Neolissochilus stracheyi ( Day 1871 )

Hoàng, Ức, Ạm, Ạnh Ph, Durand, Jean-Dominique, Ần, Ngân Tr Ọng Tr & Phan, Phúc Đình, 2015, Mahseers genera To r and Neolissochilus (Teleostei: Cyprinidae) from southern Vietnam, Zootaxa 4006 (3), pp. 551-568 : 563-565

Neolissochilus stracheyi ( Day 1871)

Specimens examined: upper Ea Krong No drainage: upper Mekong basin in montane evergreen forest in Bidoup- Núi Bà National Park, Lâm Đồng Province, Vietnam (12°14’57.47” N 108°40’31.41” E, 1101 m): UNS00603, 193 mm SL, 13 March 2012; UNS00604, 256 mm SL, 19 February 2012 (12°15’36.6” N 108°30’44.5” E, 856 m); UNS00865–871, 212– 322 mm SL, 8 March 2013 (12°15’5.25” N 108°38’32.48” E, 1025 m); UNS00863–864, 160– 163 mm SL, 5 March 2013 (12°14’57.47” N 108°40’31.41” E, 1101 m); UNS00872, 308 mm SL, 25 June 2014 (12°16’23.68” N 108°26’30.17” E, 672 m); UNS00948–949, 287– 428 mm SL, 22–24 January 2015 (12°16’48.63” N 108°31’40.85” E, 754 m); UNS00950, 534 mm SL, 22 January 2015 (12°16’47.88” N 108°30’20.75” E, 720 m); the An Lão River, Bình Định Province, Vietnam (14°40’30.6” N 108°54’13.4” E, 547 m): UNS00768, UNS00770, UNS00870, 113–130 mm SL, 21 January 2013 ( Fig. 2 ).

Diagnosis. Neolissochilus stracheyi differs from N. hendersoni and N. soroides in lateral stripe present vs. absent. Neolissochilus stracheyi differs from N. benasi in lateral scales 24–28 vs. 31–32, transverse scale rows 3/1/ 2, vs. 4/1/3. Neolissochilus stracheyi in this study is similar to N. blanci from Laos ( Pellegrin & Fang 1940, Rainboth et al. 2012) in living colour, morphometric and meristic characters.

From 13 March 2012 to 22 January 2015 a sample of 17 fresh N. stracheyi was collected from the upper Krong No River in Bidoup-Núi Bà National Park. The following data were obtained: Neolissochilus -like morph: 16 individuals, 113–534 mm SL with moderately developed lips and without a submentum on the lower lip ( Fig. 4 l, m). Among this morph, there were two body-colour types: bronze with a slate-grey lateral stripe ( Fig. 7 a, b, e) and golden lacking a lateral stripe and becoming progressively lighter to silvery white below ( Fig. 7 c). The lateral stripe appears in preserved specimens of both body colour types. Individuals of both types have the caudal fin deeply forked, but the lateral stripe type has a convex distal margin on each lobe of the caudal fin, and the golden type has a straight distal margin on each lobe.

Tor -like morph: 1 individual, 428 mm (UNS00949): rostral hood straight and pointed. Lips thick, fleshy; upper lip rolled backwards and upwards without median projection; median lobe of lower lip broad, thick and long as the most highly developed mentum in species of the genus Tor . Body-colour bronze with faint slate-grey lateral stripe ( Figs. 4 i, k and 7d).

Ecology. All specimens of the new species and new records were found in the Ea Krong No drainage, consisting of montane mixed pine and evergreen forest ( Fig. 8 c). Our survey also recorded the occurrence of N. stracheyi in the An Lão River at ~ 500 m, in the Krong Ana River at ~ 431m elevation, Chư Yang Sin National Park (12°29’50.9” N 108°20’29.6” E) and the Đồng Nai River at ~ 650 m elevation, Tà Đùng Nature Reserve (11°45’10.4” N 108°00’3.0” E). While N. stracheyi occurs along the main river and in streams between 596–1112 m, T. mekongensis and T. tambra occur in lower elevations between 596– 850 m. Water conditions where N. stracheyi occur were 17−26 °C, with pH 6.5−7.66, DO 79−88.6%, conductivity 10–34 µS.cm -1and flow velocity 0.17−0.77 m /s. Water conditions where Tor occur were 21−26 °C, with pH 7−7.66, DO 79−80.6%, conductivity 32−34 µS.cm -1and flow velocity 0.20−0.77 m /s.

Mahseers of the Krong No River occurred in lotic habitats of main streams, particularly in deep pools. In the early wet season (June −July), mature individuals move to the depositional zone in moderate flowing pools (5–7 m deep and 20–50 m wide) with detritus and fallen leaves for gonadal development (villagers, pers. com.). The juveniles often inhabit shallow areas with mixed silt and sand, slower flow and submergent plants. They share this habitat with Poropuntius sp., Hampala macrolepidota , and Onychostoma krongnoensis . During wet season surveys (October 2011, May 2013 and June 2014), many juvenile fishes were observed ( Fig. 8 a).

Mahseers of Tor and Neolissochilus usually roam in shoals of 20–30 individuals in swift currents or in slow flowing pools (2–3 m deep) for foraging ( Fig. 8 b). They feed on plant matter, fallen fruits and insects from riparian vegetation ( Rainboth 1996). Villagers claim that mahseers and carps are often found inside the underwater rock caves or trunks of large trees in the stream bank.

All specimens of T. dongnaiensis were found in the middle Đồng Nai drainage between 140−200 m ( Fig. 8 d). Water conditions were 23−26 °C, pH 7−7.66, DO 75−81.7%, conductivity 33−40 µS.cm -1and flow velocity 0.05−1.3 m /s. This species shares habitat with Labeo spp., Gyrinocheilus aymonieri , Cosmocheilus harmandi , Hampala macrolepidota , Hypsibarbus spp., Wallago attu , Bagarius yarrelli , and Hemibagrus spp.

Figures

FIGURE 2. Type localities of Tor mekongensis (black star) and T. dongnaiensis (white star), and collection localities of T. sinensis (black triangle), and Neolissochilus stracheyi (white cross).

FIGURE 4. Head of Tor sinensis UNS 00873, 205 mm SL (a, c) front view, (b, d) ventral view; T. dongnaiensis holotype UNS 00859, 240 mm SL (e) front view, (f) ventral view; T. mekongensis holotype UNS 00877, 337 mm SL (g) front view, (h) ventral view; Neolissochilus stracheyi Tor - like morph UNS 00949, 428 mm SL (i) front view, (k) ventral view; Neolissochilus stracheyi Neolissochilus - like morph UNS 00872, 308 mm SL (l) front view, (m) ventral view. Scale 10 mm.

FIGURE 7. Neolissochilus stracheyi: (a) sub-adult (UNS 00864, 163 mm SL) in life, (b) adult (UNS 00866, 238 mm SL) in life, (c) golden adult (UNS 00948, 287 mm SL) in life, (d) Tor - like morph adult (UNS 00949, 428 mm SL) in life, (e) female adult (UNS 00950, 534 mm SL) in life; lateral views. Scale 10 mm.

FIGURE 8. Mahseers in the wild: (a) juvenile Tor at night in shallow area near stream bank; (b) shoal of Neolissochilus stracheyi in slow-flowing pool, high elevation main river with riparian vegetation at type locality of Tor mekongensis; (c) Krong No River (12 ° 15 ’ 9.37 ” N 108 ° 26 ’ 23.18 ” E, 650 m); (d) Đ ồng Nai River (11 ° 39 ’ 20.8 ” N 107 ° 16 ’ 04.7 ” E, 195 m).