Morphologic evaluation of the gills as a tool in the diagnostics of pathological conditions in fish and pollution in the aquatic environment: a review

Abstract

Fish gills, owing to their status as a multifunctional organ, have always fascinated researchers. In spite of the intense work done on the morphologic examination of gills, the organ is relatively under-used in health evaluation in fish. The existing literature on this topic is reviewed here. Our review summarises important diagnostic guidelines for the examination of gill structure and describes the morphological lesions that develop under the influence of different biological and physicochemical factors. The picture that should emerge is that of an organ that is extremely sensitive to all types of handling and unfavourable changes in the external and internal environments. We conclude that studying the morphology of the fish gills provides an opportunity to assess fish health status as well as information on possible health hazards coming from their environment.

Chronic microfiber exposure in adult Japanese medaka (Oryzias latipes)

“…Tissue and cellular effects resulting from microplastic exposure have also received very little attention. Results of our SEM and histological investigations showed acute responses including epithelial lifting, increased mucus production, and eroded epithelium as well as chronic responses including erosions on surfaces of gill arches, lamellar aneurysms, and fusion of primary and secondary lamellae [75][76][77]. Separation of epithelium from the basal membrane is a symptom of disorders of osmoregulation and can act as a protective mechanism to increase distance from toxicants [78], but increased distance also impairs oxygen uptake [72].…”

“…Likewise, fusion of lamellae causes an overall reduction in surface area for gas exchange [79]. Increased mucus production also functions as a barrier against foreign substances (chemical, physical, or biological) [75,76], forming an important part of the innate immune system [76]. While mucus production is considered a defense mechanism, any change that decreases filament surface area or increases distance for gaseous exchange between external environment and blood is regarded as potentially harmful to host respiration [27].…”

“…Lamellar aneurysms and complete lamellar fusions are severe pathologies [72,81]. Lamellar aneurysms result in damage and loss of pillar cells in these areas result in the fusion of capillaries within secondary lamellae, which causes their dilation and congestion with blood [75]. Causative factors of gill aneurysms include mechanical injuries or a long list of toxicants that impair respiration [75,82,83].…”

Effect of feed supplementation with kynurenic acid on the morphology of the liver, kidney and gills in rainbow trout (Oncorhynchus mykiss Walbaum, 1792), healthy and experimentally infected with Yersinia ruckeri

“…Gills play a very important role in both respiratory processes and osmoregulation (Strzyżewska, Szarek & Babińska ). Because of their location, they are particularly exposed to the action of all kind toxic substances, and for this reason, they are considered to be one of the best and most sensitive bioindicators (Strzyżewska et al .…”

Improved fixation of the whole bodies of fish by a double-fixation method with formalin solution and Bouin’s fluid or Davidson’s fluid

“…There is increasing interest in histopathological investigation of fishes for evaluations of diseases in fish culturing, environmental monitoring, toxicity studies for environmental pollutants, screening studies for carcinogenicity or teratogenicity of chemicals, and so on 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 . Principally, conventional 10% formalin solution has been used as the histological fixative for fishes as in humans and other animals.…”