Parasite load of Atlantic cod Gadus morhua in the Baltic Sea assessed by the liver category method, and associations with infection density and critical condition

Abstract

Fish stock assessments require input data such as numbers and/or biomass of fish, natural and fishing mortality, growth and recruitment. These data, which are derived from the market sampling of commercial catches and from the monitoring surveys, are used to evaluate the present status of exploited fish stocks and project their future development (Jennings et al., 2001). Parasites can affect their hosts ranging from the level of the individual to the level of populations (Timi & Poulin, 2020). However, fish health indicators, such as parasite occurrence, are usually not part of the routine sampling on marine monitoring surveys (Lloret et al., 2012). This omission could

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

“…In conclusion, the present pathological changes and inflammatory reactions of the cod liver related to the infections of C. osculatum , together with indications that the parasite grow inside the liver, supports previous studies (Buchmann & Mehrdana, 2016; Mohamed et al, 2020; Ryberg et al, 2020, 2022) suggesting that infections with C. osculatum in cod can result in reduced liver functionality and thus reduced health status, as a result of damage to the liver tissue.…”

“…This suggests that these severely infected cod may be more susceptible to other infections. This does not have to be a direct effect of the infections with C. osculatum but can be a result of the strong association between C. osculatum infection load and nutritional condition, as cod with high C. osculatum loads generally are in a poorer nutritional condition (Horbowy et al, 2016;Ryberg et al, 2020Ryberg et al, , 2022Sokolova et al, 2018). Across taxa, including teleosts, individuals with reduced nutritional condition may experience increased susceptibility to pathogens, most likely because their immune response is compromised by their poor nutritional state (Chandra, 1997;Gulland, 1992;Johansen et al, 1997).…”

“…Taken together, this suggests that cod with high infection levels suffers from a chronic pathological liver condition (Ryberg et al, 2020). In support, the expression of immune‐related genes in the cod liver tends to be downregulated at high infection levels, suggestively due to local immune suppression in the organ caused by C. osculatum (Marnis et al, 2020), and several studies have furthermore revealed a negative association between infection levels and nutritional condition (Horbowy et al, 2016; Petrushevski & Shulman, 1955; Ryberg et al, 2020, 2022; Sokolova et al, 2018). The latter shows that cod infected with C. osculatum have a lower condition (i.e.…”

Effect of Anisakis pegreffii (Nematoda: Anisakidae) on Biochemical and Haematological Characteristics of Chub Mackerel (Scomber japonicus Houttuyn, 1782) Caught in the Dardanelles at Çanakkale, Türkiye

“…In this study, the mean HSI and GSI levels of parasite-infested chub mackerel fish were significantly lower than that in healthy ones. Previous studies showed that high numbers of parasites caused destruction of organ structures and subsequent decrease in organ size (Ryberg et al, 2020;Ryberg et al, 2022). This result is in accordance with that of Ondračková et al (2010) indicating that larval parasitic nematode Raphidascaris acus decreased GSI level in infested female Neogobius kessleri.…”

New insights into the recent collapse of Eastern Baltic cod from historical data on stock health

“…Both the increase in EBC natural mortality and reduction in growth are likely, at least partly, associated with poor body condition and a high C . osculatum load [ 22 , 49 , 72 , 73 ]. Furthermore, the present unprecedentedly small size at maturation ( Fig 4A ), in combination with poor body condition, is expected to cause mortality due to energy costs associated with reproduction [ 74 , 75 ].…”