Chelonodon patoca. (Hamilton, 1822)

Britz, Ralf, Tan, Heok Hui & Rüber, Lukas, 2024, Chelonodontops bengalensis Habib et al. 2018, a junior synonym of Tetrodon patoca Hamilton 1822, with a type species designation for Chelonodon Müller 1841, Zootaxa 5519 (4), pp. 561-570 : 563-566

In his monograph on “the fishes of the River Ganges and its branches”, Hamilton (1822) treated 272 fish species, which he encountered during his two sojourns in India, 1794–1805 and 1807–1815, in the Brahmaputra and Ganges drainages ( Britz, 2019). Among them were six new species of Tetraodontidae , all of which he placed into Tetrodon : T. fluviatilis , T. patoca , T. cutcutia , T. caria , T. gularis , and T. tepa . Of these only the first three are currently considered valid ( Kottelat 2013), as Dichotomyctere fluviatilis , Chelonodontops patoca , and Leiodon cutcutia , while T. caria and T. gularis are considered synonyms of the latter, and T. tepa a synonym of Lagocephalus lunaris .

Habib et al. (2018) described Chelonodontops bengalensis based on two specimens, 234 and 312 mm SL, collected in Bangladesh near Dubla Island, south of the Sundarbans. The species has since been recorded from other localities in the northern Bay of Bengal, off Dingha in Western Bengal in India ( Mohapatra et al. 2020) and from the east coast off Odisha ( Roul et al. 2022).

For the comparison of their new species Chelonodontops bengalensis with C. patoca, Habib et al. (2018) used the information for the latter provided in Sujatha & Padmavathi (2015) based on specimens from Visakhapatnam, Andhra Pradesh, and in Han et al. (2017), based on specimens from the fish market in Chennai. Both these locations are ca. 800 and 1400 km south of Baruipur and Lakshmipur, respectively, from where Hamilton’s (1822) illustrated type specimen of Tetrodon patoca originated. Habib et al. (2018) do not seem to have consulted Hamilton’s (1822) original description of T. patoca : they do not cite his work. This is surprising given that Hamilton’s (1822) collecting locality for the specimen of his T. patoca illustrated on Plate 18 is only 140 km (Baruipur) or 190 km (Lakshmipur), respectively, from the type locality of Habib et al. ’s (2018) C. bengalensis .

Habib et al. (2018, pp. 4, 6–7) concluded that their Chelonodontops bengalensis differs from C. patoca in the following characters: “ C. bengalensis have both back and belly with spines (vs belly only with spines in C. patoca ) … in dorsal rays (12 vs 10), anal rays (10 vs 8), and pectoral rays (19 vs 15–16). C. bengalensis has spinules on its lateral sides (vs. a patch of spinules on the back from behind the interorbital nearly to the dorsal fin and another on the throat and abdomen but absent on the lateral sides in C. patoca )…Nasal organ not covered by a small sac with two nostrils (vs in C. patoca expanded before and behind into a pair of elongate flaps). C. bangalensis (sic!) has dorsal and upper half of lateral sides of the body with spiral shaped whitish spots (vs. greenishgray to brown on the back with large round to ovate white spots in C. patoca ). C. bengalensis have blackish grey color on the sides (vs. a broad yellow band running from chin to lower caudal fin base in C. patoca )…. Genetic distance from 6.0% to 7.6% for COI and 3% to 4% for 16S gene between C. bengalensis and the closest related species C. patoca are consistent with usual congeneric differentiation value of> 2% ...”

Hamilton’s (1822) description of Tetrodon patoca mentions: “The colour of the Patoca above is blackish, with numerous large yellow spots on the back: below it is white. The fins are inclined to olive. The back and belly are armed with simple retractable prickles…The back fin is rounded, and contains eleven rays, of which the first two are undivided, and the first is the shortest. The pectoral fins are sharpish above. Each contains about sixteen rays. The anal fin is rounded, and contains ten rays, of which the first is the shortest, and, together with the second, is undivided. The tail fin is rounded, and contains ten rays, of which one on each side is undivided.”

Hamilton’s (1822) description of fin-ray number (D11, A10, P16) and colour pattern (blackish above, numerous large yellow spots on the back, white below), as well as spination (back and belly with prickles) matches the description of these characters in Habib et al. ’s (2018) new species Chelonodontops bengalensis . In addition, Habib et al. ’s (2018: Fig. 3 ) illustration of the types of C. bengalensis shows that they closely match Hamilton’s (1822) illustration of Tetrodon patoca ( Fig. 1 ), reproduced here from Britz (2019). It is clear, therefore, that the two names refer to the same species, making the former a synonym of the latter.

The species that Habib et al. (2018) mistook for Chelonodon patoca is a widespread Indo-Pacific pufferfish, first mentioned by Russell (1803) from Vizagapatam (todays Visakhapatnam in Andhra Pradesh) under the local name Kappa and illustrated in Plate 18, Fig. 25. In his description, Russell (1803: p. 18) mentioned also the characteristic colouration of this species: “The colour of the upper part a dark purplish, beautifully variegated with dusky whitish, or greenish spots, and two or three dark transverse bands; the throat and belly white, with a streak of yellow on each side. The dorsal fin dark, the caudal almost black; the anal of a light colour.” The streak of yellow, in particular, seems to be unique to this species. The literature on the fish fauna of the Western Indo-Pacific suggests that the species of Chelonodon with a yellow lateral streak is widely distributed from the coast of Pakistan ( Psomadakis et al. 2015), India ( Han et al. 2017; Kaleshkumar et al. 2018; Sujatha & Padmavathi 2015; Veeruraj et al. 2011), Myanmar ( Psomadakis et al. 2020), eastwards to Indonesia and Japan ( Matsuura 2002; Okamura & Endo 2022).

The origin of confusion regarding the name Chelonodon patoca.

Bleeker (1850) may have been the first to assume a wide distribution for C. patoca , mentioning this species from the Malay Archipelago (“indischen Archipel”) and also “ Bengalen, China, Japan ”. This was reiterated in Günther’s (1870) entry for this species in his influential Catalog, based on material from Bengal, Singapore, Penang, Amboina, the East-Indian archipelago and China. This identity and distribution subsequentlycame to be widely adopted, as evidenced in many treatises on the fish fauna of South and Southeast Asia (see e.g., de Beaufort & Briggs 1962; Matsuura in Masuda et al. 1984; Kottelat et al. 1993; Talwar & Jhinghran 1992; Vidthayanon 2008; Rainboth et al. 2012; Psomadakis et al. 2015, 2020; Nagao Natural Environment Foundation 2021). As we have shown above, however, most of these distribution records concern the species with the yellow lateral streak, not Hamilton’s (1822) Chelonodon patoca . So far, C. patoca seems to be known with certainty only from brackish and marine waters in the northern part of the Bay of Bengal from India and Bangladesh ( Habib et al. 2018; Mohapatra et al., 2020; Roul et al. 2022).

The correct name of the species of Chelonodon with the yellow streak, previously confused with C. patoca . Several names have been treated as synonyms of Chelonodon patoca : Tetrodon dissutidens Cantor 1849 , Tetraodon kappa Bleeker 1850 , Tetraodon hartlaubii Bianconi 1854 , and Tetraodon maculatus Swainson 1839 (the last is an unneeded replacement name for Hamilton’s [1822] Tetrodon patoca ). Of these, Cantor’s (1849) T. dissutidens would appear to be the oldest available name for the wide-spread species with the yellow lateral streak.

In his description of Tetrodon patoca , however, Hamilton (1822: 8) stated: “The Tetrodon kappa of Dr Russell (Indian Fishes, Vol. I No. 25) has also a considerable affinity to the Patoca, but is less prominent on the belly, and more so between the eyes, while the spots on the back are pale blue its belly yellow, and its back only rough, and devoid of visible prickles.” Hamilton listed Tetrodon kappa in the index together with the other Tetrodon species he described. Hamilton’s (1822) note and listing in the index provide the conditions for Tetrodon kappa to be treated as available for the species of Chelonodon with the yellow lateral streak. The author of the name is Hamilton (1822) by indication to Russell (1803). Russell (1803) referenced only a single specimen, the putative holotype, which he illustrated on Plate 18, fig. 25 and mentioned as measuring 3 inches and 5 lines. Accepting Hamilton’s (1822) Tetraodon kappa as an available name renders Bleeker’s (1850) Tetraodon kappa a junior primary homonym and thus unavailable, and renders Tetrodon dissutidens Cantor 1849 , and Tetraodon hartlaubii Bianconi 1854 junior synonyms of Hamilton’s (1822) T. kappa .

The easiest way by which to distinguish Chelonodon patoca from C. kappa is the colour pattern (cf. Figs. 2,3 with Figs. 4,5) and the number of fin rays Chelonodon patoca lacks the yellow lateral streak along the side of the body and the dark saddle-like blotches, both typical of C. kappa . Instead it shows an overall dark dorsal half of the body covered in small white to cream spots and elongate blotches ( Figs. 1–3 ). Chelonodon patoca according to Hamilton (1822) has 11 dorsal- and 10 anal-fin rays. Habib et al.’s (2018) specimens of Chelonodon patoca (holotype and paratype of their C. bengalensis ) were recorded with 12 dorsal- and 10 anal-fin rays. This matches our counts of dorsal- and anal-fin rays in ZRC66125, and BMNH 1889.2.1.4116. However, BMNH 1858.8.15.107 has D 12 and A 11, and another individual of C. patoca photographed by Beta Mahatvaraj ( Fig. 3 ) also shows 11 dorsal-fin rays, matching the count provided by Hamilton (1822). Based on these examples, the dorsal-fin ray count of C. patoca is thus D 11–12 and the anal-fin ray count A 10–11. Russell (1803) counted 10 dorsal- and 8 anal-fin rays in C. kappa and Sujatha & Padmavathi (2015), who collected 178 specimens of C. kappa (as C. patoca ) from around its type locality, provide a range of 9–10 dorsal- and 8 anal-fin rays for this species. We conclude that in addition to the colour pattern, the number of dorsal- and anal-fin rays distinguishes C. patoca from C. kappa .

Chelonodon vs. Chelonodontops . Hamilton’s (1822) Tetrodon patoca has long been included in the genus Chelonodon Müller (see Günther, 1870). Müller (1841) did not, when establishing the name Chelonodon , include any species in this genus. According to Tyler (1964), Rüppell (1852) was the first to list several species under Chelonodon : C. cutcutia (Hamilton) , C. psittacus ( Bloch & Schneider 1801) , and C. richei ( Fréminville 1813) .

In the same year, but after Rüppell (1852), Bleeker (1852) mentioned two species under Chelonodon : Tetraodon kappa Russell and T. kunhardtii Bleeker , and listed another three as belonging to this taxon: Tetraodon bondaroo kappa Russell , T. hispidus “Bl. ”, and T. meleagris Solander. Tetrodon patoca Hamilton , however, was assigned by Bleeker (1852) to Müller’s (1841) genus Gastrophysus . As Rüppell (1852) predates Bleeker (1852), the type species for Chelonodon could be chosen only from among the three species originally included in this genus by Rüppell (1852). This selection was made by Tyler (1964), who gave T. cutcutia Hamilton precedence over the other two originally-included species. As a result, the genus name Chelonodon has not been available for the species T. patoca Hamilton and thus the genus name Chelonodontops Smith 1958 , with the type species C. pulchellus Smith 1958 has been applied recently for this group of pufferfish species, including C. patoca ( Kottelat, 2013: 475) .

However, Kottelat (2011) pointed out that a number of Bleeker’s publications were made available as preprints before the official distribution of the respective journal volume, with these preprints predating the distributed journal sometimes by months or years. The publication year for the preprint that included Bleeker’s “Bijdrage tot de kennis der Gymnognathen van den Indischen Archipel”, was given by Kottelat (2011) as 1850. Bleeker (1850) contains reference to Müller`s Chelonodon and the above-mentioned species, and thus predates Rüppell (1852) by more than one year. It follows, therefore, that the type species of Chelonodon has to be chosen from the species included by Bleeker (1850): Tyler’s (1964) type species designation is invalid. As a type species for Chelonodon has not to our knowledge previously been selected from among the species originally referred to this genus by Bleeker (1850), we here designate Bleeker’s (1850) Tetraodon kappa as the type species of Chelonodon . Bleeker’s (1850) Tetraodon kappa is “ Tetraodon kappa Russell Corom. Fish I p. 18, fig. 25” (which, because Russell did not consistently apply the Principle of Binominal Nomenclature, is considered not to have been validly published: ICZN Art. 11.4), as he explained further on p. 16. Tetraodon kappa Bleeker 1850 , as we have shown above, is a junior primary homonym of Tetrodon kappa Hamilton , so that Tetrodon kappa Hamilton becomes the type species of Chelonodon . This selection of the type species also assures nomenclatural stability, as the genus name Chelonodon has for more than a century been used for this group of pufferfishes.

Figures

FIGURE 1. Haludar’s illustration of Tetrodon patoca. From the archive of the British Library (Mss Eur E72, p. 47), photo: Kevin Webb.

FIGURE 3. Chelonodon patoca, in life, not preserved, ca. 200 mm. Note 11 dorsal-fin rays. Photo: B. Mahatvaraj.