Assessment of fish health status in four Swiss rivers showing a decline of brown trout catches

Abstract

Abstract.A pronounced decline in catch of brown trout (Salmo trutta L.) over the last 10-20 years has been reported for many rivers in Switzerland. Impaired health status of the fi shes has been suggested as one possible cause of the decline. The present study investigated the health status of juvenile brown trout from four Swiss rivers which experienced reductions of brown trout catches during the last two decades: Emme, Liechtensteiner Binnenkanal (LBK), Necker and Venoge. A gradient approach was applied, studying at each river a headwater (HW), midstream (D1) and downstream site (D2). Fish health was assessed by the following indices: hepatic 7-ethoxyresorufi n-O-deethylase (EROD) activity, organ (liver, kidney) histopathology, and gross biometric indices (condition factor, hepatosomatic index). Hepatic EROD activities were generally low without showing signifi cant within-or between-stream differences. Histopathological alterations of the liver displayed a moderate downstream increase in the Emme, LBK and Necker, but not in the Venoge. Between-stream differences of liver pathology were small. Kidney histopathology was not different between upstream and downstream sites, except for Emme and Venoge, where fi shes at the downstream sites were infected with the parasite Tetracapsuloides bryosalmonae, the cause of the proliferative kidney disease (PKD). The fi ndings from this study point to an association of within-stream gradients in water quality, PKD prevalence, fi sh health and brown trout biomass, whereas between-stream differences of actual fi sh health status refl ecting the different levels of catch declines observed in the four rivers during the last two decades are not evident.

Response and recovery of hybrid sturgeon from subchronic oral administration of cyanobacteria

“…In wild fish, factors such as pathogens, insufficient food resources, or environmental stressors such as high water temperature or toxicant exposure influence fish health, possibly leading to altered fish survival and ultimately fish growth (Zimmerli et al, 2007). Although no obvious effect of 47-day dietary cyanobacteria exposure was observed on fish mortality, much stronger effects were observable using fish growth and feed utilization as the end-point in our study.…”

Assessment of the health status of wild fish inhabiting a cotton basin heavily impacted by pesticides in Benin (West Africa)

“…For the pesticide concentrations, an ANOVA II test was followed by Duncan's multiple range tests because no pesticide was detected at S1. Histological descriptions of tissues were qualitative and Bernet et al (1999), Zimmerli et al (2007) and Van Dyk et al (2009a,b) were used as comparison methods. However, we used an ANOVA II and Dunnett's test for the Total Index.…”

“…These indices were used to compare the occurrence severity of gonadal histological alterations between the fish from each site. To classify the It and Io results according to the severity of the histological response, the results were evaluated according to a classification system (Van Dyk et al, 2009a,b) based on a scoring scheme by Zimmerli et al (2007).…”

Assessing relationships between chemical exposure, parasite infection, fish health, and fish ecological status: A case study using chub (Leuciscus cephalus) in the Bílina River, Czech Republic

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