Comparative histopathology of livers from Baltic cod infected with the parasitic nematode Contracaecum osculatum

Abstract

Infection levels with the parasitic nematode Contracaecum osculatum in Eastern Baltic cod have increased in the last decades. Eastern Baltic cod is transport host for this parasite that has a high affinity for the liver of the fish. The liver is a highly vital organ and damage to the liver tissue can result in reduced functionality of the organ. Previous studies have revealed that cod with high infections loads reveal impaired physiological performance, reduced nutritional condition and show signs of having a liver disease. Yet, little is known about the pathological changes and inflammatory reactions of the cod liver related to the infections. In this study, we performed histological examinations on 30 Baltic cod livers caught in the eastern part of the Baltic Sea (length; 38 ± 0.9 cm, weight; 454 ± 34.8 gram) and three Sound cod livers (length; 63 ± 2.9 cm, weight; 3396 ± 300.2 gram) to categorize the degree of inflammation and its relation to pathological changes in infected cod livers. We further investigated how C. osculatum infection levels varied with intensity of inflammation and co‐infections. We found that high infection loads with C. osculatum caused severe inflammation in the liver tissue of cod and reduced fat content of the hepatocytes. Conspicuous amounts of glycogen were found in the muscle and intestinal epithelial cells of the nematodes and parasitic co‐infections occurred more frequently in the most heavily infected livers.

A study on assessing the toxic effects of ethyl paraben on rohu (Labeo rohita) using different biomarkers; hemato-biochemical assays, histology, oxidant and antioxidant activity and genotoxicity

“…During stressful conditions, glycogen inside hepatocytes is depleted because glycogen acts as a reserve for glucose. Due to these large spaces (sinusoidal spaces), hepatocytes are formed [ 51 ]. The increase in vacuolization is an indication of metabolic damage due to the toxicity caused by ethyl paraben.…”

Subtle transcriptomic response of Eurasian perch (Perca fluviatilis) associated with Triaenophorus nodulosus plerocercoid infection

“…In this study our recording system was binary, in that a given liver tissue, when examined by eye, is recorded as either being infected or uninfected and the exact degree of infection severity was not taken into account. Therefore, subsequent research should include an explicit analysis of infection intensity as well as physiological condition, as for example in Baltic cod infected by the parasitic nematode Contracaecum osculatum ( Marnis et al, 2019 ; Ryberg et al, 2020 ; Behrens et al, 2023 ). Such studies may provide additional insights into how parasite load is related to P. fluviatilis gene expression and immune response.…”