Lampetra Fluviatilis Research Articles

Temporal characteristics of downstream migration of smolts of the European river lamprey Lampetra fluviatilis in the Chernaya River

Data on the seasonal and diurnal dynamics of downstream migration of smolts of the European river lamprey Lampetra fluviatilis are obtained. On the basis of published data and surveys in nature, it is shown that in the largest part of the area the downstream migration of smolts occurs mainly in spring, in the period of high water in rivers caused by snow melting. The smolts undertake downstream migration at night, under minimal illumination. It has been determined experimentally that the smolts are characterized by negative photopreferendum (>90% of smolts preferred illumination <0.4 lx).

Experimental study of the European river lamprey, Lampetra fluviatilis (L.), migratory behavior in the period of initial dispersion of juveniles

Mechanisms of the initial dispersion of early larvae resident and anadromous forms of the European river lamprey have been experimentally explored. The flow (channel flow and underflow), type of bottom, and illumination are the key factors influencing the beginning and the end of downstream migration. Larvae leave the pebble ground of the spawning area when there is underflow and illumination is reduced to the night level, and then they migrate downstream in the channel stream. It is shown that the individuals dispersing from the spawning areas have switched to exogenous feeding. The end of the dispersion occurs after larvae reach oozy habitats of the riverbed, where they can find optimal feeding conditions.

Biological characteristics of smolts of European river lamprey Lampetra fluviatilis from the Chernaya River basin (Gulf of Finland, Baltic Sea)

Smolts of European river lamprey Lampetra fluviatilis from the Chernaya River basin are described. Expansion of variation limits is suggested on the basis of comparative analysis of taxonomically significant characters of this population and the species area. Structure of gonads and intestine of specimens preparing themselves for the feeing phase of their life cycle is described and some changes during the feeding phase are reconstructed. The scheme of analysis and description of smolts is suggested, the last may be applied to other lamprey species. The term “smolt” is rightfully used for juvenile anadromous lampreys making downstream migration. Biology of parasitic nonanadromous species of lampreys during the feeding phase (juvenile postmetamorphic phase) differs from biology of smolts.

Can navigation locks be used to help migratory fishes with poor swimming performance pass tidal barrages? A test with lampreys

Worldwide, tidal barrages reduce aquatic habitat connectivity and limit fish movements, especially for diadromous migrating species. Providing fish passage at these structures is crucial but technically and economically challenging. We measured the performance of a navigation lock, employed as a single-chamber vertical-slot fish pass, at a tidal barrage by the mouth of a tributary of the River Ouse, NE England. In autumn 2015, 265 European river lamprey Lampetra fluviatilis were tagged with Passive Integrated Transponders (PITs) and released in 11 replicate trials (n=157 in lock, n=108 immediately below lock). Fifty nine lamprey were double tagged with PIT and acoustic tags and released in the Ouse, 350m downstream of the barrage. The percentage of lamprey attempting to pass the upstream gates during PIT trials was moderate to high (55 and 93% for lamprey released below, and in the lock, respectively). Passage efficiency, for lamprey attempting to pass the upstream gates, was also high (average of 66% for releases in lock, 78% for releases below lock). Ninety percent of lamprey, released below the lock and attempting to migrate upstream passed the entire lock in <128min following release. However, acoustic-tagged lamprey displayed poor attraction to the lock under prevailing high river-discharge conditions. Overall, 36% of acoustic-tagged lamprey attempted to pass the barrage, mostly comprising lamprey released at low tide (cf. high tide), generating a high passage efficiency of 76% (16/21). However, 15 individuals passed through the sluices and only one used the lock. Nevertheless, using navigation locks as fishways has the potential to provide increased access between estuarine and river habitats for a range of biota, including those with poor swimming performance, but effectiveness is dependent on managing water discharge routes. Future studies using different operating protocols, especially to improve fish attraction under different environmental conditions and for a range of species, are encouraged.

Apoptotic death in erythrocytes of lamprey Lampetra fluviatilis induced by ionomycin and tert-butyl hydroperoxide

The work examined the effects of Ca2+ overload and oxidative damage on erythrocytes of river lamprey Lampetra fluvialtilis. The cells were incubated for 3h with 0.1–5μM Ca2+ ionophore ionomycin in combination with 2.5mM Ca2+ and 10–100μM pro-oxidant agent tert-butyl hydroperoxide (tBHP). The sensitivity of lamprey RBCs to studied compounds was evaluated by the kinetics of their death. Both toxicants induced dose- and time dependent phosphatidylserine (PS) externalization (annexin V-FITC labeling) and loss of membrane integrity (propidium iodide uptake). Highest doses of ionomycin (1–2μM) increased the number of PS-exposed erythrocytes to 7–9% within 3h, while 100μM tBHP produced up to 50% of annexin V-FITC-positive cells. Caspase inhibitor Boc-D-FMK (50μM), calpain inhibitor PD150606 (10μM) and broad protease inhibitor leupeptin (200μM) did not prevent ionomycin-induced PS externalization, whereas tBHP-triggered apoptosis was blunted by Boc-D-FMK. tBHP-dependent death of lamprey erythrocytes was accompanied by the decrease in relative cell size, loss of cell viability, activation of caspases 9 and 3/7, and loss of mitochondrial membrane potential, but all these processes were partially attenuated by Boc-D-FMK. None of examined death-associated events were observed in ionomycin-treated erythrocytes except activation of caspase-9. Incubation with ionomycin did not alter intracellular K+ and Na+ content, while exposure to tBHP resulted in 80% loss of K+ and 2.8-fold accumulation of Na+. Thus, lamprey erythrocytes appear to be more susceptible to oxidative damage. Ca2+ overload does not activate the cytosolic death pathways in these cells.

Polymorphism of spawners of the resident form of European river lamprey Lampetra fluviatilis (Petromyzontidae)

Data on polymorphism (plastic and meristic characters) are obtained for spawners of resident nonparasitic form of European river lamprey Lampetra fluviatilis from the Serebristaya River. The new data verify the diagnosis of this species and contribute to the formulation of a hypothesis on the presence of several phenotypic groups: dwarf, small-sized, and common. Analysis of plastic characters and of the number of trunk myomeres demonstrated that the values of these characters reliably depend on position of lampreys in a certain discerned group. Some aspects of biology of this species are discussed: spawning and interaction between resident nonparasitic river and migrating parasitic lampreys.

Synaptic and electotonic contacts on primary afferent axons in the lamprey Lampetra fluviatilis spinal cord

Distribution of GABA and glycine immunoreactivity was studied in synapses on primary afferent axons of the lamprey Lampetra fluviatilis spinal cord using a double labelling technique. Approximately 25% of synapses exhibit GABA immunoreactivity, while more than 70% are immunoreactive to both neurotransmitters. As in other vertebrates, axo-axonal contacts represent three-component synaptic complexes, the so-called triads, where the immunoreactive terminal make synaptic contact simultaneously with the afferent axon and the dendrite contacting this afferent. Contact zones with gap junction-like cell membrane specializations were found between adjacent afferents suggesting the presence of electrotonic interaction between them. This interaction appears to serve for the synchronization of the afferent flow and represents a structural correlate of the mechanism of rapid interneuronal communication between functionally uniform neurons, which is an important element in the organization of coordinated locomotor acts. Besides, our studies provide evidence that afferent–afferent interaction may be mediated not only electrotonically but also with the aid of chemical synapses. This finding suggests that glutamate-induced depolarization of primary afferents results not only from autoreception but also from the direct effect of glutamate on the afferent’s cell membrane.

Inferring the demographic history underlying parallel genomic divergence among pairs of parasitic and nonparasitic lamprey ecotypes.

Understanding the evolutionary mechanisms generating parallel genomic divergence patterns among replicate ecotype pairs remains an important challenge in speciation research. We investigated the genomic divergence between the anadromous parasitic river lamprey (Lampetra fluviatilis) and the freshwater-resident nonparasitic brook lamprey (Lampetra planeri) in nine population pairs displaying variable levels of geographic connectivity. We genotyped 338 individuals with RAD sequencing and inferred the demographic divergence history of each population pair using a diffusion approximation method. Divergence patterns in geographically connected population pairs were better explained by introgression after secondary contact, whereas disconnected population pairs have retained a signal of ancient migration. In all ecotype pairs, models accounting for differential introgression among loci outperformed homogeneous migration models. Generating neutral predictions from the inferred divergence scenarios to detect highly differentiated markers identified greater proportions of outliers in disconnected population pairs than in connected pairs. However, increased similarity in the most divergent genomic regions was found among connected ecotype pairs, indicating that gene flow was instrumental in generating parallelism at the molecular level. These results suggest that heterogeneous genomic differentiation and parallelism among replicate ecotype pairs have partly emerged through restricted introgression in genomic islands.

ATP-consuming processes in hepatocytes of river lamprey Lampetra fluviatilis on the course of prespawning starvation

The work was performed to establish which of the major ATP-consuming processes is the most important for surviving of hepatocytes of female lampreys on the course of prespawning starvation. The requirements of protein synthesis and Na+-K+-ATPase for ATP in the cells were monitored by the changes in mitochondrial membrane potential (MMP) in the presence of corresponding inhibitors from the peak of metabolic depression (January–February) to the time of recovery from it (March–April) and spawning (May). Integrity of lamprey liver cells was estimated by catalytic activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in blood plasma. In January–February, the share of ATP necessary for protein synthesis was 20–22%, whereas before spawning it decreased to 8–11%. Functioning of Na+-K+-pump required 22% of cellular ATP at the peak of metabolic depression, but 38% and 62% of ATP in March–April and May, respectively. Progression of prespawning period was accompanied by 3.75- and 1.6-fold rise of ALT and AST activities in blood plasma, respectively, whereas de Ritis coefficient decreased from 2.51±0.34 to 0.81±0.08, what indicates severe damage of hepatocyte membranes. Thus, the adaptive strategy of lamprey hepatocytes to develop metabolic depression under conditions of energy limitation is the selective production of proteins necessary for spawning, most probably vitellogenins. As spawning approaches, the maintenance of transmembrane ion gradients, membrane potential and cell volume to prevent premature cell death becomes the priority cell function.

Biological responses of midge (Chironomus riparius) and lamprey (Lampetra fluviatilis) larvae in ecotoxicity assessment of PCDD/F-, PCB- and Hg-contaminated river sediments.

We evaluated the utility of chironomid and lamprey larval responses in ecotoxicity assessment of polychlorinated dibenzo-p-dioxins, dibenzofurans (PCDD/F)-, polychlorinated biphenyls (PCB)- and mercury (Hg)-contaminated river sediments. Sediment samples were collected from the River Kymijoki with a known industrial pollution gradient. Sediment for the controls and lamprey larvae were obtained from an uncontaminated river nearby. Contamination levels were verified with sediment and tissue PCDD/F, PCB and Hg analyses. Behaviour of sediment-exposed chironomid and lamprey larvae were measured with Multispecies Freshwater Biomonitor© utilizing quadrupole impedance conversion technique. In addition, mortality, growth and head capsule deformity incidence of chironomids were used as ecotoxicity indicators. WHOPCDD/F+PCB-TEQ in the R. Kymijoki sediments ranged from the highest upstream 22.36ngg(-1) dw to the lowest 1.50ngg(-1) near the river mouth. The sum of PCDD/Fs and PCBs correlated strongly with Hg sediment concentrations, which ranged from <0.01 to 1.15μgg(-1). Lamprey tissue concentrations of PCDD/Fs were two orders and PCBs one order of magnitude higher in the R. Kymijoki compared to the reference. Chironomid growth decreased in contaminated sediments and was negatively related to sediment ∑PCDD/Fs, WHOPCDD/F+PCB-TEQ and Hg. There were no significant differences in larval mortality or chironomid mentum deformity incidence between the sediment exposures. The distinct behavioural patterns of both species indicate overall applicability of behavioural MFB measurements of these species in sediment toxicity bioassays. Chironomids spent less and lampreys more time in locomotion in the most contaminated sediment compared to the reference, albeit statistically significant differences were not detected. Lamprey larvae had also a greater activity range in some of the contaminated sediments than in the reference. High pollutant levels in lamprey indicate risks for biomagnification in the food webs, with potential health risks to humans consuming fish.

Reconstructing the demographic history of divergence between European river and brook lampreys using approximate Bayesian computations.

Inferring the history of isolation and gene flow during species divergence is a central question in evolutionary biology. The European river lamprey (Lampetra fluviatilis) and brook lamprey (L. planeri) show a low reproductive isolation but have highly distinct life histories, the former being parasitic-anadromous and the latter non-parasitic and freshwater resident. Here we used microsatellite data from six replicated population pairs to reconstruct their history of divergence using an approximate Bayesian computation framework combined with a random forest model. In most population pairs, scenarios of divergence with recent isolation were outcompeted by scenarios proposing ongoing gene flow, namely the Secondary Contact (SC) and Isolation with Migration (IM) models. The estimation of demographic parameters under the SC model indicated a time of secondary contact close to the time of speciation, explaining why SC and IM models could not be discriminated. In case of an ancient secondary contact, the historical signal of divergence is lost and neutral markers converge to the same equilibrium as under the less parameterized model allowing ongoing gene flow. Our results imply that models of secondary contacts should be systematically compared to models of divergence with gene flow; given the difficulty to discriminate among these models, we suggest that genome-wide data are needed to adequately reconstruct divergence history.

Evaluating the effectiveness of a Larinier super active baffle fish pass for European river lamprey Lampetra fluviatilis before and after modification with wall-mounted studded tiles

To help achieve effective longitudinal river connectivity, evaluation of the efficacy of fishway use by upstream-migrating fishes is needed. Larinier super active baffle (SAB) fishways are relatively cheap retrofit fish passes, suitable for low-head barriers, widespread in Europe and the most commonly fitted technical pass in Britain. Their suitability for non-salmonids, however, is poorly quantified. The efficacy of a 15% gradient SAB fishway and effects of flow regime and water temperature were tested for European river lamprey (Lampetra fluviatilis) using passive integrated transponder (PIT) and acoustic telemetry at a Crump weir on the River Derwent, Northeast England. In migration season 2013–14, over a wide range of flows, 90.1% of 350 tagged lamprey entered the fishway. One fish (0.3%) of those that entered the pass ascended successfully, even though measured water velocity was within laboratory-measured performance conditions for this species. Of 29 acoustic-tagged lamprey that visited the weir over the same period, four (13.8%) ascended it directly, during elevated flows. These data suggest that high turbulence and/or the physical characteristics of baffles may inhibit lamprey ascent of the pass. In migration season 2014–15, we tested the effect of adding studded modular plastic tiles adjacent to the fishway wall, employing PIT antennas separately interrogating the entrance and exit of each of the main fishway and tile routes. 85.8% (169) of 197 tagged lamprey entered the fishway, of which 72/169 (42.6%) entered the tile entrance. Passage efficiency of entrants was 7.1% (12/169), all of which used the tiled route. Reduced local flow velocity in combination with increased availability of resting habitat within the tiles may have facilitated increased passage. Although fishway passage efficiency increased after placement of the modular tiles, it remained half that measured for direct weir passage, both of which are inadequate for connectivity restoration. Quantitative tests of studded tiles placed on the sloping downstream weir face by comparison to control conditions may be more effective and are needed. This study demonstrates the importance of carrying out full-scale field tests to supplement possible solutions developed under laboratory conditions.

Photopreferendum of migratory and nonmigratory larvae of European river lamprey Lampetra fluviatilis

In the light gradient installation, the larvae of European river lamprey Lampetra fluviatilis of 0+ age, migrating downstream (downstream migrants), are distributed predominantly over the zone of dusk illumination (150–1 lx) and less so over the daylight zone (2500–150 lx) and night illumination zone (<1 lx). In 0+ larvae that passed over to the sedentary lifestyle, the photopreferendum changes: they avoid the dusk and daytime illumination and prefer nighttime illumination. Such photopreferendum is retained in later larvae of lamprey (1+ and older).

Efficacy of a side-mounted vertically oriented bristle pass for improving upstream passage of European eel (Anguilla anguilla) and river lamprey (Lampetra fluviatilis) at an experimental Crump weir

Globally, populations of diadromous anguilliform morphotype fish, such as eel and lamprey, have experienced substantial declines, partly as a result of habitat fragmentation caused by river infrastructure. In the UK, a new configuration of hydraulically unobtrusive bristle pass (side-mounted and vertically oriented) has been developed to help upstream moving European eel (Anguilla anguilla) negotiate gauging weirs. The efficacy of vertically oriented bristle passes remains untested, despite their potential as a low-cost low-maintenance solution to improve habitat connectivity at low-head structural barriers worldwide. This study assessed the ability of small (82–320mm) and large (322–660mm) European eel and adult (291–401mm) river lamprey (Lampetra fluviatilis) to pass upstream over an experimental Crump weir installed in a large open-channel flume with (treatment) and without (control) side-mounted vertically oriented bristle passes under three different hydraulic regimes. Both species were highly motivated to explore their surroundings and move upstream during the trials. Under flooded control conditions, passage efficiency (the total number of times fish passed the structure as a percentage of total attempts) and passage success (the number of fish that passed the structure as a percentage of those that attempted) were high, delay was short, and number of failed attempts before passage was low for both species. When difference in head was at its greatest (230mm) and velocity and its variation downstream were high (maximum u and σ: 2.43ms−1 and 0.66ms−1, respectively), the upstream movement of small eel and lamprey was blocked, and passage efficiency and success for large eel low (4.6% and 17.2%, respectively). For large eel that successfully passed, delay was long, and number of failed attempts before upstream passage was high. When bristle passes were installed, passage efficiency for small (91.5%) and large eel (56.7%), and passage success for large eel (76.5%) and lamprey (36.7%) was higher, while delay and the number of attempts before passage was lower for both species. Bristle passes helped European eel and river lamprey pass a small experimental Crump weir, although interspecific variation in efficacy was evident.

Low reproductive isolation and highly variable levels of gene flow reveal limited progress towards speciation between European river and brook lampreys.

Ecologically based divergent selection is a factor that could drive reproductive isolation even in the presence of gene flow. Population pairs arrayed along a continuum of divergence provide a good opportunity to address this issue. Here, we used a combination of mating trials, experimental crosses and population genetic analyses to investigate the evolution of reproductive isolation between two closely related species of lampreys with distinct life histories. We used microsatellite markers to genotype over 1000 individuals of the migratory parasitic river lamprey (Lampetra fluviatilis) and freshwater-resident nonparasitic brook lamprey (Lampetra planeri) distributed in 10 sympatric and parapatric population pairs in France. Mating trials, parentage analyses and artificial fertilizations demonstrated a low level of reproductive isolation between species even though size-assortative mating may contribute to isolation. Most parapatric population pairs were strongly differentiated due to the joint effects of geographic distance and barriers to migration. In contrast, we found variable levels of gene flow between sympatric populations ranging from panmixia to moderate differentiation, which indicates a gradient of divergence with some population pairs that may correspond to alternative morphs or ecotypes of a single species and others that remain partially isolated. Ecologically based divergent selection may explain these variable levels of divergence among sympatric population pairs, but incomplete genome swamping following secondary contact could have also played a role. Overall, this study illustrates how highly differentiated phenotypes can be maintained despite high levels of gene flow that limit the progress towards speciation.

The mitogenomes of the pouched lamprey (Geotria australis) and least brook lamprey (Lampetra aepyptera) with phylogenetic considerations

We report the mitogenomes of the pouched lamprey (Geotria australis) and least brook lamprey (Lampetra aepyptera) in the families Geotriidae and Petromyzontidae, respectively. Both of the mitogenomes contain the 37 typical vertebrate genes. Their gene order and contents are identical to those of previously described lamprey mitogenomes. The mitogenome of G. australis (17 080 bp) is the largest among the 10 reported lamprey mitogenomes, owed to two long noncoding regions. The mitogenome of L. aepyptera is 77 bp longer (16 236 bp) than that of the congeneric European river lamprey L. fluviatilis, a size difference mostly due to different copy numbers of tandem repeats in the noncoding regions. The phylogenetic analysis supports that the pouched lamprey (Geotriidae) diverged earlier from the common ancestor of lampreys than the Petromyzonids, and the placement of the least brook lamprey in the genus Lampetra.

Studies on endangered and rare non-commercial fish species recorded in the Pomeranian Bay (southern Baltic Sea) in 2010–2013

This paper presents the results of studies on endangered and rare non-commercial fish species (Spinachia spinachia, Nerophis ophidion, Syngnathus typhle, Agonus cataphractus, Pholis gunnellus, Enchelyopus cimbrius, Cyclopterus lumpus) and one lamprey species (Lampetra fluviatilis), recorded as bycatch during monitoring surveys in 2010–2013 in the Pomeranian Bay. Two species were observed for the first time in the Pomeranian Bay: A. cataphractus and E. cimbrius. Descriptions of parasite fauna are provided for C. lumpus and E. cimbrius, which were infected with four pathogenic species from Neomonada, Digenea, Nematoda, and Acanthocephala. Almost all parasite species were new in the hosts examined.

Phospholipids and fatty acids in erythrocytes of lamprey Lampetra fluviatilis during autumn prespawning period and the absorption spectrum of their lipid extract

The content of some classes of phospholipids and their fatty acid composition in erythrocytes of the lamprey Lampetrafluviatilis during the autumn period of its prespawning migration are investigated. It is found that the phospholipid spectrum of erythrocytes of the lamprey, the oldest representative of vertebrates, is similar to that of many mammals. A four-fold prevalence of phosphatidilcholine content over sphingomyelin content as well as prevalence of (ω3-acids over ω6-acids indicates the <<fluidity>> of lamprey's erythrocyte membranes - an important indicator of deformational ability of lamprey's erythrocytes. Phosphatidilethanol amine and its plasmalogenic form are the most unsaturated phospholipids (their unsaturation indices are 230 and 342, correspondingly). Phosphatidilcholine is the most saturated one (UI is 167). It is found that the basic acid indicators characterizing the fluidity of erythrocyte membranes remain unchanged during the whole period of prespawning migration of lampreys up to spawning. The blood contains several buffer systems, in particular, membrane phospholipids which neutralize acids and alkali incoming into the blood. In the process of organism life a change of pH inside erythrocytes occurs. One can suppose that the base of the system associated with buffer properties of the blood is water dissociation. Inside thin vessels of the circulatory system the hemoglobin attaches and returns molecules of oxygen due to interaction of the buffer systems with water. The property of water to dissociate as well as ion transfer produce in erythrocytes, lying within narrow vessels of the circulatory system, a local pH alteration allowing displacing/attaching the molecule of oxygen from hemoglobin.

Evolution of retinoic acid receptors in chordates: insights from three lamprey species, Lampetra fluviatilis, Petromyzon marinus, and Lethenteron japonicum

BackgroundRetinoic acid (RA) signaling controls many developmental processes in chordates, from early axis specification to late organogenesis. The functions of RA are chiefly mediated by a subfamily of nuclear hormone receptors, the retinoic acid receptors (RARs), that act as ligand-activated transcription factors. While RARs have been extensively studied in jawed vertebrates (that is, gnathostomes) and invertebrate chordates, very little is known about the repertoire and developmental roles of RARs in cyclostomes, which are extant jawless vertebrates. Here, we present the first extensive study of cyclostome RARs focusing on three different lamprey species: the European freshwater lamprey, Lampetra fluviatilis, the sea lamprey, Petromyzon marinus, and the Japanese lamprey, Lethenteron japonicum.ResultsWe identified four rar paralogs (rar1, rar2, rar3, and rar4) in each of the three lamprey species, and phylogenetic analyses indicate a complex evolutionary history of lamprey rar genes including the origin of rar1 and rar4 by lineage-specific duplication after the lamprey-hagfish split. We further assessed their expression patterns during embryonic development by in situ hybridization. The results show that lamprey rar genes are generally characterized by dynamic and highly specific expression domains in different embryonic tissues. In particular, lamprey rar genes exhibit combinatorial expression domains in the anterior central nervous system (CNS) and the pharyngeal region.ConclusionsOur results indicate that the genome of lampreys encodes at least four rar genes and suggest that the lamprey rar complement arose from vertebrate-specific whole genome duplications followed by a lamprey-specific duplication event. Moreover, we describe a combinatorial code of lamprey rar expression in both anterior CNS and pharynx resulting from dynamic and highly specific expression patterns during embryonic development. This ‘RAR code’ might function in regionalization and patterning of these two tissues by differentially modulating the expression of downstream effector genes during development.Electronic supplementary materialThe online version of this article (doi:10.1186/s13227-015-0016-4) contains supplementary material, which is available to authorized users.

Sensitivity of liver monoamine oxidase in the lamprey Lampetra fluviatilis to some tricyclic compounds

A comparative analysis of the effect of the five acridine, three phenothiazine and one xanten (pyronine G) derivatives on the activity of liver mitochondrial monoamine oxidase (MAO) in sexually mature male river lampreys Lampetra fluviatilis has been conducted. Tyramine, dopamine, serotonin, noradrenaline, benzylamine, β-phenylethylamine and N-methylhistamine have been used as substrates for analyzing the monoamine oxidase activity of heterocyclic compounds. The analyzed synthetic hexamerous tricyclic compounds exhibit irreversible inhibition of the enzyme but no specificity depending on the desaminated substrate. The number and identity of heteroatoms in the analyzed heterocyclic compounds have been established to influence their inhibitory efficiency. The data of substrate-inhibitory analysis obtained with the use of the specific substrates provide indirect evidence for the existence of a single MAO form in the lamprey liver.