Ionoregulatory and respiratory responses of brown trout, Salmo trutta, exposed to lethal and sublethal aluminium in acidic soft waters

Climatic effects on water quality in areas with acid sulfate soils with commensurable consequences on the reproduction of burbot (Lota lota L.)

Due to discharge from acid sulfate (a.s.) soils, watercourses and coastal areas in the Gulf of Bothnia are periodically heavily acidified with high concentrations of potentially toxic metals. Data on water quality from 2005 to 2014 in an embanked lake, an estuary of four rivers in western Finland, showed repeated events with acidic water (pH < 5.5) with high concentrations of Al. Size fractionation and species modeling of Al showed that a significant part of the Al occurred as highly toxic small-size fractions (dissolved < 1 kDa and colloidal 1 kDa-0.45 µm) as free ions and complexed to sulfate. The larval abundance of the burbot (Lota lota L.) was shown to be sensitive to acidity during the wintertime spawning migration and spawning. Bearing in mind the importance of estuaries of the northern Baltic Sea as spawning and nursery areas of fish, the reoccurring failure in the reproduction of fish may cause a more serious threat for the lake and adjacent coastal fish stocks than the spectacular, but less frequent, mass kills of adult fish. This demonstrates the close relationship between climate, hydrology, water geochemistry and the aquatic coastal ecosystem in areas affected by a.s. soils. As the current forecast of climate chance indicates warmer winters with more continuous runoff, the effects can become even more prominent. This study also shows that the annual larvae abundance of burbot may be used as a bioindicator and an instrument for the fisheries for obtaining more comprehensive knowledge of the ecological effects of acidic metal discharge from a.s. soils.

Physiological and behavioural responses of Gammarus pulex exposed to acid stress

Physiological and behavioural responses of the acid-sensitive amphipod Gammarus pulex exposed to a wide range of acid conditions (pH 4.1, 5.1, 6.0) under laboratory conditions were investigated. An exposure of 38 h to acid conditions caused significant decreases in survival rate, osmolality, haemolymph Na+ concentration, ventilatory and locomotor activity compared to organisms exposed to a circumneutral medium (pH 7.9). We highlighted the interest of using individual response distribution, since drastic effects can be detected in organisms exposed to pH 6.0, in particular for osmolality: The response can be divided into two groups, unimpacted and impacted organisms. Moreover this representation permitted to evaluate the health level of individual organisms through the determination of threshold values. Significant correlations between mean pH and mean physiological/behavioural responses were observed. The relationships between individual responses permitted not only to compare endpoints, but also to show that affected organisms were impacted by ionoregulation failure, hypoventilation and low locomotor activity. The energetic reallocation in favour of maintenance functions, such as osmoregulation, is discussed. The results of this study indicate that the values of haemolymph Na+ concentration, osmolality and locomotor activity in G. pulex could be effective ecophysiological/behavioural markers to monitor freshwater ecosystems and to assess the health of organisms or populations.

Plasma and tissue thyroxine and triiodothyronine contents in sublethally stressed, aluminum-exposed brown trout (Salmo trutta)

Immature female brown trout, Salmo trutta, were exposed to pH 5.0 soft water in the presence or absence of aluminum (Al) at 12.5 micrograms liter-1 and their plasma concentrations and tissue contents of thyroxine (T4) and triiodothyronine (T3) were compared with those of a control group of trout held in pH 7.0 soft water. After 120 hr, plasma cortisol, glucose, T4, and T3 concentrations were greater in the Al-exposed trout than in trout exposed to acid conditions alone, indicating that although the Al conditions were sublethal, a significant stress response was elicited. Significant increases in liver T4 content, liver 5'-monodeiodinase activity and liver T3 content indicated increased hepatic T4 to T3 conversion in the Al-exposed trout. The T4 contents of brain, gill filaments, white muscle, heart ventricle, caudal kidney, and ovary were not significantly altered by Al exposure. The T3 content of caudal kidney and ovary were significantly lower in Al-exposed trout than in control fish in neutral water but were unchanged in the brain, gill filaments, heart ventricle, and white muscle of these trout. The present data support previous observations of increased plasma T3 concentrations in sublethally Al-exposed brown trout and indicate that at least part of the increased plasma T3 concentration is due to an increased hepatic uptake of T4 and monodeiodination to T3. However, analysis of nonhepatic tissue T3 content gave no indication of increased T3 production by these tissues.