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.     

Genetic differentiation among populations of the shortfinned eel Anguilla australis from East Australia and New Zealand

Variability at seven microsatellite loci was used to survey the genetic population structure of the shortfinned eel Anguilla australis . Samples were collected from six estuaries along the east coast of Australia and from three estuaries around New Zealand. Hierarchical analysis of molecular variance of the five loci with good fit to Hardy–Weinberg genotypic proportions detected highly significant differences among samples ( F _ST= 0·016, P < 0·001). The fixation index between countries ( F _CT= 0·012, P < 0·001) was more than double the index among samples within countries ( F _SC= 0·005, P < 0·05). An unweighted pair-group method with arithmetic mean (UPGMA) tree also supported the separation of Australian and New Zealand populations, as did assignment tests, which correctly assigned 80 and 84% of the individuals to Australia and New Zealand, respectively. Isolation-by-distance appeared among samples overall ( r = 0·807, P < 0·001), but not among samples within countries ( r = 0·027, P > 0·05 in Australia; r = 0·762, P > 0·05 in New Zealand). These findings indicate that populations of A. australis in East Australia and in New Zealand may be reproductively isolated from one another. Genetic differentiation among populations of A. australis was two- to 10-fold higher than that among populations of other temperate eels in the North Atlantic Ocean, suggesting that two group of A. australis may reflect sub-species. Anguilla australis in the two countries have different genetic structures and thus require separate management. Genetic isolation between Australian and New Zealand populations indicates that juveniles recruit independently into these two regions from geographically or temporally isolated spawning areas.     

Morphological and genetic differentiation in anadromous smelt Osmerus mordax (Mitchill): disentangling the effects of geography and morphology on gene flow

Morphological analyses were combined with genetic analyses at nine microsatellite loci to examine the determinants of gene flow at 21 spawning locations of rainbow smelt Osmerus mordax along the east coast of Canada. Associations between morphology, geography and gene flow were examined using a computational geometric approach and partial Mantel tests. Significant barriers to gene flow and discontinuities in morphology were observed between Newfoundland and mainland Canada, as well as within Newfoundland samples. On regional scales, contrasting patterns were present with restricted gene flow between Newfoundland populations ( F _ST= c . 0·11) and high gene flow between mainland populations ( F _ST= c . 0·017). Within Newfoundland populations, geographic distance was significantly associated with gene flow ( r = 0·85, P < 0·001) contrasting mainland samples where gene flow was most associated with phenotypic divergence ( r = 0·33, P < 0·001). At large spatial scales, weak ( r = 0·19, P = 0·02) associations between gene flow and geographic distance were observed, and moderate associations were also observed between gene flow and morphology ( r = 0·28, P < 0·001). The presence of significant genetic isolation by distance in Newfoundland samples and the clear discontinuity associated with the Cabot Strait suggest geography may be the primary determinant of gene flow. Interestingly, the association between genetic and morphological divergence within mainland samples and overall, supports the hypothesis that gene flow may be moderated by morphological divergence at larger spatial scales even in high gene flow environments.     

Relationship between freshwater angling catch of Atlantic salmon and stock size in the River Bush, Northern Ireland

Over 25 years rod catches of Atlantic salmon Salmo salar increased proportionately as stock size increased ( r ²=0·581, P <0·001), with no overall trend between exploitation rate and stock size ( r ²=0·016, P >0·5). On a 15 year sub-set of these data annual effort ( P =0·804) and flow ( P =0·339) had little significance relative to stock size ( P <0·01) on variation in rod catches. Stock size, time, effort and flows had no influence on inter-annual variation of rod exploitation rate ( r ²=0·094, P =0·880). Pairwise correlation between variables confirmed these results. In 1998, weekly effort contributed significantly to overall catch variation ( P <0·001), while weekly flow did not ( P =0·438). These results are discussed in relation to the utility of rod catch data for deriving estimates of stock for spawning target compliance purposes.     

Nuclear abnormalities of marine fish erythrocytes

The aim of this study was to monitor erythrocyte nuclear abnormalities (NA) including micronuclei (MN) in cultured and wild sea bass Dicentrarchus labrax and wild mullet Mugil spp. Seasonal sampling was performed at seven locations along the eastern coast of the Adriatic Sea. The frequency of NA and MN was positively correlated to temperature (NA: P < 0·05, r = 0·11; MN P < 0·05, r = 0·10), and there was also a positive correlation between NA and MN frequency ( P < 0·001, r = 0·43). The lowest NA and MN values for both fish species were recorded in spring, while the highest were recorded in autumn. Significantly higher frequency of NA was seen in D. labrax compared to Mugil spp., while MN frequency was low in both species and not significantly different. There was no significant difference in NA and MN frequency between cultured and wild D. labrax sampled in the same month, and there was no difference between wild Mugil spp. sampled near or far from fish farms. In view of sampling sites, the highest values were detected in fishes from the Limski Channel, the lowest from the Janjina location.     

Influence of growth rate on white muscle dynamics in rainbow trout and brook trout

In trout, fast growth stimulated white muscle fibre hypertrophy ( P 0·001) and hyperplasia ( P <0·01) in outer fibres but not in deep fibres. Glycogen was most prevalent in outer fibres ( P <0·01) and in brook trout ( P <0·01) that on average had three to four times larger fibres than rainbow trout.     

Isolation by distance and selection effects on genetic structure of sardines Sardina pilchardus Walbaum

Allozyme data were used to analyse the genetic structure of Sardina pilchardus populations. Fifty samples from 15 locations between the North Sea and Mauritania, including samples from the Azores, Madeira and the Mediterranean Sea, were surveyed. A weak but significant structure was found between all samples ( F _ST= 0.057, P < 0·001). This structure results from a change in the most common allele of SOD* between the North African and the Azores populations separated by the greatest distance. This locus seemed to be under selective pressure according to the test of neutrality, and the variations in allele frequencies may be explained due to isolation by distance (IBD) of coastal populations (from Mauritania to the North Sea) ( r = 0·86, P < 0·001). When SOD* was removed from the analyses, IBD was not observed in coastal populations ( r = 0·236, P > 0·05) but was observed over the whole range ( r = 0·321, P = 0·05). The genetic structure of S. pilchardus is driven by both IBD and selective processes.     

Analysis of the factors related with mate choice and reproductive success in male three-spined sticklebacks

Territorial three-spined sticklebacks moved 5·3 times as far as non-territorial males in 2 min ( P < 0·001) and spent 11·1 times longer in aggression in the pools ( P < 0·001). Territorial males had slightly higher condition factors than non-territorial males. Condition factor was correlated positively with the gonad mass ( P < 0·006), carotenoid concentration ( P < 0·006) and the activity of CS in the axial muscle ( P < 0·05) and lactate dehydrogenase (LDH) in pectoral muscle ( P < 0·003). The male traits best correlated positively with female mate choice were courtship effort ( P < 0·001), coloration ( P < 0·003) and initial condition ( P < 0·025). Courtship behaviour was related to intestine mass ( P < 0·018), axial ( P < 0·028) and pectoral muscle citrate synthase (CS) activity ( P < 0·047); coloration was related to gonad mass ( P < 0·037). These muscle enzymes may be involved in ATP generation for sustained activities or in recuperation between bouts of burst activity. Females that choose to mate with assiduously courting males which bear higher CS levels may be choosing individuals that show honestly their good condition and capacity to accomplish reproductive tasks.     

Intraspecific aggression in rosyside dace, a drift-feeding stream cyprinid

Individual rosyside dace Clinostomus funduloides in a semi-natural, artificial stream displayed substantial differences in their aggressiveness and could be classified as: (1) non-aggressive (NA, 18 of 30 rosyside dace), (2) moderately aggressive (MA, 9 of 30) and (3) highly aggressive (HA, 3 of 30). Rosyside dace groups, however, did not exhibit linear dominance hierarchies and fish size was only weakly correlated with the number of aggressive acts performed per individual. Small rosyside dace (<56 mm L_F) were always non-aggressive, but larger fish were present in all three aggression classes. The difference in size between the contestants was significantly, although not very strongly, correlated with the probability of winning an agonistic interaction (r ²=0·39). Aggressive rosyside dace may have ultimately gained higher fitness than less aggressive ones. HA individuals occupied the upstream-most position within foraging groups significantly more often than other rosyside dace. This location should be the most profitable one because its occupant will be the first to encounter prey. HA rosyside dace also occupied significantly higher focal velocities that were closer to energetic optima than MA and NA ones. They also had greater foraging rates and were less solitary than less aggressive fish, but these differences only were significant at the P=0·066 and P=0·081 level, respectively. Finally, HA fish performed significantly more aggressive acts and feedings backwards than other individuals. Despite these differences, the effects of intraspecific aggression in rosyside dace appeared less substantial than those that have been observed in stream salmonids.     

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.     

An RNA:DNA-based growth model for young-of-the-year winter flounder Pseudopleuronectes americanus (Walbaum)

A laboratory calibration experiment was conducted to determine the relationship between nucleic acid-based variables and growth rate in young-of-the-year winter flounder Pseudopleuronectes americanus . Three temperatures and three feeding levels were used to produce a variety of growth rates. Nucleic acid analyses were conducted on white muscle tissue using an ultraviolet absorption assay. RNA concentration (μg mg⁻¹ wet tissue mass) and the ratio of RNA:DNA ( R _RD) were positively correlated with a mass-based instantaneous growth coefficient ( G _M) ( r = 0·42 and 0·72, respectively). Fifty-one per cent of the variability in growth rate was explained by the simple linear regression G _M=−0·02615 + 0·00848 R _RD ( P < 0·001). This model can be used to estimate recent growth rates for early juvenile winter flounder (27–52 mm standard length) at temperatures ranging from 11 to 24° C.     

The relative abundance of brown trout in acidic softwater lakes in relation to water quality in tributary streams

The influence of the water quality of tributary streams on the relative abundance in benthic gillnet catches (catch per unit effort, cpue) of allopatric brown Salmo trutta was assessed in associated acidic, softwater lakes. The study was carried out over 6 years (1989–1994) in 15 lakes located at altitudes between 230–715 m a.s.l. in two Norwegian catchments. The water quality of the main inlets and outlets varied little, as indicated by their of pH range (4·93–5·51) and calcium concentrations (0·19–0·44 mg 1⁻¹), but varied more with respect to concentrations of inorganic, monomeric aluminium (7·0–41·0 μg l⁻¹). Most of the lakes were also fed by secondary streams with better water quality: a maximum pH of 6·56, calcium levels of up to 0·74mg 1⁻¹, and inorganic aluminium levels as low as l·0 μg 1⁻¹. The cpue was inversely correlated with lake altitude ( r ²=0·50), and thus was adjusted to a mean altitude. The calcium concentration in the richest secondary stream to each lake, its richness judged on the basis of its acid-neutralizing capacity, had the highest predictive power of the variability in cpue ( r ² = 0·49).The calcium content in the other secondary streams or in the main inlets and outlets did not correlate with cpue. Alkalinity in the main outlets correlated to some extent with cpue ( r ² = 0·27). It is suggested that secondary streams with good water quality provide important refuges for the recruitment of brown trout in acidic softwater lakes.     

Climate variables and spawning migrations of the striped mullet and white mullet in the north‐western area of the Gulf of Mexico

The 'smoothed'(4253e HT smoother) 6 year time series with a monthly periodicity of catches (where the increases of the catches reflect the spawning migration) of Mugil cephalus and Mugil curema , were correlated (Pearson correlation index) against the 'smoothed' data on rainfall, water temperature, daylight and tide monthly averages. Water temperature and M. curema spawning migrations had a negative correlation ( r  = −0·77), while tide monthly averages and M. cephalus spawning migrations were positively correlated ( r  = 0·84). The two environmental variables that showed highly significant correlations were water temperature and daylight ( r  = 0·85, P  < 0·05). Meteorological tides were used as a reflection of the effect of the north winds from the Gulf of Mexico which produce an average tide rise from September to November. The relationship of these variables with spawning migrations is discussed, and it is suggested, in particular, that meteorological tides, as a reflection of the north winds, are the trigger (zeitgebers) for M. cephalus spawning in the ocean.     

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.     

Effect of feeding level and feeding frequency on specific dynamic action in Silurus meridionalis

The effect of feeding level ( F _L; 0·5 to 4% dry diet mass per wet fish body mass) and feeding frequency (once every 4 days to twice per day) on postprandial metabolic response was investigated in southern catfish Silurus meridionalis at 27·5° C. The results showed that there was no significant difference in the specific dynamic action (SDA) coefficient among the groups of different feeding levels ( P  > 0·05). The duration increased from 26·0 to 40·0 h and the peak metabolic rate increased from 207·8 to 378·8 mg O₂ kg⁻¹ h⁻¹ when the feeding level was increased from 0·5 to 4%. The relationship between the peak metabolic rate ( R _P, mg O₂ kg⁻¹ h⁻¹) and F _L could be described as: R _P = 175·4 + 47·3 F _L( r ² = 0·943, n  = 40, P  < 0·001). The relationship between the SDA duration ( D , h) and F _L could be described as D =30·97 F _L^0·248 ( r ²=0·729, n =40, P  < 0·001).     

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.     

The deposition and mortality of the eggs of the Baltic herring Clupea harengus membras L., on different substrates in the south-west archipelago of Finland

The environmental factors affecting the deposition and mortality of the eggs of the spring-spawning Baltic herring were studied in the inner Archipelago Sea of south-western Finland. On four spawning grounds, 27 study squares (area 1 m²) were surveyed by divers. In each square, one quantitative egg sample was taken and the following data were recorded: depth, temperature, bottom quality of the square and under the eggs, egg substrate, cover (%) of plants and/or the bivalve Mytilus edulis , and the heterogeneity of the environment, expressed as the total number of all bottom materials, plants and Mytilus found in the square.
Eggs were found in the depth zone of 1–4 m. Their density ranged from 6000 to 2·3 millions of eggs per square metre. Egg number had a significant negative correlation with both depth (r=-0·545, P <0·01, d.f. = 25) and temperature of the sea water ( r =-0.479,. P <0·01,d.f. = 25), and a positive correlation with the total cover (%) in the squares ( r = 0·375, P < 0·05, d.f. = 25).
The highest numbers of eggs were found on Cladophora glomerata, which the most preferred spawning substrate of those present. Mortality of the eggs varied according to the substrate. In eggs attached to Cladophora, Potamogeton and Mytilus, the proportion of dead eggs was 0.15·5%; in those attached to red algae it was significantly higher ( Furcellaria , 5·0–63·2%; Phyllophora , 0–95·2%).     

Effects of habitat complexity and predator exclusion on the abundance of juvenile red snapper

Predator exclusion and habitat complexity factors that may affect juvenile red snapper Lutjanus campechanus habitat selection were examined in field and laboratory experiments. A significant predator exclusion effect was detected. Uncaged shell habitats showed significantly lower numbers of age 0 year red snapper, and both uncaged shell and block-shell habitats showed significantly lower numbers of age 1 year red snapper compared with caged habitats ( P < 0·001). Habitat complexity also affected age 0 year red snapper, as mean abundance significantly decreased with decreased habitat complexity ( P < 0·001). In the laboratory, age 0 year red snapper association with complex habitats significantly increased with exposure to a predator Gulf flounder Paralichthys albigutta ( P < 0·001). This study showed that predator exclusion and habitat complexity were significant factors that affected the abundance of juvenile red snapper in nursery areas of the northern Gulf of Mexico. Predation may affect juvenile red snapper abundance directly through mortality and indirectly by influencing habitat selection.     

The combined effect of feeding time and ration on growth performance and nitrogen metabolism of greenback flounder

Greenback flounder Rhombosolea tapirina ( c. 2 g) fed to satiation had significantly ( P <0·01) higher feed consumption in the evening than in the morning whereas there was no difference between feeding times for flounder fed restricted rations (1 or 2% body weight per day) because they consumed all of the ration. Differences in growth performance were due to feeding time and ration. Carcass moisture, lipid and energy content were significantly ( P <0·001) different between rations; length gain was significantly affected by feeding time ( P <0·05) and ration ( P <0·001); weight gain showed a significant ( P <0·001) interaction between feeding time and ration. The relationship between feed consumption and specific growth rate showed that the exponential gradient was significantly higher ( P <0·01) for the evening fed fish and indicated feed efficiency for evening fed fish increased as feed consumption increased. Urea excretion increased from 12–20 to 58–63% of total nitrogen excretion at the 1 and 3% rations, respectively. Ammonia and urea excretion were significantly affected by ration ( P <0·001) and feeding time ( P <0·05). Fish fed the 2% ration in the evening had higher growth efficiency and significantly ( P <0·01) lower rates of urea excretion than fish fed 2 or 3% ration in the morning. It is suggested that the higher energetic costs associated with differences in ammonia and urea excretion contributed to differences in growth efficiency.     

Reproductive investment of female brown trout, Salmo trutta L., in a stream and reservoir system in northern England

Within the basin of Cow Green reservoir, upper Teesdale, the brown trout, Salmo trutta L., spend their first two seasons in running water. After this some females remain resident and others migrate to Cow Green reservoir. A cohort of 1000 females at age 2 that remains resident in tributary streams will, during the lifetime of the cohort, lay, on average, 3·0 times as many eggs as a cohort which resides in the reservoir. This conclusion is apparently not consistent with the observation that most females take up reservoir residence.
Reservoir females have a higher growth rate (Walford constant k=0·61, c.f. 0·86 for stream residents) and shorter life expectancy ( M year⁻¹= 1·19, c.f. 0·56) than the stream residents. However, they are of larger average size than the stream residents, lay larger eggs (mean 0·074 g, c.f. 0·066 g) and bury them more deeply (mean depth 11·0 cm, c.f. 8·5 cm).