A method for estimating the instantaneous mortality rate (Z) is presented which was developed from a truncated equation for average length. The model has zero bias at equilibrium, but has no explicit solution for Z so that its solution requires a numerical method.
Egypt's aquaculture production (705,490 tonnes in 2009) is by far the largest of any African country and places it 11th in terms of global aquaculture production. The aquaculture sector in Egypt is now a mature one having developed over a period of more than 30 years, but the financial performance of the sector is not well understood or documented, even though value-chain analysis provides a methodological tool to do so.
Details are given of the current database system used by the Collaborative Research Support Programme in PondDynamics/Aquaculture and Its Management. Suggestions are made regarding the design of a database.
In many countries, resource conflict is a leading risk to livelihoods. For some communities, it is a matter of survival. Yet, many development interventions aiming to address these challenges fail or fall far short of their potential. Common reasons include conflicting agendas, power and politics; poor local commitment and leadership; lack of coordination; plus high costs and low sustainability, as programs often unravel when development finance ends.
The article features two most commonly techniques for gene transfer in fish, microinjection and electroporation.
In many developing countries, availability of suitable tags for use in genetics and aquaculture research has been a problem as they are often expensive and have to be imported from other countries. A simple and inexpensive method used by scientists in Ghana that can be tried and improved by others is described in this article.
Comparative methods are presented which allow for quick and relatively reliable growth parameter estimates when growth data are not at hand. One of these methods involves the use of a newly developed "auximetric grid." An empirical equation for the estimation of natural mortality of any fish stock, given a set of growth parameters, is briefly reviewed. The methods are applied to data from the Gulf of Thailand trawl fishery, and the mortality caused by this fishery is estimated.
A method is presented through which the total mortality undergone by several fish stocks of the same species can be compared when growth parameters are poorly known or unknown. Whereas the estimate of Z obtained via the length-converted catch curve is highly sensitive to the input parameters K and L sub( infinity ), the ratio of Z estimates obtained for different stocks with the same combination of parameters is almost independent of these inputs, at least when the fit of the linear regression is good.
The use of length-structured methods for the assessment of fish stocks is reviewed in relation to the present status of tropical fisheries science. It is concluded that these methods, which emerged largely as a result of the development of sophisticated, yet relatively cheap, programmable calculators and microcomputers, will enable significant advances to be made in assessment of tropical stocks.