New species of stinging catfish Heteropneustes nani ( Siluriformes : Heteropneustidae ) from Noakhali , Bangladesh

The Meghna deltaic region in Noakhali, Bangladesh is endowed with favourable diverse freshwater ecosystems for varieties of fishes. Here a new species, Heteropneustes nani sp. nov. is described after detailed morphological examination and careful comparisons with other congeners. The new species H. nani differs from other congeners in having shortest standard length, greater head length than body depth, terminal mouth with equal jaws, separated pectoral spine from rays and bears antrorse serrae along entire inner and outer edges, and united anal and caudal fin.

The stinging catfishes are often inhabited in ponds, ditches, canals, flooded rice fields, swamps, marshes, waterlogged areas and rivers of Bangladesh.The air breathing apparatus enables the fish to survive in low water depth, even in turbid and oxygen deficit condi tions.The fishes are commercially important due to high market price and nutritional value, i.e. low fat content, and source of high amount of iron and calci um.However, to date, only H. fossilis is reported from Ban gladesh (Bhuiyan, 1964;ShaFi & QuDDus, 1982;Rahman, 1989;siDDiqui et al., 2007;GaliB et al., 2009;SamaD et al., 2010;Hossain 2011) with an observation of high level of genetic variability within and between the populations (Nasren et al., 2009).In this study, dur ing a fish biodiversity survey in 2011 -2012, we ob served that one species of Heteropneustes occurred in the freshwater ecosystems of Noakhali clearly different from its congeners and herein describe it as a new spe cies, H. nani.

Materials and methods
During a fish biodiversity survey in 19 stations of great er Noakhali district (i.e.Feni, Laxmipur and Noakhali; Fig. 1) during January 2011 to December 2012, the au thors observed a phenotypically different stinging cat fish among catches of local fishers (Fig. 2).About 100 live adult specimens of this species were collected and brought to the Fisheries Laboratory of the Institute of Marine Sciences and Fisheries of the University of Chit tagong for taxonomic identification.Moreover, data on fish habitats, abundance and socioeconomics were col lected through field visit and interview of fishers, trad ers and local residents.High resolution digital photo graphs were taken to analyze colour and morphological characteristics of the specimens.Previously published descriptions of species and morphometric data of dif ferent specimen of Heteropneustes spp.those deposited in different museum were used to make comparison with the newly described species.Measurements were made point to point for each sample with digital cali pers and the data were recorded to 0.1 mm.Counts and measurements were made on the left side of the speci mens.Subunits of head are presented as proportions of the head length (HL).HL and measurements of the body parts are given as proportions of standard length (SL).Measurements follow the keys of huBBs & laGler (2004) and include: TL (total length); SL; HL; HW (head width); ED (eye diameter); SNL (snout length); BD (body depth); AFL (anal fin length); DFL (dorsal fin length); PFL (pectoral fin length); PSL (pectoral spine length); CFL (caudal fin length); BL1 (first barbel length); BL2 (second barbel length); BL3 (third barbel length) and BL4 (fourth barbel length).The examined specimens are preserved at the Museum of the Institute of Marine Sciences and Fisheries (MMSF), University of Chittagong, Bangladesh.Moreover, H. nani differs in having body colour blackish with two indistinct lateral bands on flank, but the ventral surface lighter (vs.yellow or dark purplish brown above and ventral side lighter; H. fossilis bears two longitudinal yellowish stripes on each side: one is above the lateral line and another is below the lateral line).In case of H. kemratensis, the colour is light gray under the head and, the belly shows two narrow and pale gray longitudinal bands parallel to either side of the body, i.e. one above and one below the lateral line, fading out behind.On the contrary, H. longipectoralis characterize uniformly dark brown body without yel lowish lateral bands.H. nani also differs from other Heteropneustes species by having pectoral spines which are completely separated from rays with 9 -10 antrorse serrae along inner edge and 13 -15 in outer edge (Vs.attached to rays by membrane with 3 -4 antrorse serrae along inner edge at anterior tip in H. fossilis, separated from rays and serrated along inner edge in H. microps,   Description.The morphometric data for adult H. nani is shown in Tab. 2. Body of H. nani is short and sub cylindrical up to the pelvic fin base, compressed behind (Fig. 2).Head is depressed, head length (16.64 -19.74 % with a mean 18.01 % of SL) is less than body depth (14.42 -21.79 % with a mean 17.59 % of SL) and snout length ranges between 23.12 -27.83 % of HL with a mean 25.13% of HL.Small terminal mouth, length of jaws is almost equal to fleshy lips, teeth in villiform bands on jaws.Eye small, eye diameter ranges between 8.47 -11.12 % of HL with a mean 9.26 % of HL and about onethird of snout length.Barbel 4 pairs, 1 pair from the corners of the mouth, 2 pairs from the chin and extend to about the end of the pectoral fins, the short er 1 pair at the hinder nostrils.The first, second, third and fourth barbels length ranges between 20. 59 -27.77, 27.20 -42.24, 30.21 -39.23 and 22.42 -34.48 % of SL respectively with a mean 23.41 %, 31.10 %, 32.98 % and 26.13 % of SL respectively.Dorsal fin ranges be tween 11.82 -14.87 % of SL with a mean 12.89 % of SL and inserted above the ventral fin.First ray is sim ple and others are branched.Dorsal fin margin is con vex and its tip exceeds anal fin base.Pectoral fin ranges
Colouration.Body is blackish dorsally and lighter col oured ventrally in live.One indistinct lateral band on flank.Dorsal and pectoral fin light orange, ventral fin with gray edging.Numerous fine grey spots on the abdo men.
Etymology.We take great pleasure in naming the new species as a patronym for the eminent fisheries and aquaculture scientist Professor Dr Nani Gopal Das, in recognition of his continuous contribution to our re search.
Distribution.H. nani was collected from the freshwater ecosystem of Noakhali (Fig. 5) and is widely distributed in ponds, ditches, canals, flooded rice fields, swamps, marshes, waterlogged areas and rivers.
Biology and ecology.The airbreathing apparatus ena bles the fish to survive in low water depth, even in turbid and oxygen deficit conditions.During the winter season they can live in semiliquid mud and even when the mud dries up they take their bodies to the bottom of fissures and crevices formed by the cracking mud.During the study period, the physicochemical parameters were re corded as: water temperature 18 -28 °C, pH 6.5 -7.5, dissolved oxygen 4.5 -5.0 mg/l, and water transparency 45 -60 cm for a water body of 1.0 -1.8 m deep.The stinging catfish can be transported to distant markets and remain alive for several days in a little water.The consumer desired the fish due to its good table qual ity and nutritional value.In particular, the flesh of the fish is rich in iron and low fat, and a valuable source of protein for growing children, pregnant women and re covering patients.H. nani is represented by 10 -15% of the total Heteropneustis catch in the study area.Higher catches recorded from hook, trap and fixed net during NovemberFebruary (dry winter) and lower catch in AprilAugust (wet monsoon).Incidentally, this type of fish is able to deliver a stinging protein (known as poison) emanated from the venom glands around the pectoral spine (Satora et al., 2005).In humans, catfish venoms, which are reported to be neurotoxic and hemo    rays and bears antrorse serrae along entire inner and out er edges, and united anal and caudal fin.Significantly dif ferent regression lines of bivariate analysis (ANCOVA) for the pectoral spine length, pectoral fin length, head length, head width, snout length and body depth against SL of H. nani and H. fossilis (Fig. 3) also indicate that newly described species is different from its widely dis tributed geographical congeners.Moreover, H. nani is also readily distinguishable from its congeners by the fin formula of D 6 -7, P I/6 -7, V 6 -7, A 66 -69, C 10 -12.In case of H. fossilis, it is D 6 -7, P I/7, V 6, A 60 -79, C 19 (Day 1878); D I -II/5, P I/5 -6, V I/6, A+C 72 -74 for H. microps (arunachalam et al., 1999); D I/5, P I/8, V I/5, A 75 -84 for H. kemratensis (Fowler, 1937) and D 7, P I/8 -9, V 6, A 66 -73, C 18 for H. longipectoralis (Devi & raGhunathan, 1999).
In summary, the biodiversity of aquatic ecosystems of Noakhali, Bangladesh have been very poorly investi gated and several areas remain untouched, indicating that our understanding of the fish fauna of these areas is far from being complete.Therefore, a unified and compre hensive effort is needed to identify the species diversity therein as well as disseminate the results in the form of fully illustrated taxonomic key and identification guide for ease classification of freshwater fishes.

Fig. 1 .
Fig. 1.Catfish specimen collection sites from the greater Noakhali region of Bangladesh.
confluent with caudal fin † Present study; ∏ arunachalam et al. 1999; Ú Fowler 1937; ¸ Devi and raGhunathan 1999separated from rays with 10 -11 antrorse serrae along outer edge and 12 -13 along inner edge in H. kemraten sis and very faintly serrated anteriorly and internally in H. longipectoralis).Moreover H. nani can be easily dis tinguished by other congeners by having a united anal caudal fin (vs.separated by a distinct notch in H. fossilis, anal fin confluent with caudal without notch in H. mi crops, separated in H. kemratensis and anal fin not con fluent with caudal fin in H. longipectoralis).Regression lines of bivariate analysis (ANCOVA) against SL shown in Fig.3indicate that new species H. nani significantly differs from its widely distributed congener H. fossilis in terms of the pectoral spine length, pectoral fin length, head length, head width, snout length and body depth (P = 0.013, P = 0.003, P = 0.023, P = 0.024, P = 0.021 and P = 0.025 respectively).

Fig. 3 .
Fig. 3. Bivariate analysis of pectoral spine length, pectoral fin length, head length, head width, snout length and body depth against SL for H. nani and H. fossilis.

Fig. 4 .
Fig. 4. Pectoral spine pointed at the tip and distinctively separated from the rays with antrorse serrae along entire outer and inner edges of Heteropneustes nani.
Tab. 2. Summary of qualitative diagnostic characters of H. nani and the congener H. fossilis.
(wriGht, 2009)truction of red blood cells), can produce local numbness, inflammation and severe painful physi cal conditions of the limb under attack(wriGht, 2009).Warm water bath, application of luke warm turmeric paste, ejection of blood, and traditional herbal medicine are commonly used for healing.Local fishers remain ex tremely cautious to avoid its sting.