Structural environmental enrichment, that is, a deliberate addition of physical complexity to the rearing environment, is sometimes utilized to reduce the expression of the undesirable traits that fish develop in captivity. Increasing demands and regulations regarding usage of enrichment to promote fish welfare also make investigations on the effects of enrichment important. Here, we sythesize the current state-of-the-art knowledge about the effects of structural environmental enrichment for fish in captive environments. We find that enrichment can affect several aspects of the biology of captive fish, for example, aggression, stress, energy expenditure, injury and disease susceptibility. Importantly, these effects are often varying in direction and magnitude, and it is clear that just addition of structure is not a solution to all problems in fish rearing. Each species and life stage needs special consideration with respect to its natural history and preferences. A multitude of different enrichment types has been investigated and many studies investigate several enrichment components at the same time, making comparisons among studies difficult. To the present date, the majority of efforts have been directed to investigate salmonid fish in stock-fish hatcheries and cichlids from a basic research perspective. Some contexts are under-studied with respect to environmental enrichment, for instance effects on results in basic research and welfare effects in display aquaria. There are many research opportunities left within this field. However, future studies could utilize experimental designs which make it possible to discriminate between effects of different environmental manipulations to a higher degree than what has been performed to this date.

Environmental enrichment for fish in captive environments: effects of physical structures and substrates

P>1. Freshwater conservation has received less attention than its terrestrial or marine counterparts. Given the accelerated rate of change and intensive human use that freshwater ecosystems are submitted to, it is urgent to focus more attention on fresh waters. Existing conservation planning tools - such as Marxan - need to be modified to account for the special nature of these systems. Connectivity plays a key role in freshwater ecosystems. Threats are mediated along river corridors, and the condition of the entire catchment influences river biodiversity downstream. This needs to be considered in conservation planning.

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Addressing longitudinal connectivity in the systematic conservation planning of fresh waters

It reflects solely the views of its authors. The views, conclusions, and recommendations are not intended to represent the views of the Commission. The views of the Commission are laid out in the Commission's final report "Dams and Development: A New Framework for Decision-Making". Executive Summary iii Chapter 1 Introduction 1 Biodiversity 1 Status of the world's freshwaters 2 Status of the world's biodiversity 3 Large dams 6 The value of biodiversity 7 Chapter 2 Patterns of freshwater biodiversity 9 Longitudinal gradients 10 Latitudinal gradients 10 Moist-arid gradients 10 'Hotspots': areas rich in species and endemics 10 Phylogenetic and ecological diversity 14 Alien (exotic) species 14 Chapter 3 Impacts of dams on biodiversity 15 Species movements up and down stream 15 Movement of matter up-and downstream 16 Lateral impacts 17 Upstream 18 Downstream 23 Water basin connections 25 Estuarine and marine impacts 25 Interaction with non-dam impacts 27 Summary of dam impacts 27 Cumulative effects 39 Dam effects relative to other sectors 40 Prospects for freshwater biodiversity 40 Chapter 5 Impacts of dams vis à vis standards 47 Chapter 6 Recommendations on dams and biodiversity 49 Avoid areas of high biodiversity. 49 Minimise impacts of dam projects 49 ii Enhance situations at extant dams 50 Use of landscape management 50 Environmental standards 51 Chapter 7 Beyond dams: other solutions 53 Acknowledgements 54 References 55 iii Executive summary Although occupying a smaller area compared to land and oceans, freshwaters are home to a relatively high proportion of species, with more per unit area than other environments (10% more than land and 150% more than the oceans). While only about 45,000 species of freshwater animals, plants and microorganisms have been scientifically described and named, scientists estimate that at least an additional million more species remain to be named. Freshwater biodiversity is unevenly distributed. High numbers of species or endemics are found, for example, in the Amazon, Congo, Nile and Mekong basins. Such species-rich areas are called 'hotspots' and dominate other patterns or trends. Already human uses of freshwater threaten the survival of freshwater, brackish, coastal and terrestrial biodiversity. The global level of threat for mainly terrestrial vertebrates is 11-25%, while for freshwater groups it is 13-65%. While this paper focuses on the impacts of large dams on freshwater biodiversity, the significant effects of large dams on terrestrial biodiversity should not be overlooked. About 60% of the world's river flow is regulated. There …

Biodiversity impacts of large dams

Why do captive-reared fishes generally have lower fitness in natural environments than wild conspecifics, even when the hatchery fishes are derived from wild parents from the local population? A thorough understanding of this question is the key to design artificial rearing environments that optimize post-release performance, as well as to recognize the limitations of what can be achieved by modifying hatchery rearing methods. Fishes are generally very plastic in their development and through gene-environment interactions, epigenetic and maternal effects their phenotypes will develop differently depending on their rearing environment. This suggests that there is scope for modifying conventional rearing environments to better prepare fishes for release into the wild. The complexity of the natural environment is impossible to mimic in full-scale rearing facilities. So, in reality, the challenge is to identify key modifications of the artificial rearing environment that are practically and economically feasible and that efficiently promote development towards a more wild-like phenotype. Do such key modifications really exist? Here, attempts to use physical enrichment and density reduction to improve the performance of hatchery fishes are discussed and evaluated. These manipulations show potential to increase the fitness of hatchery fishes released into natural environments, but the success is strongly dependent on adequately adapting methods to species and life stage-specific conditions.

Environmental effects on behavioural development consequences for fitness of captive-reared fishes in the wild

Influence of salinity on the life-history traits of the West African black-chinned tilapia (Sarotherodon melanotheron): Comparison between the Gambia and Saloum estuaries

Fish distribution in relation with environmental variables was investigated in the Boubo River, a coastal river in Ivory Coast. Fourty freshwater fish species belonging to 17 families and 26 genera were captured. Five brackish water species, two introduced species and one hybrid complete the list. Seven species are reported for the first time in this river. A significant correlation between species distribution and environmental variables was found. Rocky and leaves-dead wood substrates, oxygen, canopy closure, width, depth and velocity were the main environmental variables influencing fish distribution. Our findings are opposed to the tendency for species composition to increase from the source to the mouth of the river, which is probably due to two major human activities (dam construction and discharge of waste of palm oils and motor oils in the main channel). These activities could constitute in the future a real threat for the fish population and other aquatic organisms.

Fish diversity and its relationships with environmental variables in a West African basin

The diet of the brackish water tilapia Sarotherodon melanotheron is studied in various riverine and lacustrine systems of the Bia River basin (Cote d'Ivoire). Comparison of the diet between sampling sites (upper course, lower course and man-made Lake Ayame) shows significant differences. In the man-made lake, prey described as preferential include Asterionella (Bacillariophyceae) and Bosmina(Cladocera). In the lower course, the preferential preys are represented by Lyngbya(Cyanophyceae) while in the upper course Lyngbya and chironomid larvae are preferential. These differences are related to the altered environmental conditions generated by the construction of the dam on the Bia river main stream. In the man-made lake, there is no shift in diet either with the seasons (dry and rainy seasons) or with size.

Food habits of brackish water tilapia Sarotherodon melanotheron in riverine and lacustrine environments of a West African coastal basin

Données sur la reproduction d'un tilapia estuarien (Sarotherodon melanotheron) isolé dans un lac de barrage ouest-africain

The stomach contents of 170 little tunny, Euthynnus alletteratus, sampled between June 2003 and December 2004 were examined. Fish size ranged from 27 to 81 cm fork length, and all fish were caught in gillnets deployed over the continental shelf off Cote d’Ivoire (West Africa). The type and quantity of prey ingested changed seasonally. Outside the major upwelling period the diet was more varied. Overall, fish were the dominant prey of all sizes of little tunny, far exceeding crustaceans, of which shrimps and prawns were commonest but were not found in the stomachs of juveniles (,42 cm FL) or larger adults ( 53 cm FL). Little tunny are carnivorous fish that feed opportunistically. A relationship was found between the size of the prey and the size of the predator.

Food composition and feeding habits of little tunny (Euthynnus alletteratus) in continental shelf waters of Côte d'Ivoire (West Africa)

La composition et la distribution du peuplement ichtyen de la riviere Go en Cote d'Ivoire sont etudiees pour la premiere fois. Cette etude s'integre dans une etude de reference des peuplements piscicoles qui a pour but d'estimer un eventuel impact des activites humaines d'une facon generale sur la composition de la faune piscicole. Quarante especes ont ete recoltees. Les resultats tendent a montrer une zonation longitudinale qui correspond a un accroissement de la richesse specifique du cours moyen vers l'aval par ajout d'especes aux affinites marines plutot qu'a un remplacement progressif. La presence de petits barrages hydro-agricoles sur le cours de la riviere et particulierement dans le cours superieur semble avoir influence l'ichtyofaune de maniere quantitative. Cela se justifie par des abondances relatives plus importantes des representants de la famille des Cichlidae dans les captures de cette partie de la riviere.

Tidiani Koné

Papers

Fish diversity and its relationships with environmental variables in a West African basin

Food habits of brackish water tilapia Sarotherodon melanotheron in riverine and lacustrine environments of a West African coastal basin

Données sur la reproduction d'un tilapia estuarien (Sarotherodon melanotheron) isolé dans un lac de barrage ouest-africain

Food composition and feeding habits of little tunny (Euthynnus alletteratus) in continental shelf waters of Côte d'Ivoire (West Africa)

Premières données sur l'inventaire et la distribution de l'ichtyofaune d'un petit bassin côtier Ouest Africain : Rivière Gô (Côte d'Ivoire)