Morphometric Discrimination Research Articles

Utility of body and otolith morphometry to discriminate cryptic juveniles of two sympatric red snappers (Perciformes: Lutjanidae).

The sympatric red snappers, Lutjanus erythropterus and Lutjanus malabaricus, are highly valued by commercial and recreational fishers along the tropical northern coasts of Australia and throughout their distribution. Studies on the life history and ecology of these congeners are confounded by difficulties in distinguishing the cryptic juveniles of each species (i.e., < 200 mm total length). This study aimed to validate a robust and cost-effective method to discriminate these juveniles using body and/or otolith morphometric data in a multivariate analysis. Juvenile samples were collected from the northwest (n = 71) and northeast (n = 19) coasts of Australia, and species identification was confirmed using DNA barcoding. The most parsimonious multivariate models achieved accurate species prediction rates of 98.8%, which consisted of just three body variables (dorsal fin length, the distance from the snout to the anterior edge of the eye, and either jaw length or distance from the snout to the preoperculum). The high level of discrimination for these cryptic juveniles highlights the robustness of this morphometric approach. The slightly lower rate of discrimination using otolith morphology (84.9%) was associated with greater regional variation in L. malabaricus between the northwest and northeast coasts. Slight variations in otolith shape are typically used to determine stock structure, which highlights the potential need to collect samples over a broader area of a species geographic range when using an otolith morphometric discrimination model. The method outlined in this study could be applied to distinguish other cryptic congeneric fish species, including from archived otolith collections. Moreover, this method has the potential to be utilized in assessing species compositions using body measurements from in situ stereo-video.

"Morphometric Discrimination of Six Species of the Family Nemipteridae from Indian Waters: An Illustration Using Artificial Neural Network"

Renjith RK1*, Jaiswar AK2, Chakraborty SK2, Ramteke KK2, Sreelakshmi KR1 and Sreekanth GB3 Author Affiliations 1ICAR- Central Institute of Fisheries Technology, India 2ICAR-Central Institute of Fisheries Education, India 3ICAR - Central Coastal Agricultural Research Institute, India Received: June 16, 2022 | Published: June 28, 2022 Corresponding author: Renjith RK, ICAR- Central Institute of Fisheries Technology, Kochi-29, India DOI: 10.26717/BJSTR.2022.44.007108

Morphometric discrimination in Bali cattle (Bos javanicus) at two different altitude areas of Jambi province, Indonesia

Bali cattle (Bos javanicus) is an important livestock for the farmers at Jambi Province of Indonesia for meat production purposes. This research was aimed to classify adult Bali cattle (about 3.5 years age) based on their body measurements (morphometrics). The animals in this study were collected from two different altitude areas (lowland and midland) of Jambi province. A canonical discriminant analysis (CDA) was computed in this study for discrimination of animals. A total of 480 animals collected from lowland (180 animals) and midland (300 animals) areas were used in the present study. Thus, seven (7) morphometrical measurements of body length (BL), withers height (WH), chest girth (CG), chest depth (CD), shoulder width (SW), canon circumference (CC) and rump height (RH) were measured in each animal. Research showed that four (4) body measurements, viz. BL, CG, SW and RH were described as the discriminating variables with a canonical correlation of 0.83 (very high). In conclusion, about 90% of Bali cattle at lowland and midland areas could be classified using body measurements.

Geometric morphometric discrimination between seven populations of Kawakawa Euthynnus affinis (Cantor, 1849) from Peninsular Malaysia

Small epipelagic and migratory, Euthynnus affinis (kawakawa) is one of the commercially significant tunas of Indo-Pacific tropical and subtropical waters. Unfortunately, the management and stock structure of certain migratory species in the area is not clear. The current study aimed to discriminate the E. affinis through shape and body size variations and to evaluate the variations among seven populations of E. affinis. A total of 114 individuals of E. affinis were collected from two main geographic areas; the Straits of Malacca and the South China Sea. Multivariate analyses, such as discriminant function analyses (DFA) and principal component analyses (PCA) of 11 homologous landmarks and seven morphometric variables were carried out to discriminate seven populations of E. affinis. The results revealed a significant variations among the body shape of the seven populations of E. affinis. Morphological homogenous occurred between populations obtained from the east coast of Peninsular Malaysia (Terengganu, Kelantan, and Johor). However, populations found on the west coast of Peninsular Malaysia (Selangor) were separated and formed another cluster. The variations in the body shape of E. affinis occurred in the body depth and the overall body shape. The percentage of overall correct classification for all seven populations of E. affinis is 88.6%. This present study is the first report using a geometric morphometric method performed on the E. affinis from Peninsular Malaysian waters.

Multidisciplinary approach detects speciation within the kissing bug Panstrongylus rufotuberculatus populations (Hemiptera, Heteroptera, Reduviidae).

BACKGROUND Panstrongylus rufotuberculatus (Hemiptera-Reduviidae) is a triatomine species with a wide geographic distribution and a broad phenotypic variability. In some countries, this species is found infesting and colonising domiciliary ecotopes representing an epidemiological risk factor as a vector of Trypanosoma cruzi, etiological agent of Chagas disease. In spite of this, little is known about P. rufotuberculatus genetic diversity.METHODS Cytogenetic studies and DNA sequence analyses of one nuclear (ITS-2) and two mitochondrial DNA sequences (cyt b and coI) were carried out in P. rufotuberculatus individuals collected in Bolivia, Colombia, Ecuador and Mexico. Moreover, a geometric morphometrics study was applied to Bolivian, Colombian, Ecuadorian and French Guiana samples.OBJECTIVES To explore the genetic and phenetic diversity of P. rufotuberculatus from different countries, combining chromosomal studies, DNA sequence analyses and geometric morphometric comparisons.FINDINGS We found two chromosomal groups differentiated by the number of X chromosomes and the chromosomal position of the ribosomal DNA clusters. In concordance, two main morphometric profiles were detected, clearly separating the Bolivian sample from the other ones. Phylogenetic DNA analyses showed that both chromosomal groups were closely related to each other and clearly separated from the remaining Panstrongylus species. High nucleotide divergence of cyt b and coI fragments were observed among P. rufotuberculatus samples from Bolivia, Colombia, Ecuador and Mexico (Kimura 2-parameter distances higher than 9%).MAIN CONCLUSIONS Chromosomal and molecular analyses supported that the two chromosomal groups could represent different closely related species. We propose that Bolivian individuals constitute a new Panstrongylus species, being necessary a detailed morphological study for its formal description. The clear morphometric discrimination based on the wing venation pattern suggests such morphological description might be conclusive.

Morpho-Genetic Divergence and Adaptation of Anadromous Hilsa shad (Tenualosa ilisha) Along Their Heterogenic Migratory Habitats

Migration of an anadromous fish to heterogeneous environment continuously enforces a selective pressure that incorporates a wide range of life-history strategies by which individuals adapt to the prevailing conditions. Therefore, we used the landmark-based morphometric truss network method and nextRAD genotyping-based putatively adaptive SNP loci dataset to know how the anadromous Hilsa shad (Tenualosa ilisha) morpho-genetically adapt to the heterogeneous habitats across their migratory routes by investigating 300 individuals, collected from nine strategic sampling sites covering sea, estuary, and upstream freshwater rivers. Different multivariate and clustering analyses revealed that the riverine populations were morphometrically wider (broad type) than the estuarine and marine populations (slender type). In the case of riverine population, the north-western turbid population (the Padma and Jamuna rivers) had wider body depth than the north-eastern clear water population (the Meghna river). The linear model and spatial multivariate analyses further revealed that the outcomes of morphometric dataset were in complete concordance with the results of putatively adaptive SNP loci dataset for different Hilsa shad populations. The GO enrichment analysis of the 36 genes, which are encoded by the putative adaptive SNP loci, supported the presence of multiple genes involved in the growth, metabolism, homeostasis and osmoregulation related functions. Several non-mutually exclusive hypotheses were attributed to explain the observation of continuum differentiation at both phenotypes and genotypes: i) the genetic variation largely determines the morphometric discrimination, ii) the interactive evolutionary processes and salinity gradients predominantly contribute to the morphogenetic divergence between the marine-estuarine and the freshwater riverine populations, iii) the salinity levels influence the genotypes leading to the phenotypic plasticity, and iv) the local environmental heterogeneity may contribute to the morphogenetic divergence between the riverine populations. Finally, we concluded that the genetic adaptation, phenotypic plasticity and interactive ecological and evolutionary consequences jointly determine the morphogenetic divergence of Hilsa shad. The interaction of all of these forces and their relative strength in heterogeneous environments, however, made it rather challenging to determine the most probable selective pressure, which has shaped the Hilsa shad morphogenetic divergence across their diverse migratory habitats.

Morphometric Analysis and Genetic Relationship of Rasbora spp. in Sarawak, Malaysia.

The genus Rasbora is one of the most species-rich genus among the freshwater fishes and cryptic diversity has been a major hindrance in species identification in the past four decades due to their high similarities in terms of morphology. This study aimed to investigate this issue both morphologically and molecularly. In this study, a total of 23 morphometric parameters were used to differentiate the 103 Rasbora fish samples harvested from different regions of Sarawak state of Malaysia via Multivariate Stepwise Discriminant Function Analysis (SDFA). Then, cytochrome oxidase subunit I (COI) gene was utilised to further distinguish 33 of these fishes, followed by sequence and phylogenetic analysis. Our results unravelled pre-anal length as strongest morphometric discriminant (100%) and that all eight Rasbora species tested are monophyletic except for R. sumatrana and R. caudimaculata, revealing possible cryptic Rasbora species. Further investigations are vital to enrich the data from this study for Rasbora cryptic diversity and conservation studies in future.

A Review of the Eliurus tanala Complex (Rodentia: Muroidea: Nesomyidae), with Description of a New Species from Dry Forests of Western Madagascar

Based on 372 specimens examined, we integrated information from two mitochondrial and four nuclear gene sequences, morphological comparisons and morphometric analyses, as well as distributional patterns and ecological occurrences to revise the Eliurus tanala species group (Nesomyinae), a rodent complex endemic to Madagascar's forests. These evidentiary sources generally proved concordant, supporting description of a new species, E. tsingimbato, indigenous to western dry deciduous forest, mostly associated with limestone karst (tsingy); the two other members of this species group, E. ellermani and E. tanala, are restricted to eastern montane humid forest. Phylogenetic relationships among the three species were poorly resolved, suggesting that their speciation was both recent and rapid. We encountered one instance of conflict between mitochondrial DNA and all other data sources, which we interpret as incomplete lineage sorting involving a population of the new western species. Attention was focused on molecular and morphometric discrimination of the E. tanala and E. antsingy groups where their species distributions overlap in limestone-associated forests of western and northern Madagascar. Phyletic divisions demonstrated within the E. tanala species group are discussed apropos of current models of speciation identified for Malagasy forest-dwelling organisms.

Morphometric discrimination between age groups of Martes foina (Mustelidae, Carnivora) by using baculum in Turkey

Morphometric discrimination between age groups of Martes foina (Mustelidae, Carnivora) by using baculum in Turkey

Morphometric discrimination between females of two isomorphic sand fly species, Phlebotomus caucasicus and Phlebotomus mongolensis (Diptera: Phlebotominae) in endemic and non-endemic foci of zoonotic cutaneous leishmaniasis in Iran

Objective: To delineate reliable morphological characteristics for identifying and separating female Phlebotomus caucasicus and Phlebotomus mongolensis which exist sympatrically in the main foci of zoonotic cutaneous leishmaniasis in Iran. Methods: Sand flies were collected using sticky trap papers from active colonies of rodent burrows installed from 16 catching sites. Morphometric measurements were analyzed of 87 Phlebotomus caucasicus and 156 Phlebotomus mongolensis. Univariate and multivariate analysis were carried out to determine significant morphometric variables for discrimination of the two species. Finally, seven morphological characteristics of 65 female Phlebotomus caucasicus and 124 female Phlebotomus mongolensis were described. Results: Univariate and multivariate analyses of 10 morphometric variables via Discriminant Function Analysis (DFA) and Principal Component Analysis (PCA) showed that five morphometric variables had an accuracy of 100% for discriminating female Phlebotomus caucasicus and Phlebotomus mongolensis. Moreover, PCA revealed that the five morphometric variables with the highest loadings separated these two species. Morphological studies on antennal flagellum (and its associated structures) and mouth-parts of female specimens demonstrated significant differences in several structures. Conclusions: The results show that morphological and morphometrical features can be used to discriminate two female isomorphic species, Phlebotomus caucasicus and Phlebotomus mongolensis accurately.

Morphometric discrimination of pelagic fish stocks challenged by variation in body condition

Abstract Morphometric characters have traditionally been used to describe the population structure of fishes. Body shape variation, which is often environmentally induced, may provide a good record of short-term population structuring. However, factors unrelated to environmental or genetic influences on body morphology may complicate sampling and the use of morphometric features for stock discrimination. In the present study, we used geometric morphometric variables to compare the European sardine Sardina pilchardus putative stocks of the Aegean and Ionian Seas (eastern Mediterranean). Landmark data of fish collected at seven different sites were subjected to canonical analysis of principal coordinates (CAP). The average body condition of sardines from these sites was strongly and linearly related to corresponding scores along CAP1, the axis exhibiting the highest correlation with the morphometric data cloud. The average scores along CAP2 and CAP3 appeared to be linked to morphological differentiation related to temperature effects and prey availability (mesozooplankton biomass). Despite the primary and confounding effect of body condition, discrimination of different morphotypes corresponding to the Aegean and the Ionian Sea stocks was highly significant with 81% correct reallocations for the respective CAP model.

Morphometric discrimination among three stocks of Macrobrachium amazonicum in the Brazilian Amazon

• This study evaluated morphometric variation among three stocks of Amazon river prawn Macrobrachium amazonicum . • Different characteristics at the stock-level between sexes were observed. • Stocks differences were proportional to distance between sites. The aim of this study was to compare stocks of Amazon River prawns ( Macrobrachium amazonicum ) among 3 sampling sites (Tucuruí, Cametá and Soure) in the Tocantins/Araguaia River Basin (Amazônia, Brazil) through morphometric analyses. A total of 360 specimens (180 males and 180 females) were sampled, and 21 morphometric characters were assessed and subsequently analyzed using descriptive and multivariate statistics. Principal component analyses showed a strong ability to distinguish the different stocks, especially between those at the sites most distant from each other (Tucuruí and Soure). In the discriminatory analysis, the most significant characteristics for females were total length (TL), carapace width (Cw) and palm width (Pw), whereas for males, the most significant characteristics were Pw and Cw. The cluster analysis showed different groupings for the male and female models, although the Tucuruí and Soure stocks were always separated. Therefore, the multivariate analyses identified 3 different stocks in the sampled area, and an explicit fishing management plan for each stock is suggested because this species has been shown to be imminently threatened by overfishing in the Amazon region.

Debris-flow susceptibility of upland catchments

Over the last three decades, many regional studies in mountain ranges under temperate climate revealed that it is possible to discriminate debris-flow and fluvial fans from morphometric indicators measured at the scale of the catchment and the fan itself. The most commonly used indicators are the Melton index (R), a normalized index of the gravitational energy of the catchment, and the fan slope (S). A wide range of thresholds have been proposed for discriminating purpose, but these are generally based on a small population of catchments and may be highly influenced by ambiguous fans included in the data set. A database of 620 upland catchments from several mountain ranges under temperate climate was compiled from the literature to propose robust discriminant morphometric thresholds for debris-flow versus fluvial responses. Linear discriminant analysis (LDA) and logistic regression (LR) were performed using the whole data set, and a leave-one-out cross-validation was used to evaluate performances of the models. Sensitivity and specificity scores obtained for LDA and LR were 0.96 and 0.73, and 0.95 and 0.75, respectively. It is also shown that the channel slope above which debris-flow is observed decreases with the gravitational energy of the catchment. Limitations of the morphometric discrimination are discussed.

3D comparison of average faces in subjects with oral clefts

This prospective cross-sectional, case-controlled morphometric study assessed three dimensional (3D) facial morphological differences between average faces of 103 children aged 8-12 years; 40 with unilateral cleft lip and palate (UCLP), 23 with unilateral cleft lip and alveolus (UCLA), 19 with bilateral cleft lip and palate (BCLP), 21 with isolated cleft palate (ICP), and 80 gender and age-matched controls. 3D stereophotogrammetric facial scans were recorded for each participant at rest. Thirty-nine landmarks were digitized for each scan, and x-, y-, z-coordinates for each landmark were extracted. A 3D photorealistic average face was constructed for each participating group and subjective and objective comparisons were carried out between each cleft and control average faces. Marked differences were observed between all groups. The most severely affected were groups where the lip and palate were affected and repaired (UCLP and UCLA). The group with midsagittal palatal deformity and repair (ICP) was the most similar to the control group. The results revealed that 3D shape analysis allows morphometric discrimination between subjects with craniofacial anomalies and the control group, and underlines the potential value of statistical shape analysis in assessing the outcomes of cleft lip and palate surgery, and orthodontic treatment.

Morphometric discrimination between Martes martes and Martes foina in Italy: the use of the baculum

Martes martes and Martes foina are the only two Italian species of the genus Martes . As they are very similar in morphology and coloration, their taxonomic identification may represent a hard task. We aimed to assess the reliability of baculum length as a diagnostic tool for Italian martens. A sample of 53 adult males belonging to the genus Martes was collected. The identification of individuals as pine- or stone marten followed a 2-step procedure: i) morphometric analysis and ii) cross-checking with genetic analysis. According to the diagnostic ranges of baculum length reported in the available literature, 21 individuals were classified as stone marten and 15 as pine marten, while 17 specimens remained unidentified. Using a “Baculum Index” , defined as: (Head Length + Body Length) / Total Baculum Length, the sample was split into two distinct groups: 21 individuals fell into the 6.24-8.10 range and 32 fell into the 9.52-11.17 range. Genetic analysis led to the same results. While baculum length is insufficient to identify Italian marten species with certainty, the Baculum Index showed to be a reliable diagnostic tool.

Morphometric discrimination of wild from farmed Dybowski’s frog (Rana dybowskii) based on hindlimb length

Commercial farming of anuran species that are declining in the wild raises a need to discriminate wild from farmed frogs. We hypothesized wild frogs might have extended hindlimbs due to greater frequency or intensity of jumping relative to farmed frogs, highlighting a morphometric approach to discrimination of wild from farmed frogs using hindlimb length. In the present study, Dybowski’s frog (Rana dybowskii) was used to test this hypothesis. We measured body mass (Mb) and hindlimb length (Lh) of 2-year old farmed frogs and wild frogs aged 2 to 5 years. Dybowski’s frog demonstrated significant dimorphism in Mb and Lh. Mb was significantly greater among farmed 2-year old frogs in both sexes (p=0.000), while only among females was Lh significantly greater for wild frogs (p=0.000). Lh/Mb was used as an index for origin discrimination to eliminate the influence of Mb due to variation of husbandry conditions among farms. Mean Lh/Mb for farmed frogs was significantly lower than for wild frogs (p=0.000) in the 2-year old age class. Discrimination correctly classified 84.4% of farmed and 96.3% of wild male frogs. Among females, 92.9% of farmed frogs and 90.1% wild frogs were correctly classified. The overall correctness of classification was 92.1% and 90.8% for males and females, respectively. However, Lh/Mb revealed variation with age, resulting in reduced discriminative power for frogs ≥3 years old. We introduced a coefficient Ce to adjust the Lh/Mb of frogs ≥3 years to the level equivalent to 2-year frogs. The adjustment achieved 89.5% for overall correctness of origin for wild males and 92.4% for wild females ≥3 years old. These results show that Lh/Mb is an effective index to discriminate wild from farmed Dybowski’s frog. Since the physical demands of jumping are common among anurans, this index is also potentially applicable to other anuran species.

Testing and Improving the Accuracy of Discriminant Function Tests: A Comparison between Morphometric and Molecular Sexing in Macaroni Penguins

Dimorphism in various morphological traits is widely used to sex birds. However, when a threshold is set and there is overlap in the distribution of traits between sexes, there will be an error rate. Macaroni Penguins show limited sexual dimorphism in size, with the distributions of most phenotypic traits overlapping between sexes, making using morphological characters for sexing difficult, although bill depth is used in one discrimination test. Two existing DNA-based PCR tests that use different primer pairs (P2/P8 and 2550/2781 ) were adapted for use with fluorescently labelled primers to enable the size of fragments to be accurately measured via genotyping protocols and sex to be determined. The two molecular tests were applied to the same samples to estimate the error rate within and between tests. Whilst both primer pairs reproducibly identified the sex of the penguins under study with no inconsistencies between tests, the P2/P8 primer pair had a higher success rate of amplification. To estimate the error rates of morphometric tests, they were compared with molecular tests, revealing areas of disagreement. Structure in the error indicated a bias near the morphometric discrimination threshold. We suggest that larger sample sizes in discriminant function analyses and calibration with molecular data can be used to estimate the likelihood of misidentification for any particular value of the trait. A description of where error lies can then be used to target the more expensive and time-consuming DNA tests to check individuals that are most likely to be mis-assigned.

The &lt;I&gt;Ornithodoros&lt;/I&gt; (&lt;I&gt;Alectorobius&lt;/I&gt;) &lt;I&gt;talaje&lt;/I&gt; Species Group (Acari: Ixodida: Argasidae): Description of &lt;I&gt;Ornithodoros&lt;/I&gt; (&lt;I&gt;Alectorobius&lt;/I&gt;) &lt;I&gt;rioplatensis&lt;/I&gt; n. sp. from Southern South America

A new species of argasid tick, Ornithodoros (Alectorobius) rioplatensis Venzal, Estrada-Peña, & Mangold, is described from larval and adult specimens collected in Uruguay. Further specimens from Argentina, Paraguay, and Chile are ascribed to the new species. Key distinguishing characters of larvae of the species are the number of pairs of dorsal setae (19-20 but typically 20 in O. rioplatensis, compared with 16-17 but typically 17 in O. puertoricensis and O. talaje), and the length of the hypostome, which is clearly longer in O. rioplatensis than in O. talaje. Morphological details of the adults of these species are inadequate for taxonomic purposes. The genetic distance between O. puertoricensis and O. rioplatensis, based on 16S rDNA sequencing, is approximately 12.7%. Variability in some morphological features, using multivariate morphometric discrimination to assess congruence between populations, was examined among larval specimens of O. talaje and O. puertoricensis collected from the United States, and Central and South America. Larval specimens of O. talaje from Guatemala (near the type locality of the species) were morphologically different from Mexican and southern U.S. populations originally described as O. talaje. In the absence of DNA data for these populations, and because of inadequate statistical discrimination among body characters, we prefer to refer to the Mexican and U.S. material as O. nr. talaje until further analysis of population variability is conducted using an adequate sample size.

Phylogeny and geographic differentiation of Atlanto–Mediterranean species of the genus Xantho (Crustacea: Brachyura: Xanthidae) based on genetic and morphometric analyses

The crab genus Xantho Leach, 1814 is restricted to the northeastern Atlantic Ocean and the Mediterranean Sea. It consists of four species, Xantho hydrophilus (Herbst, 1790), X. poressa (Olivi, 1792), X. pilipes A. Milne-Edwards, 1867, and X. sexdentatus (Miers, 1881). X. hydrophilus has been divided into two geographic forms, of which one, X. h. granulicarpus (Forest, 1953), is postulated to be endemic to the Mediterranean Sea. In this study, we reconstruct phylogenetic relationships of the genus Xantho and related genera from the Atlantic Ocean or Mediterranean Sea and compare different geographic populations of Xantho hydrophilus and, to a lesser extent, of X. poressa by means of population genetic and morphometric analyses. The molecular phylogeny is based on two mitochondrial genes (large subunit rRNA and cytochrome oxidase I) and indicates that X. poressa, X. hydrophilus and X. sexdentatus form a monophyletic group, the latter two species sharing identical haplotypes. On the other hand, X. pilipes shows affinities to Xanthodius denticulatus. Population genetics based on the COI gene reveal genetic differentiation within X. hydrophilus. Morphometric results also give evidence for distinct geographic forms in X. hydrophilus with a clear discrimination. In comparison, morphometric discrimination between different geographic populations of X. poressa is less clear, but still significant. We therefore suggest a recent/ongoing morphological and genetic differentiation within Xantho hydrophilus, restricted gene flow between its Atlantic and Mediterranean populations (not allowing subspecific differentiation) and possible mtDNA introgression between the species X. hydrophilus and X. sexdentatus.

Morphometric discrimination of two allozymically diagnosed sibling species of the Echinorhynchus gadi Zoega in M�ller complex (Acanthocephala) in the North Sea

Allozyme electrophoresis was used to detect biological species of the E. gadi complex from gadids from the northern North Sea. A fixed difference at one of nine enzyme loci surveyed confirmed the existence of two reproductively isolated, sympatric species. Mixed infections of two E. gadi spp. (termed A and B) were observed in Gadus morhua and Pollachius virens. E. gadi sp. B was also found in Melanogrammus aeglefinus and Merlangius merlangus. The presence of gravid females of E. gadi spp. A and B in the same host species, P. virens, and sometimes in the same host individual, indicates that neither differential host-specificity nor seasonal differences in mating time are responsible for their reproductive isolation. Morphological study of probosces from electrophoretically identified specimens demonstrated that the two species can be discriminated in graphical and cluster analyses of hook morphometrics. E. gadi sp. I (of Vainola etal., 1994) and E. gadi sp. A are probably conspecific.