Adaptive aspects of bioenergetics in sexual and asexual species of fresh-water triclads

The effects of temperature and starvation on 3 species of freshwater triclad with contrasting life cycles, distribution and methods of reproduction were investigated, to examine the relative merits of each species' strategy in relation to its environment. The 3 species - Polycelis tenuis (Iijima), Polycelis felina (Dalyell) and Dugesia tigrina (Girard) - were cultured at 5°, 10°, 15° and 20°C, under fed and starved conditions. Food intake, respiration, growth and reproductive rates, were measured for each species under each set of conditions. A study of a population of P. felina was also undertaken to seek information on field conditions. The results from fed triclads show that in general food intake, and growth and respiration rates, increase with temperature. At low temperatures (below 15°C), D. tigrina ingests little food, and growth and respiration rates are much lower than in the 2 other species. Similarly tigrina does not reproduce below 15°C, confirming its thermophilic nature. P. tenuis is more temperature sensitive than P. felina. In P. tenuis, food intake, and growth and respiration rates, reach a maximum at 20°C, whereas they are greatest in P. felina at 15°C. These differences between the 2 species are reflected in the higher Q10 values observed in P. tenuis. During starvation, the exponential rates of degrowth increase with temperature. Except for D. tigrina at 5°, 10° and 15°C, respiration rates are significantly lower in starved than in fed individuals. The respiration rates also increase with temperature, although this is less pronounced in P. felina than in P. tenuis or D. tigrina. In all 3 species, reproduction ceased soon after the onset of starvation. The field study of P. felina identified seasonal changes in temperature and food supply. An examination of potential mortality factors demonstrated that predation was likely to be negligible, and that death was most likely to occur through being washed away. In conclusion, it was suggested that the indigenous asexual reproducer (P. felina) was successful because it was eurytolerant, and because it occurred in streams where biotic stress (i.e. competition and predation) was low. Under such circumstances, the adoption of a low cost method of reproduction such as fission, was argued to be prudent. In contrast, D. tigrina, the immigrant asexual reproducer, could compete successfully with indigenous populations of lake-dwelling triclads such as P. tenuis by growing and reproducing at a very high rate

Aquaculture: a rapidly growing and significant source of sustainable food? Status, transitions and potential

The status and potential of aquaculture is considered as part of a broader food landscape of wild aquatic and terrestrial food sources. The rationale and resource base required for the development of aquaculture are considered in the context of broader societal development, cultural preferences and human needs. Attention is drawn to the uneven development and current importance of aquaculture globally as well as its considerable heterogeneity of form and function compared with established terrestrial livestock production. The recent drivers of growth in demand and production are examined and the persistent linkages between exploitation of wild stocks, full life cycle culture and the various intermediate forms explored. An emergent trend for sourcing aquaculture feeds from alternatives to marine ingredients is described and the implications for the sector with rapidly growing feed needs discussed. The rise of non-conventional and innovative feed ingredients, often shared with terrestrial livestock, are considered, including aquaculture itself becoming a major source of marine ingredients. The implications for the continued expected growth of aquaculture are set in the context of sustainable intensification, with the challenges that conventional intensification and emergent integration within, and between, value chains explored. The review concludes with a consideration of the implications for dependent livelihoods and projections for various futures based on limited resources but growing demand

Use of cassava in livestock and aquaculture feeding programs

This report reviews and reassesses the present state of knowledge concerning the use of cassava products in livestock and aquaculture feeds. An ultimate objective of summarizing these data is to provide a foundation for establishing reliable and practical guidelines by which more efficient utilization of cassava products and byproducts may enhance livestock and aquaculture feeding programs, particularly in West Africa

The evolution of aquaculture feed supply systems

First paragraph: As any fish farmer knows, feed is usually the most important variable production cost. A simple objective is therefore to minimize waste from uneaten food, which has the added benefit of reducing the risk of environmental degradation. However, decreasing feed level risks reducing growth rate, leadìng to a rise in other costs per unit of production. The optimum biological feeding rate is thus rarely the same as the optimum economic rate. In practice, these calculations are complicated as feed requirement and efficiency of conversion varies with changing environmental conditions including water temperature, oxygen concentration, water quality, current speed, light intensity and day length. Feed utilisation also varies with diet quality and physiological factors such as age/size, life-stage, stress level and endogenous rhythms. lt is therefore not surprising that these factors contrìbute towards an element of uncertaìnty regarding the amount of feed required, often leading to under or over feeding of stock and resultant under performance of the system

Can aquaculture benefit the extreme poor? A case study of landless and socially marginalized Adivasi (ethnic) communities in Bangladesh

AbstractThe Adivasi Fisheries Project, aimed at diversifying livelihood options for resource-poor Adivasi (ethnic) communities in the North and Northwest of Bangladesh, was implemented during 2007–9. Aquaculture and related technologies were introduced to a total of 3594 resource-poor Adivasi households. Baseline and end-line surveys were applied to assess the changes in their livelihoods following intervention. Household incomes of project participants rose significantly (p≤0.01), which was attributed to the increased share of aquaculture and related enterprises from 15% in 2007 to nearly 30% in 2009 in terms of annual household incomes. By contrast, the contribution of aquaculture to household incomes remained virtually unchanged (p>0.05) among non-project participants. The monthly frequency of fish, meat and egg consumption increased between 2007 and 2009 (p≤0.01), confirming improved food and nutrition security among project participants. Although non-project participants also slightly increased their fish consumption, it remained significantly lower (p≤0.01) than that of the project participants. The results from the present study contradict the prevailing view that aquaculture is inappropriate for landless, socially marginalized and extremely poor communities by demonstrating its relevance to improving livelihoods, provided that a diversified approach is followed and interventions are tailored to needs and capabilities of target households

The Role of Fish in the First 1,000 Days in Zambia

Fish is especially rich in essential omega-3 long-chain polyunsaturated fatty acids and micronutrients, including bioavailable calcium, iron and zinc. Fish features prominently in the diet of most, especially poor, Zambians. Despite this, its significance in the diet of women and children in the first 1,000 days is not well understood. Our current knowledge of the nutrient content of commonly consumed fish species in Zambia is synthesised. The importance of fish in food and nutrition security of rural and urban households and the impact of intra-household distribution on nutrient intake from fish, especially among pregnant and lactating women and children 6–23 months of age, are explored in this article. Key knowledge gaps are identified, and research priorities are highlighted. Recommendations are provided on policy, communications and technological initiatives to maximise the role fish can play in the First 1000 Most Critical Days Programme in Zambia