Nannoperca pygmaea, Morgan, David L., Beatty, Stephen J. & Adams, Mark, 2013

Morgan, David L., Beatty, Stephen J. & Adams, Mark, 2013, Nannoperca pygmaea, a new species of pygmy perch (Teleostei: Percichthyidae) from Western Australia, Zootaxa 3637 (4), pp. 401-411: 403-407

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Nannoperca pygmaea

sp. nov.

Nannoperca pygmaea  sp. nov.

Little Pygmy Perch Fig. 2View FIGURE 2 A

Holotype. WAM P. 33379 –001, 31.6 mm SL, Hay River, Western Australia (34 o 53.28 ’ S, 117 o 29.45 ’ E), collected by D.L. Morgan and S.J. Beatty, 9 September 2009 ( Fig. 2View FIGURE 2).

Paratypes. WAM P. 33380 –001, 10 specimens, 26.8 –38.0 mm SL, Mitchell River, Western Australia (34 o 53.15 ’ S, 117 o 29.27 ’ E), collected by D.L. Morgan and S.J. Beatty, 28 October 2009; WAM P. 33379.02, 1 specimen, 33.2 mm SL, Hay River/Mitchell River confluence, Western Australia (34 o 53.27 ’ S, 117 o 29.14 ’ E), collected by D.L. Morgan and S.J. Beatty, 9 September 2009; SAM FISHY 6: Esp.09001, Esp.09003, Esp.09004 ( Fig. 2View FIGURE 2), 3 specimens, 28.6–38.7 mm SL, Mitchell River and Hay River confluence, Western Australia (34 o 53.27 ’ S, 117 o 29.14 ’ E), collected by D.L. Morgan and S.J. Beatty, 9 December 2009.

Diagnosis. A species of Nannoperca  in having a small mouth, a deeply notched dorsal fin, a poorly developed two-part and interrupted lateral line. It is distinguished from the congeneric N. australis  , N. oxleyana  and N. variegata  in possessing an exposed and serrated preorbital bone and the jaws may just reach to below the anterior margin of the eye, versus possessing a smooth and hidden preorbital and the jaws reaching to at least the pupil. It is distinguished from N. vittata  by: the possession of 5–10 thin lateral stripes most obvious below lateral line; poorly developed tube scales versus well developed in N. vittata  ; a more distinct haloed blackish spot resembling an ocellus at the base of the caudal fin; the hind margin of the scales on the caudal peduncle are without distinct pigment as in N. vittata  ; and the belly is without a colour pattern. It is distinguished from N. obscura  in possessing a distinct ocellus at the base of caudal fin versus an indistinct barring, as well as a dark spot behind operculum and lack of dusky scale margins. It is distinguished from the other sympatric pygmy-perch species in the region, N. balstoni  , in possessing an exposed rear edge of the preorbital (compared to being hidden under the skin in N. balstoni  ), has fewer transverse scale rows (13 vs. 15–16), a smaller mouth (rarely reaching eye vs. reaching well beyond the eye), ctenoid body scales (vs. cycloid), generally fewer pectoral rays and a smaller maximum size.

Description. Dorsal-fin rays holotype VIII, 8 (paratypes VII –IX, 8 or 9); anal-fin rays III, 6 (paratypes III, 6 or 7); pectoral-fin rays 11 (paratypes 10 or 11); body scales ctenoid; lateral-line scales with marginally developed tubes; lateral line scales 18 + 13; horizontal scale rows at level of anal fin origin 13–15; gill rakers on first arch 3 + 7 (2–3 + 5–7); jaw just reaching to below anterior part of eye. Body relatively slender, laterally compressed, greatest body depth 3.0 (2.7–3.4) in SL. Head relatively short with pointed snout, its length 3.3 (2.9–3.6) in SL. Following proportions are in head length: snout length 4.7 (3.9–6.2), exposed maxilla length 4.9 (4.3–6.2), eye width 3.5 (3.3– 3.9), interorbital width 3.6 (3.1 –4.0), caudal peduncle depth 1.7 (1.5–2.1), caudal peduncle length 1.2 (1.1–1.4), caudal fin length 1.3 (1.2–1.6), pectoral fin length 1.7 (1.4–2.1), pelvic fin length 1.7 (1.5–1.9), first dorsal spine length 3.3 (2.8–4.2), first anal spine length 5.5 (4.7 –8.0), second anal spine length 2.7 (2.3–3.1), third anal spine length 3.0 (2.5–3.9) ( Tables 1, 2 and 3).

Longest dorsal spine 2 nd, longest soft dorsal ray 3 rd or 4 th, longest soft anal ray 2 nd or 3 rd, pelvic and pectoral fins usually equal in length. Reduced blackish spot behind edge of gill cover, coloration on ventral surface anterior to anus limited to one or two dark melanophores, a distinct ocellus at base of caudal fin, fins often orange, large brownish dorso-lateral blotches often merging, series of brownish mid-lateral blotches commencing behind operculum, terminating on caudal peduncle; hind margin of scales on caudal peduncle without distinct pigment; two spines on hind margin of operculum, almost equal; 5–10 thin lateral stripes most obvious below lateral line, tube scales poorly developed.

Coloration in preservative. Generally pale fins and lateral and dorso-lateral blotches light to dark brown in colour except for ventral surface, which appears opaque, thin ventro-lateral stipes more prominent than in live specimens, opercular spot distinct, haloed ocellus on caudal peduncle at base of caudal fin very distinct.

Etymology. The specific epithet pygmaea  is the feminised form of the Latin noun pygmaeus meaning “dwarf” applied as a noun in apposition, and in reference to this being the smallest of the pygmy perches. Common name Little Pygmy Perch applied in recognition of the relative small size.

Genetic assessment. The final allozyme dataset comprised genotypes at 56 putative loci for 41 fish from nine sites, and included sympatric series of both N. pygmaea  (n = 8) and N. vittata  (n = 8) from the Hay River catchment. An initial PCA ( Fig. 3View FIGURE 3) clearly demonstrated the presence of two major genetic lineages, diagnosable by a complete absence of shared alleles at 15 different allozyme loci ( Table 4). The absence of heterozygous individuals at any of the 15 diagnostic loci demonstrates that these two lineages do not interbreed in sympatry and display no evidence of introgression in allopatry, i.e. the unequivocal genetic signature of different biological species. The NJ tree among populations ( Fig. 4View FIGURE 4) further demonstrates their genetic distinctiveness. The two species display a mean Nei D of 0.34, considerably larger than the maximum between-population value of 0.06 within N. vittata  .

Dorsal spines Soft dorsal rays Soft anal rays

VI VII VIII IX 7 8 9 10 11 6 7 8 9 10

N. pygmaea  1 6 8 10 5 5 10

N. australis  1 14 59 2 1 19 48 8 2 38 35 1 N  . obscura 8 24 3 25 4 7 24 1

N. oxyleyana  2 27 1 1 25 4 25 5

N. variegata  19 2 14 7 10 11 N.  vittata 3 38 2 6 26 10 1 4 36 3 N.  balstoni 2 16 2 1 7 12 1 15 4 Discussion. Nannoperca pygmaea  represents the third species of pygmy perch (and the fourth percichthyid) discovered in Western Australia. The number of endemic freshwater fishes of Australia’s South West Coast Drainage Division is now nine and the proportion of endemic species in the region now stands at 82 %; the highest of any Australian drainage division. A recent molecular overview of pygmy perches (Unmack et al. 2011) revealed evidence for two very distinct genetic lineages among a handful of N. vittata  populations further to the west and north of the Hay River catchment. Unmack et al. (2011), based on genetic evidence, suggest that one of the two lineages warrants elevation to species status pending morphological diagnosis. Thus it is likely that there are at least four species of pygmy perch in this region, long recognised as one of the planet’s hotspots for biodiversity and endemism (Myers et al. 2000).

Pectoral rays Gill rakers

10 11 12 13 14 15 3 4 5 6 7 8 9 10

N. pygmaea  3 12 1 1 9 1 N  . australis 4 40 30 2 5 23 14 7 N. obscura  2 23 6 4 12 4 N  . oxyleyana 1 22 9 6 8 18 N  . variegata 15 6 3 5 13

N. vittata  2 10 18 10 1 5 22 9 N  . balstoni 13 7 2 2 11 3 2

Habitat and conservation considerations. Explanation of how N. pygmaea  evaded discovery for so long lies in the fact that its habitats are only seasonally accessible by vehicle and it has an extremely narrow range. In terms of distribution, N. pygmaea  is the most restricted species of pygmy perch, currently known from a geographical area of only 0.06 km 2, and a stream length of 1.2 km. It is one of Australia’s most geographically restricted freshwater fish species. Its habitats are tannin stained, acidic and shallow Melaleuca rhaphiophylla  streams ( Fig. 5View FIGURE 5). Flow is seasonal, characteristic of this ‘Mediterranean Climatic’ region, with the site on the Mitchell River drying out each summer. Although the Mitchell River supports intact natural vegetation, much of the Hay River catchment is cleared of its natural vegetation (52 %). The pools on the Hay River are therefore critical summer refuges for the species, although the catchment is becoming increasingly affected by secondary salinisation (Mayer et al. 2005). For example, between 1993 and 2002 the mean salinity of the Hay River was 2300 mg.L - 1, which was an overall increase of 400 mg.L - 1 from the previous decade (Mayer et al. 2005). Although mean conductivity in the Mitchell River generally remains below 0.5 - 1, the type locality in the Hay River increases in mean conductivity from <2.9 - 1 in winter and early spring, to almost 11 - 1 in late summer as these habitats decrease in size to small isolated pools. Stream secondary salinisation is a recognised threat to south-western Australia’s freshwater fishes (Morgan et al. 2003), and while the salinity tolerance of N. pygmaea  is unknown, it is likely to be similar to the sympatric pygmy perches N. balstoni  and N. vittata  , which have acute tolerances of 8.2 and 14.6 g.L - 1, respectively (Beatty et al. 2011). Mean winter temperatures are ~ 12 o C, increasing to over 23 o C in summer. As a consequence of the rarity and restricted geographic range of N. pygmaea  , the species requires urgent protection at the state and federal level.

TABLE 1. Mean and range (in parentheses) of proportional external measurements of Nannoperca vittata and type specimens of Nannoperca pygmaea sp. nov. from the Mitchell / Hay River catchment, expressed as a percentage of standard length (SL).

  121.58 (115.58–127.01) 124.7 123.69 (116.4–128.3)
Longest soft anal ray length