Mean Specific Growth Rate Research Articles

Indicators of reproductive performance in rainbow trout Oncorhynchus mykiss (Walbaum) selected for high and low responsiveness to stress

A number of indicators of reproductive performance were assessed in rainbow trout divergently selected on the basis of their plasma cortisol response to a standardized stressor. For both male and female rainbow trout Oncorhynchus mykiss (Walbaum), body weight was significantly related to stress responsiveness. High-responding (HR) females were significantly heavier than low-responding (LR) females overall, and HR males were significantly heavier than LR males overall. There was no significant difference in the specific growth rate (SGR) of HR and LR female fish during the experimental period, whereas in contrast the mean SGR of HR males was significantly greater than that of LR males. The divergent confinement-induced levels of blood cortisol in HR and LR groups were stable for more than 1 year after selection. There was no significant difference in the extent to which confinement stress reduced blood oestradiol-17β levels in HR and LR females, despite a large difference in relative blood cortisol levels. The onset and rate of ovulation was similar within the HR and LR groups. Differences in fecundity, relative fecundity and egg volume and weight were wholly attributable to the different mean body weights of the HR and LR fish. There was no difference between the sperm counts of HR and LR males. There was significantly higher mortality among eggs derived from HR parents overall between fertilization and hatch, but maximum mean mortality did not exceed 12%. Mean time to eyeing in the HR groups was 224 degree days, and in the LR groups was 244 degree days. Hatching commenced at 344 and 347 degree days in the HR and LR groups, respectively, and was complete within 412 and 416 degree days respectively. Overall, selection for stress responsiveness was associated with no significant benefits or costs in reproductive performance.

Development and bioreactor cultivation of a novel semidifferentiated tissue suspension derived from the marine plant Acrosiphonia coalita

A semidifferentiated tissue culture consisting of linear filaments in liquid suspension was established from Acrosiphonia coalita, a cold-water green macroalga known to express pharmacologically active oxylipins deriving from lipoxygenase metabolism of linolenic acid. The tissue was vegatively propagated by blending the filaments down to 1 to 5 mm in length prior to subculture. The filamentous A. coalita tissue suspension was successfully cultivated in an illuminated, 3-L stirred-tank bioreactor at 12 degrees C, 0.46-vvm aeration rate, 250-rpm mixing speed, and incident illumination intensity of 77 microE m(-2)s(-1). The mean specific growth rate over the exponential phase was 0.185 day(-1) and a final cell density of 1083 mg dry cell weight (DCW) L(-1) was achieved within 15 days of cultivation from an initial cell density of 200 mg DCW L(-1). The addition of 3500 ppm CO(2) to the aeration gas provided a maximum CO(2) transfer rate of six times the maximum CO(2) consumption rate and stabilized the pH to 8.0 during the light phase of growth, but did not improve biomass productivity.

Specific growth rates of protozooplankton in the marginal ice zone of the central Barents Sea during spring

Protozooplankton growth was measured by incubation in a walk-in cooling room at 5°C of filtered seawater from six stations on a south–north transect from open water through drift ice and into fast ice in the central Barents Sea (72°30′N–76°32′N). Eight species of naked ciliates, two species of tintinnids, seven species of athecate dinoflagellates and nine species of thecate dinoflagellates grew in the 24 and 48 h bottle incubations. Maximum potential mean specific growth rates of 0.84, 0.59, 0.39 and 0.39 d−1, respectively, indicated a hierarchy in growth rates determined by taxonomic differences where growth of naked ciliates > tintinnids > athecate dinoflagellates > thecate dinoflagellates. The mean±SD in situ temperature (4 to −1.8°C) corrected growth rates (Q10=2.8) for the six stations (0.74±0.31, 0.74±0.16, 0.25±0.16, 0.23±0.27 d−1) also suggested a higher growth for ciliates in comparison to dinoflagellates. Additionally, it revealed that the naked ciliates responded to the increased food availability, whereas this was not the case for all other groups of protozooplankton.

Effects of larger fish and size grading on growth and size variation in fingerling silver perch

This study presents two experiments addressing growth and size variation in fingerling silver perch (Bidyanus bidyanus. In the first experiment, fish close to mean population size were raised either in the presence or absence of five larger fish for 60 days. Mean specific growth rate (SGR) and increases in the coefficient of variation and skewness were lower in the presence of larger fish, indicating a negative effect of large fish on the growth of smaller ones. In the second experiment, fingerlings were graded into groups smaller and larger than the median size of the population and raised in size-sorted groups of 60 large or small fish and mixed groups of 30 fish of each size category, for 60 days. There was no difference in mean SGR among groups, nor between the mixed group ad the weighted mean of the small and large groups. Biomass gain was higher in the mixed groups than in the weighted small-and-large groups, probably due to a slightly lower survival in the groups comprised of large fish. The fact that the effect of large fingerlings on the growth of smaller ones was evident in the first, but not the second, experiment may be attributed to higher size disparity between large and small fingerlings in the first experiment.

Prior residence, aggression and territory acquisition in hatchery‐reared and wild brown trout

In an artificial stream environment, established wild brown trout initiated 44% of the mean aggressive acts whilst hatchery‐reared trout initiated 34% and introduced wild trout initiated 22%. Established wild fish maintained home stations closer to a point source of feed than did both hatchery‐reared and introduced wild conspecifics. Established wild fish were the only group to show a positive mean specific growth rate during the trials. Introduced wild fish showed a slightly negative mean specific growth rate, whilst introduced hatchery‐reared fish exhibited a considerable negative mean specific growth rate. These results suggest that established wild brown trout in a semi‐natural stream environment display a prior‐resident effect over late introductions of hatchery‐reared and wild conspecifics. Introduced hatcheryreared fish were more aggressive and exhibited a lower mean specific growth rate than simultaneously stocked wild fish, suggesting that excessive expenditure of energy for unnecessary aggression may contribute to the poor survival of hatchery‐reared fish after they are stocked into streams.

Prior residence, aggression and territory acquisition in hatchery-reared and wild brown trout

In an artificial stream environment, established wild brown trout initiated 44% of the mean aggressive acts whilst hatchery-reared trout initiated 34% and introduced wild trout initiated 22%. Established wild fish maintained home stations closer to a point source of feed than did both hatchery-reared and introduced wild conspecifics. Established wild fish were the only group to show a positive mean specific growth rate during the trials. Introduced wild fish showed a slightly negative mean specific growth rate, whilst introduced hatchery-reared fish exhibited a considerable negative mean specific growth rate. These results suggest that established wild brown trout in a semi-natural stream environment display a prior-resident effect over late introductions of hatchery-reared and wild conspecifics. Introduced hatcheryreared fish were more aggressive and exhibited a lower mean specific growth rate than simultaneously stocked wild fish, suggesting that excessive expenditure of energy for unnecessary aggression may contribute to the poor survival of hatchery-reared fish after they are stocked into streams.

Effect of irradiance and temperature on the growth rate of Thalassiosira curviseriata Takano (Bacillariophyceae), a bloom diatom in Bahia Blanca estuary (Argentina)

Long-term phytoplankton studies in the Bahia Blanca estuary showed a seasonal pattern characterized by a winter-early spring bloom of diatoms dominated by Thalassiosira curviseriata. Laboratory experiments were carried out to elucidate the influence of irradiance, temperature and salinity on the growth rate of T.curviseriata. The maximum daily growth rate was 1.93 divisions at 20°C. The compensation point (Ic) varied from approaching zero to 3.08 µmol m-2 s-1, a values were ~0.020-0.070 divisions µmol-1, and the calculated Ik (the irradiance at which initial slope line reaches the maximum rate of growth) varied between 32 and 36 µmol m-2 s-1. Growth became light saturated (when µ = µmax) between 70 and 80 µmol m-2 s-1, and was inhibited at ~150 µmol m-2 s-1 at all tempera- tures (5-20oC). The range of temperatures at which T.curviseriata can grow (5-20°C) coincides with the temperature range over which it is found in the field. In contrast, the thermal optimum for growth, 20°C, was higher than the range of temperatures (between 5 and 10°C) characteristic of the winter-early spring bloom in Bahia Blanca estuary. The mean specific growth rate of T.curviseriata was not affected by salinity over the tested range between 25 and 40 p.p.t. Field observations and experimental data support the characterization of T.curviseriata as a eurythermal and euryhaline species adapted to growth at relatively low light intensity. These characteristics may explain the ability of T.curviseriata to flourish seasonally when light conditions are apparently limiting and its presence almost year round under variable conditions of temperature and salinity.

Growth of five Asian red tilapia strains in saline environments

Growth of five Asian red tilapia strains (BFS, NIFI, FAC, PF and HL) were evaluated in brackish and seawater. Eight-week-old juveniles from the five test strains were size-matched with similarly aged Oreochromis mossambicus which served as internal reference. Fish were stocked at a ratio of 15 test:15 reference in 100-l tanks supported by a recirculating system. Commercial feed was given twice daily at 10–20% of the fish biomass. Growth, measured from length and weight increment at 10 weeks, was recorded. Statistical analyses on mean specific growth rates showed significant differences among the strains reared in seawater. The Philippine strain PF grew best in seawater while the Thai strain NIFI performed well in brackishwater. In the Philippines, red tilapias are farmed in intensive freshwater culture systems by few aquaculturists. Results of this study indicate that some Asian strains can be developed for use in more sustainable brackish and seawater culture systems.

Cohort growth of planktotrophic polychaete larvae-are they food limited?

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 178:109-119 (1999) - doi:10.3354/meps178109 Cohort growth of planktotrophic polychaete larvae--are they food limited? Benni Winding Hansen* Roskilde University, Institute I, Life Sciences and Chemistry, PO Box 260, DK-4000 Roskilde, Denmark *E-mail: bhansen@ruc.dk ABSTRACT: A 16 d mesocosm experiment was performed during summer 1995 with 6 m3 bags filled with natural fjord water and plankton in a Danish embayment, Knebel Vig. Two control mesocosms simulated in situ conditions and a further 2 were enriched with inorganic nutrients to stimulate the primary producers. Zooplankton food availability in terms of 2 to 20 µm particles in the control and the enriched mesocosms revealed a mean ± SD of 582 ± 109 and 1191 ± 505 µg C l-1, respectively. The major increase of particulate carbon in the enriched mesocosms was due to a bloom of the cryptophyte Hemiselmis virescens. Cohorts of the polychaete larvae Polydora spp., Spio/Microspio spp. and Nereis (Neanthes) succinea were identified. The natural instantaneous mortality rate of the larvae revealed a mean of 0.16 and 0.37 d-1 in the control and enriched mesocosms, respectively. Mean growth in terms of setiger increase, body length increase and carbon content increase showed a fast growth phase followed by a stationary phase for Polydora spp. and Spio/Microspio spp. During the fast growth phase Polydora spp. had a specific growth rate of 0.21 to 0.31 d-1 in both the control and the enriched mesocosms. A statistically non-significant higher pragmatic mean specific growth rate was found when enriched phytoplankton was offered Spio/Microspio spp. (both controls 0.20 d-1, enriched 0.25 and 0.28 d-1). N. (Neanthes) succinea grew more continuously throughout the study and in 1 of the enriched mesocosms with a significantly higher mean value (0.15 and 0.16 d-1 in controls and 0.19 and 0.31 d-1 in enriched mesocosms). This indicates functionally food limited growth for polychaete larvae in this summer situation despite high particulate carbon content in the controls. KEY WORDS: Planktotrophic polychaete larvae · Polydora spp. · Spio/Microspio spp. · Nereis (Neanthes) succinea · Mortality · Growth · Food limitation · Mesocosm Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 178. Publication date: March 17, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Survival, growth and reproduction of the salt-marsh amphipod Uhlorchestia spartinophila reared on natural diets of senescent and dead Spartina alterniflora leaves

The talitrid amphipod Uhlorchestia spartinophila lives in close association with standing-dead leaves of the smooth cordgrass Spartina alterniflora Loisel in salt marshes along the Atlantic coast of North America. This study probed the strength of the trophic link between the amphipod population and the decomposition process in this detrital-based ecosystem. We measured survival, growth and reproductive output in groups of amphipods reared for 6 wk on five diets derived from sheath and blade portions of S. alterniflora leaves just prior to (senescent) and during (dead) decomposition. In unfed treatments, the daily specific mortality rate was 0.391 and starved amphipods survived no longer than 11 d. Among the fed treatments, a diet of senescent sheaths resulted in the lowest survival (20%) and yielded no offspring. Groups fed senescent blades, dead sheaths, dead blades and unwashed dead sheaths had survival rates of 56 to 84% and produced 5.0 to 12.5 offspring replicate−1. Sex ratio usually favored females, but approached unity in treatments with high overall survival, suggesting that quality of available food resources may influence sex ratio in this species. Mean specific growth rates (mm mm−1 d−1) ranged from 0.013 to 0.016, and matched previous estimates of growth from field populations. Overall ecological performance (survival + growth + reproduction) was similar for all food treatments, except senescent sheaths, which yielded a final mean (±SD) dry biomass (0.4 ± 0.42 mg replicate−1) of amphipods significantly lower than that of other diets (1.7 ± 0.81 to 2.6 ± 0.69 mg replicate−1). Natural diets derived from decomposing cordgrass leaves can fulfill the nutritional requirements of U. spartinophila populations, but variation in initial amounts of living fungal biomass among the five experimental diets only partially explained the responses of amphipods in our experiment. Structural characteristics and variation in rates of fungal occupation within different portions of cordgrass leaves may affect the amphipod's ability to access plant production made available by decomposers.

Growth, filtration and respiration in the mussel Mytilus edulis:no evidence for physiological regulation of the filter-pump to nutritional needs

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 141:37-45 (1996) - doi:10.3354/meps141037 Growth, filtration and respiration in the mussel Mytilus edulis: no evidence for physiological regulation of the filter-pump to nutritional needs Clausen I, Riisgård HU The specific growth rate of blue mussels Mytilus edulis fed Rhodomonas sp. algal cells in laboratory experiments increased with increasing food concentration to obtain a maximum value of about 9.5% d-1, irrespective of a relatively high concentration of silt (5 mg l-1) added to the water. Likewise, the net growth efficiency increased with the specific growth rate to a maximum value of about 75%. Measurements of the relationship between respiration and growth showed that the energy cost of growth constituted 12% of the growth. The filtration rate of a 100 mg dry wt 'standard' mussel was high and constant (about 30 ml min-1) at algal concentrations below about 6000 cells ml-1 when measured in both short-time (5 h) and long-time (9 to 14 d) experiments. High algal concentrations of 1.3 to 2.4 x 104 cells ml-1 reduced the filtration rate by about 40%. The estimated growth, presuming maximum filtration rate, satisfactorily described the actual growth at algal concentrations <5000 cells ml-1, and the concentration necessary for maximum growth was estimated at 4500 cells ml-1 (corresponding to 5.6 µg chlorophyll a l-1). The mean specific growth rate in M. edulis transferred in net bags to a fjord system (Kertinge Nor/Kerteminde Fjord, Denmark) was about 6% d-1. The results show that there is no physiological regulation of the filtration rate to nutritional needs, and that food uptake in nature (median concentration in Danish waters = 5.1 µg chlorophyll a l-1) is characterized by the full exploitation of the capacity of the bivalve filter-pump. Actual and estimated growth · Feeding and effects of silt · Costs of growth · Net growth efficiency · Regulation of filtration rate Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 141. Publication date: October 03, 1996 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1996 Inter-Research.

Optimal protein requirements of young Arctic charr (Salvelinus alpinus) fed practical diets

Young Arctic charr, Salvelinus alpinus (L.), mean weight 2.56 ± 0.02 g, were fed nine isoenergetic (˜16.6 MJ digestible energy (DE) kg−1) practical diets formulated to supply digestible crude protein (DCP) at 40g kg−1 increments from 230 to 550g kg−1, for 84 days. Mean weight gain (MWG) and specific growth rate (SGR) were determined every 14 days while carcass composition was determined at the start and end of the experiment. Growth responses attained the highest values in the fish fed the diet with 350 g kg−1 DCP. Carcass moisture gain, protein gain and apparent net lipid accumulation increased as DCP levels increased to a maximum at 350 g kg−1 after which there were no differences among treatments. Total carcass lipid and lipid gain decreased as dietary DCP increased up to 470 g kg−1 with no differences thereafter. Apparent net protein accretion decreased with increasing DCP levels up to 350 g kg−1 after which there were few differences among treaments. Protein requirements were estimated by fitting MWG and SGR data to broken line regression, quadratic and saturation kinetics models. Results from these analyses suggest that dietary DCP should be provided at between 340 and 392 g kg−1 (equivalent to ˜370 and 420g kg−1 crude protein) for optimal growth of young Arctic charr reared in similar conditions.

Kinetic studies on the yeast Phaffia rhodozyma.

The yeast Phaffia rhodozyma, a promising microbial producer of the carotenoid astaxanthin, was cultivated in batch and continuous processes in an agitated and aerated fermenter using an acid peat extract based culture medium. For the accelerated growth phase, the mean specific growth rate and doubling time were found to be 0.038 h-1, and 18.24 hours, respectively. The production of astaxanthin was found to be basically growth associated, the maximum concentrations of the pigment produced in batch culture and continuous cultivation being similar.

Overwintering tilapia, Oreochromis spilurus (Günther), fingerlings using warm underground sea water

. The study was conducted to develop guidelines for high-density overwintering of tilapia in tanks using warm underground sea water. Seawater-acclimated fish of 20 g were stocked in 36 tanks at 250, 500 and 750/m3. Water flow was regulated at 0.1 and 0.2 l/kg fish/min. Fish were fed at the rates of 0.75% and 1.0% of biomass per day. After 135 culture days, the mean individual weight gain and specific growth rate decreased, whereas feed conversion increased significantly (P <0.0001) with the increase in stocking density. The condition factor at 500 and 750 fish/m3 was significantly lower (P<0.0005) than at 250 fish/m3. However, stocking density had no significant effect on the survival rate. Significantly better specific growth rate, condition factor and feed conversion were observed at a water flow rate of 0.2 l/kg fish/min than at 01 l/kg fish/min. Significantly higher mean individual weight gain, specific growth rate, and survival rate were observed at 1.0%/day than at the 0.75%/day feeding rate. The findings indicate that the optimum stocking density for overwintering tilapia in tanks using warm underground sea water is 750 fish/m3 with a water flow rate of 0.1 l/kg fish/min and a feeding rate of 0.75%/day.

Larval rearing of an African catfish,Heterobranchus longifilis, (Teleostei, Clariidae): a comparison between natural and artificial diet

Two feeding experiments were conducted to evaluate growth and survival rates of African catfish (Heterobranchus longifilis Valenciennes, 1840) larvae fed with different diets: live Artemia nauplii, frozen Artemia nauplii, live zooplankton (Moina micrura), frozen zooplankton (Moina micrura), a dry diet based on yeast powder and beef liver, and a commercial trout starter diet. The larvae were fed in excess, six times per day every 4 hours, from the onset of exogenous feeding up to an age of 14 days. In both experiments the final mean weight and specific growth rate of fish fed live Artemia nauplii were significantly higher than those of fish fed other diets (p > 0.05). Survival rates of fish fed Artemia (live or frozen), Moina micrura (live or frozen) and dry diet did not significantly differ (p > 0.05) and ranged from 79 to 92% and 61 to 73% for experiment 1 and experiment 2, respectively. The commercial trout diet led to significantly lower growth and survival rates in comparison to all other diets tested. Although it led to a lower growth rate than that obtained with Artemia, Moina micrura proved suitable for first feeding of H. longifilis larvae. Locally available in West African waters, this cladocera could constitute a valuable alternative for larval rearing when a shortage of Artemia is expenenced. The results also showed that the artificial feed based on yeast powder and beef liver leads to survival rates as high as those obtained with living diets and thus represents a promising way for feeding H. longifilis fry. However, further studies on the nutritional requirements of the larvae remain necessary in order to improve the efficiency of dry diet in terms of growth performance.

Growth of Wild Stunted Arctic Char after Transfer to a Commercial Rearing System

Abstract We analyzed the growth of wild stunted Arctic char Salvelinus alpinus under intensive rearing conditions. Arctic char were caught with funnel traps in a Norwegian lake. They were acclimated for 3 weeks to hatchery conditions and prepared food, then individually marked with T-bar tags and stocked in a 3-m2 tank at a density of 20 kg fish/m3 water. The fish had a mean age of 5.1 years (SD, 1.45; range, 3–10 years) and a mean weight of 27.9 g (SD, 12.59; range, 8–94 g). After 104 d, the fish had increased to a mean weight of 137.0 g (SD, 64.55; range, 30–394 g). Mean specific growth rate in weight during the period was 1.52%/d (SD, 0.315; range, –0.10 to 2.27%/d). Only 1.4% of Arctic char showed little or no growth, and mortality was insignificant. Specific growth rates were independent of age and maturity during the first months in culture. Wild stunted Arctic char seem well suited for rearing in intensive aquaculture.

Food consumption, feeding behaviour, and growth of triploid and diploid Atlantic salmon, Salmo salar L., parr

To test whether triploid Atlantic salmon (Salmo salar L.) parr were at a disadvantage compared with diploid parr the growth and feeding behaviour of individual parr in separate and mixed groups of diploid and triploid fish were studied in two experiments. At the end of the first experiment (separate groups) the diploid parr had significantly higher mean specific growth rates than the triploid parr. This was due to significantly higher growth during the first 40 days of the experiment; growth was not significantly different over the last 52 days. The consumption rates of individual parr were measured using radiography. There were no consistent differences in consumption rates between triploid and diploid parr in mixed or separate groups. However, at the start of the experiment the mean consumption rates of the triploid parr were significantly lower than those of the diploid parr and could explain their lower growth rates. There were no differences in the amount of damage to the caudal fin between triploid and diploid parr in either experiment. However, in a mixed group, damage to the dorsal fin of triploid parr was more severe than to the dorsal fin of diploid parr, which suggested that triploid parr in mixed groups were more likely to be the recipients of agonistic actions than the diploid parr. However, the specific growth rates of the diploid and triploid parr in mixed groups were not significantly different. It was concluded that under certain circumstances. triploid and diploid Atlantic salmon parr may exhibit differences in growth and feeding behaviour.

Microbial carbon utilization on the continental shelf and slope during the SEEP-II experiment

Abstract Microbial processes were measured as part of the Shelf Edge Exchange Processes II (SEEP-II) experiment, which was designed to re-examine the hypothesis that a substantial fraction of primary production on the continental shelf is exported to the slope and deeper ocean. Bacterial-mediated carbon remineralization was defined as the sum of measured bacterial production plus estimated bacterial respiration. Carbon remineralization, summed over the water column plus surficial sediment, was 90–180 mg C m−2 day−1 on the shelf and 270–540 mg C m−2 day−1 on the slope. These are equivalent to 12–24% and 33–66% of daily primary production on the shelf and slope, respectively. The majority of bacterial activity occurs in sediments on the shelf, but not the slope it is attributable to bacteria in the deep water column. Concurrent sediment trap data indicate that material sinking from surface waters overlying the slope can supply only a small fraction of carbon remineralized by bacteria in the intermediate water column. Bacterial production in slope water and sediments may be subsidized by export from the shelf. Because of the greater width of the shelf than slope, this additional demand on shelf carbon would represent only 7.5–15% of shelf primary production. Mean specific growth rates of sediment bacteria were very uniform at depths between 40 and 2000 m. This suggests bacterial growth may be limited by some common factor, although environmental factors known to affect growth rates generally vary with depth. DNA synthesis rates (measured by thymidine incorporation) were comparable to rates observed for marine bacteria in nutrient-replete culture. The implication is that sediment bacteria were not limited by nutrient availability. If true, water column and sediment bacterial production are likely to be controlled by very different processes: water-column bacteria by both nutrient limitation and grazing, and sediment bacteria by grazing alone.

Growth and secondary production of Paracapnia angulata Hanson (Plecoptera; Capniidae) in Appalachian streams affected by acid precipitation

Paracapnia angulata in West Virginia occurs in headwater streams that range in pH from 4.5 to 7.5. It is representative of a number of species of Plecoptera, which often increase in abundance in acidic streams because they are tolerant of low pH and related changes in water quality associated with acid precipitation. We compared growth rates and secondary production of P. angulata in four streams, SFR, WS4, WS3, and HSR, in which mean streamwater pH was 4.26, 5.99, 6.07, and 7.48, respectively. Mean specific growth rates, in terms of dry mass for P. angulata, were higher in the two neutral streams than in the more alkaline stream or the acidic stream. Secondary production of P. angulata was highest in the acidic stream SFR, 106.2 ± 16.4 mg∙m−2∙yr−1 (mean ± 2 SE), and was 34.0 ± 12.1 mg∙m−2∙yr−1 in WS4, 32.7 ± 3.8 mg∙m−2∙yr−1 in WS3, and 35.4 ± 3.6 mg∙m−2∙yr−1 in HSR. The increased secondary production of P. angulata was related to greater mean abundance and biomass in SFR; and the production/biomass ratio for this acidic stream was lower than for the other streams.

Migratory behaviour and growth of hatchery‐reared post‐smolt Atlantic salmon Salmo salar

Individually lagged, 1+ and 2+ hatchery‐reared smolts of Atlantic salmon were released in spring and early summer at the mouth of the R. Imsa, south‐western Norway. The post‐smolts moved mainly northwards in the sea with the coastal current. The estimated mean migratory speed (±s.d.) of those captured in the sea along the Norwegian coast was 7.45 (± 6.26) km day −1; in the fjords it was 1.63 (± 2.33) km day−2. Many of the post‐smohs ascended rivers the same year as released; 37.3% of the total number recaptured were caught in R. Imsa, upstream from the site of release, and 5.8% were caught in other rivers throughout middle and southern parts of Norway. The fish recaptured in rivers was probably sexually mature and entered rivers to spawn. Mean specific growth rate for post‐smolts caught in the sea was higher than for those caught in R. Imsa (P &lt;0.001) but not for those caught in other rivers (P&gt; 0.05). Post‐smolts ascending R. Imsa were smaller at release than those ascending other rivers. However, there was no size difference at release between post‐smolts captured in the sea and those recaptured in rivers other than the R. Imsa.