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Fish passes. Design, dimensions and monitoring.










FAO/DVWK. Fish passes. Design, dimensions and monitoring. Rome, FAO. 2002. 110p.


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    Book (stand-alone)
    The decrease in aquatic vegetation in Europe and its consequences for fish populations (1987) 1987
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    A diverse aquatic vegetation is essential to maintain a diverse fish fauna. The fish is an important part of a complex network of relations between nutrients, phytoplankton, epiphytes, herbivorous invertebrates, the aquatic vegetation and fish. In Northwest Europe and North America and probably in the rest of the industrialized world, the (submersed) aquatic vegetation (macrophytes) is rapidly disappearing from eutrophicated waters. The decrease is well documented. As a consequence of abun dant growth of epiphytes, which are better competitors for inorganic carbon and light in highly eutrophicated waters than submersed aquatic macrophytes are, the condition of the aquatic vegetation becomes worse. Shallow, eutrophic, relatively clear water that is rich in water plants, can change to phytoplankton dominated turbid water, within short time. This change may occur without a remarkable increase in the actual nutrient loading. Invertebrate grazers like snails, macrocrustaceans and cl adoceran zooplankters are able to protect aquatic macrophytes against the negative effects of this competition by removing epiphytes and phytoplanktonic algae. As a man predator on invertebrates, the fish indirectly influences the well-being of the aquatic vegetation. There is evidence that aquatic macrophytes are the source of biochemical compounds that negatively affect the growth of algae (allelopathy) and attract grazers. These processes are mainly found in model systems and under semi-na tural conditions. Their ecological significance still has to be tested in the field.A situation with turbid, phytoplankton dominated, water without aquatic vegetation can continue after removing nutrients from effluents because: (i) blue-green algae (phytoplankters) may excrete toxic substances, negatively affecting the growth of aquatic macrophytes; (ii) abundantly occurring young fish, but also invertebrate animals like mysids, prey on the bigger (phytoplankton grazing) cladocerans; (iii) acid rain, polluted bottom sediments and/or bird flocks contribute to the nutrient loading of a water body. Restoration techniques are: lowering the nutrient loading in combination with protection of the remaining stands of reed, replanting of aquatic plants, creation of artificial refugia for zooplankton and manipulation of young-of-the-year fish populations. Chemical and mechanical control of "nuisance" growth and heavy stocking with herbivorous fish including the common carp (Cyprinus carpi o) have to be omitted or executed very carefully to avoid phytoplankton-dominated turbid water. In small systems with "nuisance" growth, stocking (50-150 kg/ha, max. 250 kg/ha) with grass carp (Ctenopharyngodon idella) can improve the water quality.
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    Policy brief
    Modernizing irrigation for fisheries biodiversity and ecosystem services 2023
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    In the Lower Mekong Basin, expansive irrigation systems have disrupted aquatic habitats, notably obstructing fish migration essential for biodiversity, ecosystem health, and local food security. Despite a shift from expanding to modernizing these systems, current efforts rarely prioritize ecological considerations, largely due to a lack of intersectoral coordination. Engineering solutions, like fish ladders, have emerged as effective tools for restoring river connectivity and fish migration. For instance, successful fish ladder projects in Lao PDR and ongoing initiatives in Cambodia illustrate their potential benefits. Many countries in the Mekong region are beginning to incorporate fish migration considerations in their infrastructure policies. However, transitioning from policy to practice demands increased capacity-building, coordinated efforts, and stakeholder engagement. This brief highlights the need for adaptive management, underpinned by research, as essential for ensuring that infrastructure development remains ecologically sustainable and benefits communities reliant on fisheries.
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    Book (series)
    Review of fisheries and aquaculture development potentials in Georgia. 2010
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    The present document is a follow-up to previous FAO technical assistance efforts in the sustainable development and management of the fishery and aquaculture sector in Georgia. It aims to call attention to and provide evidences of the fact that fisheries and aquaculture have substantial development potentials in Georgia. The country is rich in both marine and inland water resources, but the potentials of the fishery and aquaculture sector are far from being exploited. The country could multiply its fish production through improvements in the administration and supervision of marine fisheries and through enhanced implementation of the rules and regulations of inland fisheries together with a reliable culture based fisheries supported by well managed hatcheries. The review emphasizes that efficient and sustainable exploitation of potentials requires the concerted and coordinated attention and actions of decision makers in the government administration and all actual and potential s takeholders of the Georgian fisheries and aquaculture sector. In order to achieve a tangible improvement, the following entry points have been identified and actions proposed: In the field of marine capture fisheries quick action is needed on assistance, to obtain export certification for fresh and processed Black Sea anchovy and to upgrade and optimize the fisheries inspection. Facilitating investment loans for the fishing fleet is another urgent task. The most obvious entry points for the deve lopment of inland fisheries and aquaculture are: finalization of the databases of surface water resources, survey of fish farm facilities, establishment of a reliable fish seed production network and rehabilitation of selected Sturgeon Hatcheries. In sector management, an updated administrative structure and upgraded Georgian fisheries laws and regulations could fix existing loopholes and provide for sustainable development and responsible management of aquatic resources. The review also pres ents the widest possible range of data and information in order to facilitate the identification and utilization of further areas of fisheries and aquaculture development in the country. To that end, detailed lists of actual and potential natural and social resources are presented and discussed, together with the most important determining factors of sector administration, management and business performance.

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