The chromosomal data within the genus Parauchenoglanis is scarce. The two main species of the genus identified in Nigeria are P. buttikoferi and P. monkei. The chromosome of P. monkei was assessed in this study to provide information on the diploid number and karyotype. Samples (n=40) were collected in Opa River, Ile-Ife, Osun State, Nigeria. The chromosomes of the specimen were extracted using the Giemsa staining technique. The mitotic chromosome spread has a diploid chromosome number of 2n=50. The autosomal fundamental number was 55, while the karyotype formula was 2n=2M+ 8m+40T. The diploid chromosome number of 50 obtained for P. monkei is within the range for catfishes

Amusan, D. J.

Popoola, M.O.

English

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CHROMOSOMAL STUDIES OF THE AFRICAN DOTTED CATFISH Parauchenoglanis monkei (KEILHACK 1910)Popoola, M.O.* and Amusan, D. J.Department of  Zoology, Obafemi Awolowo University, Ile-Ife, Nigeria*Corresponding Author: (Received: 7th February, 2022; Accepted: 15th September, 2022)The chromosomal data within the genus Parauchenoglanis is scarce. The two main species of  the genus identified in Nigeria are P. buttikoferi and P. monkei. The chromosome of  P. monkei was assessed in this study to provide information on the diploid number and karyotype. Samples (n=40) were collected in Opa River, Ile-Ife, Osun State, Nigeria. The chromosomes of  the specimen were extracted using the Giemsa staining technique. The mitotic chromosome spread has a diploid chromosome number of  2n=50. The autosomal fundamental number was 55, while the karyotype formula was 2n=2M+ 8m+40T. The diploid chromosome number of  50 obtained for P. monkei is within the range for catfishes.Keywords: Parauchenoglanis, Chromosome, Diploid number, Karyotype.popoolam@oauife.edu.ngABSTRACT371Ife Journal of Science vol. 24, no. 2 (2022)INTRODUCTIONCatfishes belong to the order Siluriformes (Suborder Siluroidei) and currently comprise 4019 valid described species and 500 genera assigned to 39 families (Fricke et al., 2022). The catfishes are distributed across South America, Africa, Europe, and Asia. Globally, the population of  catfishes is about one-third of  freshwater fish fauna (Jayaram 2009). However, the exact number of  catfish families is unclear because of  conflicting views about family-level classification (Sullivan et al., 2006; Ferraris, 2007; Diogo and Peng, 2010). According to Sullivan et al. (2006), Mochokidae, Malapteruridae, Amphiliidae, Claroteidae, Lacantuniidae, and Schilbeidae were described as the 'Big Africa' catfishes. Mo (1991) classified the family Claroteidae into two subfamilies: the Claroteinae, with seven genera, and the Auchenoglanidinae, with six genera, including Parauchenoglanis. The genus Parauchenoglanis currently comprises nine species (Ferraris, 2007). They include P. ahli (Holly, 1930), P. balayi (Sauvage, 1879), P. buettikoferi (Popta, 1913), P. longiceps (Boulenger, 1913), P. ngamensi (Boulenger, 1911), P. monkei (Keilhack 1910), P. pantherinus (Pellegrin, 1929), P. altipinnis (Boulenger, 1911), and P. punctatus (Boulenger, 1902). The distribution range of  members of  the genus Parauchenoglanis (particularly P. punctatus) includes West, Central, and Southern Africa (Geerinckx et al., 2004). Based on available data, P. monkei and P. buettikoferi are members of  the genus Parauchenoglanis and are widely distributed in Nigeria. P. buettikoferi was first reported from the Warri River (Geerinckx et al., 2004), while P. monkei has been described from the Lower Cross River (Teugels et al., 1992). P. fasciatus, P. monkei, and P. guttatus used to have individual species statuses until recently. Geerinckx et al. (2004, 2013) reported no distinguishing features to discriminate the two fishes: P. fasciatus, and P. guttatus. However, Fricke et al. (2022) showed that P. fasciatus and P. guttatus are synonyms of  P. monkei. As a follow-up to the critical review of  taxonomic status within the genus, this study assessed the chromosome complement of  P. monkei as there are no reports on the underlying chromosome complement of  the fish. Generally, the interest in the karyological data of  catfishes is hinged on its importance in aquaculture. This study, therefore, presents the first karyological data of  P. monkei. Such data is essential to provide further corroborative evidence(s) alongside other taxonomic evaluation methods to establish the taxonomic identity of  living organisms.MATERIALS AND METHODSLive samples (n=40) of  P. monkei were collected from the Opa River between November and December 2019. The fish samples were kept in a bucket with a bubble-box aerator and transported to sets of  aquaria in the Department of  Zoology, Obafemi Awolowo University, Ile-Ife, Nigeria. https://dx.doi.org/10.4314/ijs.v24i2.16372The fishes were identified using standard identification keys (Paugy et al., 2003; Geerinckx et al., 2004). P. monkei can be identified with the following features. First, the preorbital head length is not greater than its head height. The barbels are relatively short, with the maxillary barbel not reaching beyond the base of  the pectoral fin spine. The anterior edge of  its pectoral spine is coarsely serrated, with numerous small serrations, more numerous than those along the posterior edge. Overall, the colouration is light brown to greyish brown with five or six (exceptionally four or seven) dark vertical bands on flanks that sometimes appear to consist of  large, merging spots. These spots may be present between these bands, including the head and fins.Metaphase chromosomes were prepared from the gill tissue of  the specimens (n=20) and analyzed. The fishes were injected with 0.02 ml/gram of  colchicine from a stock of  0.05% wt/vol to commence the chromosome extraction. The injection was administered at the muscle base of  the dorsal fin. About three hours after the colchicine treatment, the specimens were sacrificed, and the gills were removed. The gill tissues were placed in a hypotonic solution of  0.56% KCl for 30 min (to open the cell membrane) and squashed to homogeneity in a mortar with a pestle. The suspension was spun at 1000 rpm for 10 min and the pellets were fixed in a freshly prepared Carnoy's fixative (ethanol/acetic acid: 3:1 dilution). The cell suspension was spread on a microscope slide at a height, air-dried, and stained with 6% Giemsa stain for 25 min. The images of  the chromosome spreads were obtained using a camera (Omax A35140U model, USA) attached to a trinocular microscope (Omax G013055005, USA). Further processing of  the images was done using the GNU image manipulation program, GIMP 2.10.8. Also, the length of  the chromosomes with the corresponding idiogram was determined using the software Karyotype 2.0 (Altinordu et al., 2016). The morphological conformation of  the chromosomes was classified as previously described by Levan et al. (1964).Figure 1: The picture of  Parauchenoglanis monkei.RESULTS The chromosome spread obtained for P. monkei is shown in Figure 2. The karyotype of  P. monkei revealed a diploid number of  2n = 50 (Figure 3). The karyotype consists of  four metacentric, eight submetacentr ic,  and for ty  te locentr ic  chromosomes. The corresponding autosomal fundamental number of  autosomal arms (Nf) was 55 with a karyotype formula of  2n=2M+ 8m+40T. The morphology of  the chromosome (idiogram) is presented in Figure 4. Table 1 describes the karyological parameters, i.e., the chromosome arm length arm ratio and the nomenclature of  each of  the chromosomes. The total length of  the chromosomes ranged from 0.01 to 0.03 µm. Popoola and Amusan: Chromosomal Studies of  the African Dotted Catfish Parauchenoglanis monkei373Figure 2: Mitotic chromosome spread of  Parauchenoglanis monkei (2n =50).Figure 3: Karyotype of  Parauchenoglanis monkei.Popoola and Amusan: Chromosomal Studies of  the African Dotted Catfish Parauchenoglanis monkei374DISCUSSIONThe dearth of  karyological information among the catfishes of  Africa is high (Arai, 2011), and most scientific studies have focused on the members of  the family Clariidae (Oyeyemi et al., 2011). This is the first report of  the diploid chromosome complement number of  P.  monkei, and probably the first report of  chromosome complement of  any species of  the genus  Parauchenoglanis. The diploid number of  chromosomes of  50 observed in this study is within the range of  variation in the chromosome complement number of  members of  the suborder Siluroidei. Unlike Cypriniform fishes with a highly stable chromosome number, the Siluroidei fishes exhibit a great diversity of  chromosome numbers. In the Siluriodei, each family has a broad range of  chromosome                            Measurement  (µm)                  Relative length(%)  Chromosome       ( n) Long Arm (l) Short Arm (s)  Total Length (c) Long  Arm (l’) Short Arm (s’)  Total  Length (c’) Centromeric Index(100s/c) Nomenclature  1 0.02 0.01 0.03 8.91 0.78 9.69 8.05 Median(m) 2 0.01 0.01 0.02 6.41 0.77 6.41 12.01 Sub-median(sm) 3 0.03 0.00 0.03 4.21 0.76 4.98 15.26 Sub-median(sm) 4 0.03 0.00 0.03 4.94 0.74 4.94 15.00 Sub-median(sm) 5 0.02 0.01 0.03 4.79 0.70 4.79 14.61 Sub-median(sm) 6 0.01 0.00 0.01 4.79 0 4.79 0 Terminal(T) 7 0.03 0.00 0.03 4.53 0 4.53 0 Terminal(T) 8 0.03 0.00 0.03 3.43 0 4.21 0 Terminal(T) 9 0.02 0.00 0.02 4.19 0 4.19 0 Terminal(T) 10 0.03 0.00 0.03 3.98 0 3.98 0 Terminal(T) 11 0.03 0.00 0.03 3.98 0 3.98 0 Terminal(T) 12 0.03 0.00 0.03 3.11 0 3.89 0 Terminal(T) 13 0.02 0.00 0.02 3.1 0 3.88 0 Terminal(T) 14 0.03 0.00 0.03 3.75 0 3.75 0 Terminal(T) 15 0.03 0.00 0.03 3.75 0 3.75 0 Terminal(T) 16 0.03 0.00 0.03 2.84 0 3.61 0 Terminal(T) 17 0.02 0.01 0.03 3.3 0 3.30 0 Terminal(T) 18 0.01 0.00 0.01 2.51 0 3.29 0 Terminal(T) 19 0.03 0.00 0.03 3.23 0 3.23 0 Terminal(T) 20 0.03 0.00 0.03 2.2 0 2.97 0 Terminal(T)21 0.02 0.00 0.02 2.65 0 2.65 0 Terminal(T)22 0.02 0.00 0.02 1.88 0 2.65 0 Terminal(T)23 0.02 0.00 0.02 2.51 0 2.51 0 Terminal(T)24 0.02 0.00 0.02 2.33 0 2.33 0 Terminal(T)25 0.01 0.00 0.01 1.55 0 1.55 0 Terminal(T)Table 1: The chromosome measurement and nomenclature of  Parauchenoglanis monkei.Figure 4: An idiogram of  the karyotype of  Parauchenoglanis monkei showing the morphology of  the chromosome.Popoola and Amusan: Chromosomal Studies of  the African Dotted Catfish Parauchenoglanis monkei375numbers per species, so it has been difficult to establish a general pattern of  chromosome diversification in phyletic lineages (Kim et al., 1982). For example, Liobagrus undersoni (Amblycipitidae) has 2n = 28 chromosomes (Kim et al., 1982), while Corydoras aeneus (Callichthydiae) has 2n = 132 chromosomes (Scheel et al., 1972). The situation is the same in African catfishes though few studies have been conducted. Auchenoglanis occidentalis (Claroteidae) has 2n = 56; Bagrus docmak (Bagridae) 2n = 54; Chrysichthys maurus (Claroteidae) 2n = 70; C. aurutus 2n = 72 while Clarotes laticeps 2n = 70 (Volckaert and Agnese, 1996). In addition, the karyotypes of  Clarias gariepinus and Heterobranchus longifilis (Clariidae) are 2n = 56 and 52, respectively (Ozouf-Costaz et al., 1990). However, the modal frequency of  chromosome number of  the suborder Siluriodei is 56. The increase in chromosome numbers observed across the various karyotype of  members of  the suborder Siluriodei may be due to centromeric fissions which transform a chromosome with two arms into two chromosomes with one arm (Volckaert and Agnese, 1996).Many representatives of  several fish orders, such as Characiformes, Cypriniformes, Siluriformes, and Gymnotiformes have karyotypes dominated by bi-armed chromosomes (Molina et al., 2014). However, the chromosome complement observed in the present study is mainly telocentric. Further, Molina et al. (2014), reported a prevalence of  karyotypes with few (< 33%) or many (> 66%) acrocentric chromosomes and a low number of  karyotypes with balanced numbers of  mono- and bi-brachial elements in many orders of  fishes. Also, the study observed a parallel trend toward a higher number of  karyotypes with a prevalence of  monobrachial chromosomes occurring in phylogenetically close orders (e.g., Perciformes and Tetraodontiformes, and in the order Mugiliformes) and in clades with a prevalence of  bibrachial elements (e.g. Characiformes, G y m n o t i f o r m e s ,  S i l u r i f o r m e s ,  a n d  Cypriniformes). The variation in chromosome complement is not uncommon, especially within the Siluriformes. For Pseudoplatystoma reticulatum, different authors reported different karyotype formulas showing d i f fe rent  propor t ions  of  acrocent r i c  chromosomes even for the same species (Neto et al., 2011). Such variation in chromosome complement could be pieces of  evidence of  unique biogeography history or karyotype evolution processes due to geographic isolation and an interruption in gene flow and may have no deep evolutionary or taxonomic significance compared to gross changes in chromosome number. On the other hand, these differences could also be related to methodological problems or chromosome condensation. But the spread of  this chromosome complement within the group should be assessed to determine the trend and the biological importance.In conclusion, this study is significant since karyological data have been employed in solving problems relating to chromosome number, functional arm, phyletic relationship, taxonomic status, and the possibility of  speciation among the studied species.REFERENCESAltinordu, F., Peruzzi, L., Yu, Y. and He, X. 2016. A tool for the analysis of  chromosomes: KaryType. Taxon, 65(3): 586-592.Arai, R. 2011. Fish Karyotype: A Check List. 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Chromosomal studies of the African dotted catfish Parauchenoglanis monkei (Keilhack 1910)

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Chromosomal studies of the African dotted catfish Parauchenoglanis monkei (Keilhack 1910)

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