the dominant species with Height (H) and dbh of 3.65±1.43 m and 5.06±1.07 cm respectively, followed by Lumnitzera racemosa (3.36±1.19 m and 5.81±1.06 cm, Excoecaria agallocha (4.92±2.45 m and 5.31±1.93 cm), Rhizophora apiculata (4.56±1.70 m and 4.89±0.96 cm) and Heritiera littoralis (8.80±0.849 m and 26.50±4.95 cm). The above ground biomass of Lumnitzera racemosa was recorded as 8334.89 kg/ha and Avicennia marina was recorded as 1361.13 kg/ha. Species diversity (H') of whole mangrove area studied was 0.86 and evenness (E) was 0.54. It reveals that Irakkandy Lagoon consists of fairly high biological diversity (Diversity index=0.86) of mangroves and extremely valuable for stability of the ecosystem.