The diets and parasites of larval and 0+ juvenile twaite shad in the lower reaches and estuaries of the rivers Wye, Usk and Towy, UK

Abstract

This study assessed the diets and parasites of larval and 0+ juvenile twaite shad Alosa fallax fallax in the lower reaches and estuaries of the rivers Wye, Usk and Towy, UK. There were significant differences between the diets of larvae and co-habiting 0+ juveniles, and of larvae and 0+ juveniles among sites, both within and among rivers. In the Wye and Usk, the diets of twaite shad larvae were dominated by chironomid larvae, whereas those in the Towy specialised upon cyclopoid copepods. The diets of 0+ juvenile twaite shad from freshwater (River Wye) were characterised by chironomid larvae, while estuarine (Towy Estuary) individuals specialised upon calanoid copepods. Parasites infecting 0+ twaite shad were Apiosoma sp. (Protozoa), Gyrodactylus sp. (Monogenea), Proleptinae (Nematoda) larvae, Pomphorhynchus laevis (Acanthocephala), Spinitectus sp. (Nematoda) larvae and Trichodina sp. (Protozoa). Over 60% of estuarine 0+ juvenile twaite shad were infected with Apiosoma sp., with maximal estimated loadings in excess of 3,000 parasites per fish. Other parasite taxa were generally present in only small numbers. There were no significant differences in the intensity of parasite infections among sites, or the condition of parasitised and non-parasitised 0+ twaite shad.