Ruffe Research Articles

Rapidly amplified polymorphic DNA variations in Percids

Pikeperches (Stizostedion lucioperca and S. volgense), river perch (Perca fluviatilis), and ruffe (Gymnocephalus cernuus) are important ichthio-fauna of Kuibyshev water reservoir in Russia. Now a days, the stock and production of these species are declining in this artificial lake. The recent declines of pikeperches has prompted the interest in assessing genetic structuring of their populations. The maintenance of genetic variation and rapidly amplified DNA polymorphism (RAPD) between the exploited fish populations, a product of past evolution in attributes to the ecology is the initiative to increase the overall chances that depleted population will regain and persist over the long period. The RAPD in Percids has a significant variation in among populations. Two microsatellites DNA from walleye (S. vitreum) were used as primers in this study. Each of the DNA markers (Svi-4 and Svi-18) resolved 4–6 alleles with a size range of 102-124 bp. The RAPD analysis revealed diversified polymorphic structures in different Percid populations. PCR products of both of the Stizostedion species have rapidly amplified DNA amplifications with a size range of 100–1200 bp. Most of the dominant DNA fractions of Percids were existed in the size range of 100–600 bp in both of the primers treatments. The Stizostedion had RAPD with a size range of 100–400 bp with 2–3 dominant DNA bands in 100, 140 and 200 bp. In pikeperches the amplified DNA bands are more or less similar, which demarked that these two species were evolved from the same phylogenetics and evolutionary origin. The river perch had only one dominant band and the ruffe had two DNA amplification signals. RAPD in different Percids depends on the specific size range of the DNA amplifications.

Vertical distribution of benthic community responses to fish predators, and effects on algae and suspended material

The vertical positioning of benthic invertebrates should be a trade-off between the risky, but productive, sediment surface and the safer, but physiologically harsher, conditions deeper down in the sediment. This is because the foraging efficiency of benthic fish decreases with sediment depth, whereas the sediment surface is generally better oxygenated and has a higher resource quality than lower layers. We studied how two benthic fish predators, bream (Abramis brama) and ruffe (Gymnocephalus cernuus), affected the community composition and vertical distribution of benthos, and their indirect effects on algae and suspended material, in field enclosures. Whereas bream had significant effects on the density, composition and distribution of the benthos, ruffe had no such effects. The total benthos biomass in bream treatments was an-order of magnitude lower in the upper sediment layer (0–1 cm) and three times lower in the middle layer (1–3 cm) than in the controls, whereas there were no significant effects in the deepest layer (3–10 cm). Bivalves persisted in the deepest layer although their density was reduced in shallow sediment, whereas gastropods faced the risk of local extinction in the presence of bream. As indirect effects, small-bodied cladocerans, phytoplankton, periphyton and both organic and inorganic suspended material were higher in the bream treatments. We␣conclude that the impact of bream diminished substantially with increasing sediment depth, enabling invertebrates to survive in the sediment and to persist in the presence of bream. However, there were␣no␣indications of any group adjusting their vertical position behaviourally as a response to predation threat.

Forecasting Potential Distributions of Nonindigenous Species with a Genetic Algorithm

Forecasting species' potential distributions is a leading problem for research in invasion ecology and global change biology. Given the number of freshwater organisms, especially fishes, that have been introduced intentionally and unintentionally, an urgent need exists for the development of tools for forecasting their spread. New computational techniques partially overcome the defects of earlier environment-matching methods, including sensitivity to sparse and unbalanced data, inflated statistical significance, and asymmetrical (omission versus commission) errors. Here we apply one such method, the genetic algorithm for rule-set production (GARP), to predict spatial occurrences of suitable environments for two nonindigenous fishes that so far have limited distribution in North America, Eurasian ruffe (Gymnocephalus cernuus) and rainbow smelt (Osmerus mordax). For these two species, we conclude that although spread is not inevitable, their eventual range in North America will be considerable if management actions fail to prevent additional introductions.

Competition between perch (Perca fluviatilis) and ruffe (Gymnocephalus cernuus): the advantage of turning night into day

Summary1. The outcome of interspecific competition for food resources depends both on the competitors’ sensory abilities and on environmental conditions. In laboratory experiments we tested the influence of daylight and darkness on feeding behaviour and specific growth rate (SGR) of two species with different sensory abilities.2. We used perch (Perca fluviatilis) as a visually orientated, and ruffe (Gymnocephalus cernuus) as a mechano‐sensory oriented predator and tested their growth rates and behaviour under conditions of interspecific and intraspecific competition. Three different foraging conditions were used: food supplied (i) only during the day, (ii) only during the night or (iii) during both day and night.3. In perch neither SGR nor feeding behaviour were influenced substantially by interspecific competition during daylight. During darkness their foraging behaviour changed markedly and their access to the food source as well as their SGR were negatively affected by the presence of ruffe.4. Ruffe's foraging behaviour did not change during either day or night with interspecific competition. During the night ruffe's SGR was higher with interspecific competition, probably because of a release from intraspecific competition and the competitive inferiority of perch during the night.5. Because of its seonsory abilities ruffe feeds predominantly at night, thereby reducing competitive interference from perch.

A comparison of habitat use and habitat‐specific feeding efficiency by Eurasian ruffe (Gymnocephalus cernuus) and yellow perch (Perca flavescens)

Abstract – Eurasian ruffe are invading habitats in the North American Great Lakes watershed occupied by commercially important native yellow perch. We conducted laboratory experiments to evaluate potential overlap in habitat (macrophytes, mud, cobble) and food (benthic invertebrates) use. Ruffe and yellow perch both preferred macrophytes > cobble > mud in the light, but only ruffe increased their use of mud in the dark. Neither fish density nor food availability affected habitat preferences, and competition for habitat was not evident. For both species, feeding rates were marginally lower in macrophytes but did not differ between species. Our experiments suggest that if ruffe and yellow perch share a habitat (e.g., during invasion or because of predation risk), competition for space will be weak or absent. However, within a shared habitat, competition for food may occur when food is limiting because neither species has a clear advantage in its ability to consume invertebrates in any habitat.

Diel-feeding activity in early summer of racer goby Neogobius gymnotrachelus (Gobiidae): a new invader in the Baltic basin

The first recording of the Ponto-Caspian racer goby in Poland was during 1995 in the River Bug (River Vistula system). Within 5 years, the species had spread to the downstream section of the Vistula. One of the potential impacts of invasive species on native fauna is competition for food. Therefore, the diel patterns in diet composition and gut fullness coefficient (FC) of racer goby were examined at one study site in the Włocławski Reservoir (lower River Vistula), during May 2003. An average of 20 individuals were examined each 4 h over one 24-h period (125 fish in total). The proportion of main food items and diet width did not differ among three size-groups (43–59, 60–79 and 80–97 mm total length), and the relative biomass ratio of main food categories did not differ over the diel cycle. Amphipods constituted 11–70% of total gut content biomass and were found on average in 84% of analysed alimentary tracts. The second prey types were chironomid larvae (16–63% of total food biomass; frequency occurrence: 61–91%), and to a lesser extent chironomid pupa, ceratopogonid larvae, oligochaets, dipteran imagines and copepods, with fish larvae found in the gut of eight gobies. Gut fullness coefficient (FC) differed significantly over the 24-h period, with the highest value at night and in early morning. In conclusion, racer goby forages mainly on benthos and has a nocturnal-feeding activity. No significant diet overlap was found between racer goby and native percids, i.e. Eurasian perch Perca fluviatilis and ruffe Gymnocephalus cernuus.

The dietary response of otters ( Lutra lutra ) to introduced ruffe ( Gymnocephalus cernuus ) in Loch Lomond, Scotland

In this study the diet of otters Lutra lutra was examined following the establishment of a population of non-native ruffe Gymnocephalus cernuus in Loch Lomond, Scotland. Otter spraints (n=453) were collected at monthly intervals from four sites during 2002. Overall, 98% of spraints contained at least one species of fish, invertebrates were found in 49%, 17% contained amphibians, while mammals and birds were found in 9%. The most frequent prey from all sites were ruffe, which were found in 69% of spraints. Eel Anguilla anguilla, cyprinids (roach Rutilus rutilus, dace Leuciscus leuciscus and minnow Phoxinus phoxinus) and Salmo spp. were also relatively common and were recovered in 60%, 35% and 33% of spraints, respectively. Northern pike Esox lucius (14%), perch Perca fluviatilis (12%), stickleback Gasterosteus aculeatus (9%), powan Coregonus lavaretus (14%) and lampreys Lampetra spp. (2%) were less common. The fact that ruffe were the most frequent prey in otter spraints in all regions and in all seasons of the year indicated that they are one of the most important prey for otters in Loch Lomond at the present time.

Risk analysis for species introductions: forecasting population growth of Eurasian ruffe (Gymnocephalus cernuus)

The North American distribution of the Eurasian ruffe (Gymnocephalus cernuus), an ecologically important and costly invasive fish, is presently limited to the Laurentian Great Lakes. Risk analyses for accidental introductions of ruffe to inland lakes should focus on the chance of establishment for small introductions such as those that would result from transporting ruffe as bait. Here I use Akaike's Information Criterion to select a population growth model for ruffe based on observed population dynamics during the invasion of Loch Lomond, Scotland. This population is regulated by a high carrying capacity and Allee effects were undetected. Parameter estimates obtained from this population forecast that the chance of establishment for possible introductions of ruffe to inland lakes in North America is high. A model for ruffe winter survival suggests that survivorship between introductions and spawning may be an important determinant of establishment success, but that the chance of establishment is high for introductions of only a few individuals. To prevent invasions of ruffe in inland waters, release of ruffe, whether intentional or accidental, should not be tolerated.

Rapid responses of the cupula in the lateral line of ruffe (Gymnocephalus cernuus)

Displacements of cupulae in the supraorbital lateral line canal in ruffe (Gymnocephalus cernuus) have been measured using laser interferometry and by applying transient as well as sinusoidal fluid stimuli in the lateral line canal. The cupular displacement in response to impulses of fluid velocity shows damped oscillations at approximately 120 Hz and a relaxation time-constant of 4.4 ms, commensurate with a quality factor of approximately 1.8. These values are in close agreement with the frequency characteristics determined via sinusoidal fluid stimuli, implying that the nonlinearity of cupular dynamics imposed by the gating apparatus of the sensory hair cells is limited in the range of cupular displacements and velocities measured (100-300 nm; 100-300 microm/s). The measurements also show that cupular displacement instantaneously follows the initial waveform of transient stimuli. The functional significance of the observed cupular dynamics is discussed.

Nutrient release and resuspension generated by ruffe (Gymnocephalus cernuus) and chironomids

Summary1. Benthivorous fish may play an important role in internal nutrient loading. Ruffe are highly specialised, feeding exclusively on bottom animals; thus all nutrients released via their feeding are derived from the bottom and are new to the water column. The fish can also release nutrients from the sediment through resuspension while searching for food.2. The aim of this study was to estimate experimentally in the laboratory the effect on water quality of resuspension and nutrient release by ruffe and bottom animals (chironomids).3. Ruffe released nutrients during 8 h experiments as follows: total P 1.4, dissolved PO4 0.6, total N 24.0 and NH4‐N 15.9 μg g−1 WW h−1. A decreasing trend in mass‐specific release was observed over time, probably because of starvation. The mass‐specific release of total N and NH4‐N decreased as the mean weight of fish increased. The mean ratio of excreted N : P was 32.4. In 26 h experiments with sediment and both ruffe and chironomids, ruffe increased nutrient concentrations and turbidity values significantly but chironomids had an effect only on turbidity. Neither ruffe nor chironomids affected the ratio of inorganic N : P concentrations. An interaction between ruffe and chironomids was found for turbidity.5. According to these results, benthivorous fish may increase nutrient concentrations in the water column and need to be taken into account when estimating internal loading.

Overwinter changes in mass and lipid content of Perca fluviatilis and Gymnocephalus cernuus

The body condition, lipid reserves and mortality of 0 and 1 year‐old perch Perca fluviatilis and ruffe Gymnocephalus cernuus, sampled during the winter in Lake Constance, Germany, were compared. Length‐frequency analyses did not provide evidence for overwinter mortality in either species. The fresh and dry mass of perch as well as their lipid contents decreased during winter, while ruffe were heavier and contained more lipid at the end of the winter. The superior performance of ruffe was mainly attributed to its sensory capabilities, which allowed it to ingest zoobenthos throughout the winter, while the zooplankton feeding of perch was constrained by low light levels. In lakes that undergo a process of re‐oligotrophication, this advantage of ruffe over perch may be even more pronounced, since lower food supply during the growth season and thus lower fish lipid content at the start of winter is probably better tolerated by ruffe than by perch.

DNA Polymorphism of Percidae population structure in the Kuibyshev water reservoir of Russia

The pike perches Stizostedion lucioperca and S. volgense, river perch Perca fluviatilis and ruffe Gymnocephalus cernuus are important components of the fish fauna of the Kuibyshev reservoir in Russia. We analysed genetic variation within and among populations of these species. Two microsatellite DNA from walleye S. vitreum were used as primers of this study. Each of the DNA markers resolved 6–10 alleles with locus Svi4 and Svi6 and size range of 102–169 base pairs (bp). PCR was performed with the selected primers, with temperature cycles followed a denaturing profile for 30 s at 94° C. A final 10 min elongation step was resumed at 72° C after 35 cycles. Stizostedion volgense showed the highest bp of 100 to 3000, differing by sex, age and maturity level. The populations of P. fluviatilis have variable DNA polymorphism within the range 90–1000 base pairs. We also detected a new band in the fingerprints. The degree of neutral genetic variation detected indicates that effective population sizes of the study species are large.

Competition for food between Eurasian perch (Perca fluviatilis L.) and ruffe (Gymnocephalus cernuus [L.]) over different substrate types

Abstract – Food consumption by Eurasian perch (Perca fluviatilis L.) and ruffe (Gymnocephalus cernuus [L.]) was studied in single and mixed‐species treatments in the laboratory, where alternative food resources, chironomids and zooplankton, were offered simultaneously. The effects of structural complexity, which was represented by substrate grain size, and of feeding level on food consumption were analysed. Across all experiments, the outcome of competition between perch and ruffe depended on food abundance and on the structural complexity of the environment. Perch and ruffe both changed their food consumption in the presence of a heterospecific competitor. With high food supply, perch consumed more benthic food than ruffe. With low food supply, the consumption of perch decreased strongly, while that of ruffe remained high on fine sediment. Under all conditions tested, the mechanism of competition appeared to be of interference rather than of exploitative nature. It is suggested that with decreasing lake productivity caused by re‐oligotrophication, habitat shifts of both species will occur, which will alleviate interspecific competition. Ruffe will forage over fine sediment and perch over coarse sediment, whereby both species will achieve the highest foraging efficiency under conditions of low food supply.

Evidence that 4-pregnen-17,20β,21-triol-3-one functions as a maturation-inducing hormone and pheromonal precursor in the percid fish, Gymnocephalus cernuus

Behavioral, biochemical, and electrophysiological studies suggest that the trihydroxylated progestin steroid, 4-pregnen-17,20β,21-triol-3-one (20β-S) stimulates oocyte maturation and pheromone release in the Eurasian ruffe, a freshwater percid fish. Behavioral observations found that female ruffe undergoing oocyte maturation (OM) release a pheromonal cue that stimulates swimming activity and social interactions among conspecific males. Neither vitellogenic nor ovulated females released the cue. Pheromone production was directly associated with elevated plasma levels of 20β-S in maturing female ruffe which in vitro incubation suggested to be a possible maturation-inducing hormone (MIH) in this species along with 4-pregnen-17,20β-diol-3-one (17,20βP). However, neither of these steroids appear to be the pheromone because electrophysiological and behavioral studies found them to lack olfactory (EOG) and behavioral activity. Instead, studies of the odor of steroid-injected fish suggest the pheromone is a metabolite of 20β-S. In particular, inter-peritoneal injection of 20β-S (but not 17,20βP) consistently induced release of a urinary cue with strong behavioral activity. The pheromone may be a highly polar and novel metabolite because it could not be extracted using octadecylsilane resin (C18) which has proven effective for other teleost hormonal pheromones.

Morphophysiological aspects of the embryonic development of ruffe, Gymnocephalus cernuus (L.) under different thermal conditions

Background. Ruffe, Gymnocephalus cernuus is a small fish inhabiting vast areas of Europe, Asia, and also North America. Its substantial geographical dispersal range in different climatic zones, in waters of different parameters indicates that this is a particularly plastic species. Recent implementation of new fish-processing machinery has increased dramatically the economical importance of ruffe, which is now treated as a gourmet food. In the wake of the increased interest in this fish we decided to study aspects of its developmental biology. Methods. Fertilised eggs and the developing embryos of ruffe were incubated under five different temperature regimes. They were monitored in two planes, horizontal and vertical, using a light microscope fitted with a digital camera and connected to a computer with a monitor and a VCR. The data collected were processed using MultiScan software.Materials and methods.Results. Perivitelline space in ruffe constitutes as much 65% of the egg volume. This facilitates movements of an embryo and enhances processes of gas exchange through mixing of perivitelline fluid. It finally contributes to the distribution of the hatching enzyme on the inner surface of the egg shell. Similarly as in the other percid fish, the lack of integration between the "lipid raft" and the embryonic disc, causes the fall of the disc on the lateral side of the vitelline sphere. This lateral position persists throughout all sequential stages of the embryogenesis. The diversified thermal regimes of the development affect the timing of the embryogenesis, as well as the condition, weight, and the size of newly-hatched ruffe larvae. The highest rate of specimens hatched in good condition-marked by the highest weight and body length-was observed at the optimal temperature range of 16-18oC. Newly-hatched larva is small (5 mm body length, 0.10 mm3 of yolk sac volume), active, and fully prepared for independent life in the water. Under the optimal temperature range, determined in the present study, the duration of embryonic development of ruffe (from fertilisation to hatching) was 2122 dh (accumulated degree-hours).Conclusion. The present study constitutes a contribution to the knowledge of the embryonic development of ruffe and its biological sense, emphasizing the morpho-physiological differences between this species-living under, specific, diversified ecological conditions-and other fish.

The Effects of Zebra Mussels (Dreissena polymorpha) on the Foraging Success of Eurasian Perch (Perca fluviatilis) and Ruffe (Gymnocephalus cernuus)

AbstractComplex habitat structures can influence the foraging success of fish. Competition for food between fish species can therefore depend on the competitors' abilities to cope with structural complexity. In laboratory experiments, we comparatively assessed effects of zebra mussels (Dreissena polymorpha Pall.) on the foraging success of Eurasian perch (Perca fluviatilis L.) and ruffe (Gymnocephalus cernuus (L.)). In single‐species and mixed‐species experiments, the fish were fed caddisfly larvae (Tinodes waeneri (L.)) over complex (mussel‐covered stones) and less‐complex (bare stones) substrates. With intraspecific competition, food consumption by perch and ruffe decreased significantly when the complex substrate was used. With interspecific competition, food consumption by perch and ruffe did not change with substrate complexity, but perch clearly out‐competed ruffe on both substrates. Zebra mussel beds provide a refuge for macrozoobenthos against predation by ruffe and probably also by perch. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Fish introductions and their management in the English Lake District

AbstractFor biogeographical reasons, the English Lake District contains relatively few native fish species although it encompasses 14 major lakes and many smaller water bodies. Nevertheless, it is nationally important for fish biodiversity because of the presence of vendace, Coregonus albula (L.), whitefish, Coregonus lavaretus (L.), and Arctic charr, Salvelinus alpinus (L.), while recreational angling contributes significantly to the local tourism industry. Several recent illegal introductions of fish species have been observed at several lakes, probably as a result of anglers live‐baiting for pike, Esox lucius L., including roach, Rutilus rutilus (L.) and ruffe, Gymnocephalus cernuus (L.), where they now threaten native species through competition and predation. As the removal of introduced populations is practically impossible, their management is limited to preventing further introductions. A description is given of legislation introduced in 2002 to achieve this objective by banning the use of live‐baits in 14 lakes of high conservation importance.

Diet of Larval Ruffe ( Gymnocephalus cernuus) in the St. Louis River Harbor, Lake Superior

The diet of larval (3-17 mm total length) ruffe ( Gymnocephalus cernuus) is described from samples collected in 1994 at two locations in the St. Louis River Harbor, a tributary to Lake Superior. Copepoda, Daphnia spp., and Bosmina longirostris dominated the diet of larval ruffe in the St. Louis River Harbor. Larger Copepoda and Daphnia spp. occurred more often and in larger numbers as ruffe total length increased, whereas smaller Bosmina longirostris occurred less often and in smaller numbers as ruffe total length increased. Ruffe from Whaleback Bay consumed Daphnia spp. rarely and in very small numbers whereas ruffe from Allouez Bay consumed Daphnia spp. often and in large numbers. A general decrease in Copepoda and increase in Daphnia spp. occurred in the second and third weeks of June for ruffe from Allouez Bay, but not Whaleback Bay.

Upstream migration activity of cyprinids and percids in a channel, monitored by a horizontal split-beam echosounder

A 200 kHz digital echosounder (HTI) with two split-beam transducers was aimed horizontally to monitor the upstream migration activity of fish, from 24 April to 28 June, in Äijälänsalmi channel (mean width 35 m, length 700 m, and maximum depth 5 m) from large mesotrophic Lake Päijänne to small eutrophic Lake Jyväsjärvi. This study was part of a larger project which aims to analyse the movement of commercially unimportant fish species and reduce the abundance of these fish in L. Jyväsjärvi. Catch samples were collected with a trap net located immediately upstream from the acoustic beams. The most common species in the catch were roach ( Rutilus rutilus), perch ( Perca fluviatilis), bream ( Abramis brama), ruffe ( Gymnocephalus cernuus), and white bream ( Abramis bjoerkna). The upstream migration of fish was correlated with water temperature ( r = 0.40) with time lag of 1 d. In spring, L. Jyväsjärvi warmed faster than L. Päijänne, causing spawning migration from L. Päijänne to L. Jyväsjärvi. Clear diurnal rhythm in activity was observed. The migration rate through the channel peaked around dawn and dusk. Catch per unit effort of the trap net suggested that the peak of the spawning migration of different species was separate. Upstream migration was induced by the temperature difference between two lakes, and the activity of the migration was regulated by temperature changes and light rhythm.

Occurrence and life cycles of Dermocystidium species (Mesomycetozoa) in the perch (Perca fluviatilis) and ruff (Gymnocephalus cernuus) (Pisces: Perciformes) in Finland and Estonia

In Finland Dermocystidium percae Reichenbach-Klinke was first recorded by Pekkarinen in the fins of a perch in 1988. Because it is a poorly known parasite, its occurrence and life stages are studied here. In occasional sampling during 1995-1998 and 2001, and more systematic sampling during 1999 and 2000 in two different lakes (one oligotrophic, the other slightly eutrophic), it was found to occur almost continuously, although sometimes very sparsely, in both lakes. The life cycle is maintained from year to year by overwintering cysts. Young perch acquire first infections in their first summer of life, and fish over 3 years possibly develop some immunity. In Estonia, in the Kasari River and the Matsalu Bay, the parasite seems to be very rare. Cysts of D. percae, capable of sporogenesis, can occasionally occur in the ruff, too. In perch in Finland, cysts were found differing from the longish and thin-walled cysts typical of D. percae. These roundish to dumbbell-shaped cysts with thicker walls are here suggested to belong to a different Dermocystidium species, called D. sp. Cysts of D. percae occurred in the skin of all fins, but most often in abdominal fins and rarely elsewhere. In ruff, cysts of D. percae were also found in the gills. Of the fins D. sp. favoured the first dorsal fin, but also occurred elsewhere, e.g. in the head region of perch. Cysts of D. percae develop from thin-walled, round plasmodium mother cells, about 10 µm in diameter, by elongating and increasing in size. The nucleus of the plasmodium mother cell degenerates, and a reticular chromatin-containing structure with dense centra spreads out between conspicuous lipid droplets in the plasmodium. Nuclei reappear during fragmentation of the plasmodium. The sporonts thus formed divide to form sporoblasts, which in addition to small lipid droplets acquire a non-lipid 'central' inclusion. The inclusion grows in size to the typical inclusion of the ultimate Dermocystidium spore. Sporogenesis both in D. percae and D. sp. takes place mostly in summer, and at least in D. percae can continue until autumn. In addition, both species can produce numerous zoospores from their spores within 2 days in water at 25°C and at slower rates at lower temperatures. The body of the zoospore is about 1.2-2.2 µm in length and the flagellum is about six times the body length. The zoospores may then slightly grow in size and transform into amoebae. Small cysts, which possibly originated from an experimental infection by zoospores of D. sp., developed in 0-group perch kept in an aquarium at 17°C. The two Dermocystidium species here discussed can be grouped together with some other species, in which nuclei reappear and the plasmodium divides late in development and in which sporogenesis, unlike that in D. vejdovskyi Jírovec and D. cyprini Červinka and Lom, does not take place in compartments.