PATTERNS OF RELATIVE GROWTH IN NEREOCYSTIS LUETKEANA (PHAEOPHYTA)1

Plants of Nereocystis luetkeana (Mert.) Post. et Rupr. of different sizes were held on a raft at the surface of the sea, off the Friday Harbor Laboratories, San Juan Island, Washington for 5-day periods for obseruation of detailed relative growth of different parts. Each stipe was marked at intenlals with injected Indian ink and each blade was punched with a series of holes. Measurements of diameter, length, width and thickness were made before and after the 5-day periods. Blades showed a very similar pattern of relative growth rate (R) ovler an 18-fold range of sizes. The maximum local R in length was about 0.2 day⁻¹ and occurred at 6.5% of the distance from the bulb to the tip, declining to 0.01 at half way. Half the linear growth occurred in the proximal one tenth of the blade and 95% within the proximal half: The relative growth rate of the whole blade declined only slightly with increased size and lay between 0.03 and 0.06 day⁻¹ (approx. 3-6% day⁻¹). The linear growth rate therefore increased with blade size, the maximum observed being 14 cm day⁻¹. The maximum relative growth rate in blade width was slower, and sited more distally than that in length. Unless fertile tissue was involved all blade tissue, except that closely adjoining the bulb, became thinner duringgrowth. R in volume reached 0.3 day⁻¹. Presumably because the plants were held near the sea surface stipes grew slowly, with a maximum linear rate of 9 mm day⁻¹. The maximum R in length decreased with stipe length. Bulb R in volume also decreased as size increased, from a maximum of 0.3 day⁻¹.     

GROWTH OF BLADES OF NEREOCYSTIS LUETKEANA (PHAEOPHYTA) IN DARKNESS 1

Short term measurements were made of the relative growth rate of the fast growing portions of blades of Ncreocystis luetkeana (Merl.) Post. et Rupr. during exposure to natural daylight and during prolonged darkness. Growth was only slightly, but significantly, faster during the 12 h of daylight than during the 12 h that included 8 h of darkness. Clearly considerable growth occurred at night. In blades amputated 1 cm beyond the zone measured, growth was slower during both night and day. In continuous darkness growth continued for up to 12 days. It was not influenced by amputation of distal blade tissue but it was increased by severance from the bulb and stipe. A mean volume increase of 50% of the blade tissue was recorded. While the organic content decreased, the drop was half that required to support the increase in volume. There was some evidence against translocation. It is possible that cellular biochemical rearrangements allow a light-independent increase in organic material.     

Growth and loss of distal tissue in blades of Lessonia nigrescens and Lessonia trabeculata (Laminariales)

Meristematic growth and loss of distal tissue from blades of two ecologically important species in the south-east Pacific, Lessonia nigrescens and Lessonia trabeculata, was evaluated during 1 year. Comparative growth was determined by a hole-punch method, loss of distal tissue from the blades was determined by subtracting final blade length (with loss) from expected blade lengths (without loss); growth and tissue loss were transformed to fresh biomass units for calculation of inter-algae differences. The results showed that blade elongation rate increased at the beginning of spring, and declined towards the end of summer, with mean values between 0.40 and 0.08 cm day⁻¹ for L. nigrescens, and 0.65–0.17 cm day⁻¹ for L. trabeculata. Loss of distal tissue varied seasonally when examined as length units for both species; with mean values between 0.24 and 0.10 cm day⁻¹ for L. nigrescens, and 0.51–0.25 cm day⁻¹ for L. trabeculata. Variations in fresh biomass units were only observed in Lessonia trabeculata, increasing in spring, with mean values to 0.13 g (fresh weight) day⁻¹. Annual growth and loss of distal tissue were higher in L. trabeculata (0.41 and 0.39 cm day⁻¹, respectively) than in L nigrescens (0.19 and 0.15 cm day⁻¹). When growth and tissue loss were considered as fresh biomass, monthly gains significantly outweighed loss of distal tissue in both species, but parallel results based on length data followed a different trend. L. trabeculata released about 50% of its growth biomass as particulate organic matter, while the comparative value for L. nigrescens was about 20%.     

GROWTH,DARK RESPIRATION AND PHOTOSYNTHETIC PARAMETERS OF THE COCCOLITHOPHORID EMILIANIA HUXLEYI (PRYMNESIOPHYCEAE) ACCLIMATED TO DIFFERENT DAY LENGTH-IRRADIANCE COMBINATIONS1

Growth, dark respiration rate, photosynthetic parameters, and chemical composition were determined for Emiliania huxleyi (Lohmann) Hay et Mohler acclimated to different combinations of day length (12, 18, 24 h) and irradiance (30, 100, 200, 800 μmol·m⁻²·s⁻¹). Specific growth rate (μ, day⁻¹) and carbon-specific dark respiration rate (r^C_d, day⁻¹) were independent of day length, but increased significantly with increasing irradiance. The photosynthetic parameters depended on the initial acclimation day length and irradiance: Chlorophyll a-specific maximum photosynthetic rate (P_m^B) increased up to threefold with decreasing day length and twofold with increasing irradiance. The maximum light utilization coefficient (α^B) and maximum quantum yield (φ_m) increased up to threefold with decreasing day length. α^B increased almost four-fold with decreasing irradiance, whereas φ_m was independent of irradiance. Literature data for phytoplankton indicate that P_m^B consistently increases with increasing irradiance, and day length-irradiance responses of α^B and φ_m are species specific. Results from the present experiment and other studies indicate that if day length-irradiance variability in the photosynthetic parameters are neglected, this may cause an over- or underestimation up to a factor of two in the photosynthetic rate estimation based on these parameters.     

PHYSIOLOGICAL INVESTIGATIONS ON ALARIA ESCULENTA (LAMINARIALES,PHAEOPHYCEAE). II. ROLE OF TRANSLOCATION IN BLADE GROWTH1,2

Laboratory studies on blade growth in Alaria esculenta (L.) Grev. showed 3 periods of rapid blade elongation during the year: October–November, February–April and late June. The first two periods are characteristic of many Laminariales; the unique June peak may reflect local nutrient conditions. While the distal blade functions as a source, supplying organic matter to the blade meristem, the stipe can be a source during periods of rapid growth or a sink during late summer when blade growth is slow. Maximum enhancement of elongation rate of blade meristems was observed in 40–50 cm blades; longer blades showed no further increase in growth rate. This blade length-growth promotion relationship may be independent of seasonal variations in meristematic activity. ¹⁴C tracer experiments suggested that separate growth promotion effects by distal blade, sporophylls and stipe were not additive in the intact thallus. The preferential source of assimilate for blade meristem growth was the distal blade. Secondary sources: sporophylls, which were activated following excision of the primary source; and stipe, which began to translocate assimilate when both sources were removed. The role of secondary sources in nature is discussed. Profiles of radioactivity in alcohol-soluble organic matter in blades are evaluated in relation to tracer profiles in higher plants and mechanisms of translocation.     

Nutrition and growth of coniferous seedlings at varied relative nitrogen addition rate

The growth of two provenances of Pinus sylvestris L. were compared with two provenances of Picea abies (L.) Karst. and with Pinus contorta Dougl. when grown in solution cultures with low nutrient concentrations. Nitrogen was added at different exponentially increasing rates, and the other nutrients were added at a rate high enough to ensure free access of them to the seedlings. During an initial period of the culture (a lag phase), when the internal nutrient status was changing from optimum to the level of the treatment, deficiency symptoms appeared. The needles yellowed and the root/shoot ratio increased. The initial phase was followed by a period of exponential growth and steady-state nutrition. The needles turned green again, and the root/shoot ratio stabilized at a level characteristic of the treatment. These patterns were the same as previously reported for other tree species. The relative growth rate during exponential growth was numerically closely equal to the relative nitrogen addition rate. The maximum relative growth rates were about 6 to 7.5% dry weight increase day^-1. This is a much lower maximum than for broad-leaved species (about 20 to 30% day^-1) under similar growth conditions. The internal nitrogen concentrations of the seedlings and the relative growth rates were stable during the exponential period. Close linear relationships were found between these parameters and the relative addition rate up to maximum growth. During steady state the relative growth rates of the different plant parts were equal. However, there were large differences between genotypes in absolute root growth rate at the same seedling size because of differences in root/shoot ratio. Lodgepole pine had the highest root growth rate, whereas that of Norway spruce, especially the southern provenance, was remarkably low. Yet, Norway spruce had a high ability to utilize available nutrients. In treatments with free nutrient access, growth allocation to the shoot had a high priority in all genotypes, but there was still a marked tendency for luxury uptake of nutrients. Nitrogen productivity (growth rate per unit of nitrogen) was lower than in broadleaved species and highest in lodgepole pine. The relevance of the dynamic factors, i.e. maximum relative growth rate, nutrient uptake rate, nitrogen productivity, growth allocation and root growth rate, are discussed with regard to conifer characteristics and selection value.     

Modelling the uptake of nitrate by a growing plant with an adjustable root nitrate uptake capacity

A new model is presented to predict the plant uptake of nitrate supplied by diffusion and mass flow to its roots. Plant growth, root-shoot ratio and the plant's nitrate uptake capacity are all set dependent on the plant's N nutrition state. By thoroughly integrating processes occurring in both plant and soil, the model enables to control the relative importance of both under a wide range of different nutritional scenarios.Soil parameters D₀ diffusion coefficient in water (m² day^-1) - D_e diffusion coefficient in soil (m² day^-1) - C nitrate concentration in soil (mol m^-3) - f tortuosity (-) - volumetric moisture content (-) - R radial distance from root axis (m) Plant parameters b₁, b₂ parameters of biomass partitioning Equation (10) - IR interroot distance (m) - K_mU Michaelis-Menten constant of the uptake system (mol m^-3) - K_mNRA Michaelis-Menten constant of nitrogen reduction system (mol g^-1) - k₁, k₂, k₃ parameters of growth model Equation (9) - L_v Root length density (m m^-3) - NO_{3 set} ^- Set point of the cytoplasmatic nitrate pool (mol g^-1 dw) - NO_{3 c} ^- cytoplasmatic nitrate concentration (mol g^-1 dw) - NO_{3 v} ^- vacuolar nitrate concentration (mol g^-1 dw) - NRA_max maximum nitrate reductase activity (mol g^-1 dw day^-1) - N_re reduced nitrogen content (mol) - N_remax maximum reduced N concentration in the plant (mol g^-1 dw) - P partitioning coefficient of nitrate between cyplasm and vacuole - R(1) root radius (m) - RGR relative growth rate (day^-1) - U uptake rate (mol day^-1 m^-2) - U_max maximum uptake rate (Eq. 6) (day^-1 m^-2) - Vo water flux at root surface (m day^-1) - W_r root dry weight (g) - W_sh shoot dry weight (g) - X model parameter: number of root compartments - Y model parameter: number of nodes     

Age and growth of early-life-stage Atlantic tarpon (Megalops atlanticus) from the northcentral Gulf of Mexico

Age and growth of early-life-stage Atlantic tarpon Megalops atlanticus collected from Mississippi coastal waters in the northcentral Gulf of Mexico (GOM) are described using otolith microstructure analysis. Tarpon leptocephali (n = 95, 16.0—27.8 mm standard length, L_S) collected from June throughOctober 2013—2018, ranged in age from 22 to 43 days (mean = 30.9 ± 0.5 days). Leptocephalus somatic growth rates ranged 0.46—1.24 mm day⁻¹ (mean = 0.76 ± 0.02 mm day⁻¹), and leptocephalus otolith growth rates ranged 1.78—3.97 μm day⁻¹ (mean = 2.58 ± 0.04 μm day⁻¹). Growth rates were inversely correlated to leptocephalus age, indicating the shrinkage phase associated with leptocephalus metamorphosis. Juvenile tarpon (n = 358, 50—359 mm fork length, L_F) were collected from August through December 2007—2018. Juveniles exhibited a positive allometric relationship (adjusted R² = 0.99, P < 0.001) between length and mass. The age of 100 juveniles (71—277 mm L_F) ranged from 76 to 174 days. Juvenile growth rate was estimated as 1.56 ± 0.11 mm day⁻¹. Significant (P < 0.001) linear relationships were found between juvenile age and otolith metrics, including otolith mass (R² = 0.81) and radius (R² = 0.68). Evaluation of the backcalculated hatch dates suggests that specimens in the collection hatched from late May through mid-September with slight peaks during July and August. A Rao's Spacing Test of Uniformity indicates the presence of significant lunar periodicity in leptocephalus hatch dates (n = 95, U = 250.1, P < 0.05), with 50% of the leptocephali hatched within 5 days (before or after) of the full moon. This study fills critical gaps in the scientific knowledge of tarpon and provides estimates of early-life-history metrics for an iconic game fish at the northernmost extent of its GOM range.     

Feeding and growth of juvenile sea bass: the effect of ration and temperature on growth rate and efficiency

The effect of ration on the growth of pairs of juvenile sea bass Dicentrarchus labrax fed squid mantle was recorded at four temperatures: 6, 10, 14 and 18) C, covering the range typical of Welsh coastal waters. Initial weight of the fish ranged from 2.8 to 15.9 g. A predictive model for the maximum meal size (M_max) at temperatures between 10 and 18) C, accounted for 95% of the variance in lnM_max. Even when offered excess food, bass at 6) C had a low rate of food consumption [0.19% body weight (BW) day^?1] and lost weight (G=?0.04% day^?1). Predictive regression models for specific growth rate (G) accounted for 86% of the variance at reduced rations and 70% at maximum meals. The relationship between G (calculated for total biomass per tank) and ration was a decelerating curve. G at maximum meals increased with temperature, at lower rations G decreased with temperature. For a pair of bass with a combined weight of 15 g, predicted maintenance ration ranged between 0.7 and 2.3% BW day^?1 and increased with temperature. Maximum meal size was more sensitive to temperature than maintenance ration. At 18) C optimum ration was 7.4% BW day^?1. At lower temperatures, the optimum ration was the maximum meal. The maximum gross growth efficiency was 17.4% at 18) C. Mean absorption efficiency was 94.8%. Ration level had no significant effect on absorption efficiency, which was lowest at 6) C. Condition indices (Fulton condition factor, wet and dry liver—somatic indices and body depth index) increased with meal size at all temperatures except 6) C. An increase in temperature between 10 and 18) C generally resulted in a decrease in condition indices at a given ration. When comparisons were made at a given standard length, gut and carcass weight increased with ration. Visceral fat and gut weight decreased with increased temperature.     

KINETICS OF GROWTH AND DEATH IN ANABAENA FLOS-AQUAE (CYANOBACTERIA) UNDER LIGHT LIMITATION AND SUPERSATURATION

The kinetics of population growth and death were investigated in Anabaena flos-aquae (Lyngb.) Bréb grown at light intensities ranging from limitation to photoinhibition (5 W·m⁻² to 160 W·m⁻²) in a nutrient-replete turbidostat. Steady-state growth rate (μ, or dilution rate, D) increased with light intensity from 0.44·day⁻¹ at a light intensity of 5 W·m⁻² to 0.99·day⁻¹ at 20 W·m⁻² and started to decrease above about 22 W·m⁻², reaching 0.56·day⁻¹ at 160 W·m⁻². The Haldane function of enzyme inhibition fit the growth data poorly, largely because of the unusually narrow range of saturation intensity. However, it produced a good fit (P < 0.001) for growth under photoinhibition. Anabaena flos-aquae died at different specific death rates (γ) below and above the saturation intensity. When calculated as the slope of a v_x⁻¹ and D⁻¹ plot, where v_x and D are cell viability (or live cell fraction) and dilution rate, respectively; γ was 0.047·day⁻¹ in the range of light limitation and 0.103·day⁻¹ under photoinhibition. Live vegetative cells and heterocysts, either in numbers or as a percentage of the total cells, showed a peak at the saturation intensity and decreased at lower and higher intensities. The ratio of live heterocysts to live vegetative cells increased with intensity when light was limiting but decreased when light was supersaturating. In cells growing at the same growth rate, the ratio was significantly lower under light inhibition than under subsaturation and the cell N:C ratio was also lower under inhibition. The steady-state rate of dissolved organic carbon (DOC) production increased with light intensity. However, its production as a percentage of the total C fixation was lowest at the optimum intensity and increased as the irradiance decreased or increased. The rate and percentage was significantly higher under photoinhibition than limitation in cells growing at the same growth rate. About 22% of the total fixed carbon was released as DOC at the highest light intensity. No correlation was found between the number of dead cells and DOC.     

Growth of three submerged plants below different densities of Nymphoides peltata (S. G. Gmel.) Kuntze

We evaluated one-sided competition from the floating-leaved plant Nymphoides peltata (non-indigenous in Sweden) on three submerged plant species, Ceratophyllum demersum, Elodea canadensis and Ranunculus circinatus, in a controlled experiment. The three submerged species were allowed to grow for 21 days in the absence of N. peltata and with the species present at densities of approximately 33, 66 and 100% cover. All species retained a positive relative growth rate (RGR) based on length at all N. peltata densities, but responded with negative growth based on weight for several treatments. C. demersum achieved RGR of 0.03 day⁻¹ in the absence of N. peltata, RGR of 0.02 day⁻¹ in the lowest N. peltata density but negative RGR in the two denser treatments. E. canadensis responded similarly with RGR of 0.04 day⁻¹ in the absence of N. peltata, RGR of 0.01 day⁻¹ in the lowest N. peltata density and negative RGR in the two denser treatments. R. circinatus, on the other hand, never achieved positive RGR based on weight. These results suggest that one-sided competition from floating-leaved plants has a profound effect on the submerged plant community.     

COENOBIAL CELL NUMBER IN SCENEDESMUS QUADRICAUDA (CHLOROPHYCEAE) AS A FUNCTION OF GROWTH RATE IN NITRATE-LIMITED CHEMOSTATS1

The relative numbers of cells growing as coenobia of different cell number are functions of growth rate when Scenedesmus quadricauda (Turp.) Bréb. is grown axenically in nitrate-limited, steady-state chemostats in continuous light. Unicells decreased from a maximum fraction of 0.04–0.05 of the total number of cells at 0.1 day^?1 to 0.01 or less as growth rate increased. The fraction of cells that grew as two-celled coenobia decreased from about 0.2 to 0.01–0.02. The fraction that grew as 4-celled coenobia increased from about 0.7–0.8 at 0.1 day^?1 to near unity at 0.5–0.6 day^?1, and then decreased sharply. The fraction of 8-celled coenobial cells increased from very small values below 0.6 day^?1, to ca. 0.9 at 1.0 day^?1.     

Growth and reproductive patterns of <Emphasis Type="Italic">Undaria pinnatifida</Emphasis> sporophytes in a cultivation farm in Busan,Korea

Monthly growth and reproduction of Undaria pinnatifida sporophytes were examined over a period of 5 months in a cultivation farm in Korea. A total of 11 characters of Undaria were measured to determine a reliable morphological character representing its growth and reproduction. Plant weight of Undaria sporophytes increased steadily over the experimental period, but it increased in four different ways. Undaria pinnatifida increased body weight by growth in length and width (October–early December), and by growth in width with the thickening of blade and stipe when sporophytes began to be fertile (December–January). In the middle of January, growth in length and width had almost stopped with the maturation of Undaria sporophytes. Finally, the weight of Undaria increased again by growth in width at the end of February. Present results indicate that Undaria sporophytes increase body weight by growth in length and width at different times, and the relationship between reproduction and vegetative growth is exclusive. Plant weight was positively correlated and fitted well with stipe width and blade width. The blade of Undaria was very thin (ca. 254 μm) and breakable by wave action, but its stipe was strong and relatively thick (ca. 8.7 mm). Furthermore, the fertility of U. pinnatifida was fitted better with stipe width than blade width. Thus, we suggest that the stipe width is the most feasible character with which to estimate the growth and reproduction of U. pinnatifida sporophytes in the cultivation farm.     

Primary production of the kelp Lessonia corrugata varies with season and water motion: Implications for coastal carbon cycling

Kelp forests provide vital ecosystem services such as carbon storage and cycling, and understanding primary production dynamics regarding seasonal and spatial variations is essential. We conducted surveys at three sites in southeast Tasmania, Australia, that had different levels of water motion, across four seasons to determine seasonal primary production and carbon storage as living biomass for kelp beds of Lessonia corrugata (Order Laminariales). We quantified blade growth, erosion rates, and the variation in population density and estimated both the net biomass accumulation (NBA) per square meter and the carbon standing stock. We observed a significant difference in blade growth and erosion rates between seasons and sites. Spring had the highest growth rate (0.02 g C · blade⁻¹ · d⁻¹) and NBA (1.62 g C · m⁻² · d⁻¹), while summer had the highest blade erosion (0.01 g C · blade⁻¹ · d⁻¹), with a negative NBA (−1.18 g C · m⁻² · d⁻¹). Sites exhibiting lower blade erosion rates demonstrated notably greater NBA than sites with elevated erosion rates. The sites with the highest water motion had the slowest erosion rates. Moreover, the most wave-exposed site had the densest populations, resulting in the highest NBA and a greater standing stock. Our results reveal a strong seasonal and water motion influence on carbon dynamics in L. corrugata populations. This knowledge is important for understanding the dynamics of the carbon cycle in coastal regions.     

Growth of Ecklonia cava (Laminariales, Phaeophyta) sporophytes transplanted to a locality with different temperature conditions

Transplanting experiments were carried out to determine whether the small type sporophytes with short stipe of Ecklonia cava Kjellman (Laminariales, Phaeophyta) growing in a locality with warm temperatures, change into larger type with a long stipe when transplanted to a locality with cooler temperatures. Juvenile E. cava sporophytes, having a stipe shorter than 5 cm long were collected from Tei in Tosa Bay (southern Japan) (seawater temperature 15–29°C) and transplanted to Nabeta Bay (central Japan) (seawater temperature 13–25°C), where larger type E. cava sporophytes characterized by long stipe (ca 1 m) grow. They were attached to artificial reefs at the sea bottom (9 m depth) in Nabeta Bay to monitor their growth. For comparison, juvenile E. cava sporophytes of almost similar size growing in Nabeta Bay were also transplanted in the same way to the same experimental site. Observations of growth of sporophytes from Tei and Nabeta were carried out monthly for 2 years from November 1995 to October 1997. The transplanted Tei and Nabeta sporophytes showed an increase in stipe length and diameter from winter to spring, whereas almost no increase was observed during summer and autumn. At the end of the study period, the stipe of Nabeta sporophytes reached 25.6 cm in length and 17.0 mm in diameter, whereas that of Tei sporophytes reached 11.1 cm in length and 11.2 mm in diameter. The primary blade length was 16.0 cm in Nabeta sporophytes, whereas it was 5.5 cm in Tei sporophytes. Thus, Tei sporophytes still remained smaller than Nabeta sporophytes even under the same environmental conditions.     

Growth rates of young-of-year shovelnose sturgeon in the Upper Missouri River

Information on growth during the larval and young‐of‐year life stages in natural river environments is generally lacking for most sturgeon species. In this study, methods for estimating ages and quantifying growth were developed for field‐sampled larval and young‐of‐year shovelnose sturgeon Scaphirhynchus platorynchus in the upper Missouri River. First, growth was assessed by partitioning samples of young‐of‐year shovelnose sturgeon into cohorts, and regressing weekly increases in cohort mean length on sampling date. This method quantified relative growth because ages of the cohorts were unknown. Cohort increases in mean length among sampling dates were positively related (P < 0.05, r² > 0.59 for all cohorts) to sampling date, and yielded growth rate estimates of 0.80–2.95 mm day⁻¹ (2003) and 0.44–2.28 mm day⁻¹ (2004). Highest growth rates occurred in the largest (and earliest spawned) cohorts. Second, a method was developed to estimate cohort hatch dates, thus age on date of sampling could be determined. This method included quantification of post‐hatch length increases as a function of water temperature (growth capacity; mm per thermal unit, mm TU⁻¹), and summation of mean daily water temperatures to achieve the required number of thermal units that corresponded to post‐hatch lengths of shovelnose sturgeon on sampling dates. For six of seven cohorts of shovelnose sturgeon analyzed, linear growth models (r² ≥ 0.65, P < 0.0001) or Gompertz growth models (r² ≥ 0.83, P < 0.0001) quantified length‐at‐age from hatch through 55 days post‐hatch (98–100 mm). Comparisons of length‐at‐age derived from the growth models indicated that length‐at‐age was greater for the earlier‐hatched cohorts than later‐hatched cohorts. Estimated hatch dates for different cohorts were corroborated based on the dates that newly‐hatched larval shovelnose sturgeon were sampled in the drift. These results provide the first quantification of growth dynamics for field‐sampled age‐0 shovelnose sturgeon in a natural river environment, and provide an accurate method for estimating age of wild‐caught individuals. Methods of age determination used in this study have applications to sturgeons in other regions, but require additional testing and validation.     

Interactions of feeding rates on growth,food conversion and body composition of the freshwater catfish Mystus vittatus (Bloch)

Food intake, growth, conversion efficiency and body composition of the non-air breathing catfish Mystus vittatus (Bloch) were studied in relation to different feeding levels. Fish weighing 817.9 ± 104.00 mg was found to consume a maximum of 156.0 mg live Tubifex worm/g day^-1. Geometrically derived feeding rates of 6.75, 23.00 and 26.00 mg dry food/g live fish day^-1 represent the maintenance, optimum and maximum levels respectively. The SDA increased from 6.75 mg/g day^-1 at maintenance to 13.50 mg/g day^-1 at maximum feeding rate. Starvation brougt about increase in body water content, while there was concomitant decrease in fat and crude protein.     

Growth and habitat separation in eight cohorts of three species of cyprinids in a subalpine lake

Synopsis Distribution and growth of the embryos, larvae and juveniles of Rutilus rutilus (roach), Scardinius erythrophthalmus (rudd) and Leuciscus cephalus (chub) from an oligotrophic subalpine lake in Tyrol, Austria, were studied during the first three to four months after hatching. R. rutilus was the first to spawn, a single cohort hatching around May 23rd. Four cohorts of S. erythrophthalmus hatched between June 19 and August 1. Three cohorts of L. cephalus hatched between July 3 and 25. The length/weight relationship of all species changed at a length of approximately 15–16 mm. R. rutilus, hatching at the lowest temperature, also showed the lowest growth rate during early life (maximum 10.4 per cent fresh body weight day^–1). In the other two species relative growth rates up to 20% day^–1) were measured. Rudd and chub remained in the shallow littoral during the whole period of observation, whereas roach left the littoral a few weeks after hatching and migrated into deeper water. A subtle shift in vertical distribution was observed for the first cohort of rudd which moved into slightly deeper water when the second cohort made its appearance.To whom correspondence should be addressed     

Effect of water flow velocity on growth and morphology of cultured <Emphasis Type="Italic">Undaria pinnatifida</Emphasis> sporophytes (Laminariales,Phaeophyceae) in Okirai Bay on the Sanriku coast,Northeast Japan

Undaria pinnatifida sporophytes, originating from the same strain, were cultured at the commercial cultivation site exposed to wave action and the uncultivated site protected from water action of Okirai Bay, Northeast Japan, from January to April 2007; simultaneously, water flow velocity, water temperature, salinity, NO₃ + NO₂, and chlorophyll a were monitored to investigate the effect of water environment on their growth and morphology. Water temperature and salinity fluctuated within the optimal range for their growth whereas water flow velocity at the cultivation site was greatly fast compared with that at the uncultivated site. Successive chlorophyll a increases synchronized with NO₃ + NO₂ decreases were observed only at the uncultivated site for over a month; indicating developments of phytoplankton blooms and their nutrient consumption under the low-flow condition. Meanwhile, blade growth rate of cultured sporophytes was higher at the cultivation site than at the uncultivated site. Their thallus size expressed by six morphological characters (blade length, stipe length, blade wet weight, stipe wet weight, blade width, and undivided blade width) at the cultivation site became large in comparison with that at the uncultivated site. Their three morphological correlations (correlations between blade length and thallus length; blade wet weight and thallus wet weight; and undivided blade width and blade width) differed between the sites. They produced a thick and flat blade at the cultivation site but formed a thin and wrinkled blade at the uncultivated site. These results show the significant impact of water flow velocity on their growth and morphology.     

Reproductive phenology,growth and primary production of Phyllariopsis purpurascens (Phyllariaceae,Phaeophyta) from the Straits of Gibraltar

Two populations of Phyllariopsis purpurascens from the Straits of Gibraltar area were investigated during 1990 and 1991. This area has very strong currents (～2·5 m s^-1 at spring tide). The first sporophytes (less than 0·5 cm in length) were observed in April; they disappeared after the first storm period in October. The estimated number of spores produced in an unilocular sporangium was 64. The fertility period started in May and continued until October, but the maximum sorus surface area (27%) was reached in September. The maximum sporangial density was 1476±236 mm^-2. The slow development of fertility and its correlation with the seasonal increase in temperature suggest that sporangial development is controlled by temperature and not by photoperiod. The drag effect produced by the strong currents (at spring tides and storm periods) is sufficient to break adult plants (with 0·01 m² in surface intercepting the current). At the beginning of the sporophytic production cycle (210 days), the meristematic zone produces more tissue for blade growth than for stipe growth. Holdfast growth occurs in the first 3 months. The mortality was 90% for sporophytes 0–10 cm in length, and decreased to ～50% in adult plants. One cohort in the cycle has been identified. The net primary production (calculated by the graphic model of Allen) was 0·04 g dry weight m^-2·day^-1 from April to October (210 days). The production is among the lowest values estimated for seaweeds.