Indicators of fish condition

In some sensitive lakes and streams, acidification has completely eradicated fish species, such as the brook trout, leaving these bodies of water barren. In feet, hundreds of the lakes in the Adirondacks surveyed in the NSWS have aridity levels indicative of chemical conditions unsuitable for the survival of sensitive fish species. 

DISOLVED OXYGEN (DO). One t>r the- most important indicators of the condition of a water supply for biological, chemical, and sanitary investigations. Adequate dissolved oxygen is necessary for the life of fish and other aquatic organisms, and is an indicator of corrosivity or water, photosynlhctie activity, septieity. etc. 

Many fundamental concepts in modem biology have been established through studies on aquatic organisms. Fish are of special interest to research workers, because some of their metabolic features characterized early vertebrates. Fish have also evolved numerous adaptations, which have permitted them not only to survive but also to thrive in recent times. The range of structural and functional adaptations and metabolic flexibility, combined with individual specializations, has resulted in an immense diversity of fish - more than 20 000 species - which greatly exceeds that of amphibians, reptiles, birds and mammals. As the final link in many food chains, fish can be reliable indicators of the condition of complex ecosystems. Studies on fish provide an understanding of the pathways of metabolic substances and of energy transformations in bodies... 

The relatively modest importance of fish in trophic dynamics is greatly exceeded by their economic importance, and so by the research effort put in by workers from many countries. Further knowledge of the biology of fish is still required. Fish are also suitable subjects for the study of adaptation and evolution. Being a top link in the trophic chain, they can also serve as an indicator of the condition of the whole ecosystem. 

Although laboratory assays under controlled flow conditions can help work out the mechanism for predator avoidance, to unequivocally demonstrate that prey actually use the chemical scent of predators to avoid predation in nature, field experiments are required. In an attempt to investigate this behavior in the field, Sih et al. (1992) manipulated fishless stream pools to produce pools with and without fish. Fish were held in a perforated bucket on the bottom of treatment pools and covered with opaque mesh screening that blocked visual and mechanical indications of fish presence, but allowed diffusion of chemical cues. Behavior of laboratory-reared amphibian larvae (no prior exposure to fish) was quantified... 

This section of the Ebro River is under the direct impact of the Flix chlor-alkali plant and of its residue sediments. Contamination of Hg and OCs is maximal in these sediments, and there is evidence that it leaks downstream as far as at least to Xerta, 37 km away Flix ([8, 9], Fig. 4a, d). Fish populations in Flix show poorer condition and fecundity than their counterparts sampled in Riba-roja or the Delta [38]. In addition, HSI and CF in carps showed good correlation (positive and negative, respectively) with OC burden (Fig. 4c). These data indicate that the pollution by Flix residues and, specifically, by OCs, affects the growth and health status of fish from the low Ebro River. 

---