Challenges in sustaining and increasing fish production to combat hunger and poverty in Asia

Fish and fisheries make a major contribution to nutritional security and the fight against hunger and poverty in Asia. An additional 37 million t of food fish will be needed by 2020 to meet the needs of the growing population, changing dietary habits and increasing income levels. Production from capture fisheries has reached a plateau, with most fisheries having reached their maximum sustainable yields or being overexploited. A number of challenges need to be addressed if the present production from capture fisheries is to be sustained and aquaculture production increased to bridge the gap between the supply and the growing demand for fish. This needs the commitment of governments to implement policies that foster growth of fisheries and aquaculture and to allocate adequate human and financial resources to the development of the sector.

A computer software package for assessing and managing risks posed by experiments with genetically modified fish and shellfish

Assessment and management of risk is needed for sustainable use of genetically modified aquatic organisms (aquatic GMOs). A computer software package for safely conducting research with genetically modified fish and shellfish is described. By answering a series of questions about the organism and the accessible aquatic ecosystem, a researcher or oversight authority can either identify specific risks or conclude that there is a specific reason for safety of the experiment. Risk assessment protocols with examples involving transgenic coho salmon, triploid grass carp and hybrid tilapia are described. In case a specific risk is identified, the user is led to consider risk management measures, involving culture methods, facilities design and operations management, to minimize the risk. Key features of the software are its user-friendly organization; easy access to explanatory text, literature citations and glossary; and automated completion of a worksheet. Documented completion of the Performance Standards can facilitate approval of a well designed experiment by oversight authorities.

Fish seed production and marketing in northeast Thailand

In northeast Thailand, fish seed production by private hatcheries is being encouranged by the Department of Fisheries. Dissemination of technical knowledge to hatcheries has considerably improved fish seed availability over the last decade, which has stimulated the adoption of fish culture.

Production-related risk in rice-fish culture: a target MOTAD analysis

The article is a summary of the preliminary results of an AFSSRN-funded study on Risk Programming of Rice-Fish Production Systems in the Philippines conducted early 1993 by the AFSSRN-CLSU team. The results show that rice-fish culture leads to a higher rice production compared to rice monoculture.

Markets, marketing and production issues for aquaculture in East Africa: the case of Uganda

Aquaculture is currently responsible for an insignificant proportion of total fish production in Uganda. However, given the increasing demand for fresh fish in urban and peri-urban araes, and threats to the supply of fish from natural catch fisheries, the potential exists for a strong market in aquaculture. Small-scale fish farmers located relatively close to markets or all-season roads, and who can supply consistent and high quality produce, will have the widest range of marketing opportunities, and will likely be within the area of operation of potential traders and intermediaries that deliver fish to markets. Fish farmers that are not close to roads, or produce unreliable quantities and variable quality products may face high transaction costs of marketing their product, and decreasing net returns to production. The authors found that significant on-farm labor, and access to input markets are important factors leading to positive net returns to fish production. Areas with high population density and relatively low wages will be well suited to labor intensive aquaculture. The authors concluded that aquaculture development has good potential in certain areas of Uganda and should therefore be pursued as a potential development pathway. However, policy makers should consider the importance of the price of fresh fish relative to the cost of labor, as well as other factors including the importance of smallholder credit and access to extension services, when directing investments in aquaculture technology.

A preliminary study on the feasibility of using fenced brushparks for fish production in Lake Chilwa, Malawi

A study to investigate the feasibility of using fenced brushparks for fish ranching in Lake Chilwa was conducted for five months at the Kachulu Harbor. In a water depth of 1.4 m enclosures constructed from bamboo sticks embedded in the sediment and surrounded by a 13 mm seine net, were filled with three different subrates (Typha, bamboo, and Sesbania branches) and a no substrate enclosure served as a control. Netting materials contributed 57 per cent towards the total cost (US$ 0.24-0.30/m2) of brushpark contruction. Fish productivity was highest in the Typha, bamboo and control treatments and lowest in the Sesbania treatments. The decomposition of substrates did not affect water quality. The results indicate that enclosed brushparks may be a feasible technology for enhancing fish yields and providing alternative income sources to fisherfolk in small lakes and water bodies.

Physico-chemical factors and bacteria in fish ponds

Analyses of pond water and mud samples show that nitrifying bacteria (including ammonifying bacteria, nitrite bacteria, nitrobacteria and denitrifying bacteria) are in general closely correlated with various physico-chemical factors, ammonifying bacteria are mainly correlated with dissolved oxygen; denitrifying bacteria are inversely correlated with phosphorus; nitrite bacteria are closely correlated with nitrites, nitrobacteria are inversely correlated with ammoniac nitrogen. The nitrifying bacteria are more closely correlated with heterotrophic bacteria. Nitrobacteria are inversely correlated with anaerobic heterotrophic bacteria. The correlation is quite weak between all the nitrite bacteria which indicates that the nitrite bacteria have a controlling and regulating function in water quality and there is no interdependence as each plays a role of its own. The paper also discusses how the superficial soil (pond mud down to 3.5 cm deep) and different layers of the mud affect the biomass of bacteria. The study shows that the top superficial layer (down to 1.5 cm deep) is the major area for decomposing and converting organic matter.

Length-fecundity relationships of Nigerian fish populations

Parameters of the exponential body length (L)-fecundity (F) relationship of the form F=a.L super(b) are presented for 47 populations and 26 species of Nigerian fishes. Estimates of b varied between 1.563 (Ilisha africana) and 5.771 (Barbus callipterus) with a mean of 3.054 (s.d. = 1.024). The maximum sizes of fish populations examined did not significantly influence the relative magnitudes of b. The parameters Alpha and Beta of the linear length-fecundity relationships of the form F = Alpha + BetaL are also presented for five fish populations. Estimates of Beta ranged from 243.5 (Chrysichthys walkeri) to 1,334,895 (Tilapia mariae).

Growth performance of Nigerian fish stocks

Parameters of the von Bertalanffy growth function are presented for 42 fish stocks belonging to 16 families, 22 genera and 27 species. The growth performance index, Phi '(= log K + 2logL sub( infinity )), was computed for each stock and was found to be highest in male Gymnarchus niloticus (Gymnarchidae) from Lake Chad and lowest in Chrysichthys auratus (Bagridae) from the Cross River. Mean Phi ' for major fish genera and families are also presented and was highest in brackishwater fishes, closely followed by freshwater and inshore marine water fishes.

Weight-fecundity relationships of Nigerian fish populations

Parameters a and b of the power body weight (W) - fecundity (F=a W super(b)) are presented for 25 populations comprising 15 species of Nigerian fishes. Estimates of b varied between 0.511 (Parauchenoglanis akin) and 1.654 (Periophthalmus barbarus) with a mean of 1.087 (s.d.=0.520). The maximum weight of populations examined did not significantly influence the relative magnitude of b. The parameters proportional to and beta of the linear weight-fecundity relationship (F= proportional to + beta W) are also presented for 27 fish populations from 22 species. Estimates of beta ranged from 4.22 (Chromidotilapia guntheri) to 2,062.94 (Pellunula min), with a mean of 243.80 (s.d.=477.89). The magnitude of beta declined with increasing maximum weights of fishes examined.

Identification of Sex and Female’s Reproductive Stage in Commercial Fish Species through the Quantification of Ribosomal Transcripts in Gonads

The estimation of maturity and sex of fish stocks in European waters is a requirement of the EU Data Collection Framework as part of the policy to improve fisheries management. On the other hand, research on fish biology is increasingly focused in molecular approaches, researchers needing correct identification of fish sex and reproductive stage without necessarily having in house the histological know-how necessary for the task. Taking advantage of the differential gene transcription occurring during fish sex differentiation and gametogenesis, the utility of 5S ribosomal RNA (5S rRNA) and General transcription factor IIIA (gtf3a) in the molecular identification of sex and gametogenic stage was tested in different economically-relevant fish species from the Bay of Biscay. Gonads of 9 fish species (, Atlantic, Atlantic-chub and horse mackerel, blue whiting, bogue, European anchovy, hake and pilchard and megrim), collected from local commercial fishing vessels were histologically sexed and 5S and 18S rRNA concentrations were quantified by capillary electrophoresis to calculate a 5S/18S rRNA index. Degenerate primers permitted cloning and sequencing of gtf3a fragments in 7 of the studied species. 5S rRNA and gtf3a transcript levels, together with 5S/18S rRNA index, distinguished clearly ovaries from testis in all of the studied species. The values were always higher in females than in males. 5S/18S rRNA index values in females were always highest when fish were captured in early phases of ovary development whilst, in later vitellogenic stages, the values decreased significantly. In megrim and European anchovy, where gonads in different oogenesis stages were obtained, the 5S/18S rRNA index identified clearly gametogenic stage. This approach, to the sexing and the quantitative non-subjective identification of the maturity stage of female fish, could have multiple applications in the study of fish stock dynamics, fish reproduction and fecundity and fish biology in general.

18S rRNA V9 metabarcoding for diet characterization: a critical evaluation with two sympatric zooplanktivorous fish species

The potential of the 18S rRNA V9 metabarcoding approach for diet assessment was explored using MiSeq paired-end (PE; 2 9 150 bp) technology. To critically evaluate the method's performance with degraded/digested DNA, the diets of two zooplanktivorous fish species from the Bay of Biscay, European sardine (Sardina pilchardus) and European sprat (Sprattus sprattus), were analysed. The taxonomic resolution and quantitative potential of the 18S V9 metabarcoding was first assessed both in silico and with mock and field plankton samples. Our method was capable of discriminating species within the reference database in a reliable way providing there was at least one variable position in the 18S V9 region. Furthermore, it successfully discriminated diet between both fish species, including habitat and diel differences among sardines, overcoming some of the limitations of traditional visual-based diet analysis methods. The high sensitivity and semi-quantitative nature of the 18S V9 metabarcoding approach was supported by both visual microscopy and qPCR-based results. This molecular approach provides an alternative cost and time effective tool for food-web analysis.

Length-weight relationships of fish from the lagoon of New Caledonia

Length-weight relationships of 335 species of fish of New Caledonia, belonging to 65 families of coral reef fishes, were computed (80%) or assembled from the literature (20% of all cases) to facilitate, among other things, estimation of coral reef fish biomass from visual census.