Mortality rates estimates for Metapenaeus monoceros (Fabricius) of Maputo Bay

The species Metapenaeus monoceros in Maputo Bay recruits to the fishery almost all over the year, but the main recruitment occurs over a short period of time, each year, during April-May. Growth curves were constructed by following the progression of modes over a period of time. The von Bertalanffy growth parameters were estimated as L∞=31.9 mm and K(monthly)=0.25, for males, and L∞=48.3 mm and K(monthly)=0.14, for females (Brinca and Sousa, 1984). Using data on growth and length composition of the catches, the following methods were applied to estimate mortality rates of M. monoceros: estimation of natural mortality by using approximative methods; use of c.p.u.e. data; catch curves; cohort analysis; average age and length methods.

Livelihood and seed mortality related vulnerability of carp seed traders of Bangladesh

Carp seed traders in Bangladesh are considered as one of the poorest, most vulnerable and least studied sub-population. Millions of fingerlings are transported annually to various parts of the country using bus tops and/or truck-beds in open and hand agitated method by the traders and as a result they encounter mass seed mortality. They are the key players in augmenting aquaculture activities by distributing fish fry and fingerlings to the fish farmers. Assessment of the seed sources and the livelihood of the traders are important to identify their point of entry to the aquaculture sector and further improvement. Status of household asset, income profiles, and risks involved were examined using DFID's sustainable livelihood approach (SLA) framework. Tools used to collect data included group discussions (GD), semi-structured and structured household (HH) survey. Samples (n=637) were randomly drawn purposefully from 10% of the carp seed traders within 11 districts. Sampled HH were classified into six land classes.

Identification of causes of Thai pangas mortality in ponds and their control strategies

Mass mortality of Thai pangas (Pangasius hypophthalmus) is reported to be a big threat to monoculture of the species in Bangladesh. Twenty affected and twenty control Thai pangas ponds were investigated around Mymensingh district in order to identify the causes of pangas mortality. Sixty affected and sixty unaffected fish samples were examined and compared to find the fish-level variables associated with the disease. A range of haemorrhagic signs on snout, skin and fins were recorded during examination with naked eyes. Aeromonas spp. and Edwardsiella spp. were isolated from 87% and 80% of the affected fish, respectively. Even 4% of the seemingly healthy fish carried Aeromonas spp. on their skin. Among the four water quality parameters monitored, remarkably higher total ammonia (1.5 ppm) was found in water of the affected ponds compared to that of the unaffected ones (0.4 ppm). High ammonia in affected water caused by excessive organic decomposition and poor pond management might have reduced the immunity of fish, which predisposed them for bacterial invasion and consequent disease outbreak.