Life history of South African snoek, Thyrsites atun (Pisces: Gempylidae): a pelagic predator of the Benguela ecosystem

Snoek (Thyrsites atun) is a valuable commercial species and an important predator of small pelagic fishes in the Benguela ecosystem. The South African population attains 50% sexual maturity at a fork length of ca.73.0 cm (3 years). Spawning occurs offshore during winter−spring, along the shelf break (150–400 m) of the western Agulhas Bank and the South African west coast. Prevailing currents transport eggs and larvae to a primary nursery ground north of Cape Columbine and to a secondary nursery area to the east of Danger Point; both shallower than 150 m. Juveniles remain on the nursery grounds until maturity, growing to between 33 and 44 cm in the first year (3.25 cm/month). Onshore– offshore distribution (between 5- and 150-m isobaths) of juveniles is deter-mined largely by prey availability and includes a seasonal inshore migration in autumn in response to clupeoid recruitment. Adults are found through-out the distribution range of the species, and although they move offshore to spawn—there is some southward dispersion as the spawning season progresses—longshore movement is apparently random and without a seasonal basis. Relative condition of both sexes declined dramatically with the onset of spawning. Mesenteric fat loss was, however, higher in females, despite a greater rate of prey consumption. Spatial differences in sex ratios and indices of prey consumption suggest that females on the west coast move inshore to feed between spawning events, but that those found farther south along the western Agulhas Bank remain on the spawning ground throughout the spawning season. This regional difference in female behavior is attributed to higher offshore abundance of clupeid prey on the western Agulhas Bank, as determined from both diet and rates of prey consumption.

Exploratory analysis of resource demand and the environmental footprint of future aquaculture development using Life Cycle Assessment

Increases in fish demand in the coming decades are projected to be largely met by growth of aquaculture. However, increased aquaculture production is linked to higher demand for natural resources and energy as well as emissions to the environment. This paper explores the use of Life Cycle Assessment to improve knowledge of potential environmental impacts of future aquaculture growth. Different scenarios of future aquaculture development are taken into account in calculating the life cycle environmental impacts. The environmental impact assessments were built on Food and Agriculture Organization statistics in terms of production volume of different species, whereas the inputs and outputs associated with aquaculture production systems were sourced from the literature. The matrix of input-output databases was established through the Blue Frontiers study.

Life history and behaviour of Indian prawns

Studies on life history and behaviour of prawns form an essential background for the understanding of the disposition of their fisheries and for the formulation of effective methods of exploitation and measures of conservation.

Life history of prawns: a review of recent studies with special reference to Indian species

The paper contains a brief review of the studies on the life histories of Indian species of prawns chiefly belonging to the family Penaeidae. References to similar work carried out outside India are furnished where significant variations have been observed. The three main larval stages viz., Nauplius, Protozoea and Zoea (Mysis) and their important characteristics, including modes of locomotion, are described. The post-larval development of one species that has been studied in detail (Metapenaeus dobsoni) is indicated in outline. Some aspects of the bionomics of these prawns, especially breeding and migration, are also briefly dealt with in view of their relevance in their life cycle. An outline of the life histories of some Palaemonid prawns of both fresh water and marine habitats is added at the end and the need for well- planned investigations in regard to species of such economic value as Palaemon carcinus (Macrobrachium rosenbergii) is indicated.

Storage life of silverbelly (Leiognathus sp.) with delayed icing

Silver belly (leiognathus splendens) caught in September spoiled faster than the fish caught in May. This could be due to seasonal changes. For silver belly, Total Volatile Base (TVB) value could be used as a measure of spoilage. At the beginning of spoilage TVB value is between 30-40 mg. N/100g sample. The main spoilage for silver belly appears to start between 6 and 8 hours (at 28° C-30°C) after landing on board. Therefore it is not necessary to ice silverbelly immediately; it seems to be sufficient if icing can be done within 6 hours of landing on board.

Increase of storage shelf life of locally produced salted/dried fish by redrying and/or packeting

Experiments were undertaken to prolong the storage life of salted/dried fish by re-drying and/or packing. The storage life under normal conditions is 51 days; re-drying the fish at 50°C for 12 hours extends the storage life only by 7 days. However, re-drying and packing gizzard shad (Gonialosa manminna ) in polyethylene maintains the fish in excellent conditions for well over 87 days. The use of air tight bags for storing good quality salted dried fish is recommended.

Management of the nile perch, Lates niloticus, fishery in Lake Victoria in light of the changes in its life history characteristics

Nile perch, Lates niloticus Linnaeus, 1758, is a predatory fish of high commercial and recreational value. It can grow to a length of 2 m and a weight of 200 kg. In Uganda, Nile perch was originally found only in Lake Albert and the River Nile below Murchison Falls. The species is, however, widely distributed in Africa, occurring in the Nile system below Murchison Falls, the Congo, Niger, Volta, Senegal and in Lakes Chad and Turkana (Greenwood 1966).