Effect of initial stocking size of the predatory African sharptooth catfish (Clarias gariepinus) on recruits, growth performance, survival and yield of mixed-sex Nile tilapia (Oreochromis niloticus) in concrete tank culture system

This article is available at www.Springerlink.comProlific breeding and production of high percentage of recruits are main problems in mixed-sex Nile tilapia (Oreochromis niloticus) culture in earthen ponds. The current study assessed the efficiency of different sizes of African sharptooth catfish (Clarias gariepinus) in controlling recruitment in mixed-sex Nile tilapia cultured in tanks and its effect on growth performance, percentage survival and yield. Three treatments consisting of triplicate ponds stocked with mixed-sex Nile tilapia in monoculture and in polyculture with large (62.50 ± 3.26 g) and small (40.00 ± 2.68 g) African sharptooth catfish were fed on a 297.50 g kg-1 crude protein diet for 126 days. Results showed that, the number of recruits was significantly lower in larger African sharptooth catfish predator than smaller ones and monoculture of Nile tilapia. Polyculture with larger African sharptooth catfish resulted in significantly higher growth performance of Nile tilapia. Large African sharptooth catfish in polyculture reduced the amount of small, low-value recruits, while the yield of large and high value Nile tilapia was increased. This study revealed that fish farmers can reduce prolific breeding, obtain higher growth performance and produce larger size of marketable Nile tilapia by predominantly stocking ponds with large African sharptooth catfish predator of at least 60 g.Tanzania Commission for Science and Technology (COSTECH) through ‘‘KILIMO KWANZA’’ programm

Monitoring climate change and anthropogenic pressure at Lake Tanganyika

The African Great Lakes are under threat from global and local environmental challenges including climatic change,water pollution and overfishing. To address those issues,managers need observations based on regularly monitored environmental indicators. However, environmental monitoring of the African Great Lakes is often lacking or not based on harmonised methods. The presentmanuscript is a case study based on Lake Tanganyika, impacted by climate change and anthropogenic pressure affecting water quality, fisheries and biodiversity changes. The implementation of environmental monitoring has often not been continuous or standardised among bordering countries. This prevents managers from taking data-based decisions and opens a risky field where speculation may overcome a rational approach. Long-term monitoring observations are essential to guide management measures to adapt to climate changes and decrease, whenever possible, unfavourable human impact on the Great Lake environment. A regionally standardised long-term monitoring programme is proposed. The sustainability of such monitoring requires that it remains inexpensive and focuses on a fewessential parameters. Its strength would be its uninterrupted implementation. Setting up a long-termintegratedmonitoring programme is also a goal of the Lake Tanganyika Authorities (LTA) with mandated national authorities and stakeholders. A Lake Tanganyika Regional IntegratedMonitoring Programme (LTRIEMP) needs to be widely encouraged and supported to ensure its sustainability. General principles from the Lake Tanganyika case study could be useful to develop a wider harmonised sustainable long-term regional monitoring network of the African Great Lakes in a multi-lakes collaborative approach

Adoption and consequences of new light-fishing technology (LEDs) on Lake Tanganyika, East Africa.

Maintaining sustainable fisheries requires understanding the influence of technological advances on catch efficiency, as technological creep can ultimately contribute to increased efficiency. Fisheries using light sources for attraction could be widely impacted by the shift to light emitting diode (LED) light systems. We studied the transition from kerosene lanterns to LED lamps in Lake Tanganyika, East Africa, examining factors that led to adoption as well as the impact of the new light sources on fish catch and composition. We used a combination of field experiments with catch assessments, fisher surveys, underwater light spectra measurements, and cost assessments to evaluate the impact of switching from kerosene to LED lamps. Overall, we found a very rapid rate of adoption of homemade outdoor LED light systems in Lake Tanganyika. Most of the batteries used to power these lamps were charged from the city power grid, rather than photovoltaic cells, although the potential exists for a reduction in greenhouse gas emissions. The LED light spectra was distinct from the kerosene light and penetrated much deeper into the water column. Regardless of light type, most of the fish caught within the two dominant species were below maturity. Although the LED lamps were associated with a slight increase in catch, environmental factors, particularly distance offshore, were generally more important in determining fish catch size and composition. The main advantages of the LED lamps were the lower operating costs and their robustness in bad weather. Thus, the primary effect of the use of battery-powered LED lighting systems to attract fish in Lake Tanganyika appears to reduce economic costs and increasing efficiency. However, overall the lake's fishery remains vulnerable to overfishing