African Journal of Fisheries Science

African Journal of Fisheries Science ISSN 2375-0715 Vol. 8 (3), pp. 001-009, March, 2020. © International Scholars Journals

Full Length Research Paper

The status of mangrove mud crab fishery in Kenya, East Africa

Esther N. Fondo*, Edward N. Kimani and Dixon O. Odongo

Kenya Marine and Fisheries Research Institute, P. O. Box 81651 – 80100, Mombassa, Kenya.

Accepted 07 November, 2019

Abstract

Mangrove mud crabs, Scylla sp. are among crustaceans of commercial value along the Kenyan coast and in many mangrove areas in the Western Indian Ocean region. In Kenya the crabs are landed by artisanal fishermen. Rising population in the coastal areas and high demand for the crabs has led to increased pressure on the crabs. The population structure and maturity stages of Scylla serrata from Ngomeni - Fundisa area of Malindi were investigated from July 2005 to July 2006. The size of crabs caught ranged from 50 to 125 mm carapace length, with crabs of 75 mm carapace length dominating. Male crabs dominated in the captured population. Linear relationships were obtained for both female and male crabs for the Carapace length - Carapace width. The size at first maturity was at 75 and 70 mm carapace length for male and female crabs respectively. There is an indication of exploitation pressure on the population and to ensure sustainable management, regulation on the minimum size of the crabs to be caught is recommended.

Key words: Malindi, mangroves, maturity stages, mud crab, population structure, Scylla serrata.

African Journal of Fisheries Science ISSN 2375-0715 Vol. 8 (2), pp. 001-007, February, 2020. © International Scholars Journals

Full Length Research Paper

Zooplankton-based assessment of the trophic state of a tropical forest river

ImoobeTunde Ohiokhioya Thadeus* and Adeyinka Muideen Lekinson

Department of Animal and Environmental Biology, University of Benin, Benin City, Edo State, P. M. B. 1154, Nigeria.

Accepted 15 October, 2019

Abstract

In this study, we explored the usefulness of zooplankton as a tool for assessing the trophic status of a Nigerian forest river. The river was sampled monthly and investigated for water physico-chemistry and zooplankton community structure using basic statistical measurement of diversity indices to characterize the zooplankton fauna. The trophic status of the river evaluated from the physico-chemical parameters indicates that the river is oligotrophic. The zooplankton composition was typical of a tropical freshwater river, with a total of 40 species made up of 16 rotifers, 12 cladocerans and 12 copepods and their developing stages in the following order of dominance; Rotifera > Cladocera > Cylopoida > Calanoida. The zooplankton community was dominated by numerous species of rotifers and crustaceans, which are typical of oligotrophic to mesotrophic systems, amongst these includes Conochilus dossuarius and Synchaeta longipes. However, the most dominant zooplankton species in West Africa freshwater ecosystems namely, Keratella tropica, Keratella quadrata, Brachionus angularis, Trichocerca pusilla, Filinia longiseta, Pompholyx sulcata, and Proales sp. amongst others which are indicator species of high trophic levels were not recorded in the river. We therefore, conclude based on these facts that the river is clear, oligotrophic and it can be used for all manner of recreational activities.

Key words: Trophic status, zooplankton, forest river.

African Journal of Fisheries Science ISSN 2375-0715 Vol. 8 (2), pp. 001-009, February, 2020. © International Scholars Journals

Full Length Research Paper

Reproductive performance, egg and larval quality and egg fatty acid composition of hatchery-reared Spotted Babylon (Babylonia areolata) broodstock fed natural and formulated diets under hatchery conditions

S. Sangsawangchote¹, N. Chaitanawisuti²* and S. Piyatiratitivorakul¹

¹Department of Marine Science, Faculty of Science, Chulalongkorn University, Phya Thai Road, Bangkok, Thailand.

²Aquatic Resources Research Institute, Chulalongkorn University, Phya Thai Road, Bangkok, Thailand.

Accepted 19 October 2019

Abstract

A 120 day feeding trial was conducted to evaluate the reproductive performance, egg and larval quality and egg fatty acid composition in Spotted Babylon (Babylonia areolata) broodstock fed with natural food (fresh meat of carangid fish, Seleroides leptolepis,) and one of four experimental formulated diets containing 5 or 15% of dietary lipid from either tuna oil or a mixture of tuna oil and soybean oil (6:4) labeled as 5% TO, 15% TO, 5% MO and 15% MO respectively. Using trash fish as a control food resulted is the lowest levels of in 20:5 n - 3, 22:6 n - 3 and 20:4 n - 6 fatty acids compared to those of all experimental diets, while the highest contents of those fatty acids were found in the 5% TO diet. Statistically significant differences in reproductive performance between dietary treatments with the best reproductive performance were found only for females fed the 5% TO diets, but egg and larval quality showed no variability among females fed trash fish and all experimental diets. No significant differences were observed in the survival duration in the starvation tolerance test for females fed trash fish or any of the experimental diets. However, the fatty acid profile of egg capsules was significantly affected by the dietary treatments. The levels of major fatty acids (20:5 n - 3, 22:6 n - 3 and 20:4 n - 6) in egg capsules produced from females fed diets containing 5% tuna oil (5% TO) was significantly higher than those from females fed trash fish or other experimental diets. We therefore conclude that formulated diets resulted in successful reproduction and high essential fatty acids in egg capsules comparable to the use of trash fish.

Key words: Babylonia areolata, broodstock diet, reproductive performance, egg and larvae quality.

African Journal of Fisheries Science ISSN 2375-0715 Vol. 8 (1), pp. 001-005, January, 2020. © International Scholars Journals

Full Length Research Paper

Study of the natural and fishing mortality and exploitation rates of bigeye kilka (Clupeonella grimmi) in the southeast part of the Caspian Sea (Babolsar)

Ghasem Karimzadeh

Administer of Fishing Office, Mazandaran Province, Fisheries Administration, Babolsar, Iran. E-mail: [email protected]. Tel: 00989111152191. Fax: 00981125231452.

Accepted 09 October, 2019

Abstract

The natural, fishing and total mortality survival and exploitation rates of bigeye kilka were studied. The survival rate and natural mortality were calculated using catch curve and Pauly methods, respectively. Natural and fishing mortality have been estimated up to 0.881 and 0.309 yr^-1, respectively. According to the catch curve method, the annual survival rate of bigeye kilka has been estimated to be 0.304 yr^-1. Owning to this survival rate, the instantaneous coefficient of the total mortality of bigeye kilka has been estimated up to 1.19 yr^-1, while the exploitation rate of bigeye kilka has been estimated up to 0.260. The catch amounts of bigeye kilka decreased gradually mainly due to overfishing, predators and ecological disturbances which occurred in the Caspian Sea. Using the conclusion of this study and the previous studies of other researchers, it is suggested that the population of bigeye kilka were overexploited in the past years and were vulnerable to their natural predators.

Key words: Clupeonella.grimmi, natural mortality, fishing mortality, total mortality, survival rate, exploitation rate.

African Journal of Fisheries Science ISSN 2375-0715 Vol. 7 (11), pp. 001-008, November, 2019. © International Scholars Journals

Full Length Research Paper

Aquaculture ponds, a Jamaican study: The impact of birds on fish production

S. Seian Morrison* and Peter Vogel

Department of Life Sciences, University of the West Indies, Mona Kingston 7, Jamaica, West Indies.

Accepted 19 July, 2019

Abstract

The increasing use of freshwater fish farms by water birds poses conservation and economic problems as birds compete with man. This study sought to assess bird species diversity of an artificial wetland and the impact of birds on Tilapia production. The farm had a relatively high diversity (0.714) as 16 species of birds foraged on the farm as either residents or visitors each day. Eight of these birds were previously identified as problem species on aquaculture farms and may result in large losses in fish crops. Predation loss per grow-out period (PLOP) was calculated to be 20.92% for the fish farm and was due mainly to the Brown Pelican, Great Egret, Least Tern and Snowy Egret. This was 2.95% less than the average loss per pond and may be higher as loss due to Black-crowned Night Herons at nights was not assessed. There was a positive correlation with success, fish density and distance from the farm house. The findings indicate that bird predation has a negative impact on Tilapia production. Farm construction, stocking densities, the length of the grow-out period, and the use of non-lethal depredation strategies are important factors in reducing loss associated with bird predation.

Key words: Tilapia, aquaculture, negative impact, predation, water birds.