Preorbital Length Research Articles

Description of a Remarkable New Skate Species of Leucoraja Malm, 1877 (Rajiformes, Rajidae) from the Southwestern Indian Ocean: Introducing 3D Modeling as an Innovative Tool for the Visualization of Clasper Characters.

A remarkable new deep-water skate, Leucoraja longirostris n. sp., is described based on eight specimens caught during different expeditions to the southern Madagascar Ridge in the southwestern Indian Ocean. The new species differs from all congeners by its remarkably long and acutely angled snout (horizontal preorbital length 17.2-22.6% TL vs. 8.5-11.9% TL and 4.2-6.1 vs. 1.7-3.5 times orbit length, snout angle 65-85° vs. 90-150°). Furthermore, it is apparently endemic to the Madagascar Ridge, distant from the known distribution areas of all congeners. In addition to L. fullonica and L. pristispina, L. longirostris n. sp. is also the only species with plain dorsal coloration. Furthermore, the new species is the only Leucoraja species with an external clasper component dike and, besides L. wallacei, the only one with four dorsal terminal (dt) cartilages. The shape of the accessory terminal 1 (at1) cartilage with four tips is also unique within the genus. A new approach for the visualization of the clasper characters is introduced based on 3D models of all skeletal and external features. This enables a much easier and much more precise interpretation of every single clasper component, of the entire structure, and, in particular, the relationship between external features and skeletal cartilages. A new English translation of the first diagnosis of Leucoraja is provided, along with a revised generic diagnosis and a key to the species of Leucoraja in the Indian Ocean.

INTRA-SPECIFIC DIVERSITY OF THE SILVER GRUNT (Pomadasys Hasta) IN THREE LOCATIONS OF BANGLADESH BASED ON MORPHOMETRIC ANALYSIS

Morphometric variation is a useful tool for studying a species' population structure. The present study was performed to assess the intra-specific diversity between three stocks of the Silver grunt Pomadasys hasta (Khulna, Satkhira and Patuakhali of Bangladesh). Length-weight relationship, condition factor and few other morphometrics were analyzed using both univariate and multivariate approaches. A total of 105 samples were subjected to the analysis (weight (95.05 ±44.22 g) and length (16.18±2.57cm). A total of eleven morphometric traits including standard length (SL), head length (HL), pre dorsal length (Pre DL), dorsal length (DL), pre-anal length (Pre AL) , pre-pelvic length (PreVL) , pre pectoral length (PrePL), pre-orbital length (PrOL), body depth (BD), eye diameter (ED) and pre orbital length (PreOL) were measured. Significant differences were found in four morphometric measurements including head length (HL % of total length), eye diameter (ED % of HL), dorsal length (DL %) and pre dorsal length (PreDL%). A negative allometric growth was observed, as the slope b was far below 3. The highest value of b was found in Satkhira (2.7) and the lowest value of b was found in Khulna (2.07). Three separate stocks of P. hasta exhibited morphological variations in their attributes. The divergence among the stocks could have resulted from both environmental and genetic variances. The outcomes of the study will be helpful for management and conservation of natural population of Datina (P. hasta) in Bangladesh.

Morphometric and meristic traits of giant sea catfish <em>Arius gigas</em> (boulenger 1911) from new Calabar river and Degema River, Rivers State, Nigeria

Morphometric and meristic characters of the Arius gigas species were examined from two study areas (New Calabar and Degema Rivers) for a period of six months in Rivers State, Nigeria. Total of 200 individuals, 100 from each study site, were examined and analyzed. A majority of the values for external morphometric parameters of A. gigas were higher in the New Calabar River than those from Degema River population, with no significant differences exist (p<0.05) across the morphometric parameters except for pre-orbital length, post-orbital length and eye length. The meristic characters revealed variations in the mean values of dorsal fin spine (8.55±0.11 and 7.07±0.38), pectoral fin ray (5.96±0.06 and 4.23±0.26), and pelvic fin ray (14.99±1.21 and 7.51±0.52) in the study. A significant difference was noted in the number of dorsal fin spine (p< 0.05) between the two populations. The mean percentage of the Length of caudal peduncle (LoCP),1st and 2nd dorsal fin (DF), length of interdorsal fin (LoIDF) and length of adipose fin (LoAF) of A. gigas in the New Calabar River were significantly higher (p<0.05) than Degema River. Growth variability for standard length and all external parameters displayed allometric growth of A. gigas from Degema River. Further studies are recommended to corroborate the findings of the two populations using molecular markers for making conservation plans for exploitable A gigas species.

Phenotypic variation of protandrous hermaphrodite fish Eleutheronema tetradactylum (Shaw, 1804) from Thailand coastal waters

This study was conducted to investigate the intraspecific variation of Eleutheronema tetradactylum (Shaw, 1804) using traditional morphometric measurements. In total, 136 samples were collected from four fishing areas across Thailand coastal waters. Raw data were standardized and then evaluated with univariate analysis of variance, canonical discriminant function analysis, and dendrogram of cluster analysis regarding to site, size, and sex. Result from ANOVA test exhibited that all morphological characters were significantly different among sites (P < 0.05). Nevertheless, forty-one morphometric characters were significantly different among size of male and female fish (P < 0.05) except for pre-orbital length, pupil diameter, eye diameter, and depth of maxilla for male fish. Forty-four morphometric characters were significantly different (P < 0.05) except of fork length among sex. From CDFA, E. tetradactylum showed phenotypic heterogeneity and two distinct stocks in the four selected fishing areas. Phenotypic variation on sites was determined by six morphological characters (MnFL, DFAF, DOM, HW, PeBFL and ED) for males, while eight characters for females (PrOL, AFSL, PeBFL, DOM, UJL, PD, AFRL and ED) in decreasing order. Differentiations between fish size classes, relied on PrDFL2, BD and UCFL in males and PrOL, PrePeFL and DFAF in females. Among sexes, PeFAF, PrDFL2, MxFL, MnFL, PrePeFL, HSDF and PrePFL were highly influential. Discriminate functions (DF1) clarified that 83.60% and 94.10% of the total variance were found among the sites of males and females, and 99.20% and 93.20% of the total variance were found among the sizes of males and females, respectively. and 73% of the total variance were found among the sexes. In the confusion matrix of CDFA, the overall assignments of individuals into their correctly classified original population were 98.68% and 100% for males and females based on site and size, and 75.74% of sex groups, respectively. Our study highlighted that the hermaphroditism of E. tetradactylum showed that three distinct stocks of males and two stocks of females inhabited Thai coastal waters.

Spatial Variability of Morphometric Characters of Freshwater Food Fishes from River Ganga of Districts, Kanpur, Prayagraj and Varanasi of Uttar Pradesh, India

The morphometric characters were evaluated to assess the population status of the commercial valuable food fishes collected from River Ganga at three different locations, Kanpur, Prayagraj and Varanasi. In this study, seventeen morphometric parameters were considered to examine during the month of October, 2022 to January, 2023. Usually, the various species of fishes consumed from the river Ganga. For present study, the morphometric characters like total length, fork length, standard length, pre-orbital length, post-orbital length, eye diameter, head length, pre-pectoral length, pre-dorsal length, pre-pelvic length, pre-anal length, length of dorsal fin, length of pectoral fin, length of caudal fin, length of caudal peduncle, body depth and body weight of four fish species, Labeo rohita, Rita rita, Wallago attu and Cyprinus carpio examined. A total of 25 specimens of each species were collected and the quantitative measurement of each aforesaid morphometric character provided crucial data regarding the development of fish body parts. Additionally, the positive correlations have been significantly (p &lt; 0.01 and p &lt; 0.05) detected amongst the selected morphometric characters of fishes. This study will be very crucial for fisheries management. Also, the findings will distribute the important standards for the geographical distribution of the commercially valuable food fishes. Further, the study defines that the growth of all fishes is suitable and the river Ganga ecosystem on three sites, Kanpur, Prayagraj and Varanasi is enormously favourable to the aquatic fauna especially fishes.

Taxonomic and Otolith Shape Parameters of Nine Sympatric Catfishes Commercially Harvested in Pakistan

Abstract Accurate reorganization of harvested species is essential for appropriate fisheries monitoring but often unnoticed. In this study, an attempt was made to provide an accurate species description based on fish taxonomy and otolith shape parameters of nine sea catfishes living in Pakistan. The lapillus, the largest otolith of catfishes, includes the position of the umbo, the structure of the anterior mesial projection (amp), the incisura linea basalis (ilb) and sulcus lapilli marks (slm) in nine ariid catfishes were evaluated. Discriminant function analysis was performed using twenty-two morphometric parameters showed significant variations between the length of the maxillary barbel, adipose length and preorbital length, which were highlighted as basic discriminating characters. Species without barbells, such as Batrachocephalus mino and Osteogeneiosus militaris, were found to be distant. The taxonomic characters of the genera Netuma and Plicofollis overlapped due to a short adipose fin length. Nevertheless, species Arius arius, Sciades sona and Nemapterxy caelatus differed in a moderate adipose fin length. The preorbital length of Netuma bilineata has a short and rounded snout, while N. thalassina has a long and pointed snout, which is a distinguishing characteristic of both species. The coincident use of fish taxonomy and otolith shape parameters is an effective tool for catfish identification could be helpful in appropriate fisheries sampling programs and management in Pakistan whenever implemented.

Using integrative taxonomy to distinguish cryptic halfbeak species and interpret distribution patterns, fisheries landings, and speciation

Context Species classification disputes can be resolved using integrative taxonomy, which involves the use of both phenotypic and genetic information to determine species boundaries. Aims Our aim was to clarify species boundaries of two commercially important cryptic species of halfbeak (Hemiramphidae), whose distributions overlap in south-eastern Australia, and assist fisheries management. Methods We applied an integrative taxonomic approach to clarify species boundaries and assist fisheries management. Key results Mitochondrial DNA and morphological data exhibited significant differences between the two species. The low level of mitochondrial DNA divergence, coupled with the lack of difference in the nuclear DNA, suggests that these species diverged relatively recently (c. 500 000 years ago) when compared with other species within the Hyporhamphus genus (&gt;2.4 million years ago). Genetic differences between the species were accompanied by differences in modal gill raker counts, mean upper-jaw and preorbital length, and otolith shape. Conclusions On the basis of these genetic and morphological differences, as well as the lack of morphological intergradation between species along the overlapping boundaries of their geographical distributions, we propose that Hyporhamphus australis and Hyporhamphus melanochir remain valid species. Implications This study has illustrated the need for an integrative taxonomic approach when assessing species boundaries and has provided a methodological framework for studying other cryptic fish species in a management context.

Resurrection of Lethrinus scoparius Gilchrist amp; Thompson, 1908 (Perciformes: Lethrinidae), from South African waters.

Lethrinus nebulosus (Forsskl, 1775) is distributed throughout the Indian Ocean, Indonesia and the West-central Pacific. Given recent evidence suggesting two cryptic species of L. nebulosus in the southwestern Indian Ocean, we implemented a multispecies coalescent approach using nuclear and mitochondrial DNA loci and conducted Bayesian tests of species delimitation. One population extends from southern Mozambique to Kenya, and the other from northern KwaZulu-Natal (South Africa) southwards, with a zone of overlap between them. This study confirms that the South African population can be identified as a separate species, previously identified as Lethrinus scoparius Gilchrist Thompson, 1908, and can be distinguished from L. nebulosus by live and fresh colouration and with genetic data, but not consistently by morphometric or meristic parameters, other than in preorbital length cf. head length. Lethrinus scoparius is resurrected and redescribed herein.

Morphometric characteristics, sexual dimorphic characters, length-weight relationship and feeding behavior of Chitala chitala from river Indus, Punjab, Pakistan

Chitala chitala commonly known as clown fish is an important fresh water fish found worldwide. A study on the morphometric characteristics, length-weight relationship and feeding habit from stomach and gut analysis of C. chitala was conducted on 32 specimens collected from different zones of River Indus, Pakistan during the month of January and April. These samples were examined in Fisheries lab, Zoology department, Ghazi University, Dera Ghazi Khan. Various external and internal morphometric characters were studied to know their correlation with reference to size (TL and W). Correlation coefficient (r) value (0.98) showed high significant relationship between total length and wet weight, while growth pattern was near to isometric as value of ‘b’ being 2.86. The interrelationship of total length to the eye diameter (0.63), length of dorsal fin (0.44), pectoral fin length (0.69), pre orbital length (0.59), IOD (0.36), DFB(0.53), PFB (0.47) show poor correlation to total length (p>0.05). All other external parameters are highly significant to the total length (p

A descriptive and comparative neurocranium morphology of Anguilliformes fishes in Taiwan waters.

Taiwan is one of the richest in the world in terms of eel fauna. In this study, we examined the osteological and morphological characteristics of eels under order Anguilliformes. Furthermore, we focused on the neurocranium of total of 30 Anguilliformes fishes under family Congridae (10), Muraenesocidae (1), Muraenidae (7), Nemichthyidae (1), Nettastomatidae (2), Ophichthidae (5), Synaphobranchidae (4), which are caught in Taiwanese waters. This paper shows the results of a comparative study on osteological characters of the neurocranium including the ratio of seven length characters using its NCL (neurocranium length), NCW (neurocranium width), OBL (orbit length), MFW (maximum frontal width), NCDB (neurocranium depth at basisphenoid), PEVW (premaxilla-ethmovomer width) and mPOBL (mid pre-orbital length), and 20 morphological diagnostic characters for 30 eel species. Results shows that species under family Nemichthyidae and Nettastomatidae have the highest values on the ratio of NCL/MFW, NCL/NCDB, and NCW/mPOBD. In morphological characters, it shows that species of the same family mostly share similar formation of the PEV plate and frontal structure. The usage of the length measurements and morphological diagnostic characters of neurocranium allowed for a more in depth understanding of how similar or different these eels can be. The neurocranial description and morphological characters may prove valuable for identification purposes and might be necessary tool for further studies on the status of order Anguilliformes.

Description of a new species of giant guitarfish, Glaucostegus younholeei sp. nov. (Rhinopristiformes: Glaucostegidae) from the northern Bay of Bengal, Bangladesh.

A new species of giant guitarfish, Glaucostegus younholeei sp. nov., is described from 13 specimens, 730933 mm total length, collected from fish landing center of Bangladesh Fisheries Development Corporation in Cox's Bazar district of Bangladesh. The new species is distinguished from congeners in having the following combination of characters: Body brownish or greyish in color with a narrowly wedge-shaped disc, and long narrow bluntly pointed snout (angle 3140°), and broad oblique nostrils with the narrow anterior opening. Nostrils about half of the mouth width, subequal (0.981.33) to internasal width; ~5557 nasal lamellae; anterior nasal flaps slightly penetrating into internasal space, their interspace 2.20 2.61 in length of the posterior nasal aperture. Orbit very small in adults, diameter 8.1911.62 in preorbital length, 2.252.69 in interorbital space. Rostral ridges almost joined along their entire length; margin of cranium sharply demarcated before eyes. Spiracular folds very short and widely separated. Skin rough, densely covered with small denticles, more coarsely granular on the dorsal surface than ventrally, enlarged between orbits and in a distinct band between nape and first dorsal fin. Tail relatively longer, length 1.151.48 in disc length; dorsal fins narrowly spaced, interspace 1.322.11 in base length of the first dorsal fin. Clasper length in adult male 4.375.70 in total length. Phylogenetic analysis of DNA barcode sequences also shows the clear divergence of Glaucostegus younholeei from other congeneric species obtained from GenBank. A key is provided to the 8 known members including new species of the genus Glaucostegus.

Fundulus herminiamatildae: a new species of killifish (Teleostei: Fundulidae) from the upper Río Soto La Marina basin, Nuevo León, México

Fundulus herminiamatildae: a new species of killifish (Teleostei: Fundulidae) from the upper Río Soto La Marina basin, Nuevo León, México María Elena García-Ramírez, María De Lourdes Lozano-Vilano, Mauricio De La Maza Benignos Abstract Fundulus herminiamatildae sp. nov. Is endemic from the Marmolejo stream, a head water tributary of Río Soto La Marina basin, in the municipality of Aramberri, Nuevo León, México. Geologically, it is located in the Northeastern province of México, specifically in the Sierra Madre Oriental subprovince. The water temperatura is a determinant and important factor for the species differentiation. Its closest relative is F. philpisteri. Fundulus herminiamatildae is distinguished from other killifishes by a large number of conspicuous and simple lateral bars, body with high profile, and the following proportions in cephalic length: snout (2.5- 2.9, mean 2.7) eye diameter (4.1-4.9, mean 4.5), and Preorbital length (2.7-3.1, mean 2.9). Full Text: PDF DOI: 10.15640/aijb.v9n2a2

Short Communication: The presence of Bull shark Carcharhinus leucas (Elasmobranchii: Carcharhinidae) in the fresh waters of Sumatra, Indonesia

Abstract. Hasan V, Widodo MS. 2020. Short Communication: The presence of Bull shark Carcharhinus leucas (Elasmobranchii: Carcharhinidae) in the fresh waters of Sumatra, Indonesia. Biodiversitas 21: 4433-4439. A single subadult specimen of Bull shark Carcharhinus leucas was photographed and captured by local fisherman using casting net on June 2020 in the upper Indragiri River, Riau Province, Indonesia. Carcharhinus leucas are one of only a few species of elasmobranchs that live in both marine and freshwater environments. This species currently listed as a near-threatened species based on the IUCN Red List Status. Singel specimen identified as C. leucas by the coloration of fresh specimen: white belly and greyish back, first dorsal fin high, tip of second dorsal and caudal fins black. Meristic characters measurement results as follows: total length 102 cm; fork length 86.3 cm; preanal length 65.1 cm; pre pelvic length 51.9 cm; pre pectoral length 22.5 cm; pre-orbital length 8.3 cm; head length 25 cm; pre-first dorsal length 29.4 cm; pre-second dorsal length 56 cm, and pre-caudal length 78.1 cm. This photo is considered as the third record from freshwaters of Sumatra after in the Batang Hari River, Jambi Province in 1997, and in the Musi River, South Sumatra Province in 2019. The photographic records indicate that a single specimen of C. leucas was found in the upper Indragiri River recorded more than 150 km inland. These results enhanced the understanding of C. leucas distribution in Sumatra freshwaters. Monitoring is needed to assess the possibility of the importance of the upper Indragiri River as a migration route, nursery, and growth ground of C. leucas. Studying small scale habitat use of C. leucas is challenged by their preferred habitats in freshwaters environments with fast-changing environmental conditions. Water conditions in the upper Indragiri River, namely salinity 0‰, temperature 25-27°C, dissolved oxygen 3.9-11.1 mg/l, are ideal for A. leucas habitat.

Stock identification of minor carp, Cirrhinus reba, Hamilton 1822 through landmark-based morphometric and meristic variations

BackgroundWild fish populations stock is continuously diminishing in the Indo-Ganges river basin, and the population status of most fishes is unidentified. The identification of the population status and the conservation of commercially important and endemic wild fish populations in this region are crucial for the management. The aim of this paper was to identify the population status of Cirrhinus reba, a promising aquaculture but vulnerable species in the Indo-Ganges river basin in Bangladesh.MethodsC. reba samples were collected from four isolated populations of the Brahmaputra (n = 30), the Padma (33), the Karatoya (31), and the Jamuna Rivers (30) in Bangladesh, and the population status was evaluated using morphometric and landmark comparisons. Data were analyzed with the Kruskal-Wallis test, univariate analysis, discriminant function analysis, and the formation of a dendrogram.ResultsThree meristic characters (Pectoral fin rays, caudal fin rays, scale in lateral lines), four morphometric characters (head length, pre-orbital length, post-orbital length, maximum body depth), and truss measurement (4–7) were significantly different among the stocks. The step-wise discriminant function analysis retained 15 variables from morphometric and landmark measurements that significantly differentiated the populations based on the constructed DFI and DFII. Discriminate function analysis also showed that 91.2% of the original groups were classified into their correct samples. The cluster analysis of Euclidean distances placed the Jamuna population in one cluster and the Brahmaputra, the Padma, and the Karatoya populations in the second one.Conclusion Morphological differences among the stock were probably due to different ancestral origin. This is the first report about population status of C. reba in their natural habitat of the Indian subcontinent. Further genetic studies and the evaluation of environmental impact on C. reba populations in Bangladesh are suggested to support our findings.

Analysis and interdependence of morphometric characters in the Hill stream fish Mastacembelus armatus (Lacepede) from Garhwal Himalaya

Study of morphometric characters is generally carried out for species identification in fish biology. It includes the measurements of all body lengths and their inter relationships in terms of ratios and percentages to the independent lengths (Total length, standard length and head length). Present paper deals with the analysis of various morphometric characters with species characteristics in Mastacembelus armatus (Lacepede), which is one of the most important eel like hillstream fish belonging to order Mastacembeliformes and family Mastacembelidae from river Western Nayar (290 45’ to 300 15’ latitude and 780 34’ to 790 12’ longitude ). Total length, standard length and head lengths were considered as an independent variables in ratio of which other lengths (caudal length, pre orbital length, post orbital length, maximum body depth, snout length and eye diameter) were analysed. The maximum size of fish was observed as 60 cm and the minimum being 10 cm. By using regression and correlation analysis, the modelling of data is presented to find out their interrelationship. The closest correlation was in between total length and standard length (r= 0.999) and the farthest between total length and caudal length ( r= 0.878). The linearity of regression was tested by the analysis of variance (ANOVA) which showed that all the relationships were significant at the level of 5 % significance. The multivariate analysis was also done by using cluster technique which sowed except caudal length rest all characters were forming a close cluster.

Morphometric and Meristic traits of four flatheads (family: Platycephalidae) occurring along the East coast of India

Study on a meristic traits of Kumococius rodericensis Sorsogona tuberculata Platycephalus indicus and Rogadius serratus (family Platycephalidae), occurring along the East coast of India, was conducted to find easily differentiating traits. The study was based on the samples collected from landing centers situated along the East coast of India, during February 2015 to March 2016. A total of thirty-one morphometric and meristic characters were measured, counted and subjected to statistical analysis using software Statistica. Among eighteen morphometric measurements, five measurement (distance between upper and lower jaw, length of upper preopercular spine, snout length, maximum length of first dorsal spine, maximum length of second dorsal spine) did not show difference when subjected to factor analysis. Varimax raw factor rotation on factor loading 0.7 were selected for scatterplot of canonical score among root 1 and root 2, which revealed existence of distinct group of species. Number of gillrakers, spot on caudal fin, number of pored scale on lateral line and preopercular spine revealed significant variations among the species. The proportional measurements with their head length (HL) viz. Preorbital length: head length (POL:HL), Inter orbital width: head length (IOW:HL), and maximum eye diameter: head length (MED:HL) also revealed significant difference among the species. The study revealed certain morphological characters those can easily identify the flathead species.

Morphological comparison of western and eastern populations of Caspian kutum, Rutilus kutum (Kamensky, 1901) (Cyprinidae) in the southern Caspian Sea

This study aimed to investigate morphological differences of western and eastern populations of Caspian kutum Rutilus kutum in the southern Caspian Sea and its providing length-weight relationships and condition factor (CF). A 13-landmark based morphometric truss network system was used to investigate the hypothesis of population fragmentation of western and eastern populations of this species. The studied populations were differentmorphologically based on pre anal, body height, distance from pectoral fin to ventral fin, distance from pectoral fin to anal fin, caudal peduncle length, head length, pre orbital, pre ventral, and dorsal length. The results also revealed a negative allometry (b<3) of length-weight relationships for both sexes. Maximum condition factors was found in March. The results suggest distinct stocks in the western and eastern of Caspian Sea for fisheries management.

Apletodon gabonensis, a new species of clingfish (Teleostei: Gobiesocidae) from Gabon, eastern Atlantic Ocean

The clingfish Apletodon gabonensis sp. nov. is described on the basis of seven specimens and colour photographs from Gabon, eastern Atlantic Ocean. The species is small, apparently not exceeding 20 mm total length; it is characterized by having 5 dorsal-fin rays, 4-5 anal-fin rays, 25-27 pectoral-fin rays, head width in males 2.6-4.7 in SL, anus in males with urogenital papilla present but not pronounced; snout long, broad, anteriorly truncate in male, narrower and rather pointed in female; preorbital length 1.8-3.8 in head length; conspicuous maxillary barbel absent in both sexes; disc with 10-12 rows of papillae in region A, 5 rows of papillae in region B, and 5-7 rows of papillae in region C. The new species is compared with the other species of the genus; a key to the males of the 6 known species of the eastern Atlantic genus Apletodon is presented.

Trophic specialization and morphological divergence between two sympatric species in Lake Catemaco, Mexico.

The association of morphological divergence with ecological segregation among closely related species could be considered as a signal of divergent selection in ecological speciation processes. Environmental signals such as diet can trigger phenotypic evolution, making polymorphic species valuable systems for studying the evolution of trophic‐related traits. The main goal of this study was to analyze the association between morphological differences in trophic‐related traits and ecological divergence in two sympatric species, Astyanax aeneus and A. caballeroi, inhabiting Lake Catemaco, Mexico. The trophic differences of a total of 70 individuals (35 A. aeneus and 35 A. caballeroi) were examined using stable isotopes and gut content analysis; a subset of the sample was used to characterize six trophic and six ecomorphological variables. In our results, we recovered significant differences between both species in the values of stable isotopes, with higher values of δ15N for A. caballeroi than for A. aeneus. Gut content results were consistent with the stable isotope data, with a higher proportion of invertebrates in A. caballeroi (a consumption of invertebrates ten times higher than that of A. aeneus, which in turn consumed three times more vegetal material than A. caballeroi). Finally, we found significant relationship between ecomorphology and stable isotopes (r = .24, p < .01), hence, head length, preorbital length, eye diameter, and δ15N were all positively correlated; these characteristics correspond to A. caballeroi. While longer gut and gill rakers, deeper bodies, and vegetal material consumption were positively correlated and corresponded to A. aeneus. Our results are consistent with the hypothesis that morphological divergence in trophic‐related traits could be associated with niche partitioning, allowing the coexistence of closely related species and reducing interspecific competition.

Sexual dimorphism in black jaw tiliapia (Sarotherodon melanotheron) and banded jewelfish (Hemichromis fasciatus) from the Great Kwa River, Calabar, Nigeria

AbstractIn this study, the pattern and magnitude of sexual dimorphic differences have been investigated in black jaw tilapia (Sarotherodon melanotheron) (n = 160; 74 males and 86 females) and banded jewelfish (Hemichromis fasciatus) (n = 120; 42 males and 78 females) from the Great Kwa River, Calabar, Nigeria. Fish samples were collected between July and December 2015. Fourteen morphometric variables, including body weight, total length, standard length, body depth, cheek depth, pre-orbital length, postorbital length, pectoral fin length (right and left), pelvic fin length (right and left), head length, gonad weight, eye diameter and four meristic variables, including number of pectoral fins (right and left) and number of pelvic fins (right and left), were taken using standard methods. Size-adjusted morphometric measurements subjected to step-wise discriminant function analysis were used to determine predictor variables to morphologically differentiate sexes for both species; magnitude of dimorphism between sexes was estimated using percentage classification accuracy of the discriminant function analysis. From the discriminant function analysis, the pectoral fin length and gonad weight positively contributed significantly to morphometric dimorphism (magnitude=69.2%) in male and femaleS. melanotheronsuggesting adaptation for reproductive function; while forH. fasciatusthe body depth and standard length were important contributors to sexual dimorphism (magnitude=84.2%) suggesting size dimorphism for aggressiveness, territorial behavior and improving swimming performance. Overall, our results indicate that the different magnitude of sexual dimorphism between the two species could be attributable to the type and functional role of sexual dimorphic traits.