Perch Eggs Research Articles

Cathepsin L in eggs and larvae of perch Perca fluviatilis: variations with developmental stage and spawning period

This study describes changes in cathepsin L activity during early development in Eurasian perch (Perca fluviatilis) and determines to which extend a precocious proteolysis of the yolk reserves by activated cathepsin L could be involved in the seasonal decline of egg and larval quality. During embryogenesis and early larval stages, samples were collected for determination of fertilization and hatching rates, assays of cathepsin L activity, and evaluation of larval resistance to stress (osmotic shock and fasting). Cathepsin L activity increased significantly during the embryonic development, reaching a maximum of 177.1±12.3 nmol min−1mg fresh weight−1 on day 1 post-hatching and significantly decreasing on day 3. Activity increased significantly during the spawning season and individual variations between egg strands became very high during the second half of the spawning period. An inverse relationship was established between the cathepsin L activity in 7-day old eggs and the decrease of hatching rate. A negative exponential regression was calculated between the cathepsin L activity of eggs and the resistance of corresponding newly-hatched larvae to osmotic shock. Resistance to fasting was significantly reduced in larvae from eggs with cathepsin L activity higher or lower than 20 nmol min−1 mg−1 (lethal time50=4.7±0.7 and 3.5±0.4 days, respectively). The involvement of cathepsin L in the degradation of yolk reserves and its potential consequences on the quality of perch eggs and larvae are discussed in relation to results reported in salmonid fishes.

Countertactics of the japanese aucha perchsiniperca kawamebari against brood parasitism by the japanese minnowpungtungia herzi

Japanese aucha perch males taking care of eggs and fry are often brood-parasitized by a Japanese minnow. When the minnows are ovipositing in the perch nests, some of the perch eggs in the nests are often eaten by other fishes. The minnows’ eggs are subsequently guarded by the perch males until hatching. Countertactics of the perch against such brood parasitism were examined in a river of western Japan. Perch males did not employ any countertactics such as ejection of parasites’ eggs or nest desertion. On the other hand, perch females avoided spawning in nests with greater numbers of perch eggs and produced smaller clutches during the parasitic period than in the non-parasitic period. These behavior can be regarded as anti-parasitism tactics because minnows prefer to spawn in nests with higher numbers of perch eggs.

Evaluation of the toxicity and efficacy of hydrogen peroxide treatments on eggs of warm- and coolwater fishes

The use of hydrogen peroxide in aquaculture is growing and there is a need to develop fundamental guidelines to effectively treat diseased fish. The safety (toxicity) of hydrogen peroxide treatments was determined on eggs of representative warm- and coolwater fish species. Eggs of northern pike ( Esox lucius), walleye ( Stizostedion vitreum), yellow perch ( Perca flavescens), white sucker ( Catostomus commersoni), lake sturgeon ( Acipenser fulvescens), paddlefish ( Polyodon spathula), common carp ( Cyprinus carpio), and channel catfish ( Ictalurus punctatus) were cultured in egg jars or aquaria. Treatments were initiated with non-eyed eggs and continued until all viable eggs had hatched. Eggs were treated daily for 15 min Monday through Friday with either 0, 500, 1000, 3000, or 6000 μl l −1 of hydrogen peroxide. For all species, the mean percent hatch was greater in eggs treated with 1000 μl l −1 hydrogen peroxide for 15 min than in the untreated controls. Common carp, lake sturgeon, and paddlefish were the least sensitive to hydrogen peroxide with percent hatch ranging from 40 to 48% in the 6000 μl l −1 hydrogen peroxide treatment. Fungal infections reduced or eliminated the hatch in most controls whereas nearly all treated eggs remained free of infection; hydrogen peroxide inhibited fungal infections on fish eggs.

SOLAR ULTRAVIOLET RADIATION AND THE SPAWNING HABITAT OF YELLOW PERCH,PERCA FLAVESCENS

Dissolved organic carbon (DOC) strongly influences the underwater levels of potentially damaging solar ultraviolet radiation (UVR) in freshwater lakes. Even so, little is known about how DOC-related variation in UVR may influence natural populations and communities in lakes. Past studies of fish recruitment have emphasized the importance of temperature, food limitation, and predation in controlling year-class strength in fish. Here we report that high UVR levels in low-DOC lakes also may modify the spawning depth, hatching success, and thus recruitment of certain freshwater fishes. We examined how UVR influences the spawning habitat and hatching success of yellow perch (Perca flavescens) eggs in two lakes with different DOC levels and thus different UVR environments. Yellow perch eggs were incubated at the same depth (0.8 m) in quartz tubes (with mesh ends for water exchange) in both lakes in a modified reciprocal transplant experiment. Solar radiation was manipulated to provide three treatments that included exposure to full solar radiation (quartz alone), shielding from UV-B with wavelength selective filters (Mylar D), and dark controls that removed all wavelengths of solar radiation. All eggs in the light treatments in the high-UVR lake perished, whereas survival to hatching of eggs in all treatments in the low-UVR lake and in the dark controls in the high-UVR lake were ≥96%. Survival time in the high-UVR lake was longer in UV-B-shielded than in fully exposed (quartz) treatments, and eggs collected from the high-UVR lake survived longer than those collected from the low-UVR lake in identical UVR treatments. A survey of natural spawning depths in the two lakes revealed a much deeper spawning depth in the high-UVR lake (median = 3.2 m) than in the low-UVR lake (median = 0.4 m). Deeper spawning depths in the high-UVR lake suggest that yellow perch can avoid direct UVR damage in low-DOC lakes. DOC and hence UVR in lakes may be altered by both anthropogenic and natural disturbances in the surrounding watershed, suggesting that these disturbances may have consequences for the spawning habitat of fish.

Influence of temperature and size of females on the timing of spawning of perch, Perca fluviatilis, in Lake Geneva from 1984 to 1993

The influence of temperature and the size of reproducing females on the timing of spawning of perch in Lake Geneva has been studied for 10 consecutive years (1984–1993) by means of artificial spawning substrates. The clutch of perch is an egg ribbon with a width proportional to the size of the reproducing female, so that the size structure distribution of the female population can be estimated from measurements of the width of the egg ribbons. The survey of egg-ribbon size revealed a succession of 3 cycles (period of increasing mean size followed by a sharp decrease) lasting 3, 3 and 4 years which were due to the occurrence of 3 strong year classes born in 1982, 1985 and 1988 respectively. This phenomenon can be explained by the effect of intraspecific predation exerted by strong year classes on the offspring of the 2 following years rather than by fluctuations in the success of reproduction in relation to climatic changes. In Lake Geneva, perch spawn in May. The water temperature exerted only a minor influence on the date of the beginning of the spawning period but had a greater effect on its intensity. A rise in temperature in May stimulated spawning while bad weather decreased spawning intensity. The larger perch had a tendency to spawn later than the small ones. The date of the mid-spawning period was well correlated with the yearly mean width of perch egg ribbons but no correlation could be detected between it and the water temperature.

Timing of Spawning and Host‐nest Choice for Brood Parasitism by the Japanese Minnow, Pungtungia herzi, on the Japanese Aucha Perch, Siniperca kawamebari

AbstractA field study of the breeding ecology of the Japanese aucha perch, Siniperca kawamebari, and brood parasitism by the Japanese minnow, Pungtungia herzi, on nests of the perch was carried out from 1989 to 1991. Observations of perch nests under natural conditions in 1990 showed that brood parasitism by the minnow was concentrated on host nests in which nest owners had just begun their nesting cycle. When spawned in a perch nest with recently spawned perch eggs, parasite eggs always hatched earlier than host eggs. An experiment with imitation perch eggs in 1991 confirmed that changing colour of host eggs was the cue for the parasites to distinguish between different developmental stages of host eggs. Parasite eggs rapidly disappeared without guarding by a host male (Baba et al. 1990). This loss was caused by predation by fishes. Parasite fry left the nest immediately after hatching, so parasite eggs spawned in a host nest in an early stage should be well guarded until they hatch. In the field, minnows deposited their eggs in perch nests which had larger numbers of newly spawned perch eggs. Since the perch males always deserted their nests when their own eggs disappeared, the parasite's choice of host nests with larger numbers of host eggs may ensure survival of the parasite eggs. The timing of egg deposition and choice of host nest by the minnow appear to be adaptive in terms of brood parasitism on nests of the perch.

The influence of triploidy and heat and hydrostatic pressure shocks on the growth and reproductive development of juvenile yellow perch ( Perca jlavescens)

We evaluated triploidy induction as a means to sterilize yellow perch ( Perca flavescens) and reduce the diminution of growth associated with the onset of sexual maturation. Treatment of perch eggs with heat shocks (28–30°C, for durations of 10–25 min, beginning at 2–5 min post-fertilization) or hydrostatic pressure shocks (9000 or 11 000 psi, for durations of 8 or 12 min, beginning at 5 min post-fertilization) resulted in triploidy induction rates of 30–70%. In one experiment, juvenile heatshocked triploid perch grew faster than heat-shocked diploids. In a second experiment, heat-shocked triploid perch grew slower than unshocked diploids up to 25 g, but subsequent growth of fish from the two groups was not different. In a third experiment, unshocked diploids grew faster than fish subjected to either heat or pressure shocks, and among shocked fish, triploids outgrew diploids. Histological inspections revealed that gonadal development of juvenile triploid perch of both sexes was retarded compared to that of diploids. These findings show that heat and pressure shocks exert a negative influence on growth that is independent of changes in ploidy, and that triploid perch may have the potential to outgrow diploids if the negative effects of such shocks can be avoided.

Effect of salinity on the development of silver perch ( Bidyanus bidyanus) eggs and larvae

1. 1. Silver perch eggs were transferred into different salinities at selected times post-fertilization. Hatching rate depended on transfer time. Eggs transferred within 1 hr post-fertilization had a lower hatching rate than those transferred after 1 hr. No larvae hatched when the salinity exceeded 18 ppt and all larvae hatched from water with a salinity above 9 ppt died within 4 days. 2. 2. At a salinity of 6 ppt, eggs transferred at an early stage (20 min and 1 hr post-fertilization) had a much lower survival rate than those transferred at 5, 11 and 16 hr post-fertilization. This effect may depend on the water hardening process of silver perch eggs. 3. 3. Larvae hatched at a salinity of 6 ppt showed a better survival rate than those hatched in freshwater during the first 20 days post hatching. This effect may be due to the inhibition of microbial pathogens by saline water.

Manipulation of ploidy in yellow perch ( Perca flavescens) by heat shock, hydrostatic pressure shock, and spermatozoa inactivation

Heat shocks, hydrostatic pressure shocks, and ultraviolet radiation were evaluated for their efficacy as methods of manipulating ploidy in yellow perch ( Perca flavescens). The most effective methods of inducing triploidy were heat shocks of 28–30°C applied at a time of initiation (TI) of 5 min postfertilization for durations of 10 or 25 min, and hydrostatic pressure shocks of 9000 or 11 000 psi applied at a TI of 5 min for a duration of 12 min. These treatments resulted in triploidy induction rates that ranged from 54–100%, and embryonic survival rates of 16–80%. Cold shocks of 0°C had no effect on the ploidy or survival of embryos. For perch, hydrostatic pressure shock offered several advantages over heat shock as a method of manipulating ploidy. The most effective methods of inducing tetraploidy were hydrostatic pressure shocks of 9000 psi applied at a TI of 192 min for durations of 16 or 24 min. Ultraviolet radiation of perch sperm with doses of 3240–6480 ergs/mm 2 resulted in 100% inactivation of paternal chromosomes, and perch eggs fertilized with inactivated sperm had survival rates of > 50%, thereby establishing methods for producing gynogenetic perch. Studies comparing the growth and performance of diploid vs. triploid perch are underway. Tetraploid perch are being reared to sexual maturity to evaluate their potential as brood fish.

The toxicity of selenium in experimental freshwater ponds.

Flue Gas Desulphurization equipment installed in coal-fired power stations to reduce sulphur dioxide emissions produces effluent containing several contaminants, including selenium. To assess the effects that this might have on fish reproduction and biological community richness, selenate and selenite were added to freshwater pond systems to achieve duplicated nominal concentrations of 0 (control), 2, 10 and 25 μg Se/L. Perch (Perca fluviatilis), grass carp (Ctenopharyngodon idella Val.) and stickleback (Gasterosteus aculeatus) were placed in each pond in the early summer and left relatively undisturbed until the following spring. A spawning tray was then placed in each pond and monitored regularly for the appearance of perch egg ropes. When ropes were found, they were removed to the laboratory and either placed in uncontaminated well water or exposed to selenium. Almost half the perch exposed to 25 μg Se/L died during the pond experiment, but there were no observed deaths at the lower concentrations. No grass carp were recovered from the 25 μg Se/L ponds but all were recovered from the other ponds. Stickleback were missing from all treatments, presumably due to predation by the perch. Perch egg ropes were found in seven of the eight ponds, and all but one rope showed signs of successful fertilisation. Hatching success in the laboratory was highly variable for eggs obtained from the 0, 2, and 10 μg Se/L ponds, but was always above zero. No eggs hatched from ropes obtained from the 25 μg Se/L ponds. Effects of selenium on plants, macroinvertebrates and zooplankton in the ponds were generally limited. Accumulation of selenium in fish was dose-related and comparable with results reported from other contaminated systems. The results from this experiment suggest that mean environmental concentrations of approximately 25 μg Se/L may seriously affect the reproductive capacity of perch, but no clear effects on reproduction are evident at mean concentrations of 10 μg Se/L and below. Selenium-induced effects occur during gametogenesis, but only become evident between fertilization and hatching.

Salinity Tolerance of Yellow Perch Eggs and Larvae from Coastal Plain Stream Populations in Maryland, with Comparison to a Pennsylvania Lake Population

We measured the salinity tolerance of eggs and larvae of yellow perch, Perca flavescens, from three Coastal Plain stream populations in Maryland and a Pennsylvania lake population during a series of continuous flow-through laboratory experiments. Fertilized eggs were incubated in freshwater (mean total hardness of 39.8 mg/liter as CaCO,) and three salinities (7-129o or parts per thousand) until hatching (15-17 days) or death. Yolk-sac larvae were exposed to freshwater and nine salinities (2-139k) for test periods of 5-8 days. The exposures were ramped; salinities were increased from freshwater to treatment conditions at an average rate of 2.7%o/h. Mean cumulative mortalities for Maryland eggs were 4.0% (freshwater), 16.7% (7%o), 28.5% (9%o) and 100% (129/,). The LT50 value for eggs exposed to 129o salinity was 139 h. Mean cumulative mortalities for Maryland larvae was 21.3% (freshwater), 0.0% (2%o), 2.0% (4 and 600), 4.0% (700), 0.0% (8 and 9%o), and 100% (12 and 13%o). Mean LT50 values for larvae exposed to the 12 and 139o salinity treatments were 73 and 50 h. Abnormal behavior was observed in groups of larvae exposed to salinities of 8-1300. Larvae from the Pennsylvania lake population exhibited cumulative mortalities of 18.0% (freshwater, 4 and 6%o) and 100% (8 and 10oo). LT50 values were 158 and 71 h for the Pennsylvania larvae exposed to the 8 and 10 oo salinity treatments. Abnormal behavior was observed in groups of Pennsylvania larvae exposed to salinities of 6-10%o. Pennsylvania larvae were slightly more sensitive to salinity changes than Maryland larvae; LC50 values were 6.3 and 9.1/, respectively. Our laboratory results suggest that yellow perch populations in Maryland Coastal Plain streams can tolerate a relatively wide range of salinities during the egg and early larval stages at mean temperatures of 10-13 C. These populations should be capable of successful reproduction in habitats that range from 0 to 6 or 7%o salinity.

Lipid classes and fatty acid composition of the eggs of some Australian fish

1. 1. Wax esters, triglycerides, sterols and their esters and phospholipids were found in the eggs of six species of Australian fish. 2. 2. The high proportion of wax ester in golden perch eggs is interpreted as an adaptation to provide bouyancy rather than an additional energy source. 3. 3. Fatty acids of both the ( n-3) and the ( n-6) series were found in the eggs of all species, but the relative proportions of the two fatty acid series indicated a greater dependence on the ( n-3) than on the ( n-6) series in barramundi and golden perch than in the other species.

Spawning and egg development ofPerca fluviatilis in Lake Z�rich

Egg survival and development rate of perch eggs were investigated in Lake Zurich, Switzerland. A transplant experiment was carried out to examine whether individual females choose different depths for spawning because of an expected advantage for the development of their eggs. Egg masses which had been deposited on fir branches stuck into the ground of the lake were either left untouched or transplanted horizontally or vertically at depths of 3 and 6 m. Spawning occurred between 28 April and 9 June 1987. Egg survival to the eye pigment stage (EPS) was high in all treatments (\(\bar x = 99\% \), minimum 92%). There was no significant difference in egg survival between treatments, suggesting that females do not choose the spawning site because of individual fitness differences related to the depth of spawning. Early egg masses which were exposed to lower temperatures developed more slowly (120–140 day degrees to the EPS) than late egg masses which were exposed to higher temperatures (80–100 day degrees). The observed differences are in agreement with the hypothesis of a constant sum of day degrees necessary for egg development using the corrected formula derived by Guma'a (1978) which deducts an estimated threshold temperature of 5°C below which development of perch eggs effectively stops, from the actual temperature.

Potential Predation by Fish and Invertebrates on Early Life History Stages of Striped Bass in the Pamunkey River, Virginia

Field surveys in the Pamunkey River, Virginia, indicated that numerous fish and invertebrate predators varied in their spatiotemporal coincidence with eggs and larvae of striped bass Morone saxatilis on spawning grounds. In the laboratory, the cyclopoid copepod Acanthocyclops vernalis was observed to attack and kill striped bass larvae, In addition, juveniles or adults of satinfin shiner Notropis analostanus, spottail shiner N. hudsonius, tessellated darter Etheostoma olmstedi, white perch Morone americana, striped bass, bluegill Lepomis macrochirus, pumpkinseed Lepomis gibbosus, channel catfish Ictalurus punctatus, and white catfish I. catus ate yolk-sac larvae under laboratory conditions. Consumption of larvae by spottail shiners and satinfin shiners increased with increasing prey density to a maximum observed ingestion of 150 and 81 larvae per predator per hour, respectively. At prey concentrations simulating ambient Pamunkey River conditions (20–100 larvae/m3), consumption by both species ranged from 0 to 5 larvae/h, but these estimates were considered to be lower limits because prey densities were not maintained during the experiment. In contrast to these laboratory results, neither eggs nor larvae of striped bass were positively identified in guts of field-collected fishes, although various fish species consumed many eggs of the white perch.

Fish species distribution in relation to water quality gradients in the North Branch of the Moose River Basin

The distribution of fish species in the North Branch of the Moose River (Lake Rondaxe to headwaters of Big Moose Lake) was determined by intensive netting and electrofishing surveys of lakes and streams in the watershed during 1982–83. A chronology of changes in fish species occurrence in the drainage system was reconstructed from earlier published surveys conducted in 1882 and 1931 and unpublished survey data obtained by the NYSDEC during the period 1948–1975. Native species present in 1882 were also collected in 1931. Smallmouth bass (Micropterus dolomieu) were introduced in the early 1900's and were present in collections made in 1931. Major changes in the fish community have taken place since 1931. The smallmouth bass and many of the native species found in the earlier surveys were either absent or restricted in occurrence to downstream sites (eg. L. Rondaxe and Moss L. sub-drainage) in 1982. Non-native species introduced after 1931 (yellow perch,Perca flavescens; central mudminnow,Umbra limi; banded killifish,Fundulus diaphanus) are currently widely distributed throughout the drainage system. In particular, the yellow perch is now a dominant species in the larger lakes of the basin. Comparisons of survival rates for caged fish transferred from high to low pH sites in the Big Moose drainage system demonstrated relatively greater acid tolerane of non-native species (yellow perch, mudminnow, killifish) than native cyprinids. Watershed acidity gradients (pH and aluminum concentrations) and relative physiological acid tolerance are major determinants of currently observed fish species distribution patterns in the North Branch of the Moose River. Differences in age and size structure of fish populations inhabiting acidic and non-acidic lakes of the drainage system were apparent, but difficult to interpret without additional information onpopulation size and potential density dependent parameters such as age specific growth and survival rates. Differential hatching success was observed for yellow perch eggs reciprocally transferred between acid (Big Moose) and neutral (Moss L.) lakes. Eggs transferred from Moss L. to Big Moose L. exhibited poor hatching success as a result of alterations in egg membrane structure that inhibited normal egg expansion and the hatching process. This effect was not evident in eggs from the same parents reared in Moss Lake nor in eggs from the Big Moose parents reared in both lakes. These experimental observations suggested possible genetic adaptation to acid stress by the yellow perch population inhabiting Big Moose Lake.

The influence of water pH on the perivitelline fluid of perch ( Perca fluviatilis) eggs

1. 1. The diameter, trans-chorion potential difference and perivitelline-fluid pH of the eggs of perch ( Perca fluviatilis) have been measured in a range of water pH (8–4.5). The water used was relatively nutrient rich. 2. 2. Eggs transferred from pH 8 to pH 4.5 shrink; probably as a result of loss of water from perivitelline fluid. 3. 3. Trans-chorion potential differences are close to zero over the range of pH. Mean perivitelline-fluid pH is higher than external water pH at pH 6.7 and above. Below pH 6.7, mean perivitelline-fluid pH is approximately the same as external water pH. The results suggest a non-Donnan distribution of hydrogen ions. 4. 4. The results are compared with data on salmonid eggs in nutrient-poor waters.

The consumption of eggs of the perch, Perca fluviatilis L., by macroinvertebrates in the field

SUMMARY. 1. Perch egg masses, in a late stage of development, were collected from a small stillwater and the composition of the egg masses and the number of invertebrates which colonized them was recorded.2. All of the invertebrates that colonized the egg masses were tested serologically for the presence of perch eggs and the ability of some invertebrates to eat live and dead perch eggs in the laboratory was determined.3. Of the nineteen taxa that colonized the egg masses, only two species of flatworm and three species of caddisfly larva ate perch eggs in the field and, of these, only one genus of caddisfly larva ate live eggs in the laboratory.4. It is concluded that the invertebrates present were not important predators of perch eggs.

Yellow perch egg masses deter predators

The entire seasonal reproductive effort of female yellow perch (Perca flavescens and Perca fluviatilis) is contained in a single, tubular, gelatinous egg mass. Predation on these egg masses is potentially a major mortality factor among perch, although reports of its occurrence are lacking. This suggests the egg masses may be protected by an antipredator mechanism that renders them inedible. In a series of feeding trials, no egg masses were consumed when offered to a number of species considered potential predators (eel, white sucker, brown bullhead, yellow perch, three- and nine-spined sticklebacks), although alternate food items were frequently consumed when provided. Examination of stomach contents of potential predators (eel, white sucker) collected from perch spawning sites at the peak of the reproductive period contained no egg masses. Egg masses were not lethal when ingested by a nonselective test fish, hatchery-reared brook trout, suggesting that an unpalatable rather than a toxic substance protects perch egg masses from predation.

Copper-stimulated respiration in the unfertilized egg of the Eurasian perch, Perca fluviatilis (l.)

1. The addition of Cu 2+ (0.1–1.0 mM) to respiring, unfertilized eggs produced a marked stimulation in the rate of respiration whereas Zn 2+ had no effect over the same concentration range. 2.In the absence of Cu 2+, temperature had little effect on unfertilized egg respiration but the Cu 2+ stimulated respiratory rate showed the more normal response with a Q 10 of 1.86 (10–20°C). 3.It appears that perch egg respiration is rate-limited by a physical event and it is suggested that Cu 2+ may act by dissipating an oxygen permeability barrier located at the chorion.

Sediment Effects on Eggs and Larvae of Striped Bass and White Perch

Eggs and larvae of white perch Morone americana and striped bass Morone saxatilis were exposed to a range of suspended-sediment concentrations. Percent hatch of white perch eggs was not significantly affected by 50–5,250 mg/liter of suspended sediment, but developmental rates were significantly lower at sediment concentrations above 1,500 mg/liter. Hatch of striped bass eggs was not significantly affected by 20–2,300 mg/liter suspended sediment, but development was slowed significantly at concentrations above 1,300 mg/liter. Four concentrations of suspended sediment in the range of 1,626 to 5,380 mg/liter resulted in 15–19% mortality of white perch larvae during 1-day exposures and 23–49% mortality during 2-day exposures. Four suspended-sediment concentrations in the range of 1,557 to 5,210 mg/liter caused 20–31% mortality of striped bass larvae during 1-day exposures, and 25–57% mortality during 2-day exposures. Covering the white perch eggs with a sediment layer greater than 2 mm thick (to about 1.2 mm above the top of the egg) resulted in 100% mortality; layers less than 0.45 mm thick did not influence hatchability. Rate of egg development was significantly lowered when sediments were over 0.8 mm thick. Eggs and larvae of both species were resistant to high sediment concentrations.