Growth, diet and metabolism of common wolf–fish in the North Sea, a fast–growing population

The von Bertalanffy growth parameters for common wolf–fish Anarhichas lupus in the North Sea were: male: L ∞=111·2 cm, t ₀=–0·43 and K =0·12; and female: L ∞=115·1 cm, t ₀=–0·39 and K =0·11, making this the fastest growing stock reported. Resting metabolic rates (RMR±S.E.) and maximum metabolic rates (MMR±S.E.) for six adult common wolf–fish (mean weight, 1·39 kg) at 5° C were 12·18±1·6 mg O₂ kg^–1 h^–1 and 70·65±7·63 mg O₂ kg^–1 h^–1 respectively, and at 10° C were 25·43±1·31 mg O₂ kg^–1 h^–1 and 113·84±16·26 mg O₂ kg^–1 h^–1. Absolute metabolic scope was 53% greater at 10° C than at 5° C. The diet was dominated by Decapoda (39% overall by relative occurrence), Bivalvia (20%) and Gastropoda (12%). Sea urchins, typically of low energy value, occupied only 7% of the diet. The fast growth probably resulted from summer temperatures approximating to the optimum for food processing and growth, but may have been influenced by diet, and reduced competition following high fishing intensity.     

Comparison of several techniques for mobility and activity estimates of smallmouth bass in lentic environments

Mean daily mobility estimates for smallmouth bass Micropterus dolomieu from mark-recapture (47·5±12·5 m) were less than from conventional telemetry (77·1±10·6 m). The relationship developed in a respirometer between the activity transmitter and swimming speed ( r 2=0·99, P < 0·001, n =6) when applied to field activity data estimated mean daily movement at 27 408±4085 m, i.e. >100 times mark/recapture or telemetry estimates. Using these estimates in the activity parameter of a bioenergetics model resulted in different model outputs. These results highlight the potential underestimates in activity associated with using traditional mark-recapture and locational telemetry and reaffirm that fish expend a significant portion of their activity budgets undertaking localized movements.     

Temporal and spatial variation in length of larval life and size at settlement of the Hawaiian amphidromous goby Lentipes concolor

Larvae of the Hawaiian amphidromous goby Lentipes concolor settled after a mean length of larval life (LLL) of 86·2±8·5 days (n=236, range=63–106 days) at a mean size of 16·0±0·7 mm LT (n=154, range=14·1-17·9 mm). Mean LLL for L. concolor was about twice that typically reported for tropical marine gobiids. Variation in LLL (CV=10%) and size at settlement (CV=4%) were low, and comparable to that for marine gobiids. LLL and L_T were weakly positively correlated (Pearson's correlation coefficient r=0·50, P<0·0001). Larvae settled after shorter planktonic lives and at smaller sizes during months with warmer ocean temperatures. Inter-island variation in LLL did not support a dominant south-east to north-west larval drift, following the dominant south-east to north-west flow of prevailing currents in the Archipelago. Instead, recruits on Maui Island, centrally located in the archipelago, had shorter LLL than recruits to upstream Hawai'i and downstream Kaua'i islands. These findings have important implications for understanding the complex life history dynamics of amphidromous fishes as well as their management.     

The relationship of oocyte diameter and incubation temperature to incubation time in temperate freshwater fish species

Based on the analysis of six egg variables and incubation temperature of 65 temperate freshwater fish species, the possible relationships between oocyte diameter, incubation time and incubation temperature were reassessed and compared to the results obtained from marine fishes. Most freshwater species have eggs (mean ± s . d . 2·19 ± 1·52 mm) larger than marine species, that are chiefly demersal and develop stuck to various substrata, such as plants or rocks. A strong negative relationship was found between incubation time ( t , days) and incubation temperature ( T , ° C): t = 186·23e^{−0·197 T} ( r ²= 0·87). A strong dependence of incubation time on oocyte diameter ( Ø , mm) and incubation temperature was also found and was defined as: log₁₀ t = 3·002 + 0·599 log₁₀ Ø − 1·91 log₁₀ ( T + 2), which explained 92% of the variance of the data set. Five major groups of species were defined based on the principal component analysis (PCA) of four quantitative variables. There were two distinct groups of salmonids, displaying demersal and non-adhesive eggs with a long incubation time at low temperature, the eggs of which required a high number of degree-days. There was a large group of species possessing small, mostly demersal and adhesive eggs developing at high temperature during a short period of time, and requiring a low number of degree-days. Between these two extremes, there was a fourth group displaying intermediate values and a fifth group including three species with large, adhesive and demersal eggs incubating at high temperatures during a short period of time. The burbot Lota lota displayed an unusual combination of variables compared to the remaining species in the data set.     

Seasonal changes in the habitat use and movements of adult European grayling in a large subarctic river

In late summer (13 August–13 September 1998), at water temperatures of 12·0–15·7° C, grayling ( n =14) stayed mainly in the riffle-section where they were captured in a large regulated river in northern Finland, moving little between consecutive days. In autumn (2–30 October 1998), at 1·7–6·7° C, the fish ( n =16) migrated to potential overwintering sites 0–14 km up- or downstream by mid October, moving mainly short distances thereafter. The daily movement rates, and the total ranges covered by the fish in late summer and autumn were 54±32 m (mean± s.d ) and 1053±1636 m, and 190±168 m and 3135±1850 m, respectively. In autumn the fish used deeper habitats (most suitable range 150–400 cm) with lower current velocities (20–80 cm s⁻¹) and finer bottom substrata (mainly sand) than in late summer (depth 100–325 cm, velocity 30–110 cm s⁻¹, and cobble-boulder substrata).     

Thermal tolerance of a northern population of striped bass Morone saxatilis

Thermal tolerance of age 0+ year Shubenacadie River (Nova Scotia, Canada) striped bass Morone saxatilis juveniles (mean ± s . e . fork length, L _F, 19·2 ± 0·2 cm) acclimated in fresh water to six temperatures from 5 to 30° C was measured by both the incipient lethal technique (72 h assay), and the critical thermal method ( C _m). The lower incipient lethal temperature ranged from 2·4 to 11·3° C, and the upper incipient lethal temperature ( I _U) from 24·4 to 33·9° C. The area of thermal tolerance was 618° C². In a separate experiment, the I _U of large age 2+ year fish (34·4 ± 0·5 cm L _F) was 1·2 and 0·6° C lower ( P < 0·01) than smaller age 1+ year fish (21·8 ± 0·5 cm L _F) at acclimation temperatures of 16 and 23° C. Using the C _m, loss of equilibrium occurred at 27·4–37·7° C, loss of righting response at 28·1–38·4° C and onset of spasms at 28·5–38·8° C, depending on acclimation temperature. The linear regression slopes for these three responses were statistically similar (0·41; P > 0·05), but the intercepts differed (25·3, 26·0 and 26·5° C; P < 0·01). The thermal tolerance of this northern population appears to be broader than southern populations.     

Thermally induced phenotypic plasticity of swimming performance in European sea bass Dicentrarchus labrax juveniles

The vulnerability of embryonic and larval stages of European sea bass Dicentrarchus labrax to environmental temperature and the longer-term consequences for the early juveniles was demonstrated. This phenotypic plasticity was highlighted by subjecting D. labrax at 15·2 ± 0·3 or 20·0 ± 0·4° C (mean ± s . d .) up to metamorphosis and then at the same temperature (18·5 ± 0·7° C). After 4–6 weeks at the same temperature, the measurement of critical swimming speed at four exercise temperatures (15, 20, 25 and 28° C) showed a significantly higher swimming capacity in the fish initially reared at 15° C than for fish initially reared at 20° C. This performance was correlated with significant differences in the phenotype of red muscle. Thermally induced phenotypic plasticity was clearly demonstrated as an important mechanism controlling swimming performance in early juveniles of D. labrax .     

The direct epifluorescent filter technique (DEFT): increased selectivity, sensitivity and rapidity

With the direct epifluorescent filter technique (DEFT), differentiation of bacteria was achieved by a modified Gram-staining procedure using acridine orange as the counterstain. The method enumerated viable Gram-negative and all Gram-positive bacteria. Counts of clumps of orange fluorescent cells (Gram-negative DEFT count) correlated well with colony counts of Gram-negative bacteria in samples of raw milk ( r = 0·94). The use of stainless steel membrane filter supports and the addition of citrate-NaOH buffer (0·1 M, pH 3·0) during filtration enabled 10 ml samples of milk to be filtered, thereby increasing the sensitivity of the DEFT five-fold. The relationship between colony and DEFT counts with 10 ml samples was better ( r = 0·90) than that using standard 2 ml samples ( r = 0·88). Alternatively, these modifications in procedure allowed the preincubation time for 2 ml milk samples to be reduced from 10 to 2 min. Sonication was successful in dispersing bacterial clumps in both pure cultures and in raw milk samples to yield a bacterial count by DEFT which should give a better indication of the hygienic status and keeping quality of a product, than counts of colony forming units.     

Osmoregulation during the development of glass eels and elvers

Drinking rates in glass eels and elvers of the European eel increased with environmental acclimation salinity from 0·07±0·02 (FW) to 0·70±0·09 μl g-¹ h-¹ (SW) at month 1 and from 1·12±0·42 (FW) to 12·85±1·05 ± l g-¹ h-¹ (SW) at month 5. Drinking rates increased with time in both FW and SW groups. FW acclimated eels when challenged acutely with SW increased drinking rate rapidly immediately upon transfer (0–15 min) and the magnitude of this response increased with developmental time from month 1 to month 5.     

Temporal resource partitioning varies with individual competitive ability: a test with Arctic charr Salvelinus alpinus visiting a feeding site from a refuge

The relationship among relative size, growth rate and diel visits into a feeding compartment were studied in Arctic charr Salvelinus alpinus , a species known for its flexible activity patterns. Individual swimming activity from a refuge compartment into an uncovered feeding compartment was studied using an automated passive integrated transponder system. Approximately half of the individuals in four groups of S. alpinus spent 70–80% of their time in the feeding compartment, regardless of the time of day. The remaining individuals spent nearly as much time (70–80%) in the feeding compartment during the night, but only spent c. 20% of their time in the feeding compartment during the day. These individuals had a lower mean ± s . d . masses (13·17 ± 4·34 g) and growth rate (daily growth coefficient, G = 0·80 ± 1·19) than those individuals that spent most of their time in the feeding compartment during the day (mass = 16·65 ± 5·73 g and G = 2·04 ± 0·81). This indicated that some smaller fish were absent from the feeding compartment during daytime, possibly to avoid aggression from larger conspecifics. In the open compartment, the aggressive interactions were more frequent in daylight than during night and always low in the covered compartment.     

The use of a surface adhesion immunofluorescent (SAIF) method for the rapid detection of Yersinia enterocolitica serotype O:3 in meat

This study examined the attachment kinetics of Yersinia enterocolitica serotype O:3 to determine the optimum conditions for its isolation from meat enrichment systems using a novel surface adhesion technique. Minced beef was inoculated with Y. enterocolitica at an initial level of 10 cfu g⁻¹ and incubated at 25 °C in an enrichment broth. Yersinia was recovered from enriched samples on polycarbonate membranes by surface adhesion and enumerated using immunofluorescence microscopy. The surface adhesion immunofluorescence technique (SAIF) had a minimum detection limit of approximately 4·0–4·5 log₁₀ cfu ml⁻¹ and provided good correlation between the estimation of the numbers of Yersinia in the enrichment broth derived from plate counts on Yersinia Selective agar (CIN) and those determined by SAIF ( r ² ₌ 0·94; rsd ₌ ± 0·21). A derived regression equation of the SAIF count vs plate counts was used to predict Y. enterocolitica numbers in spiked meat samples stored at 0 °C for up to 20 d. The numbers as predicted by the SAIF method showed good correlation with counts derived by plating techniques ( r ² ₌ 0·78; rsd ₌ ± 0·42). The application of the SAIF technique for the rapid detection of Y. enterocolitica serotype O:3 from meat is discussed.     

Breeding season, litter size and nestling mortality of the Harvest mouse, Micromys minutus (Rodentia: Muridae), in Britain

Data are presented on the breeding biology of Micromys minutus in Britain. It is shown that although litters are produced over a protracted period (May-December), 74% of the litters are born in August and September. Mean litter size is 5·40±0·16( n = 62), which is a significant reduction on the mean litter size of 6·75±0·40( n = 16) calculated from pre-1917 literature. Litter size was found to be constant throughout the breeding season, and there was no difference in mean litter size between two samples collected close to the northern and southern limits of the known British range. By comparing the mean litter size of samples 1–5, 6–10 and 11+ days old, no significant loss of individual mice within litters could be detected, although 12·3% of all litters died prior to weaning. This loss was predominantly of autumnal litters, cold and wet being important climatic factors that terminate the breeding season. Comparisons are made with data from other parts of the animal's range.     

Poikilothermic traits and thermoregulation in the Afrotropical social subterranean Mashona mole-rat (Cryptomys hottentotus darlingi) (Rodentia: Bathyergidae)

When acclaimated for two months at 26 C the social Mashona mole-rat Cryptomys hottentotus darlingi (±S.D.) resting metabolic rate (RMR) of 0·98±0.·14cm²O₂g _-1 h_-1 ( n =21), within a thermal neutral zone (TNZ) of 28 31·5 C ambient temperature (Ta). The body temperature (Tb) of the mole-rat is very low. 33·3±0·5 C, and remained stable between 25 31·5 C ( n =28). Above 33 C. Tb increased to a mean of 34·±0· C (n=28) (Ta range 33 39 C). Below Ta 25 C. Tb showed strong poikilothermic tendencies, with Tb dropping to a mean of 26·8±1·16 C. whereas above Ta25 C. Tb varied in a typically endothermic pattern. The conductance is high 0·19±0·03 cm² O_2g¹ C ¹ (n=28) at the lower limit of thermoneutrality. The mean RMR at 18 C (the lowest Ta tested) was 2·63 ± 0·55 cm³ O₂g ¹ h ¹ (n=7) which is 2·6 times that of the resting metabolic rate in the TNZ.     

Effects of angling on feeding by largemouth bass

Angling practice significantly effected the time required for largemouth bass Micropterus salmoides to begin feeding. Mean ± s.e. time until feeding resumed was longest for fish that experienced a simulated tournament (15·6 ± 2·2 h) followed by fish that were caught and released (8·4 ± 2·2 h) and controls (0·3 ± 1·6 h). Effects on feeding related to angling practices were maintained throughout the 48 h observation period. Using multiple logistic regression and bioenergetics simulations, decreased growth in fish subjected to competitive or catch-and-release angling events was predicted. Fish subjected to multiple captures in a pond experiment had greater mass loss than those not captured, supporting model predictions.     

Heat resistance of Salmonella enteritidis PT4: the influence of prior exposure to alkaline conditions

Salmonella enteritidis phage type 4 incubated in broth at pH 9·2 ± 0·2 for 5 min or longer became significantly more heat-resistant ( P < 0·001) when subsequently heated at pH 7·0 but not when heated at pH 9·0. The induction of enhanced heat resistance was not associated with an increase in cell numbers, occurred rapidly and was probably phenotypic.     

Spawning characteristics of the anadromous brown trout in a small Swedish stream

The spawning pattern of the anadromous brown trout Salmo trutta was studied in Själsöån, a small stream in Gotland, Sweden, during eight winters between 1992–1993 and 1999–2000. The total length ( L _T) at spawning was normally distributed (185–890 mm) for females and multimodal for males (300, 400 and 550 mm most frequent length classes). Spawning males were significantly younger (2+ to 4+ years) than females (3+ to 5+ years). The sex‐ratio at the beginning and at the end of the spawning season favoured males. The mean ±  s . d . number of spawners was 70 ± 16 individuals per year. Migration into and out of the stream occurred between November and June. The highest number of spawning fish was found in the stream at the end of November or at the beginning of December. Migration mainly occurred during high water flow and at night. The majority of the females entered the stream and spawned the same (29·3% of all the females) or the next night (32·8% of all the females) while males may have stayed for 2 to 3 weeks (21·3% of all the males) in the stream before spawning. Males usually remained much longer in the stream (mean ±  s . d . 45 ± 56 days) than females (16 ± 30 days). Females lost more mass in the stream (mean ±  s . d . 17·3 ± 8·6%) than males (7·7 ± 9·6%). For both sexes, mass loss was positively correlated with the time spent in the stream. Only 7·3% of the males and 5·7% of the females occurred in the stream for >1 year. Spawning took place only during the night.     

The angle of attack of the body of common bream while swimming at different speeds in a flume tank

The body attack angle of common bream Abramis brama varied with swimming speed and was best described by θ = −3·32 (±0·24) − 9·23 (±0·54)e^{− u} ( r ² = 0·56, P  < 0·0001; ±1 s . e . given in parentheses), where θ is the body attack angle and u is swimming speed. The hypothesis that neutrally buoyant fishes may swim with body attack angles deviating increasingly from 0° as the swimming speed decreases is supported.     

Differences in size and growth rates of male and female migrating Japanese eels in Pearl River, China

The Sr/Ca ratios in otoliths of silver Japanese eels Anguilla japonica , in Pearl River, China, indicated that both sexes did not stay in brackish water and grew in fresh water from the glass eel stage until spawning migration. This did not support the hypothesis that females tended to distribute upstream and males might be restricted to estuaries. The back-calculated total length of males at glass eel stage was not significantly different from that of females, indicating that the hypothesis that small glass eels became males and larger ones became females may not be true. The mean (±S.D.) age and total length of males at migration were 6·4±1·6 years and 48·3±4·5 cm, which were significantly smaller than for females, 8·3±1·6 years and 61·4±4·1 cm. The age of migration was related inversely to growth rate for both sexes. Growth parameters of the von Bertalanffy growth equation were K =0·21 cm year°1, L _∞=55·7 cm and t _o=-0·55 year for males and K =0·14 cm year⁻¹, L _∞=77·5 cm and t _o=-0·60 year for females. The difference in asymptotic length ( L _∞) between males and females may be because females postpone migration to achieve larger size for maximizing reproductive success.     

Cohesive social behaviour shortens the stress response: the effects of conspecifics on the stress response in lake sturgeon Acipenser fulvescens

An examination was made of whether social interactions can have a beneficial effect through the attenuation of the stress response in a social species. In the first experiment, one larger (mean ± s . e . 194·0 ± 12·5 g) and seven smaller (32·0 ± 2·6 g) juvenile lake sturgeon Acipenser fulvescens were placed in tanks to determine whether a classic dominance effect would be established based on body size ( n = 6). Large fish did not establish a territory or aggressively interact with smaller fish, as there were no significant differences in nearest-neighbour distances and an absence of aggressive behaviour (biting, chasing and pushing). In the second experiment, it was hypothesized that the presence of conspecifics would have a beneficial effect through an attenuation of the stress response. Fish in groups or isolation were stressed by a brief aerial exposure (30 s), and blood plasma was measured at regular time intervals (0, 20, 40, 60, 120 and 240 min) following the stressor via an implanted cannula ( n = 9–11). The presence of conspecifics did not affect the peak cortisol response, however, the overall cortisol response was shorter in duration compared to fish in isolation. Furthermore, secondary stress variables (plasma ions and glucose) showed differences between fish in groups and isolation. The results of these experiments suggest that social interaction plays an important and beneficial role in regulating the stress response in cohesive social species such as A. fulvescens .     

Muscle fine structure reflects ecotype in two nototheniids

The fine structure of swimming (pectoral) and myotomal (axial) skeletal muscle and myocardium of two species of Antarctic nototheniid fishes were studied by electron microscopy, comparing the cryopelagic Pagothenia borchgrevinki and the benthic Trematomus bernacchii . Mean fibre size varied by a factor of four among muscles within each species and may have reflected the locomotory power available, being larger in pectoral oxidative (red) and axial glycolytic (white) muscle of P. borchgrevinki . Both species use labriform locomotion, and the more active P. borchgrevinki had a greater capillary supply, expressed as a capillary to fibre ratio, than T. bernacchii to both red (3·48 ± 0·36 v . 1·63 ± 0·14, mean ±  s . e .; P  < 0·01) and white (2·70 ± 0·20 v . 1·53 ± 0·18, mean ±  s . e .; P  < 0·01) regions of the pectoral musculature. The greater aerobic scope of P. borchgrevinki was strikingly demonstrated in the higher mitochondrial content of all skeletal muscle types sampled, and the ventricular myocardium (0·269 ± 0·011 v . 0·255 ± 0·012 mean ±  s . e .; P  < 0·05). Minor differences were found in other elements of fibre composition, with the exception of a five‐fold greater lipid content in pectoral red fibres of P. borchgrevinki (0·074 ± 0·014 mean ±  s . e .) v . T. bernacchii (0·010 ± 0·003; P  < 0·05). Differences in muscle fine structure among species clearly reflected differences in their ecotype.