Immunization of adult brook trout, Salvelinus fontinalis (Mitchill), fails to prevent the infectious pancreatic necrosis virus (IPNV) carrier state

Abstract. Adult brook trout, Salvelinus fontinalis (Mitchill), mounted a strong humoral immune response after injection with inactivated infectious pancreatic necrosis virus (IPNV) in Freund's complete adjuvant (FCA). However, this immunization did not prevent the fish from becoming IPNV carriers. After an injection challenge with virulent IPNV, the immunized and control fish (FCA or water) shed virus in the faeces and reproductive products and had IPNV-infected leucocytes and visceral organs. Initially, from 1 to 3 weeks post-challenge (wpc), immunized fish had a lower prevalence of infection and virus titres in the plasma, and fewer infected leucocytes than the control fish. Immunization did not prevent the eventual infection of the leucocytes; over 75% of the immunized and control fish had leucocyte-associated viraemia from 6 to 15 wpc. When the organs were tested at 15 wpc, the immunized fish showed fewer infected organs per fish, and a lower prevalence of infection and virus titres in individual organs than the control fish, but these differences were not significant. Immunized male and female fish shed IPNV in the reproductive products, suggesting that immunization of adult fish would not prevent vertical transmission of IPNV to progeny.     

Blood parameters in brook trout Salvelinus fontinalis (Mitchill, 1815), affected by columnaris disease

Mass death of farmed brook trout Salvelinus fontinalis reared in raceway culture on a commercial fish farm was recorded in May. The condition was caused by natural infection with external signs of Flavobacterium columnare. Haematological analyses were carried out from peripheral blood from 10 fish from each group. Anaemia was characterized by a reduced erythrocyte count and lower haemoglobin levels; the values of mean corpuscular volume and mean corpuscular haemoglobin were higher and the values of mean corpuscular haemoglobin concentration were decreased. Clinical chemistry analyses in blood plasma indicated decreased levels of total protein, glucose and total calcium and an increase in the urea level. Among the four enzymes analysed, a catalytic activity reaching multiples of the normal level was found in alanine aminotransferase, aspartate aminotransferase and lactate dehydrogenase. The catalytic concentration of alkaline phosphatase was decreased. Electrophoretic analyses of the plasma protein indicated a reduced level of albumin. The moribund fish had a higher hepatosomatic index and their condition coefficient after Fulton and after Clark was also higher.     

Seasonal habitat use by brook trout,Salvelinus fontinalis (Mitchill), in a second-order stream

Abstract Seasonal habitat use by over-yearling and under-yearling brook trout, Salvelinus fontinalis (Mitchill), was examined in a second-order stream in north-central Pennsylvania, USA. The habitat occupied by brook trout and available habitat were determined in a 0.5-km stream reach during the spring, summer and autumn of 1989 and the spring and summer of 1990. Cover, depth, substrate and velocity were quantified from over 2000 observations of individual brook trout. Habitat used by under-yearling brook trout was more uniform between seasons and years than that used by over-yearling brook trout. Over-yearling brook trout occupied areas with more cover and greater depth than did under-yearling brook trout, suggesting ontogenetic shifts in these variables. Differences for velocity and substrate were not as great as those for cover and depth. The selection of areas with low water velocities governed trout habitat use in spring, whereas cover and depth were the most important habitat variables in summer and autumn. Principal component analysis showed that available habitat and trout habitat centroids diverged most in spring, indicating that habitat selection by brook trout may be greatest at this time.     

Fry age and size effects on immersion immunization of brook trout, Salvelinus fontinalis Mitchell, against infectious pancreatic necrosis virus

Abstract. Brook trout, Salvelinus fontinalis Mitchell, fry were divided into eight age groups of 1–8 weeks post-hatch (wph) and immunized by a single direct immersion in formalin-inactivated infectious pancreatic necrosis virus ( ipnv ). After a direct-immersion ipnv challenge given 4 weeks later, only fry immunized at 2, 3 and 6wph showed protection. The relative per cent survival 60 days after ipnv challenge was highest in 2 and 3 wph fry (45–50%) and decreased as fish increased in age or size. The same response was obtained one year later when four age groups of fry, from 1 to 4wph, were immunized with a different serotype and dose of ipnv . The 2 and 3 wph fry had mean weights between 49 and 60mg at immunization. Killed vaccines administered by immersion have not previously been reported as inducing protection in salmonid fry of such low weights. Analysis of the growth of the fry suggests that protection against IPNV requires immunization in the eleutheroembryo phase, during the time of slow weight gain. This appears to be in direct contrast to the stage of ontogeny and weight growth rate required for successful immunization against the bacterial pathogen Vibrio anguillarum. Although immunization with two ipnv serotypes reduced mortalities from challenges with these same virus isolates, it did not prevent ipnv infection of fry in any age group.     

Efficacy studies of passive immunization against Aeromonas salmonicida infection in brook trout, Salvelinus fontinalis (Mitchill)

Abstract. Aeromonas salmonicida , the aetiologic agent of furunculosis, causes high mortality in cultured salmonids. Experiments were conducted to determine the therapeutic and prophylactic efficacy of passive immunization against furunculosis in brook trout, Salvelinus fontinalis (Mitchill), infected by immersion. Rabbit hyperimmune serum was produced against a virulent strain of A. salmonicida and an aliquot of this serum was absorbed with cells of a non-virulent strain of A. salmonicida. Immunoglobulins from aliquots of the absorbed and non-absorbed serum were purified using affinity chromatography. Each serum or immunoglobulin preparation was tested in passive immunization experiments. Brook trout were infected by immersion in a suspension of virulent A. salmonicida , and passively immunized by intraperitoneal injection at the time of experimental infection, or at various periods after experimental infection. Passive immunization of brook trout against furunculosis was therapeutically efficacious when effected either at zero, 24 or 48h post-infection, but not at 72 or 96h. Purified rabbit immunoglobulins specific to virulent A. salmonicida were as protective as the initial rabbit hyperimmune serum in protecting brook trout against furunculosis. To determine the prophylactic efficacy of this treatment, the groups of fish passively immunized at the time of the experimental infection were challenged a second time at either 14, 35, 41 or 56 days after passive immunization. Brook trout were protected against a second experimental bath challenge with virulent A. salmonicida for a period of 35–41 days.     

Food availability and growth of the brook trout, Salvelinus fontinalis (Mitchill), in a French Alpine lake

Plan Vianney lake, situated in the Oisans massif (French Alps) at an altitude of 2250 m, has a fish fauna composed of brook trout, Salvelinus fontinalis (Mitchell), and Artic charr, Salvelinus alpinus (L.). The present study examines the feeding behaviour of S. fontinalis in 1993–94 but also gives some data on S. alpinus . The brook trout represented 80% of the fish fauna of the lake. Dietary analysis showed that this species is an opportunistic feeder and revealed similarities in the trophic niches of S. fontinalis and S. alpinus and a low level of potentially available food resources. The annual growth of S. fontinalis was short and the growth rate was slow compared with other populations. Under these extreme conditions, female fish required several summers to replenish their reserves of energy and were only in condition to spawn once every 2 or 3 years. Although the fecundity of the population was low, it was sufficient to maintain the species in the lake which is not exploited.     

Influence of water temperature and fish age on mortality in brook trout (Salvelinus fontinalis) infected with infectious pancreatic necrosis virus (IPNV)

Brook trout, Salvelinus fontinalis, from hatching up to 31 weeks of age, were tested for susceptibility to IPNV at experimental temperatures of 5, 10 and 15°C. There were two different intervals of physiological age demonstrating specific characteristics of sensitivity to IPN viral infection in these fish. From 6 to 12 weeks of age, the peak mortality manifested itself around 21 days postinfection. In fish 15–21 weeks of age, mortality peaked as early as 10 days post-infection. Before or after these age intervals the fish did not appear to be sensitive to the virus. Moreover, the disease was produced at 10 and 15°C but fingerlings appeared resistant at 5°C.     

Relevance of Renibacterium salmoninarum in an asymptomatic carrier population of brook trout, Salvelinus fontinalis (Mitchill)

Abstract. These studies were done to determine the prevalence of infection, over time, of progeny from a population of 1988 year class brook trout, Salvelinus fontinalis (Mitchill), that was asymptomatically infected with Renibacterium salmoninarum , the causative agent of bacterial kidney disease. This population and its progeny from the 1991 and 1992 spawnings were monitored for approximately 3 years for prevalence of R. salmoninarum and development of bacterial kidney disease. Ovarian fluid samples from the 1991 and 1992 spawnings, and from a 1993 spawning of the 1991 progeny, were analysed for R. salmoninarum by enzyme linked immunosorbent assay (ELISA) and the membrane filtration fluorescent antibody technique. Kidney and spleen tissues of the 1988 year class were assayed by ELISA following the 1992 spawning. The progeny of the 1991 and 1992 spawnings were followed for increased prevalence of R. salmoninarum by the ELISA. Kidney tissues were assayed and sampling began once the fish were large enough. Each population of progeny was sampled quarterly for one year. Overall, the progeny displayed decreasing prevalence of R. salmoninarum and all ovarian fluids of the 1991 progeny (in 1993) were negative. Brood fish and progeny remained asymptomatic during the course of the study.     

Cytogenetic and histological studies of the brook trout, Salvelinus fontinalis (Mitchill), and the Arctic char, S. alpinus (L.) hybrids

Although brook trout and the Arctic char hybrids are able to reproduce, individuals with decreased fertility or even fish that are unable to produce any gametes have been also described. Abnormal gonadal development and disturbances in the gamete production in the char hybrid offspring may be triggered by the odd chromosome number and disturbances in their pairing during meiosis. To verify this hypothesis, cytogenetic examination and the gonadal histology analysis of the brook trout x Arctic char hybrids were carried out. Diploid chromosome number in the studied char (F₁) hybrids varied from 82 to 84 (FN = 99–102). Among 28 hybrids, 12 males, three females, nine intersex individuals and two sterile specimens were described. In the case of two individuals, gonads were not found. Diploid chromosome numbers in the males and intersex individuals varied from 82 to 84. Chromosome numbers in the females were 82 and 83 chromosomes. Two sterile fish exhibited karyotypes composed of 82 and 84 chromosomes. Predominance of the ovarian component in the intersex gonads and gonadal sex ratio distortion towards the males suggested hybrid females had problems with gonadal differentiation. However, the lack of the clear relationship between chromosome number and gonadal development in the studied hybrids did not support our hypothesis that odd chromosome number may be responsible for such reproductive disturbances in the hybrid individuals. We have presumed that sterility and intersexual development of the gonads may be caused by interactions between brook trout and Arctic char genes on the sex chromosomes and autosomes rather than unpairing of the parental chromosomes.     

Volume regulation in glutathione-treated brook trout (Salvelinus fontinalis) erythrocytes

Brook trout erythrocytes that were washed with and suspended in Ringer's solution with reduced glutathione (1.0 mM) maintained steady state cell volume for up to 24h, while those without the thiol-protective agent steadily shrank. Changes in cell volume (measured as packed cell volume, PCV) were evoked by acidic media (Ringer's at pH 6.8), hypoosmotic solutions (or both) and intracellular K⁺ and Cl⁻ concentrations were monitored over 4h. Acid-swollen cells failed to volume regulate or release K⁺ but had significantly elevated intracellular Cl⁻ Osmotically-swollen cells at pH 7.8 but not at pH 6.8 underwent regulatory volume decrease (RVD) and returned to initial levels in 2h, accompanied by release of K⁺ and Cl⁻ In contrast, osmotically-shrunken cells did not show regulatory volume increase. The regulatory volume decrease and concomitant K⁺ release were dependent on Cl⁻ implying a direct or indirect coupling of K⁺ to Cl⁻ transport in volume regulation. RVD was partially blocked by 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS, 0.1 mM), an anion exchange blocker, but was unaffected by amiloride (1.0 mM) which blocks Na⁺/H⁺ exchange. Amiloride and DIDS prevented the swelling response to low pH but had no effect on control cells, suggesting involvement of Na⁺/H⁺ and Cl⁻/HCO₃ ⁻ exchanges in acid-induced cell swelling. Quinine (1.0 mM) a known blocker of K⁺ channels, exacerbated the osmotically-induced swelling but had little effect on the subsequent RVD and release of KCl. The results suggest that low extracellular pH inhibits neutral C⁻-dependent K⁺ release and the resultant regulatory volume decrease in osmotically-swollen cells.     

Association between initial weight and weight gain in brook trout, Salvelinus fontinalis Mitchill, and brown trout, Salmo trutta L.

Abstract. Individual weighings of samples of brook trout, Salvelinus fontinalis Mitchill, and brown trout, Salmo trutta L., al the initiation and termination of their growth period, enabled estimating the association of weight gain on initial weight. In both cases the regressions were positive and the correlations significant. Variation in initial weight among tested individuals and groups is expected to bias growth estimates of these groups in programmes of genetic testing, as a result of this association. Obviating this bias requires an adequate correcting technique, involving the estimation of an environmentally generated correction factor. Phenotypic regression coefficients, as estimated in this investigation, cannot serve as correction factors, but may be regarded as maximum estimates.     

Sanguinicola fontinalis sp nov. (Digenea: Sanguinicolidae): a blood parasite of brook trout, Salvelinus fontinalis (Mitchill), and longnose dace, Rhinichthys cataractae (Valenciennes)

Abstract. Sanguinicola fontinalis sp. nov., from the branchial, renal and cardiac blood vessels of brook trout. Salvelinus fontinalis (Mitchill), and longnose dace, Rhinichthys cataractae (Valenciennes), is described. The new species most closely resembles, hut differs from, Sanguinicola davisi of steelhead and rainbow trout, Salmo gairdneri Richardson. The adult differs from all known North American species in having 29–33 lateral tufts of blunt spines. The snail host is Leptoxis (Mudalia) carinata (Bruquière, 1792). Lodged and migrating miracidia caused considerable gill damage in the brook trout, resulting in high mortality when the fish were moved. To remove the hazard, the most severely affected brook trout were destroyed and the ponds drained and disinfected. Adult worms from Pennsylvania brook trout and West Virginia longnose dace were studied, as well as infected snails.     

Changes in lipid classes and trypsin activity during the early development of brook chair, Salvelinus fontinalis (Mitchill), fry

Fertilized eggs of brook charr, Salvelinus fontinalis (Mitchill), (Nashua X Baldwin domestic strains) held for 86 days under laboratory conditions from eggs to fry were split into three groups: FWF2, FWF3 and SWF2. Breeders originated from the same broodstock, but rearing procedures were different; FWF2 and FWF3 were always kept in fresh water, whereas SWF2 had spent the previous summer in sea water. The SWF2 and FWF2 females were sexually mature before the FWF3 females. The feeding experiment started 16 weeks after fertilization. Juveniles were fed with the same commercial pellets at three different levels, a complete ration (R1) and two restricted rations, 50% and 25% of R1. Eggs and fry were analysed for size, dry weight, total lipids, lipid classes (polar lipids, cholesterol and triglycerides), soluble proteins and trypsic activity. Although dry weight, mean length, soluble protein and trypsic activities increased with food availability lipid changes showed a permanent use of the endogenous reserve. No lipid synthesis was detected in any developmental stage, even though exogenous food sources were used. When the 25% restricted ration was given, fry mortality increased. Unexpectedly fry survival tended to increase in individuals from small eggs. The data from this study showed that reserve distribution and its use can improve the resistance of fry hatching from small eggs and prompt better survival despite changes in the nutritional environment. The two factors related to the breeders, summer environmental rearing conditions and sexual maturation time, had significant effects on the response of progeny to feeding conditions.     

Alterations in iron, zinc and major plasma proteins of rainbow trout, Oncorhynchus mykiss (Walbaum), and brook trout, Salvelinus fontinalis (Mitchill), with sterile peritonitis induced by oil-adjuvanted multivalent bacterin vaccination

The early humoral responses of rainbow trout, Oncorhynchus mykiss (Walbaum), and brook trout, Salvelinus fontinalis (Mitchill), with sterile inflammation induced by intraperitoneal Lipogen Triple vaccination were compared to determine if genetic differences in susceptibility to furunculosis in salmonids correlated with different acute phase responses to vaccination. Similar severe acute sterile peritonitis occurred in response to Lipogen Triple in both species. Both species also had a rapid transient reduction in plasma iron concentration at 3 days. Moderate hypoferraemia persisted to day 14 in brook trout, but returned to normal by day 7 in rainbow trout. Plasma zinc decreased sharply 3 days after vaccination in rainbow trout and returned nearly to control levels by day 10; however, plasma zinc did not change in brook trout. Two-dimensional sodium dodecyl sulphate polyacrylamide electrophoresis of plasma proteins revealed that increased amounts of a 48-kDa protein group coincided with the hypoferraemic response in rainbow trout. In addition, a modest elevation in a 16-kDa protein group also occurred in rainbow trout. These studies demonstrated the rapid changes in plasma iron in both species and mild elevation of two putative acute phase plasma proteins associated with vaccine-induced inflammation in rainbow trout.     

Movements of Atlantic salmon, Salmo salar L., parr and brook trout, Salvelinus fontinalis (Mitchill), in lakes, and their impact on single-census population estimation

Three small Newfoundland lakes were fished to estimate the population sizes of Atlantic salmon, Salmo salar L., parr and brook trout, Salvelinus fontinalis (Mitchill), and to study within-lake movements of the species. The whole shoreline of the lakes was seined, the catches in different sections were recorded separately and the fish were given different marks. Estimates for the lakes derived from different subareas were constantly lower than the estimate derived by using the data from the whole shoreline. If estimates of the different sub-areas were extrapolated according to their proportion of the shoreline, they were positively biased, and showed higher variance. Significant correlations between the movement rates and the accuracy of sub-area population estimates and recapture rates were found. Validation of the assumption of random mixing of marked and unmarked fish, when a spatially stratified sampling is carried out, is emphasized.     

Survival, growth, sexual maturation and reproduction of brook charr, Salvelinus fontinalis (Mitchill), Arctic charr, Salvelinus alpinus L., and their hybrids

Survival of hybrids (FA, AF) between brook charr, Salvelinus fontinalis (Mitchill), (FF) and Arctic charr, Salvelinus alpinus L., (AA) were compared at three fish farms. Survival of hybrids and Arctic charr was impaired in warm water. In cold water, brook charr and hybrids showed similar survival percentages until the spawning period. Each spawning period was followed by an increase of mortality, but to a much higher degree in brook charr. Growth was studied in the best (cold water) fish farm. During the first 2 years of rearing, brook charr had the highest relative weight. The weight of the two hybrids approached that of brook charr in the third year because of the drastic decrease of growth rate in brook charr after the spawning period. No differences between genotypes of either females or males could be detected in the eviscerated weights, the dressing percentages, or the gonado-somatic indexes. The two hybrids matured sexually, but their sperm quality was inferior to that of the pure species. Crosses between the 4-year-old breeders from the F1 population (FF, FA, AF and AA) were achieved. Survival from the eyed stage to 6 weeks post-hatching was significantly lower in F2 progeny than in back-crosses or pure species crosses. Even though the survival following spawning periods and the total biomass produced were better in hybrids than in brook charr raised in cold water, we believe the farming of this hybrid should not be carried out. The full development of sexually mature hybrids does not resolve problems linked with precocious sexual maturation in brook charr farming carried out in eastern Canada.