Abstract
Parasites in fish are ecological indicators, as they reflect the host's migration routes, feeding behavior and immune status. We performed a parasitological investigation of sea-running Baltic salmon to study the use of parasites as indicators for this fish stock. The host-a strain of Atlantic salmon Salmo salar-has been isolated for several millennia in the semi-enclosed brackish Baltic Sea, with limited migration to and from the North Sea. Twenty-four salmon (total body weight: 4.2-14.2 kg; total body length: 80-105 cm) were caught by spoon bait in the southern Baltic Sea during feeding migrations, necropsied shortly afterwards and internal organs subjected to parasitological investigation focusing on endoparasitic helminths. The pyloric region was heavily parasitized by the cestode Eubothrium crassum (100% prevalence; intensity: 97-273 parasites per infected fish), reflecting a diet of smaller pelagic fishes. The stomach contained the hemiurid digeneans Brachyphallus crenatus (95.8% prevalence; intensity: 8-151) and Hemiurus luehei (58.3% prevalence; intensity: 2-13), indicating a diet of clupeids. Schistocephalus solidus (25% prevalence; intensity: 1-2), liberated from ingested sticklebacks, the acanthocephalan Echinorhynchus truttae (54% prevalence; intensity: 1-13) and the adult nematode Hysterothylacium aduncum (29% prevalence; intensity: 1-13) were found in the intestine. The liver was parasitized by third-stage nematode larvae of Contracaecum osculatum (45.8% prevalence; intensity: 1-4), but these were growth-stunted and encapsulated. The parasite fauna differs markedly from salmon in North Atlantic waters, and the lack of purely marine parasite species indicates that the Baltic salmon has remained in the Baltic Sea during its life history.
Highlights
Baltic salmon is a sub-stock of Salmo salar populating the Baltic Sea, the semi-enclosed brackish water system located between the coastlines of Denmark, Sweden, Finland, Russia, the Baltic republics (Estonia, Latvia, Lithuania), Poland and Germany
We performed a study on endoparasitic helminths of Baltic salmon caught during their feeding migration in the southern Baltic Sea, and we present biological information on feeding and migration routes extracted from the parasite fauna recorded
The acanthocephalan Echinorhynchus truttae and adult nematodes of the species Hysterothylacium aduncum occurred sporadically, whereas third-stage nematode larvae Contracaecum osculatum were found in livers more frequently (Table 2)
Summary
Baltic salmon is a sub-stock of Salmo salar populating the Baltic Sea, the semi-enclosed brackish water system located between the coastlines of Denmark, Sweden, Finland, Russia, the Baltic republics (Estonia, Latvia, Lithuania), Poland and Germany. Salmon-running rivers supplying fish to the Baltic are found in all these countries except Denmark, and smolts migrate from their home river to the Baltic feeding grounds, returning to their spawning sites after 1−4 yr (Karlsson & Karlström 1994). Data from other marine areas suggest that basic biological information concerning feeding and immune status can be extracted by analyzing the presence of certain parasite species in a fish population, e.g. in salmon from the White Sea (Dogiel & Petruschevski 1934), Canada (Hicks & Threlfall 1973) and the Pacific (Margolis 1965). We performed a study on endoparasitic helminths of Baltic salmon caught during their feeding migration in the southern Baltic Sea, and we present biological information on feeding and migration routes extracted from the parasite fauna recorded
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