Organic pollution in culture water resulting from excess feed and metabolite buildup

Penaeus monodon postlarvae were subjected to increasing feed concentrations and their growth and survival rates were recorded. Measurements were made of dissolved organic matter, and ammonia and nitrite-nitrogen concentrations. Survival was highest at the lowest feeding level and decreased as feed concentration increased. It is concluded that although organic matter enriches the food supply for P. monodon postlarvae, at higher concentration levels it can pollute the culture water, which in turn leads to mass mortality of the postlarvae. Secondly, the survival rate of P. monodon postlarvae is directly related to dissolved organic matter concentration, oxygen tension, and ammonia-nitrogen concentrations in the culture water. Even at sublethal levels these adverse environmental conditions decrease the survival rate.

Inactivation of Vibrio parahaemolyticus in drinking water

A study was conducted in the Cochin area of India to determine the effect of drinking water on Vibrio parahaemolyticus, a bacterium that contaminates fish harvested from marine and estuarine environments. Times of fresh-water exposure required to inactivate these bacteria are given. Findings indicate that the washing of fish and equipment used to handle the fish in drinking water may decrease in the number of viable Vibrio cells and thus aid in prevention of food poisoning.

Copper and manganese forms in Lake Edku sediments, Alexandria, Egypt

Lake Edku is one of the Nile Delta lakes. It is subjected to contaminations by several anthropogenic materials such as trace elements and other wastes. The distribution of the different chemical forms of copper and manganese has been studied using sequential extraction techniques. Chemical analysis of the sediments shows that CaCO sub(3) ranged from 3.7% to 9.6% and organic matter from 3.06% to 8.11%. The results indicate that the distribution of manganese among the six chemical forms in the sediments of the lake obeys the following order: Mn-residual>Mn-carbonate>Mn-moderately reducible>Mn-organic form>Mn-exchangeable > Mn-easily reducible fraction. Also, the data revealed that more than 50% of the total manganese was found in the residual form, while the remainder was distributed among the other forms. In contrast, more than 70% of the total copper content was associated with the five chemical forms (exchangeable, carbonate, easily and moderately reducible and organic forms). Generally, the enrichment of manganese in the residual form revealed the important role in building up of clay minerals, while the distribution of copper among the different forms reflects an important role in biological and biochemical processes.

Identification of mesopelagic fish (with emphasis on major family) in Iranian water of the Oman Sea

This project was done for identifying the mesopelagic fish of the Iranian waters of Oman Sea, during two year from 2008 to 2010. The specimens were collected using two trawler vessel from nine station. All the specimens were fixed in formalin then in 70% alcohol and carried to the laboratory. In total of 19 species belonged to 14 families of 6 orders identified including: Echinorhinidae, Stomidae, Phosichthyidae, Synodontidae, Paralepididae, Myctophidae, Acropomatidae, Priacanthidae, Pentacerotidae, Champsodontidae, Gempylidae, Trichiuridae, Nomeidae and Congridae. Of which 17 species were identified up to species level including: Echinorhinus brucus, Bathophilus indicus, Chauliodus sloani, Harpadon nehereus, Lestrolepis japonica, Benthosema pterotum, Diaphus garmani, Diaphus effulgens, Bolinichthys photothorax, Acropoma japonicum, Synagrops adeni, Cookeolus boops, Histiopterus typus, Champsodon sagittus, Neoepinnula orientalis, Trichiurus lepturus, Cubiceps baxteri. Vinciguerria was identified up to genus level because only one specimen caught during the survey and one species (Congridae) was identified up to family level because only 3 specimens of this fish in early stage of life were caught and their characters were not suitable for identify up to species level. The highest species belong to Myctophidae family of Myctophiformes order.

Study on biological characteristics, sexual maturation and reproduction of Liza abu in the water of Khozestan Province

As the most of the fish resources are known and exploited, protecting their generation is of the greatest importance. Aquaculture is one of the efficient procedures in protecting and reviving fish resources and knowing about the reproductive cycle and gonads development has an important role in approaching this aim. Liza abu belongs to the family Mugilidae that according to its resistance to the environmental condition and its fast growth , can be introduced as a fish with economical value. As there is no scientific data on the reproductive biology of this species , study on the reproductive biology and gonad development is considered as the aim of this research . For this purpose , 360 samples of this species were investigated during the period from February 2007 to January 2008 in Khozestan Province . After studing morphological and histological characteristics of gonad specimen , they were prepared through histological method. Samples were prepared through usual histological method and studied under light microscope. According to the results, the maturity stages of male and female Liza abu were separated to six different successive stages. In ovaries , these stages were as follow : In stage І, the oocytes were small , this stage was observed from July to October . In stage ІІ, considerable growth was observed in the oocytes . This stage was observed from October to January . In stage III, due to vitellogenesis, the maximum growth was observed and three layers of theca, granullosa and follicle cells were visible. This stage was observed during January and February . In stage IV, migration of germinal vesicle was observed and due to hydration of the oocytes , their diameter was increased. The ovaries were yellowish and in maximum size and ovules could be easily observed with naked-eye . This stage was observed in February and March . In stage V, spawning occured. This stage was observed in April . In stage VI, ovaries consisted of immature and atretic oocytes and also empty follicles. This stage was observed in May and June. In testes , these stages were as follow : In stage I , the testes were small in size and contained the spermatogonia which were the only cellular components.This stage was observed in August and September . In stage II (maturing virgin ) , the spermatogonia and the primary spermatocytes were visible. This stage was observed in October . In stage III (developing), intensive spermatogenesis was occured and the primary and the secondary spermatocytes were the most visible cells during this stage .This stage was observed from November to January. In stage IV(developed), cells of all stages of spermatogenesis could be seen but the secondary spermatocytes and spermatids were in large number. This stage was observed from January to March. In stage V , the testes were filled with sperms. This stage was observed in March and April .In stage VI, residual spermatozoa and the spermatogonia were visible in the testes. This stage was observed from May to August. According to cyclic changes in GSI, sexual maturation in breeding begins in January and spawning occurs in April. The ova diameter ranged from 30.75 μ in stage I to 472.19 μ in stage IV. In this study , the sex ratio was 1:2.7, and male and female percentage were 27.02% and 72.98% respectively. This means that females predominate males. In this study absolute fecundity was calculated and changing between 30805.44 to 431247.3 was observed and absolute fecundity was calculated 111275.3 in average.

Distribution of endangered native fish fauna and their conservation in Lake Victoria

Lake Victoria in East Africa, supports socio-economically important fisheries for more than 30 million inhabitants in the lake basin. The lake had until the 1970's a diverse fish assemblage dominated by haplochromines species which formed at least 83% of the fish biomass (Kudhongania & Cordone 1974). The more than 500 haplochromine species in Lake Victoria, over 99% of them endemic, exploited virtually all the food sources in the lake (Witte and van Oijen 1990). Each species had its own unique combination of food and habitat preference (Goldschmidt et al., 1990).

The decline of Alestes baremose Boulenger, 1901 and Hydrocynus forskahlii (Cuvier, 1819) stocks in Lake Albert: implications for sustainable management of their fisheries

The fish stocks of Lake Albert face immense exploitation pressure which has led to “fishingdown” of their fisheries, with some larger species having been driven to near-extinction, while others such as Citharinus citharus have almost disappeared. Both A. baremose (Angara) and H. forskahlii (Ngassia) historically formed the most important commercial species in Lake Albert until the early 2000s but recent Catch Assessment Surveys (2007-2013) revealed a sweeping decline in their contribution to the commercial catch from 72.7% in 1971 to less than 6% in 2013. The catch per unit effort also registered a two-fold decline from 45.6 and 36.1 kg/boat/day to 22.6 and 18.1 kg/boat/day for A. baremose and H. forskahlii respective between 1971 and 2007. Over 50% of illegal gillnets, below the legal minimum limit of four inches (101.6 mm) used on Lake Albert target the two species. Gillnet experiments found the three inch (76.2 mm) gill net mesh size suitable for sustained harvest of the two species. The study concludes that optimal utilization of the two species and probably other non target fish species is achievable through species specific management strategies, coupling species specific licensing, and controlling harvest of juvenile individuals, overall fishing effort and fish catch on Lake Albert and protecting the vulnerable fish habitats.

Fish species diversity, and the biology and ecology of common fish species in Lake Albert

Lake Albert contributes about 10% to the national fish production. It supports a multi-species fishery based on endemic species. To local fishermen, Lake Albert is a lifeline providing food and income.

The evolution of the fishery of Oreochromis niloticus (Pisces : Cichlidae) in Lake Victoria

The Lake Victoria ecosystem has experienced changes associated fishing levels, arise in lake level of the 1960s, fish introductions and human activities in the drainage basin. Following the fish introductions of the 1950s and 1960s, niloticus has become the most abundant and commercially important species among the tilapiines. It appears to be the only species which has managed to co-exist with the Nile perch not only in Lake Victoria but also in Lake Kyoga where the two species were also introduced. There is, however, little published information on the biology and ecology of the species in the habitats. It has therefore been found necessary to initiate studies as have been developed for Lates niloticus, especially as the two species have assumed major role in the lake's fisheries.

Trolling for Nile perch (Lates niloticus) in Lake Kyoga

Nile perch were introduced into Lake Kyoga in the mid·1950s from Lake Albert. Murchison Falls on the River Nile, between the two lakes, prevented Nile Perch and other elements of the typical nilotic fish population from naturally reaching Lake Kyoga. The introduction has been successful and considerable stocks of Nile Perch now exist in Lake Kyoga. In 1967, 13,000 tons of Nile Perch were estimated to have been landed by the commercial fishermen, fish of 200 lb. being now caught and specimens of 100 lb. being fairly common. Large Nile perch are caught commercially on long lines baited with live Protopterus' spp. or Clarias spp. Large mesh gillnets uccasionally take Nile Perch of up to 30 lb., but the high cost of the nets does not, at the moment, appear to justify this method of fishing; a 10 in. net, stretched 100 yards long (unmounted). 15 meshes deep and 60-ply nylon. costs approximately U. Shs. 300. The long·lines used are extremely simple and cheap to make, but considerable labour is needed to catch bait. Small Protopterus are normally caught by turning over floating rafts of grasses and papyrus, and extracting the fish from the root mass; this is hard and dirty work. Other small fish, more readily available, do not, according to fishermen, work as well, possibly because they are not as durable as the Protopterus or Clarias. Dead bait is never used.

Observations on the taxonomy and biology of Lates (Cuvier 1828) in Lake Albert

Both in terms of commercial landings and biological importance, the Nile Perch is one of the most prominent fish in Lake Albert. It can bear considerable further exploitation, is the source of stockings elsewhere, and it is, therefore, important to know whether more than one species is being dealt with, and, if so, what differences there are in the ecology of the different species.

Freshwater medusae in Lake Kyoga

Freshwater medusae have been observed in Lake Kyoga by several members of the Fisheries Department on a few isolated occasions over the past two years. Sightings have been made at Lwampanga at the western end of the lake, at Bukungu near the inlet of the River Nile into Lake Kyoga, and at Lalle, on the eastern extremity of the main lake. Most sightings have been made near the margin of the lake under very calm conditions. At Lalle and Lwampanga large numbers of medusae have been seen swimming near the surface; on these occasions, the medusae were pulsating regularly and maintained a position within a few inches of the surface. Apart from noting that sightings have occurred under calm conditions near the lake margin, no other observations to indicate when medusae are likely to be seen have been made. Most of the medusae are of similar size, the largest being 12 mm in diameter.

The feeding of three commercially important fish species in Lake Chilwa, Malawi

The diets of the three species of fish that predominate in the Lake Chilwa fishery are described in relation to various parameters using a semi-quantitative method of analysis of the digestive tract contents. Barbus paludinosus Peters fed during the day on zooplankton, non-filamentous green algae and some higher plant material; small fish fcd predominately on zooplankton but with increasiug size the diet was more varied. Clarias mossambicus Peters fed throughout the day and night and had a highly varied diet with fish becoming the major food item in large fish, Tilapia shirana chilwae Trewawas fed mainly during the day on higher plant material, filamentous green algae and zooplankton; smaller fish fed predominately on zooplankton. The importance of flexibility in the diet of the three fish species is stressed.

The potential for clupeid fishery in Lake Kainji, Nigeria

The potential for a clupcid fishery in Lake Kainji has been examined using both experimental fishing samples and the results obtained from those of the commercial fishermen. A total annual production of 1,400 tons has been estimated. In money terms, this amounls to N198.800 (£99,400) per annum. This production has been sustained by the abundant zooplankton food available the year round on the lake. Recommendations for the effective methods of cropping clupeids were made, bearing in mind the need to maintain the fishery on a sustained yield basis. The place of c1upeids in the ecology of the lake was examined and on the basis of the evidence available it was recommended that Pellonula afzeluisi could be exploited on a large commercial scale without any adverse effects on the fishery in the lake.