[incomplete diagram - redrawn from various sources (for personal used only)]Clariidae or walking catfishes naturally occur in Africa, Minor Asia, the Indian subcontinent and East and Southeast Asia. In Asia, only three genera are known (Teugels et al., 2001) but Nelson (2004) only mentioned two genera, vis. Encheloclarias and Clarias which is the most diverse with some 18 species presently recognised as valid (Ferraris, 2007). Many of the species are of great economical importance in both fisheries and aquaculture. The taxonomy of the Asian Clarias is only recently well established.
The genus Clarias is a group of fish commonly known as walking catfishes, an air-breathing fish naturally found in inland waters bodies throughout much of the Old World. They are easily identified by an anguilliform body, long-based dorsal and anal-fins, head dorsoly depressed, a broad terminal mouth with four pairs of barbels, eyes with free orbital margin and located dorsolaterally, large and well-developed neurocranium and the presence of an accessory breathing organ comprised of modified gill arches. The diversity of the clariid catfishes of Southeast Asia have increased tremendously in the past few years. Although most of Clarias diversity is found in Africa (Teugels, 1986), at least 18 species which are currently considered valid are known from Southeast Asia.
At least seven species of clariid catfishes, vis. Clarias batrachus (Linnaeus, 1758), Clarias batu Lim & Ng, 1999, Clarias leiacanthus Bleeker, 1851, Clarias macrocephalus Gunther 1864, Clarias meladerma Bleeker, 1846, Clarias nieuhofii Valenciennes, 1840 and Clarias sulcutus Ng, 2004 thrived naturally in inland waters including in islands around Peninsular Malaysia. Of the seven species, Clarias batu and Clarias sulcutus were only found in Pulau Tioman and Pulau Redang, respectively and the rest have a natural distribution throughout the country. Ng (1999) erected three artificial species-group of Southeast Asian Clarias; (i) short body with 60-76 dorsal-fin rays and an extremely short distance between the tip of the occipital process and the origin of the first dorsal-fin ray, (ii) short body, with 62-74 dorsal-fin rays but a longer distance between the tip of the occipital process ant the base of the origin of the first dorsal-fin ray than the first group, and (iii) long and slender body with 87-106 dorsal-fin rays with distance between the tip of occipital process to the origin of the first dorsal-fin ray similar to the second group. Walking catfishes of Peninsular Malaysia that falls in the first group are C. batrachus, C. macrocephalus, C. meladerma and C. sulcutus. The second group includes C. batu and C. lieacanthus while the third group consists of C. nieuhofii.
Two species of the walking catfishes, vis. C. batu and C. sulcutus are islands’ endemic, thus catfish species that found on the mainland of Peninsular Malaysia, i.e. C. batrachus, can be distinguished from the other species (C. leiacanthus, C. meladerma and C. nieuhofii) by using the diagnostic characters of C. batrachus – narrow snout, in dorsal view with straight lateral outline and convex anteriorly, 63-74 dorsal-fin rays (vs. 82-108 in C. nieuhofii), distance between occipital process and origin of dorsal-fin relatively long (5.5-8.9% SL vs. 1.2-5.6% SL in C. macrocephalus, C. meladerma), frontal fontanelle long and thin (vs. short and squat in C. leiacanthus and C. nieuhofii), anterior margin of pectoral spine rugose and with irregular bumps (vs. with distinct serrations in C. meladerma). Other non-diagnostic characters: tip of supraoccipital process rounded, with narrow base (vs. base slightly wider in C. leiacanthus), distance from base to tip is slightly bigger in C. batrachus (vs. a bit smaller in C. leiacanthus and C. neiuhofii).
According to Ng & Kottelat (2008), C. batrachus is only known to river drainages in Java and records of other C. batrachus from mainland Southeast Asia and the rest of Sundaic Southeast Asia are probably to refer to two separate, undescribed species. The Malay peninsula and Borneo (identified by the authors as C. aff. batrachus ‘Sundaland’) which is not considered conspecific with the Javanese materials because the C. batrachus ‘Sundaland’ population have wider frontal fontanelle than those from Java. For now, the material from Peninsular Malaysia is referred as C. batrachus in its widest sense until its true identity is resolved.
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