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Title: Studies on the growth, diet and metazoan parasites of brown trout (Salmo trutta L.) in two areas of north east Scotland
Author: Bwathondi, Philip O. J.
ISNI:       0000 0001 3513 0583
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1976
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Loch of Strathbeg is a coastal dune lake, about 40 miles north of Aberdeen. The loch is fed by one burn, Burn of Savoch. The River Don tributaries are about 35 miles west of Aberdeen. The main groups of aquatic invertebrates include Hirudinea, Oligochaete, Crustacea, Coleoptera, Diptera, Hemiptera, Ephemeroptera and Mollusca. The terrestrial forms are mainly Coleoptera, Hymenoptera, Diptera and Hemiptera. The loch is also rich in avifauna especially in autumn and winter. Fish species include trout, sticklebacks, flounders and eels. The Don tributaries are comparatively poor in species of inverte-brates. Most insects belong to two orders, Ephemeroptera and ple-coptera. In addition, there are numerous freshwater shrimps, Gammarus pulex, which form one of the major food items of trout and other fish in the area. The piscifauna of the area include trout, salmon, eels, brook lamprey and sticklebacks. Strathbeg trout do not live for more than 4+ years. Growth of trout in Loch of Strathbeg, Burn of Savoch and Don tri-butaries has been calculated. Loch fish grow more than double their length when they enter the loch in their second year (1+) during this year. In the other two habitats, growth is more gradual. This is dearly demonstrated by their specific growth rates (Fig 4 p.23.). The average length of fish at different ages are equal for both Burn of Savoch and Don fish but almost half the size of their loch counterparts. Growth of trout 'at Strathbeg and Don has been suggested to be influenced mainly by the food, temperature and the availability of spawning facilities. The Don area has good spawning grounds and therefore supports more populations of trout which ultimately results in the decrease in the growth rate due to competition for food and space. This even-tually leads to fast growth of fish due to lower competition for food and space. Trout are surface feeders between May and October, and bottom feeders between November and April. Surface food is predominantly of terrestrial origin and emerging insects, while bottom food is both of permanent e.g. molluscs and shrimps, or temporary bottom origin e.g. insect larvae. Terrestrial food is either washed into the water by waves or blown into the water by wind or is captured when flying over the loch (see Table 6). The main food In the loch includes Diptera larvae, pupae and adults, Hemiptera (mainly corixids), Ephemeroptera (mainly Cloeon simile), Coleoptora (mainly terrestrial beetles) and Trichoptera. Molluscs (mainly P jenkinsi) form about 2.8% of the total food consumed by trout in the loch. sticklebacks form an important dietary item of larger trout. A total of 18 helminth species and one molluscan parasite were recorded in Strathbeg and Don trout, with 14 species, including glochidia larvae, in the former and 12 in the latter. Two species of crepidostomum, C metoecus and C farionis, were recovered from the two habitats studied. Attempts have been made to separate the two species. C. metoecus is a parasite mainly of the pyloric caeca while C farionis is mainly a parasite of the intestine and the gall bladder. C metoecus is more abundant than C. farionis. A clear seasonality has been recorded for C. metoecus. Mature worms disappear in July/August and juveniles appear at the same time. Three additional intermediate hosts of Crepidostomum have been recorded. These are Cloron simile, Siphlonurus lacustris and Bphemerella ignita. Two species of diplostomuli have been observed in the lens and humour of trout. Infection of trout at Strathbeg with both meta-cercariae takes place in the loch. Infection of trout with humour specimens is significantly higher than that of the lens specimens in both Strathbeg and Don fish. Infection with both species of parasites increases with the age of fish. Infection increases with the age of fish from 1+ to 4+. Younger fish (0+) are not infected by these tapeworms. It is concluded that intermediate hosts and their consumption by trout are the major factors affecting the intensity of infection of these fish. It is added that when considering the parasite fauna of a stocked body of water, the history of the fish and the habitat before stocking should be taken into consideration, Factors that affect parasite transmission to trout include availability of hosts, temperature of the environment, feeding behaviour of trout and movement of trout to and from infected areas. From the result of this work, infection of Strathbeg trout with both Diphyllobothrium and Eustrongylides is to a large extent responsible for the total disappearance of fish older than 4+ in the loch.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available