Effects of artificial freshets on substratum composition,benthic invertebrate fauna and invertebrate drift in two impounded rivers in mid-Wales

Artificial discharges of water from reservoirs caused a six-fold and three-fold increase in discharge in the R. Tywi and R. Elan respectively but did not significantly alter particle size composition (by weight) and the porosity of the substratum or the organic matter content of fine particles (<0.5 mm). Freshets in both rivers resulted in a consistent, though not significant, reduction in total densities of invertebrates and the densities of many major taxa and abundant species. During the freshet in the R. Elan, maximum concentration and total load of suspended solids were about 11 and 35 times greater than pre-release values respectively while invertebrate drift was dominated by Chironomidae (65%) and Plecoptera (25%). Total numbers and densities of drifting chironomids increased immediately in response to the flow increase; in contrast, numbers and densities of plecopterans increased later, during the night.     

The food of brown and rainbow trout (Salmo trutta and S. gairdneri) in relation to the abundance of drifting invertebrates in a mountain stream

Summary The diet of Salmo gairdneri and S. trutta in a Pyrenean stream was very similar, and was also similar to the percentage composition of the drift but not the benthos. There was a good correlation between diel changes in the amount of food (both numbers and biomass) in the stomachs and diel changes in the abundance of drifting invertebrates. The major feeding period was in the early hours of the night when the trout fed chiefly on benthic invertebrates in the drift. This was the only feeding period in experiments 1 and 2 (mean water temperatures 4.7 and 7.3° C) but in experiment 3 (10.8° C), there was a second feeding period in the day when terrestrial invertebrates and emerging aquatic insects formed a large proportion of the diet.Neither species was consuming a greater amount of food than the other. The weight of food consumed/trout/day increased with water temperature, and was close to the daily food requirements for resting metabolism in experiment 1. for twice resting metabolism (active metabolism) in experiment 2, and for four times resting metabolism in experiment 3. Therefore the energy of the second meal in experiment 3 was available for growth.The effect of temperature, on rates of gastric evacuation was the chief factor which determined the number of meals/day; the availability of food organisms in the drift determined the time of feeding; and the requirements for metabolism (affected by temperature and body weight) determined the amount of energy left for growth.     

The effects of electrofishing on the invertebrates of a Lake District stream

Summary The experiments were performed in Dale Park Beck, a stony stream in the English Lake District. Two operators electrofished the sampling area (length 20 m in April and July 1970, and 40 m in May 1971) three times (runs 1, 2, 3) in each experiment.Electrofishing caused a marked increase in the number of invertebrates drifting out of the sampling area, and nearly all taxa taken in the bottom samples were also found in the drift samples. The fish shocker was chiefly responsible for the increased drifting of Plecoptera, Ephemeroptera and Gammarus pulex, and these taxa were dislodged from the substratum more easily than Trichoptera, Coleoptera, Diptera and Polycelis felina. The increased drifting of the latter taxa was chiefly due to the disturbance of the substratum by the two operators.Most of the invertebrates drifting from the upstream end of the experimental section returned to the bottom within the sampling area. The invertebrate drift out of the sampling area came chiefly from the downstream end of the section, and was equivalent to a loss of only 5% from the total benthos in the sampling area (losses varied between <1 and 13% for individual taxa).     

Effects of trout on the diel periodicity of drifting in baetid mayflies

Some benthic invertebrates in streams make frequent, short journeys downstream in the water column (=drifting). In most streams there are larger numbers of invertebrates in the drift at night than during the day. We tested the hypothesis that nocturnal drifting is a response to avoid predation from fish that feed in the water column during the day. We surveyed diel patterns of drifting by nymphs of the mayfly Baetis coelestis in several streams containing (n=5) and lacking (n=7) populations of rainbow trout, Oncorhynchus mykiss. Drifting was more nocturnal in the presence of trout (85% of daily drift occurred at night) than in their absence (50% of daily drift occurred at night). This shift in periodicity is due to reduced daytime drifting in streams with trout, because at a given nighttime drift density, the daytime drift density of B. coelestis was lower in streams occupied by trout than in troutless streams. Large size classes of B. coelestis were underrepresented in the daytime drift in trout streams compared to nighttime drift in trout streams, and to both day and night drift in troutless streams. Differences in daytime drift density between streams with and without trout were the result of differences in mayfly drift behaviour among streams because predation rates by trout were too low to significantly reduce densities of drifting B. coelestis. We tested for rapid (over 3 days) phenotypic responses to trout presence by adding trout in cages to three of the troutless streams. Nighttime drifting was unaffected by the addition of trout, but daytime drift densities were reduced by 28% below cages containing trout relative to control cages (lacking trout) placed upstream. Drift responses were measured 15 m downstream of the cages suggesting that mayflies detected trout using chemical cues. Overall, these data support the hypothesis that infrequent daytime drifting is an avoidance response to fish that feed in the water column during the day. Avoidance is more pronounced in large individuals and is, at least partially, a phenotypic response mediated by chemical cues.     

The effects of carp (Cyprinus carpio L.) on sediment export from a small urban impoundment

Significantly higher concentrations of suspended inorganic matter were observed in the outflows than the inflows of three impoundments along an urban stream in southern Ontario during baseflow conditions. This pattern was observed during two summers at two of the reservoirs. After carp (Cyprinus carpio L.) were eliminated (490 kg ha^–1) from the third reservoir, significantly less suspended sediment was found in the outflow. Burrowing benthic invertebrates (Chironomus sp. and Tubificidae) which dominated the benthic fauna were replaced by less tolerant, more lithophilic taxa after carp removal. Tubifids dominated the fauna again after carp recolonized the impoundment. These data suggest that carp removal can have a significant positive effect on water quality.     

Observations on the settling of Simulium damnosum larvae on artificial substrates,in the Ivory Coast

The settling rates of the larvae of the blackfly Simulium damnosum Theobald, were monitored at a Simulium breeding site on the Bandama River in the Ivory Coast. Significantly greater numbers of larvae were found to settle during the night than during the day, and there was a significant increase in the settling rate immediately following the onset of darkness.The drifting larval population contained significantly greater numbers of smaller larvae than the general population.     

Diet partitioning in sympatric Atlantic salmon and brown trout in streams with contrasting riparian vegetation

Prey intake by Atlantic salmon Salmo salar and brown trout Salmo trutta was measured across different riparian vegetation types: grassland, open canopy deciduous and closed canopy deciduous, in upland streams in County Mayo, Western Ireland. Fishes were collected by electrofishing while invertebrates were sampled from the benthos using a Surber sampler and drifting invertebrates collected in drift traps. Aquatic invertebrates dominated prey numbers in the diets of 0+ year Atlantic salmon and brown trout and 1+ year Atlantic salmon, whereas terrestrial invertebrates were of greater importance for diets of 1+ and 2+ year brown trout. Terrestrial prey biomass was generally greater than aquatic prey for 1+ and 2+ year brown trout across seasons and riparian types. Prey intake was greatest in spring and summer and least in autumn apart from 2+ year brown trout that sustained feeding into autumn. Total prey numbers captured tended to be greater for all age classes in streams with deciduous riparian canopy. Atlantic salmon consumed more aquatic prey and brown trout more terrestrial prey with an ontogenetic increase in prey species richness and diversity. Atlantic salmon and brown trout diets were most similar in summer. Terrestrial invertebrates provided an important energy subsidy particularly for brown trout. In grassland streams, each fish age class was strongly associated with aquatic, mainly benthic invertebrates. In streams with deciduous riparian canopy cover, diet composition partitioned between conspecifics with older brown trout associated with surface drifting terrestrial invertebrates and older Atlantic salmon associated with aquatic invertebrates with a high drift propensity in the water column and 0+ year fish feeding on benthic aquatic invertebrates. Deciduous riparian canopy cover may therefore facilitate vertical partitioning of feeding position within the water column between sympatric Atlantic salmon and brown trout. Implications for riparian management are discussed.     

Interspecific differences in drift behaviour between the native <Emphasis Type="Italic">Gammarus pulex</Emphasis> and the exotic <Emphasis Type="Italic">Gammarus roeseli</Emphasis> and possible implications for the invader’s success

“Drifting” is known to subject aquatic invertebrates to intense predation by drift feeding fish. Consequently, interspecific variations in drifting behaviour could lead to differences in predation pressure between coexisting prey species. Predation being an important factor determining the success of invaders, differences in drift patterns could advantage either native or exotic invertebrates through differential predation by native fish predators. The exotic freshwater amphipod (Gammarus roeseli) has now largely colonized Western Europe where it is often found in sympatry with a native species (Gammarus pulex). Here we documented interspecific differences in drifting behaviour that might have favored the invader’s success through differential predation. Benthic and drifting amphipods were sampled three times at the same site to compare the proportion of each species within and between sample types (benthos or drift) across time. Compared with the benthos, where the invader (G. roeseli) was significantly less abundant than the native (G. pulex), G. roeseli was proportionally overrepresented in the drift but displayed a very different drifting pattern. While G. pulex drift rates remained roughly constant over a 24 h period, G. roeseli showed a marked diel periodicity with low diurnal and high nocturnal drift rates. Such drifting behaviour could procure this species with a competitive advantage regarding predation as most drift feeding fish are diurnal. As a result, the native appears more disadvantaged with respect to drift. This may partly explain the ability of G. roeseli to coexist with G. pulex in a habitat more suitable to the native.     

A comparative study of the dispersal of 10 species of stream invertebrates

1. Apart from downstream dispersal through invertebrate drift, few quantitative data are available to model the dispersal of stream invertebrates, i.e. the outward spreading of animals from their point of origin or release. The present study provides comparative data for 10 species, using two independent methods: unmarked animals in six stream channels built over a stony stream and marked animals in the natural stream. Experiments were performed in April and June 1973 and 1974, with initial numbers of each species varying from 20 to 80 in the stream channels and 20 to 60 for marked animals. 2. Results were the same for marked invertebrates and those in the channels. Dispersal was not density‐dependent; the number of dispersing animals was a constant proportion of the initial number for each species. The relationship between upstream or downstream dispersal distance and the number of animals travelling that distance was well described by an inverse power function for all species (exponential and log models were poorer fits). Results varied between species but were similar within species for the 4 months, and therefore were unaffected by variations in mean water velocity (range 0.04–0.35 m s^?1) or water temperature (range 6.7–8.9 °C in April, 12.1–14.8 °C in June). 3. Species were arranged in order, according to their dispersal abilities. Three carnivores (Perlodes, Rhyacophila, Isoperla) dispersed most rapidly (70–91% in 24 h, maximum distances 9.5–13.5 m per day), followed by two species (Protonemura, Rhithrogena) in which about half their initial numbers dispersed (50–51% in 24 h, 7.5–8 m per day), and four species (Ecdyonurus, Hydropsyche, Gammarus, Baetis) in which less than half dispersed (33–40% in 24 h, 5.5–7 m per day). Dispersal was predominantly upstream for all nine species. Few larvae (20%) of Potamophylax dispersed, with similar maximum upstream and downstream distances of 3.5 m per day. The mean time spent drifting downstream was known for seven species from previous studies, and correlated positively with their dispersal distances. Therefore, the species formed a continuum from rapid to very slow dispersers. These interspecific differences should be considered when evaluating the role of dispersal in the maintenance of genetic diversity in stream invertebrates, and in their ability to colonise or re‐colonise habitats.     

Life history and production of filter-feeding insects on stone dikes in the lower Mississippi River

Population and production dynamics of two filter-feeding macroinvertebrates, the caddisfly Hydropsyche orris and the midge Rheotanytarsus sp., were examined in the lower Mississippi River Miles 510–515. Samples were collected from September to November 1987, May to December 1988, and March to May 1989 from stone dikes that protrude into the river. Developmental synchrony was high among individuals in both populations, and seasonal changes in the relative abundance of instars indicated bivoltine and trivoltine life cycles for H. orris and Rheotanytarsus sp., respectively. The size frequency method was used to estimate production (P) and biomass (B) of each cohort in each population. P/B ratios for spring and fall cohorts of H. orris equaled 4.5 and 3.7. Spring, summer, and fall cohorts of Rheotanytarsus sp. had P/B ratios of 4.0, 4.7, and 4.1, respectively. Annual production, estimated as the sum of cohort production values, of the H. orris and Rheotanytarsus sp. population equaled 10.1 and 0.359 g m^–2 (dry weight). Annual P/B ratios equaled 10.8 and 16.1 for the H. orris and Rheotanytarsus sp. populations, closely matching values expected for bivoltine and trivoltine populations, respectively. Annual production of H. orris is in the low end of the range of published estimates for other lotic hydropsychid populations inhabiting coarse substratum in warm, lowland rivers of medium size or small, trophically enriched streams. Annual production of Rheotanytarsus sp. is the first such estimate based on a simultaneous assessment of life cycle and production. Given the lack of naturally occurring gravel and cobble substrate in the lower Mississippi River, stone dikes are an especially important habitat for H. orris and Rheotanytarsus sp.     

Invertebrate drift in a large, braided New Zealand river

1. The spatio-temporal patterns of drifting macroinvertebrates in a large, braided New Zealand river were determined by sampling with drift nets, seasonally, for 1 year. 2. Drift densities were greatest in autumn, and at night in all seasons except winter. A greater proportion of larger animals drifted at night than during the day in all seasons. Mean annual drift densities were ninety-six animals 100m^?3 and 47 mg dry weight 100 m^?3. 3. There were relatively few taxa in the drift, and the mayfly Deleatidium spp. comprised more than 85% of the drifting aquatic invertebrates in all seasons except autumn. Chironomidae and terrestrial forms were the only other groups to occur at densities of more than one animal 100 m^?3 in all seasons. 4. Drift density was positively correlated with benthic density, which in turn was adversely affected by floods, particularly during spring and summer.     

Presence of sculpins (Cottus gobio) reduces drift and activity of Gammarus pulex (Amphipoda)

Introduction of sculpins into a stream previously devoid of these predators significantly reduced drift rate of Gammarus pulex. The drift of insect larvae was not affected. High amounts of exudates after implantation of sculpins were probably responsible for the low number of drifting G. pulex specimens. Laboratory experiments confirmed reduced locomotory activity of G. pulex when exposed to caged sculpins, an observation that excludes reduced drift activity as a result only of predation.The average size of drifting G. pulex specimens was larger during the night than during the day. This result is in accordance with the hypothesis that large individuals should, in relation to small ones, turn nocturnal because of greater predation risk during daytime. Presence of sculpins did not alter the size composition of drifting G. pulex.     

Collected and self‐secreted building materials and their contributions to compression and tension structures

Animals that build structures have only two ways of obtaining their building materials: collecting them from the environment or secreting them. We identify a clear pattern among invertebrates: collected materials dominate in structures that bear loads predominantly in compression, whereas self‐secreted materials dominate in structures that bear loads in tension. Among vertebrates, by contrast, structures in tension are much less common and may make use of either self‐secreted or collected materials. Two possible explanations are examined for the difference between invertebrates and vertebrates. It may be that there has been evolutionary constraint on bodily secretions of vertebrates. Alternatively, the cost‐effectiveness of self‐secreted building materials diminishes with the load they bear in tension, and most vertebrates, because of their characteristically greater weight compared with invertebrates, exceed the viability threshold. Invertebrates have adapted biochemically varied secretions from a variety of glands to perform specialized mechanical roles. However, vertebrates have secretions with the potential to become building materials, in particular keratin, but only mucus‐like secretions have evolved as building materials. The cost of suspended structures is predicted to become relatively greater with increased weight, whilst it will also become more difficult to find supports rigid enough to resist the forces they impose. This conforms to the relatively small size and small number of vertebrate structures in tension. The much larger, heavier suspended structures built by some social insects demonstrate that ecological factors may have important effects on the determination of weight thresholds. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 112 , 625–639.     

Two levels of spacing and limits to local population density for settled larvae of the ascidian Clavelina moluccensis: a nearest-neighbour analysis

Among sessile marine invertebrates, the dispersion patterns of settling larvae are likely to strongly affect the nature and strength of subsequent intraspecific interactions. We use a recently developed graphical analysis technique to examine in situ spacing among settled larvae of the colonial ascidian Clavelina moluccensis. Larvae were mapped at settlement each day for 1 month at the time of their release from adults. Experimental plots measuring 90×90 mm were located on naturally occurring bare patches of wood on pier pilings which were extensively encrusted with sponges and ascidians. An inclusive one-tailed nearest-neighbour analysis applied at the time of the maximum number of individuals per plot revealed consistent fine-scale regular spacing between settled larvae. Furthermore, a two-tailed goodness-of-fit analysis indicated two modes of spacing: one at about 4.5 mm and the other at around 9 mm. No contact between larvae was observed at settlement and the spatial regularity is interpreted as a response of settling larvae to water-borne cues released from settled individuals. The two modes of spacing indicate the possibility of kin recognition as has been demonstrated for bryozoans. Water-borne cues may also limit local population density, as those plots with a high density of settlers showed a much greater decrease in settlement rate over time than low-density plots. Our findings are consistent with the hypothesis that intraspecific competitive interactions shape the patterns of dispersion of these invertebrates on hard substrata in the field.     

The relationship between sediment mobilisation and the entry of Baetis mayflies into the water column in a laboratory flume

Mass bedload movement is thought to play a key role in initiating stream invertebrate drift during extreme flood events. However, little is known of the importance of the shear of invertebrates from stone surfaces relative to their entrainment along with bed material at different discharges. In particular, it is unclear whether so-called catastrophic drift only occurs once mass bedload movement, and hence entrainment of invertebrates, occurs. We investigated the relationship between the mobilisation and transport of bed sediments and the entry of Baetis mayflies into the water column in a laboratory flume. Experiments quantified the percentage of Baetis drifting at a range of discharges that mobilised between 0 and 95% of the flume-bed sediments. Control experiments quantified drift losses from sediment fixed to the bed of the flume, such that sediments were immobile even at the highest discharges. Drift losses increased with increasing discharge and velocity in the flume. Sediment mobility contributed significantly to drift (ANCOVA, p < 0.001), with consistently greater drift losses in mobile sediment experiments than in those with fixed sediment. The discharge which resulted in a loss of 100% of Baetis from the mobile sediment bed (discharge 30 l s^–1) resulted in a loss of approximately 50% of individuals from the fixed bed. Results indicate that once bed sediments are mobilised, entry of Baetis into the drift is greater than expected from the shear of animals from stone surfaces alone. Thus, entrainment of animals along with sediment contributes significantly to drift at high flows. This implies that differences in bed stability between sites or streams, or temporal changes in sediment characteristics within a site, could influence patterns of drift.     

三峡水库175 m试验性蓄水期库区及其上游江段鱼类群落结构时空分布格局

根据2010—2012年在三峡水库及其上游江段5个江段的商业性渔获物调查结果,对该区域鱼类群落结构的时空分布格局进行了分析。调查中共收集到鱼类87种,隶属于8目18科63属。沿坝前江段溯河而上至库尾以上流水江段,鱼类种类数逐渐增加。采用聚类分析(CA)和非度量多维标度(NMDS)方法对三峡水库175 m试验性蓄水期间各江段的鱼类种类组成进行分析,发现这5个调查江段的鱼类种类组成可以分为两个类群:类群Ⅰ包括秭归、巫山、云阳3个库区的江段,其鱼类种类组成在各年间的差异程度较大;而类群Ⅱ包括库尾的涪陵江段以及上游的江津江段,其鱼类种类组成在各年间差异程度较小。采用CA和NMDS方法对鱼类群落结构时空分布格局的分析结果表明,5个调查江段的鱼类群落结构在各年间可以分为不同类群;云阳与涪陵江段的鱼类群落结构的相似性逐年增加,而与秭归、巫山江段的相似性逐年减少;涪陵江段与江津江段的鱼类群落结构相似性也呈逐年减少趋势。总体而言,175m试验性蓄水对库中和库尾江段的鱼类群落结构的影响较大,但对库首以及库尾以上流水江段的影响均较小。     

Control of foraging behavior of individuals within an ecosystem context: the clam Macoma balthica and interactions between competition and siphon cropping

Macoma balthica (L.) is a common clam of the estuarine seafloor, belonging to an important group of invertebrates possessing the capacity to choose between the two fundamental modes of feeding available, using its siphon to inhale either suspended food particles from the water or food particles deposited on the sediment surface. Field experiments demonstrate that intraspecific competition, effects of other competing benthic invertebrates, and complex interactions between competition and partial predation (siphon cropping by fishes) modify the foraging behavior of Macoma. When protected by caging from siphon nipping by fishes, Macoma demonstrated greater siphon regeneration at lower density, indicating the importance of competition for limited resources. In the absence of siphon croppers, these same clams also exhibited more deposit feeding at the lower density either because of improved ability to deposit-feed with longer siphons or because deposited foods become more rapidly depleted than suspended foods on local spatial scales. Addition of siphon-nipping fishes caused greater reductions in siphon size of clams at lower density, presumably because the intensity of nipping per clam was greater where clam targets were fewer and because deposit feeding, which was more intense at lower densities, confers a greater risk of cropping from greater siphon extension and activity than characterize suspension feeding. Deposit feeding by Macoma was reduced in the presence of siphon croppers at both high and low density of clams, but the intensity of deposit-feeding activity at low density was substantially higher than predicted by additive effects of clam density and cropping. This suggests operation of a balancing strategy in Macoma whereby it is accepting greater risks of partial predation when rewards of greater food harvest are larger. The surprising failure to adopt a risk-averse stratery may be explained by the non-lethal nature of partial predation, which renders siphon loss an energetic penalty replacable through regeneration. The presence of a bed of suspension-feeding Rangia cuneata also altered foraging behavior of Macoma by inducing a switch to more intense deposit feeding, in response either to the documented near-bottom depletion of suspended foods or to likely enhanced biodeposition from feces and pseudofeces. The induction of greater deposit feeding by the presence of this competing suspension feeder led to greater siphon losses during exposure to croppers because Macoma was practicing more risky feeding behavior. This enhanced loss of siphon tissues to croppers in the presence of the suspension-feeding Rangia induced an interaction between the effects of siphon croppers and Rangia, such that Macoma exhibited a larger switch away from deposit feeding in the presence of siphon croppers when Rangia were also present. Clearly, the foraging decisions made by individuals can only be understood in a broad holistic context of population, community, and ecosystem processes.     

The drift of zooplankton and microzoobenthos in the river Strandaelva,western Norway

The drift of zooplankton (rotifers, cladocerans, cyclopoid copepods) and microscopical zoobenthos (mainly bdelloid rotifers and small chironomid larvae) was investigated by filtering samples of river water. The number of drifting benthic rotifers varied between 1 000 and 6 000 ind. m^–3 in the lake inlet, and between 30 and 500 ind. m^–3 in the lake outlet, without any seasonal trend. The number of drifting insect larvae was approx. equal in the lake inlet and outlet, with a maximum in summer (250–300 ind. m^–3) and minimum in winter (ca. 10 ind. m^–3). Increasing water flow resulted in an increasing number of drifting zoobenthos. Downstream from the lake, the number of drifting benthic rotifers was increasing from approx. 300 ind. m^–3 in the outlet to 6 500 ind. m^–3 3.4 km downstream, while the number of insect larvae was ca. 100 ind. m^–3 in the outlet and leveled off at approx. 300 ind. m^–3 after 200 m. The number of drifting zooplankton in the lake outlet varied between 20 and 2 000 ind. m^–3 for crustaceans, and between 300 and 20 000 ind. m^–3 for rotifers, both with a maximum in late summer/autumn and a minimum in winter. The number of drifting zooplankton decreased by some 45% in the first 200 m from the lake outlet, but some zooplankton was still found in the drift 3.4 km downstream. The largest species was removed first from the drift. The diurnal variation in the number of drifting zooplankton in lake outlets appear to be related to the vertical migration in the lake, i.e. the largest number drifting when most animals are in the upper water layers.Contribution from the Voss Project, University of OsloContribution from the Voss Project, University of Oslo     

Effects of osmotic pressure on prolactin and growth hormone secretion from organ-cultured eel pituitary

Summary Effects of medium osmotic pressure on the release of prolactin (PRL) and growth hormone (GH) from the pituitary of the Japanese eel, Anguilla japonica, were examined during long-term organ culture in a defined medium. Prolactin and GH release, as measured by homologous radioimmunoassays, increased gradually for 7 days during incubation in isosmotic medium (295 mOsmolal). On day 7, 3 to 5 times more PRL and GH were released than on day 1. The amount of GH released was about 100 times greater than that of PRL. Electron microscopic observation revealed that both PRL and GH cells were in good condition after 7 days incubation. The reduction of medium osmotic pressure from 295 (isosmotic) to 235 or 260 mOsmolal significantly stimulated PRL release for 4 days. By contrast, an increase in medium osmolality from 295 to 360 mOsmolal was without effect. These treatments produced no significant alterations in GH release. The stimulatory effect of hyposmotic medium (235 mOsmolal) was no longer evident by 12 h after the pituitaries were returned to isosmotic medium. The isosmotic but low-sodium medium, prepared by adding mannitol to the hyposmotic medium, did not stimulate PRL release from the pituitary. These results indicate that plasma osmolality may be an important physiological factor controlling PRL release during freshwater adaptation of the eel.Abbreviations GH growth hormone - OAPBS PBS with 1% ovalbumin - PAGE polyacrylamide gel electrophoresis - PBS phosphatebuffered saline - PRL prolactin - rER rough endoplasmic reticulum     

HORMONAL REGULATION OF EPIPHYLLOUS BUD RELEASE AND DEVELOPMENT IN BRYOPHYLLUM CALYCINUM

The effects of various concentrations of several auxins and cytokinins separately and in combination on epiphyllous budding of Bryophyllum calycinum were investigated, using a marginal leaf strip method. The number of buds released per leaf in 10⁻⁶ m benzyladenine (BA) was 2.8 times greater than those in water, and 1.6 times greater in 10⁻⁵ m isopentyladenine (IPA). BA, IPA and kinetin were antagonistic to indoleacetic acid (IAA) or naphthaleneacetic acid (NAA) when used in combination treatments. The IAA oxidase co-factor p-coumaric acid (PCA) increased the number of epiphyllous buds to twice that of the water controls. This stimulatory effect of PCA on bud release suggests that an increase in IAA oxidase activity may be one of the significant changes that precedes the release of epiphyllous buds.