Host size-dependent anisakid infection in Baltic cod Gadus morhua associated with differential food preferences

Abstract

A significant increase in the infection level of Baltic cod Gadus morhua with the anisakid nematode larvae Contracaecum osculatum and Pseudoterranova decipiens has been recorded during recent years due to the expanding local population of grey seals Halichoerus grypus, which act as final hosts for these parasites. Here, we report from an investigation of 368 cod (total length [TL] 6−49 cm; caught in ICES Subdivision 25) that the infection level of juvenile cod (TL 6−30 cm) with larvae of C. osculatum and P. decipiens is absent or very low, whereas it increases drastically in larger cod (TL 31−48 cm). A third nematode Hysterothylacium aduncum was rarely found. The study indicates that the prey animals for large cod act as transport hosts for the parasite larvae. Analyses of stomach contents of cod caught in the same area (2007−2014) showed that small benthic organisms (including polychaetes Harmothoë sarsi) are preferred food items by small cod, the isopod Saduria entomon is taken by all size classes, and sprat Sprattus sprattus are common prey items for cod larger than 30 cm. Parasitological investigations (microscopic and molecular analyses) of H. sarsi (100 specimens) and S. entomon (40 specimens) did not reveal infection in these invertebrates, but 11.6% of sprat (265 specimens examined) was shown to be infected with 1−8 C. osculatum third stage larvae per fish. Analyses of sprat stomach contents confirmed that copepods and cladocerans are the main food items of sprat. These observations suggest that the C. osculatum life cycle in the Baltic Sea includes grey seals as final hosts, sprat as the first transport host and cod as second transport host. It may be speculated that sprat obtain infection by feeding on copepods and/or cladocerans, which could serve as the first intermediate hosts. One cannot exclude the possibility that the size-dependent C. osculatum infection of cod may contribute (indirectly or directly) to the differential mortality of larger cod (> 38 cm) compared to smaller cod (< 30 cm) recently recorded in the Baltic cod population.

A follow‐up study of selected biomarkers of health in cod Gadus morhua L. collected from the southern Baltic off the Polish coast

“…In fish with intrahepatic adult parasites, there was severe hepatocellular necrosis associated with migration tracts and marked vasculitis and haemorrhage; some worms were apparently residing within necrotic blood vessels and the most severe lesions correlated with a lower CF suggesting a negative health impact on the fish. Our data on high prevalence of anisakid nematodes in Baltic cod are in agreement with reports of marked increase in the infection level of third‐stage larvae of Contracaecum osculatum and Pseudoterranova decipiens as confirmed by PCR studies (Zuo et al., ). The potentially zoonotic anisakid nematodes are becoming a serious problem in fish from the Baltic due to increasing populations of the final host, the common seal ( Phoca vitulina ) (Buchmann & Kania, ; Haarder, Kania, Galatius, & Buchmann, ; Nadolna & Podolska, ).…”

Metazoan Endoparasites as Biological Indicators of Baltic Cod Biology

“…Fish predating on these animals become infected with the third-stage larva. Sprat and herring will often act as an important paratenic host as they obtain infection by ingesting third-stage larvae contained in copepods, and cod will then acquire infection when predating on these clupeids [43,44]. Cod will often carry infections in the liver.…”

Primer reporte de Anisakis spp. en peces de agua dulce en Huacho, Perú

“…Los peces y calamares pueden ser consumidos directamente por los mamíferos marinos cuando la larva de la tercera etapa (L3) muda a L4 y luego madura a la forma adulta del parásito (Lin, 2015). A lo largo de la red trófica, en peces depredadores de otros peces, las larvas pueden encapsularse (Zuo et al, 2016). El comportamiento de las larvas es variable, la mayoría de los parásitos permanen en la cavidad visceral del pez o dentro de los órganos viscerales, mientras que en otros casos migran a la musculatura de los peces (Cipriani et al, 2016; Levsen y Lunestad, 2010; Mattiucci et al, 2017).…”