Parasites of Salmo trutta L. from the Tirino River. Part IV. Intermediate hosts of Cyathocephalus truncatus (Pallas, 1781) and Dentitruncus truttae Sinzar, 1955

During studies on helminth parasites of brown trout (Salmo trutta L.) from the river Tirino (L'Aquila - Italy), the intermediate hosts of Cyathocephalus truncatus (Pallas, 1781) and Dentitruncus truttae Sinzar, 1955 have been searched for. A total of 15,444 amphipoda belonging to the following 3 species: Echinogammarus roco Karman, 1973, Echinogammarus tibaldii Pinkster and Stock, 1970, and Gammarus italicus Goedmakers and Pinkster, 1977, have been dissected. E. roco, E. tibaldii and G. italicus were found infected with procercoid of Cyathocephalus truncatus (new hosts record and first procercoid record in Italy). E. roco, E. tibaldii and G. italicus were found infected with acanthella and cystacanth of Dentitruncus truttae (first record of intermediate hosts). Accordingly the ecology of the cestod C. truncatus and of the acanthocephalan D. truttae in their intermediate hosts has been studied considering principally the incidence and the seasonal occurence of the parasites.     

Parasites of Salmo trutta L. from the Titino River. Part III. Histological observations of parasites of the intestinal tract

During researches on helminth parasites of Salmo trutta L. from the River Tirino (L'Aquila - Italy) histological studies of the intestinal tract of brown trout infected by the following species: Crowcrocaecum testiobliquum (Wisnewski, 1932) Skrjabin e Koval, 1956; Cyathocephalus truncatus (Pallas, 1781);o Truttaedacnitis truttae (Fabricius, 1794) Petter, 1974 and Dentitruncus truttae Sinzar, 1955 have been carried out. The attachment of the single species and the histological changes in the host gut due to parasite species have been described.     

Wild adult hybrids of Salmo salar L. and Salmo trutta L.

Ovarian development was impaired in three adult Salmo salar L. × S. trutta L. hybrids identified among adult salmonids in Scottish fisheries. Species-specific variation at enzyme loci indicated that the fish were F1 hybrids and mitochondrial DNA analysis showed them to be the progeny of S. salar females.     

Parasitic fauna of Salmo trutta L. of the Tirino river. I. Redescription of Dentitruncus truttae Sinzar, 1955 and considerations on the genus Dentitruncus Sinzar, 1955]

Dentitruncus truttae Sinzar, 1955 is redescribed and figured from specimens from Salmo truttae L. collected in the Tirino river (L'Aqula-Italy). The diagnosis of the genus Dentitruncus is completed and the characteristics separating Dentitruncus Sinzar, 1955 from Pseudorhadinorhynchus Achmerov e Drombrowskaja-Achmerova, 1941 are discussed.     

Movements of brown trout, Salmo trutta L., in the River Gwyddon, South Wales

Movements of native brown trout, Salmo trutta , 1 + and older, were limited with up to 93% of recaptured marked fish occupying sites where previously caught. Movements > 50 m were rare with the majority < 15 m. Between sampling occasions, the population could be separated into a static component and a smaller mobile component but there was no evidence of a permanently mobile group. The proportion of mobile native fish increased after stocking with hatchery-reared trout. Displaced native trout (1 + and older) showed the ability to home from 75 m upstream to 111 m downstream of a release site.     

Rates of gastric evacuation in brown trout, Salmo trutta L.

Brown trout of similar length and weight were fed a standard meal which contained a known number of food organisms of the same size-group and taxon (seven taxa were used). The weight of digestible organic matter in a trout stomach decreased exponentially with time. i.e. at a constant relative rate. At a particular water temperature, the food organisms were either evacuated from the stomach at similar rates (Group 1: Gammarus pulex, Baetis rhodani, Chironomidae, Oligochaetes) or at progressively slower rates (Group 2: Protonemura meyeri, Hydropsyche spp., Tenebrio molitor). Rates of gastric evacuation were not significantly different for food organisms of different size groups of the same taxon, or for different sized meals, or for different sizes of trout (range 20–30 cm), or for mixed and multiple meals (three meals over 16 h). Times are given for the gastric evacuation of 50%, 75%, 90% and 99% of the digestible organic matter in a meal. Starvation periods of 1, 2, 3,4 and 5 days prior to feeding did not affect evacuation rates. The rates were slightly, but not significantly, slower for starvation periods of 6 and 7 days, and were often significantly slower for starvation periods of 10, 15 and 20 days. Evacuation rates increased exponentially with increasing water temperature. It was possible to estimate both the rate and time for the gastric evacuation of different meals at water temperatures between 3–8°C and 19·1°C.     

'Ferox' trout, Salmo trutta L. of Loughs Mask and Corrib

Sets of scales with the relevant information were collected by the Irish Specimen Fish Committee from large or specimen brown trout taken by angling from Loughs Mask, and Corrib. The relationship between lengths and age were determined for those fish for which the necessary information was available. It was concluded that those fish destined to become specimens (10 lb or over in weight) had adopted a fish-eating habit to enable them to maintain a high rate of growth.     

D(+)-Glucose permeability in brown trout Salmo trutta L. erythrocytes

D(+)-Glucose penetration in trout erythrocytes was studied with osmotic and tracer methods.
Results give no evidence for a carrier mediated diffusion system like that concerned with glucose permeability as in human red cells. The data show that glucose fails to stimulate erythrocyte respiration.     

Egg, fry and smolt production from salmon, Salmo salar L. and sea trout Salmo trutta L. reared entirely in fresh water

For five years hatchery reared salmon and sea trout which had spent their entire lives in hatchery tanks were stripped each Autumn to investigate the survival of the resulting offspring.     

Carotenoids in fish. XX. Carotenoids in Salmo gairdneri rich. And Salmo trutta morpha fario L.

The author investigated the presence of various carotenoids in Salmo gairdneri Rich. and Salmo trutta morpha fario L. from the trout fish farm (artificial food) and from the river as the natural conditions (natural food).The findings of these investigations indicate that the trout bred in natural conditions are richer in carotenoids, provitamins of vitamin A, than are trout from the trout fish farm. In all probability the variety of food available in natural conditions provides better facilities for the accumulation of carotenoids in the body of trout in their natural habitat.     

The interactions of water hardness and pH with the acute toxicity of zinc to the brown trout, Salmo trutta L.

Exposure of brown trout, Salmo trutta , to zinc under continuous flow conditions over 96 h showed that both water hardness and pH exert major influences on the toxicity of the metal. 96-h LC50 values for total zinc ranged from <0.14mg 1⁻¹ in alkaline soft water (pH 8; lOmg 1⁻¹ as CaCO₃) to 3.20 mg 1⁻¹ in acidic hard water (pH 5; 204 mg 1⁻¹ as CaCO₃). A variable reduction in zinc toxicity in hard water compared with soft water over the pH range 4–9 was attributed to high external calcium. Zinc toxicity was positively correlated with decreasing acidity over the pH range 5–7, the metal being most toxic at pH 8–9 where metal complexes predominate. Below pH 5 metal toxicity also increased, irrespective of hardness. Water hardness and pH interacted with zinc toxicity in a complex manner, apparently dependent on physical and chemical transformations of the metal, and as changes in uptake. detoxification and excretion by the fish.     

The downstream drifting of eggs of brown trout, Salmo trutta L.

The occurrence of eggs in the drift samples was not related to fluctuations in flow rates, but was probably related to the presence of eggs in the gravel. Both the number ( Y eggs 3h⁻¹) and density ( Y eggs 100⁻¹ m⁻³) of eggs in the drift samples increased with increasing water velocity ( V m sec⁻¹), and the relationship between the two variables was well described by the regression equation Y=a V^b where a and b are constants. Comparisons were made between two streams and different, years.     

Acidophilic granular cells in the epidermis of the brown trout,Salmo trutta L.

Summary Acidophilic cells occur in the epidermis of several species of salmonid fish, although their abundance fluctuates considerably between individuals within the same population and at different times during the life cycle. The histology, histochemistry and ultrastructure of an acidophilic, granular celltype in the epidermis of the brown trout, Salmo trutta L., is described. At the light microscope level this cell type is easily distinguished from the large, mucus-secreting, epidermal goblet cells by its acidophilic, proteinaceous secretion. At the ultrastructural level this secretion consists of membrane-bound granules formed by the very active Golgi region. It is argued that the acidophilic, granular cell is not a transformed blood cell but constitutes a normal epidermal component of the brown trout. Possible roles of this cell in the function(s) of the epidermis are discussed.     

Otolith shape discriminates between juvenile Atlantic salmon, Salmo salar L., and brown trout, Salmo trutta L.

Otoliths of Atlantic salmon, Salmo salar L., are more slender than the otoliths of brown trout, Salmo trutta L. Discriminant analysis on otolith measurements of juvenile Atlantic salmon and brown trout from four river systems revealed a discriminant function which distinguished more than 94% of the cases. This function was tested by using data from a fifth river with cohabiting Atlantic salmon and brown trout: all Atlantic salmon and 91 % of the brown trout were correctly classified.     

Spawning characteristics of brown trout and sea trout Salmo trutta L. in Kirk Burn, River Tweed, Scotland

The upstream spawning migrations of brown trout and sea trout were studied using stationary traps placed in Kirk Burn, a tributary of the upper Tweed. The sea trout spawning period extended from early November to the first week of December, while that of brown trout occurred from the middle of October to the third week of December. Sea trout were predominantly maiden spawners of ages 2.1+ and 3.1+ while brown trout were mostly age 2+ and 3+. Male-female sex ratios approximated 1:1.4 in sea trout but 6 : 1 in brown trout. Brown trout males participated in the spawning activities of sea trout. Low water conditions in Kirk Burn hindered the upstream movement of spawning sea trout, while sudden increases in water level appeared to stimulate the upstream migration of both brown trout and sea trout. The suggestion is advanced that the freshwater resident brown trout of the Tweed which migrate upstream into the smaller tributaries to spawn is wholly, or at least partially, the progeny of anadromous parents.     

Histochemical analysis of mucous cells in the epidermis of brown trout Salmo trutta L.

A histochemical study of the epidermal mucous cells of brown trout revealed that they contained both neutral and acidic mucosubstances which were diastase-resistant, PAS-reactive. Neuraminidase treatment, methylation and combined staining procedures suggested that the acidic nature of the mucins was due mainly to the presence of sialic-acid containing glycoprotein. These results augment data derived from biochemical analyses of the epidermal mucus of salmonid fish.