Histopathological alterations of the heart in fish: proposal for a standardized assessment

Abstract

Histopathological alterations in the heart are often reported in fish as a result of exposure to a variety of chemical compounds. However, researchers presently lack a standardized method for the evaluation of histopathological alterations in the cardiovascular system of fish and the calculation of an 'organ index'. Therefore, we designed a method for a standardized assessment and evaluation of histopathological alterations in the heart of fish. As a model species, we used rainbow trout Oncorhynchus mykiss, but the protocol was also successfully applied to other fish species belonging to different taxonomic orders. To test the protocol, we re-evaluated sections of atenolol-exposed and unexposed rainbow trout obtained in a previous study. The results were in accordance with those previously published, demonstrating the applicability of the protocol. The protocol provides a universal method for the comparative evaluation of histopathological changes in the heart of fish.

Insects in Rainbow Trout (Oncorhynchus Mykiss) Feed: Effect on Growth, Fatty Acid Composition and Sensory Attributes

“…Partial fish meal replacement with processed insect meal without negative effect on the growth of salmonids was reported Gasco et al (2014), who successfully replaced up to 50% of fish meal with mealworm larva meal, and Stamer et al (2014), who used BSF meal in the rainbow trout diet. Fish meal replacement with insect meal ≥50% was associated with significantly reduced growth in the majority of studies (St-Hilaire et al 2007b, Sealey et al 2011, Stamer et al 2014, although total FM replacement with BSF meal without deterioration of growth parameters was reported by Lock et al (2014) in Atlantic salmon. Potential utilization of live or raw insects in salmonid mass culture is problematic; however, a collaboration of fish and insect farming may be possible with local producers.…”

“…Inclusion of the black soldier fly, Hermetia illucens (BSF), larvae and mealworm, Tenebrio molitor, has been assessed in salmonid diets. Replacement of 25% to 50% of the FM with BSF meal in a rainbow trout diet showed no significant effects on weight gain and feed conversion ratio but resulted in lower levels of omega-3 fatty acids in fillets (St-Hilaire et al 2007b, Stamer et al 2014. Sealey et al (2011) reported satisfactory growth of rainbow trout fed a diet replacing 50% of FM with BSF reared on manure enriched with trout offal, while a diet containing BSF reared on manure only was associated with significantly slower growth compared to the commercial diet.…”

A proposal of standardization for histopathological lesions to characterize fish diseases

“…This communication also highlights some of the limitations of the histological scoring systems applied to date: A comprehensive, organ‐by‐organ protocol is currently lacking. Studies have classically included gills, liver, kidney and skin, only (Bernet et al 1999; Steinbach et al 2016). Most of the scoring systems have been focused on the effects of pollution and contamination (Bernet et al 1999; Au 2004).…”

“…Bernet et al (1999) developed a histopathological scoring system in fish that has been widely used across the literature (Zimmerli et al 2007; Poleksic et al 2010; Saraiva et al 2015; Steinbach et al 2016; Gregorc et al 2018; Lei et al 2018), with more than 800 citations in Google Scholar ® and 450 citations in Web of Science ® (Table 1). Originally, this system was designed to assess changes induced by aquatic pollutants on the most susceptible organs (gills, kidney, liver and skin) and did not include other tissues susceptible to alteration by other different disease processes.…”

“…Bernet’s protocol has been adapted to other disease processes and organ systems, such as heart or intestine (Steinbach et al 2016; Lei et al 2018), but it is rarely used to characterize infectious or parasitic diseases. For instance, Steinbach et al (2016) recently proposed a standardization method to evaluate heart lesions in the rainbow trout ( Oncorhynchus mykiss ), which may be also applied to other species. Indeed, a well‐developed and harmonized scoring system should be transferable to other fish species with minor adjustments.…”