River-based cage aquaculture of tilapia in Northern Thailand : sustainability of rearing and business practices

Whereas most studies of cage culture have been carried out in ponds, lakes or reservoirs, cage-based aquaculture in rivers and other public water bodies raises issues of natural resource management that are closer to fisheries management than aquaculture in fish ponds on private land. This paper analyzes an emerging industry in the Upper Ping River in northern Thailand which helps serve the large and growing demand for farmed fish in Chiang Mai. Farmers appear to pay attention to environmental and market factors that pose risks to profitability of their operations, as good water quality means aquaculture can continue

Longitudinal river zonation in the tropics: examples of fish and caddisflies from endorheic Awash river, Ethiopia

Primary Research PaperSpecific concepts of fluvial ecology are well studied in riverine ecosystems of the temperate zone but poorly investigated in the Afrotropical region. Hence, we examined the longitudinal zonation of fish and adult caddisfly (Trichoptera) assemblages in the endorheic Awash River (1,250 km in length), Ethiopia. We expected that species assemblages are structured along environmental gradients, reflecting the pattern of large-scale freshwater ecoregions. We applied multivariate statistical methods to test for differences in spatial species assemblage structure and identified characteristic taxa of the observed biocoenoses by indicator species analyses. Fish and caddisfly assemblages were clustered into highland and lowland communities, following the freshwater ecoregions, but separated by an ecotone with highest biodiversity. Moreover, the caddisfly results suggest separating the heterogeneous highlands into a forested and a deforested zone. Surprisingly, the Awash drainage is rather species-poor: only 11 fish (1 endemic, 2 introduced) and 28 caddisfly species (8 new records for Ethiopia) were recorded from the mainstem and its major tributaries. Nevertheless, specialized species characterize the highland forests, whereas the lowlands primarily host geographically widely distributed species. This study showed that a combined approach of fish and caddisflies is a suitable method for assessing regional characteristics of fluvial ecosystems in the tropicsinfo:eu-repo/semantics/publishedVersio

Effects of replacing fishmeal with wastes derived from local fisheries on the growth of juvenile tilapia, <i>Oreochromis niloticus</i>

A feeding trial was conducted to investigate the effects of partially and totally replacing fishmeal with by-product derived from local fisheries on growth performances of tilapia <i>(Oreochromis niloticus)</i>. Tilapia fingerlings (average initialweight 0.38±0.05 g) were fed with 5 different diet formulas composing of fish meal protein replacement levels of 0%, 25%,50%, 75, and 100%. Tilapia were raised in 80 x 80 x 80 cm3 hapa in an earthen pond for 8 weeks. Each treatment contained3 replications. No feeding trial was applied as negative control. The result showed that fish by-product powder could substitute for fishmeal on a crude protein basis at a level of not more than 25%. As a result, feed cost can only be cut down approximately 3 US cents/kg. Specific growth rate, weight gain, survival rate and feed conversion ratio were not significantly different between the fish fed with the 75% and 100% fishmeal containing diets (P>0.05). The outcome would beapplied to reduce the solid wastes from fish processing and partially replace the imported fishmeal. This can also be used as guideline for farmers in small communities to produce their own tilapia feed