Clostridium botulinum type C in healthy swine in Japan.

Healthy cattle and swine bred in a district of Japan were examined for the presence of Clostridium botulinum in their liver. Liver specimens were cultivated in chopped meat-glucose medium and the cultures were examined for botulinum toxin. In cattle, none of the cultures of 100 liver specimens yielded the toxin. In swine, however, C1 or C2 toxin was demonstrated in 8 of 100 liver specimens from 36 farms. One of the five farms where the carrier-state swine were present was surveyed for about 2 years to determine whether the carrier-state was transient or resident. C. botulinum type C was found in swine livers and feces, and environmental specimens at extremely high rates during the surveillances, with 76% of specimens yielding botulinum toxin following the culture. These data suggest that it is not uncommon for healthy swine to carry C. botulinum type C in the liver and that there is a close relationship between C. botulinum carrier-state in swine and the presence of this organism in their raising environments. In 20 cattle and 20 swine suffering from parturient paresis of unknown etiology no evidence for involvement of C. botulinum type C was obtained.     

Prevalence of Clostridium botulinum type E and coexistence of C. botulinum nonproteolytic type B in the river soil of Japan.

Soil samples from 98 sites in the whole systems of four rivers in Japan were examined for the presence of Clostridium botulinum. Type E organism was prevalently shown throughout the whole river systems including upper part; detection rates of type E toxin in soil culture ranged from 33 to 82%. This type was also detected in soil of adjacent mountainous district. Type B and C toxins were detected at 7% and 9% of the sites examined, respectively. C. botulinum type E and nonproteolytic type B strains were isolated from enrichment cultures of soil samples. These results suggest that the terrestrial origin of type E organism would be considered as one of the reasons for the high incidence of this organism in the sea areas, and prove that C. botulinum nonproteolytic type B exists in the soil of Japan.     

Selective haematological parameters in steelhead trout, Salmo gairdneri Richardson

Fifteen steelhead trout, Salmo gairdneri , were assayed for selective blood parameters. The trout were reared under flow-through conditions at the salmonid aquaculture facility at the University of Rhode Island. The means of the measured haematological parameters were: pH, 7·59 ± 0·05; pCO₂, 8·5 ± 1·05 mmHg; HCO₃-, 11·9 ± 1·9 meq/1; Ferri-Hb, 21·7 ± 2·0%; C1-, 147 ± 17·8 meq/1; Hct, 30·7 ± 4·8%.     

Migration of hatchery‐reared Atlantic salmon and wild anadromous brown trout post‐smolts in a Norwegian fjord system

Hatchery‐reared Atlantic salmon Salmo salar ( n  = 25) and wild anadromous brown trout (sea trout) Salmo trutta ( n  = 15) smolts were tagged with coded acoustic transmitters and released at the mouth of the River Eira on the west coast of Norway. Data logging receivers recorded the fish during their outward migration at 9, 32, 48 and 77 km from the release site. Seventeen Atlantic salmon (68%) and eight sea trout (53%) were recorded after release. Mean migratory speeds between different receiver sites ranged from 0·49 to 1·82 body lengths (total length) per second (bl s⁻¹) for Atlantic salmon and 0·11–2·60 bl s⁻¹ for sea trout. Atlantic salmon were recorded 9, 48 and 77 km from the river mouth on average 28, 65 and 83 h after release, respectively. Sea trout were recorded 9 km from the release site 438 h after release. Only four (23%) sea trout were detected in the outer part of the fjord system, while the rest of the fish seemed to stay in the inner fjord system. The Atlantic salmon stayed for a longer time in the inner part than in the outer parts of the fjord system, but distinct from sea trout, migrated through the whole fjord system into the ocean.     

Influence of sex, body size, and reproduction on overwinter lipid depletion in brook trout

Expressed as percentages of total fresh body weight, lipids of brook trout Salvelinus fontinalis declined between October and April: reproductive males from 2·89 to 1·22%, reproductive females from 3·19 to 1·84%, and non-reproductive males and females from 2·75 to 2·08%. The absolute and proportional overwinter reduction in lipids among reproductive trout was more than twice that of non-reproductive trout, with reproductive males losing significantly more lipids than reproductive females. Larger reproductive individuals lost more lipids during winter, relative to body size, than smaller individuals, although such an effect was not evident among non-reproductive trout. The average overwinter reduction in lipids for reproductive males (58%), females (42%), and non-reproductive trout (24%) was negatively associated with mark-recapture estimates of overwinter survival probabilities of 0·27, 0·36, and 0·58, respectively, providing support for the hypothesis that energy is allocated to reproduction to the detriment of post-reproductive survival. Our emergent hypothesis that reproductive costs differ between sexes, and the life history consequences thereof, merit further study.     

Effects of fish farm effluents on egg-to-fry development and survival of brown trout in artificial redds

Egg-to-fry development and survival of brown trout Salmo trutta were compared in two rivers of the Pyrenean piedmont, the Nive d'Arnéguy, with few human activities, and the Nive des Aldudes, with many anthropogenic activities including 11 fish farms and two sewage treatment plants (STPs). Survival was estimated between spawning (early December) and emergence time (early March) by means of capsules, 7 cm³ in volume, filled with green eggs then inserted into the gravel of artificial redds at spawning sites. In the Nive des Aldudes, three sets of conditions were studied: a fish farm near the springs, a fish farm and an STP in a village, and a series of fish farms and an STP in a village. In each situation, two artificial redds were created upstream and two others downstream from the fish farms. In the Nive d'Arnéguy, four sites were equipped: each of the two downstream sites with two artificial redds, and the two upstream sites with one redd. Substratum characteristics (proportion of fine particles) and the quality of surface and interstitial water (oxygen content, ammonia and nitrite nitrogen) were periodically measured. There was no redd substratum difference between sites upstream and downstream of fish farms. Survival to fry emergence was higher in the Nive d'Arnéguy (63·5%) than in the Nive des Aldudes (47·7%). In this latter river, the nitrogen released from the STPs was 0·5% that from fish farms. Fish farming impaired survival close to fish farm effluents (31·6%), as compared to survival upstream (63·6%), and induced a development delay during the yolk-sac fry stage. These differences were mainly linked to a drop in the dissolved oxygen content in interstitial water induced by the nitrogen flow in surface and interstitial waters.     

Evaluation of the contribution of supplemental plantings of brown trout Salmo trutta (L.) to a self-sustaining fishery in the Sydenham River, Ontario, Canada

An autumn planting of 4000 tagged yearling brown trout Salmo trutta (L.) in 1969 resulted in an over-winter survival of 26%, an angler recovery the following year of 8·1 % and made up 22 % of the March, 1970 standing population of the species. August standing populations of brown trout increased from 142 trout/ha (17·6 kg/ha) in 1969 to 360 trout/ha (39·3 kg/ha in 1970 while angler harvest of the species increased from 61 trout/ha (12·7 kg/ha) at a rate of 0·26 fish/h to 89 trout/ha (18·5 kg/ha) at a rate of 0·34/h. Using angler recovery and standing population as criteria the planting contributed substantially to the fishery. Actual contribution of stocked trout however, is questioned after detailed analysis of resident population structure and the potential of natural recruitment. It is suggested that the true benefit of stocked trout may be measured by the presence of those stocked fish in excess of the number of resident trout of that size predictable from a normal length distribution curve in waters with self-sustaining populations. Complexities in evaluating the merits of supplemental plantings of hatchery-reared brown trout to existing stream fisheries are examined.     

Thermal dependence of swimming endurance in juvenile brown trout

The maximum swimming stamina of hatchery reared juvenile brown trout Salmo trutta , swimming against a fixed-velocity water flow of 36·6 cm s^-1 (6·97 L s^-1), was achieved at 16·1° C, and a 90% performance level occurred over a breadth of 7·7° C (12·2–19·9° C). The wide range of temperatures at which swimming performance is close to the maximal capacity could be a consequence of the implications for survival of this function.     

Differences in susceptibility to sea lice infection between a sea run and a freshwater resident population of brown trout

Two experimental groups comprising mixed Norwegian sea run and freshwater resident brown trout Salmo trutta were infected with sea lice Lepeophtheirus salmonis in replicate tanks. Comparison of mean abundance and louse development between the sea run and resident groups revealed highly significant differences in lice abundance. The resident trout had an average abundance ± of 6·3±0·37 and 6·6±0·43 lice whilst the sea trout had an average abundance of 3·5 ±0·25 and 3·3 ±0·28 lice 29 days post infection at 9° C. No differences in development of lice, of either sex, were detected between the groups. As host groups were naive to sea lice at the start of the experiment, this suggests that there was a significant difference in susceptibility to sea lice infection between them, which may be genetically determined.     

Radio-transmitted electromyogram signals as indicators of swimming speed in lake trout and brown trout

Swimming speed and average electromyogram (EMG) pulse intervals were highly correlated in individual lake trout Salvelinus namaycush ( r ²=0·52–0·89) and brown trout Salmo trutta ( r ²=0·45–0·96). High correlations were found also for pooled data in both lake trout ( r ²=0·90) and brown trout of the Emå stock ( r ²=0·96) and Lærdal stock ( r ²=0·96). The linear relationship between swimming speed and average EMG pulse intervals differed significantly among lake trout and the brown trout stocks. This successful calibration of EMGs to swimming speed opens the possibility of recording swimming speed of free swimming lake trout and brown trout in situ . EMGs can also be calibrated to oxygen consumption to record energy expenditure.     

Maturation of male age-0 Atlantic salmon following a massive, localized flood

Maturation of male age-0 Atlantic salmon Salmo salar parr in New England, U.S.A. streams is rare (˜5%), but age-0 parr maturation was high (74%) by autumn in the Sawmill River following a massive, localized flood. Maturation was low in two other study streams (3, 7%) in the same year as the flood, and in the Sawmill River (6%) and the other rivers (5%) in the subsequent year, suggesting that high maturation rates were related to the flood. The high age-0 maturation rates appear to have been the result of greater growth opportunity following the flood. Masses of fish in October were two-fold greater in the Sawmill River (13·2 g) than in the other rivers (6·5, 6·9 g). Mechanisms contributing to the fast growth may include community reorganization following the flood and water temperature differences among rivers. The flood caused an age-0 year-class failure for brook trout Salvelinus fontinalis and brown trout Salmo trutta and a large reduction (69%) in the number of salmon compared to the other rivers, possibly reducing competition or agonistic interactions among remaining fish. Average water temperatures were slightly warmer in the Sawmill River (17·0° C) than in the other rivers (15·5, 14·9° C). By influencing community structure and growth of remaining fish, it appears that a strong environmental disturbance can also alter the direction and timing of life histories in Atlantic salmon.     

The distribution of salmonids in upland streams in relation to depth and gradient

The distribution of various age classes of salmon and trout was assessed in upland streams by electrofishing. Water depths and site gradients were measured and correlated to fish densities. The fry of both species were significantly more abundant in shallow water; up to 75·3% of salmon fry and 72·2% of trout fry were captured in sites of mean depth < 20 cm. Older trout were found mainly in the deeper areas, with a maximum of 7·4% captured in sites < 20 cm mean depth. Yearling fish were found in all the depth-ranges sampled, but with a tendency for higher numbers in mid-range depths. There were similar correlations in the abundance of each age class with the actual areas of shallow, mid-range and deep water habitat available within sites. Correlations of fish density with gradient indicated that trout were limited in their distribution to areas of lower flow, whereas salmon were not. Since depth and gradient were significantly negatively correlated, there was an apparent preference of trout for slightly deeper habitats than the equivalent year classes of salmon. The observed habitat segregation is discussed in terms of competition and selection.     

The immunoglobulin of the brown trout, Salmo trutta and its concentration in the serum of antigen-stimulated and non-stimulated fish

Immunoglobulin production in the primary and secondary immune response of brown trout to keyhole limpet haemocyanin has been investigated including the effect of dose size, route and number of injections, and the use of adjuvant. Antibody activity was found in the first fraction from Sephadex G200 and in the second from Sepharose 6B. Trout immunoglobulin had β₂—Γ₁ electrophoretic mobility, and S_app of 16·7 and an approximate molecular weight of 670 000 daltons. It was sensitive to dithiothreitol and stable at 56°C for 30 min. Immunoglobulin concentrations were measured by single radial immunodiffusion with a specific rabbit antiserum. Sera from non-injected trout had a mean immunoglobulin level of 7·3 ± 0·3 mg ml⁻¹ which accounted for 10% of the total serum protein. Phosphate buffered saline-injected controls contained 6·7 ± 0·2. In fish given a single injection the mean concentration ranged from 7·5 to 12·9 and in those given more than one injection from 12·6 to 16·8. The use of adjuvant resulted in higher immunoglobulin concentrations. Neither dose nor route had any significant effect on the primary response. However, in the secondary response the intramuscular route resulted in significantly increased immunoglobulin production.     

Bacillus thuringiensis populations naturally occurring on mulberry leaves: a possible source of the populations associated with silkworm-rearing insectaries

Mulberry leaves were examined for the occurrence of Bacillus thuringiensis. This organism was recovered from both abaxial and adaxial surfaces: a total of 186 B. thuringiensis colonies were isolated from 24 (96·0%) out of 25 mulberry trees, and from 112 (11·2%) out of 1004 leaves from 25 trees. The frequency of B. thuringiensis colonies was 3·2% among 5900 colonies belonging to the Bacillus cereus/B. thuringiensis group. Single colonies were associated with 75·9% of the B. thuringiensis -positive leaves and 2–16 colonies were occasionally found on a single phylloplane. Flagellar (H) serotypying of the isolates revealed that, among the 19 H serotypes (serovars) detected, the H serotype 13 (serovar pakistani ) was the predominant, followed by the H serotypes 3abc ( kurstaki ), 6ac ( oyamensis ), 16 ( indiana ), 24 ( neoleonesis ), 4ac ( kenyae ), 7 ( aizawai ) and 10 ( darmstadiensis ). Larvicidal activity, against the silkworm ( Bombyx mori ) and/or the mosquito ( Aedes aegypti ), was exhibited by 18 isolates (9·7%) belonging to H serovars kurstaki, kenyae, canadensis and aizawai , and an unidentified H serogroup.     

The feeding response of diploid and triploid Atlantic salmon and brook trout

Pair and group experiments were conducted to determine whether differences exist in feeding success between juvenile diploid and triploid salmonids in a competitive situation. In the pair experiments, 22 pairs (one diploid and one triploid) of size-matched Quebec-strain brook trout Salvelinus fontinalis (7·2–46·3 g) were fed an unlimited number of pellets three times a day for 5 days. Dominance was assigned to the fish which ate the most pellets within each pair. In the group experiments, groups of three diploid and three triploid size-matched fish were fed a restricted ration three times a day for 5 days. Hierarchical rank within the group was assigned based on the number of pellets consumed by each fish. The group experiment was repeated 10 times with Atlantic salmon Salmo salar (5·1–62·7 g), Quebec-strain brook trout (11·8-110·8 g), and large UNB-strain brook trout (18·2–33·0 g), and 12 times with smaller UNB-strain brook trout (0·6–2·0 g). A statistically significant difference in rank between ploidies was found only for the smaller UNB-strain brook trout in the group experiments, with diploids dominant over triploids. This suggests that there may be a difference in competitive feeding success between diploid and triploid brook trout early in development, but that this difference diminishes as the fish grow.     

Effects of cadmium chloride on the development of rainbow trout Oncorhynchus mykiss early life stages

The sub-chronic (28–56 days) effects of exposure to low concentrations of cadmium (Cd; 0·05, 0·25, 0·50 and 2·50 μg l⁻¹) shortly following fertilization on embryos, larvae and juvenile rainbow trout Oncorhynchus mykiss were examined. Premature hatching occurred at lower concentrations (0·05 and 0·25 μg l⁻¹ Cd), however, delayed hatching was seen in the 2·50 μg l⁻¹ Cd group, with >90% of hatching occurring on the last day of the hatching period. Larval growth was negatively affected by Cd exposure in a concentration-dependent manner. Larvae exposed to 2·50 μg l⁻¹ Cd were 13·9 ± 0·8% shorter in total length ( L _T) and weighed 22·4 ± 3·5% (mean ± s . e .) less than controls at the end of the exposure period. Plasma sex steroid concentrations (oestradiol in juvenile females and 11-ketotestosterone in juvenile males) were elevated (four- to 10-fold over controls) in exposed fish in both males and females, following 28 days of exposure to 0·05, 0·25 and 0·50 μg l⁻¹ Cd, respectively. These results suggest that environmentally realistic concentrations (in the μg l⁻¹ range) of Cd can affect the development of O. mykiss impacting embryos, larvae and juvenile fish.     

The trout (Salmo trutta) population of the Afon Cwm, a small tributary of the Afon Dyfi, mid-Wales

Data are presented from a 10-year (1984 to 1993) study of a Salmo trutta population in the Afon Cwm, a small tributary of the Afon Dyfi, mid-Wales. The stream is a spawning and nursery area for sea trout. Growth of trout within the stream can be summarized by a von Bertalanffy growth coefficient ( K ) of 0·310, with asymptotic length (1∞) 21·6 cm and with length at age 1 of 7·6 cm. Mean population density in the whole stream varied from year to year between 0·05 and 0·60 0-group trout m⁻² and between 0·05 and 0·70 older trout m⁻². Mean biomass varied, between years, from 0·1 to 3·5 g m⁻² for 0-group and from 1·3 to 10·4g m⁻² for older trout. Loss between 3 and 5 months of age appeared to be proportionate at about 50 to 60% and instantaneous loss rate from 5 to 53 months of age varied from 0·04 to 0·10 month⁻¹ and was positively correlated with cohort number at 3 months of age. Production between 3 and 53 months of age varied between cohorts from 3 to 8 g m ⁻² live weight.     

The seasonal variation of thermophilic campylobacters in beef cattle, dairy cattle and calves

The epidemiology of clinical cases of campylobacter in temperate climates shows a striking seasonality. In the search for a seasonal environmental reservoir changes in the carriage rate and population size of campylobacters in bovine hosts with time have been measured. Most probable number (MPN) methodology was used to enumerate thermophilic campylobacters in samples taken from the small intestines of beef cattle at slaughter and the fresh faeces of four dairy herds and new-born calves. Statistical analyses revealed significant evidence for seasonal periodicity in the data from dairy herds ( P = 0·044). Not only was there a departure from constancy within a 12-month interval but these data revealed a true seasonality, that is, the same periodicity in numbers from one year to the next. Each herd had two peaks per year, in approximately spring and autumn. Peaks coincided in herds on neighbouring farms but those on farms in the north preceded those on farms in the south by 2 and 1 months, respectively ( P = 0·0057). Intestinal carriage by beef cattle at slaughter was 89·4% ( n = 360) with an average MPN campylobacters per gram fresh weight (MPN gfw⁻¹) of 6·1 × 10². Average MPN gfw⁻¹ in faeces from the dairy herds and calves were 69·9 ( S.D. 3) and 3·3 × 10⁴ ( S.D. 1·7 × 10²). There was no evidence of seasonal periodicity in the size of the campylobacter population in beef cattle at slaughter. Calves were campylobacter free at birth but became colonized within a few days.     

Circadian rhythms of demand-feeding and locomotor activity in rainbow trout

Under free-running conditions, most rainbow trout displayed circadian feeding rhythms, although the expression of circadian rhythmicity depended on the experimental condition: 16·7% of fish under constant dim light (LL dim), 66·1% under a 45 :45 min light-dark cycle (LD pulses), and 83·8% under constant light (LL). Under LD pulses, the period length of the free-running rhythms for feeding was significantly shorter (21·9 ± 0·7 h, n =8) than under LL (26·2 ± 0·3 h, n =10). Period length for locomotor activity under LL was 25·8 ± 0·6 h ( n =4). Under LD conditions, the daily demand-feeding profile was always confined to the light phase and chiefly composed of two main episodes, directly after lights on (light elicited) and in anticipation to lights off (endogenous). Contrasting to feeding, the diel locomotor activity profile varied remarkably: a diurnal activity pattern at the bottom, while a clearly nocturnal pattern at the surface. These results contribute to a better understanding of feeding and locomotor rhythms of rainbow trout, providing evidence for the existence of a biological clock involved in their circadian control. This finding contrasts with the previously recorded lack of an endogenous oscillator in the pineal organ driving the rhythmic secretion of melatonin, which suggests different locations from the pineal for the circadian pacemakers in this species.     

Pools as refugia for brown trout during two summer droughts: trout responses to thermal and oxygen stress

In non–drought years (1977, 1985), temperatures and oxygen concentrations from 1 to 14 July at the deepest point in each of five pools in Wilfin Beck were similar with ranges of 12–18° C and 7·8–9·8 mg l^–1. Trout Salmo trutta were present in all pools. In drought years (1976, 1983), temperature increased and oxygen concentration decreased as pool size decreased. In the two smallest pools, they were outside the thermal and oxygen limits for trout (ranges for both pools 24–29° C, 1·2–2·5 mg l^–1), and trout were absent. Values in a medium–sized pool were close to the incipient lethal levels and a few juvenile trout were present in both drought years. The lowest temperatures and highest oxygen concentrations were recorded in the two largest pools (ranges 20–25° C, 3·6–4·8 mg l^–1) and trout of all ages (0+ to adults) were present in both drought years. In these two pools, both temperature and oxygen concentration decreased from the surface to the deepest point in the pool. Trout preferred lower temperatures near the pool bottom rather than higher oxygen concentrations near the surface, but some fish moved towards the surface at night when the pool cooled slightly. These field results were discussed in relation to lethal values recorded for brown trout in the laboratory, and there was general agreement between field and laboratory values. Trout in the drought years occurred at temperatures close to, or below, the incipient lethal value of 24·7° C (+0·5) and also at the highest oxygen concentrations, but only when these were at temperatures below the incipient lethal value.