The potential gross primary productivity of the mangrove stands at Kadolkele in Meegamuwa (Negombo) estuary was studied in relation to vegetation structure with a view to understanding the salient structural components that affect functioning of mangrove ecosystems. Structure of mangrove stands under study was characterized with plant species richness, plant (stem) density, frequency of occurrence of constituent species, plant basal area and height. The structural complexity index values calculated from above parameters revealed a statistically significant (p < 0.01) positive relationship with the potential gross primary productivity of the mangrove stands that has been calculated using data on absorption of photosynthetically active radiation (PAR) by the stands that were measured using a light meter with a quantum sensor. Leaf area index (LAI) values were calculated using absorption data and potential gross primary productivity was estimated using an assimilation coefficient. Mean values of structural parameters were used to ordinate the mangrove sites through principal component analysis. Ordination showed a productivity gradient among the mangrove sites where species richness, stem density, plant height and leaf area index were the key factors that affect potential gross primary productivity of mangrove stands.DOI: 10.4038/sljas.v13i0.2209Sri Lanka J. Aquat. Sci. 13 (2008): 95-108

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Asian sea bass (Lates calcarifer) is a high valued seafood throughout the world. Bacterial infections can cause huge losses in Asian sea bass culture and among them Aeromonas hydrophila is ubiquitous. Inclusion of bioactive compounds present in seaweeds into fish diets can enhance the fish growth and immunity combating the bacterial diseases. This study was conducted to determine whether feeding with Sargassum wightii incorporated feed could enhance immunity of the fish to bacterial infections. A feed trial was conducted using four treatments comprising a commercial feed, two formulated feeds incorporated with 20 g/kg and 40g/kg of S. wightii in each feed and a formulated feed without seaweed as the control diet. Three replicate tanks stocked with 15 advanced fingerlings were used for the each treatment and reared 40 days under the optimum conditions. Growth parameters were tested and effect of different feeds on growth performance was evaluated. Fish survival rate and cost of formulated feed were calculated. At the end of feed trial, nine fishes from each treatment were artificially challenged with 1.50 ppm dose of A. hydrophila and observed for 7 days. There was a significant difference in weight gain in commercial feed compared to other three treatments (P<0.05), while there was no significant difference in FCR and SGR among all experimental diets (P>0.05). The challenge with A. hydrophila showed 11.1% disease prevalence in L. calcarifer fed with 20g/kg of seaweed incorporated feed. Highest disease prevalence of 100% was recorded in fish that had been fed with the seaweed free formulation. The highest level of immunity enhancement was reported using the feed that contained 20g/kg seaweed. Production cost of formulated feed was lower than the commercial feed.

This study was conducted to evaluate the effects of different fertilization levels on growth performance of micro propagated water trumpet, Cryptocoryne wendtii to find the most suitable hardening medium. Micro-propagated ninety-six individual plants potted in the commonly used substrate of coir particles were used for the experiment and subjected to different fertilization levels of Albert's solution. Plants were potted just after being taken from the vessels and eight plant pots kept in the tanks (25.5 L water) containing 0.5 gL -1 , 1.0 gL -1 , and 2.0 gL -1 of Albert's solution, and fertilizer was not added into the control. Each treatment and control had three replicates and the experiment was conducted for nine weeks under natural light and temperature conditions. At the end of the experiment, plant growth performance in terms of plant height, root height, number of leaves etc. and water quality parameters were compared in One Way Analysis of Variance using SPSS (16.0). The electrical conductivity (EC) of the 0, 0.5, 1.0, 2.0 gL -1 treatments were 0.075, 0.75, 1.5, 3.0 µS/m, respectively. At the end of the experiment, plants grown in 0.5 gL -1 showed the best growth performance giving significantly highest plant height (11.77 ± 0.40 cm), root height (5.77 ± 0.03 cm), number of leaves (10.0 ± 0.3), number of roots (8.3 ± 0.3), wet weight of whole plant (0.3180 ± 0.0200 g), dry weight of whole plant (0.0206 ± 0.0003 g) and the largest leaf area (2.54 ± 0.01 cm 2 ) in compared to other two treatments and control. In contrast, the uptake of Albert's solution significantly increased with the increasing EC level. The results of this study revealed that, 0.5 gL -1 Albert's solution is the most suitable fertilization level among tested three fertilization levels for the hardening process of micro-propagated C. wendtii.