Schizodon dissimilis ( Garman, 1890 )

Garavello, Júlio Cesar & Britski, Heraldo Antonio, 2019, Redescription of Schizodon dissimilis and appraisal of the dark barred species of the genus (Characiformes: Anostomidae), Neotropical Ichthyology 17 (3), pp. 1-10 : 3-6

Schizodon dissimilis ( Garman, 1890)

( Figs. 2 , 3 )

Anostomus dissimilis Garman, 1890: 22 [original description; type-locality: rio Puty (=Poti), Brazil]. — Borodin, 1931: 44 [syntypes examined, rio Poti]. — Vari, Howe 1991: 4 [literature reference]. — Gómez, Chebez, 1996: 53 [literature reference].

Schizodon dissimilis . — Eigenmann, 1910: 425 [rio Poti, Piauí, Brazil]. — Fowler, 1954: 211 [catalogue]. — Garavello, Britski in Reis et al., 2003: 80 [catalogue]. — Britski, Garavello in Buckup et al., 2007: 27 [catalogue]. — Abreu et al., 2009: 8 [rio Poti, Teresina, Piauí]. — Ramos et al., 2014: 3 [rio Parnaíba].

Schizodon fasciatus . — Fowler, 1941: 175 [rio Jaguaribe, Russas, Ceará, Brazil]. — Roberts, 1973: 226–227 [rio Parnaíba, Barra do Longá, near Buriti dos Lopes, Piauí, Brazil]. — Sales, Nogueira, Lopes, 1984: 57-62 [açude Joaquim Távora, Jaguaribe, Ceará].

Schizodon dissimile . — Géry, 1987: 154 (literature reference).

Diagnosis. Schizodon dissimilis is a member of the Schizodon fasciatus species group distinguished by having four conspicuous dark brown bars along the trunk and lacking any sort of dark stripe or elongate blotch along the lateral-line scale row vs. having a dark midlateral stripe running from the opercle to the caudal peduncle (some specimens of S. knerii , S. isognathus , S. scotorhabdotus and S. nasutus ) or from the vertical through the dorsalfin origin to the caudal peduncle ( S. vittatus , and some specimens of S. knerii , S. altoparanae and S. jacuiensis ); or a dark elongate blotch on caudal peduncle ( S. altoparanae , S. nasutus , S. platae , S. rostratus and some specimens of S. knerii ). Schizodon dissimilis is distinguished by other members of the S. fasciatus species group by having 42-43 lateral-line scales vs. 40-42 in S. borellii and S. intermedius , 44-45 in S. fasciatus and S. corti , 44-46 in S. australis . It is further distinguished from S. australis by possessing 4 transverse scale rows above and 4-4.5 below the lateral line (vs. 5.5/5.5 in S. australis ). Schizodon dissimilis is further distinguished from S. australis , S. corti and S. fasciatus by the lack of a dark blotch on the base of the caudal peduncle (vs. the presence of such a blotch in S. australis , S. corti and S. fasciatus ). Schizodon dissimilis is distinguished by S. intermedius in relative values of body depth in SL (3.9 to 4.9, mean 4.0 in S. dissimilis vs. 2.9 to 3.9, mean 3.5 in S. intermedius ). The color pattern of S. dissimilis is most similar to that of S. intermedius and S. borellii , and the meristic characters of S. dissimilis and S. borellii overlap partially. Despite the morphological similarity between these species, both are considered distinct herein based on their morphometric separation in the sheared PCA and their allopatric distribution. Molecular data are also informative on the distinction among S. dissimilis , S. fasciatus , S. borellii and S. intermedius (see discussion section below).

Description. Morphometric and meristic data of S. dissimilis are presented in Tab. 3 . Body fusiform; greatest body depth at or just anterior to dorsal-fin origin. Dorsal profile of head gently curved from snout tip to vertical through anterior margin of eye, rising nearly straight to vertical through posterior margin of opercle, then leveling off to dorsal-fin origin; predorsal region from vertical through posterior margin of opercle to dorsal-fin base slightly convex, forming gentle hump; dorsal-fin base straight, slightly descending; profile from dorsal-fin to adipose fin straight, descending more gradually than dorsal-fin base; caudal peduncle slightly concave. Ventral profile from lower jaw to anal-fin insertion slightly convex with point of maximum inflection at pelvic-fin insertion; base of anal-fin straight, ascending; caudal peduncle slightly concave.

Mouth small, upper and lower jaws horizontally aligned with median region of orbit when the mouth is closed. Upper and lower lips smooth. Maxillary slightly curved along ventral margin and widening posteriorly into a flat rhomboidal plate. Each premaxillary and dentary with four serrate teeth (n=26 including lectotype), forming serrated cutting edge. Teeth slightly graded in size; symphysal teeth largest on each jaw; most distant tooth from symphysis much smaller. Anterior and posterior nostrils horizontally aligned with upper lip and upper quarter of orbit. Infraorbitals large; supraorbital positioned at anteriodorsal margin of orbit. Branchiostegal rays and opercular membrane connected at isthmus.

All specimens of S. dissimilis (n=26 including lectotype) with one extremely small anterior unbranched ray in dorsal fin followed by two major unbranched rays and seven branched rays with the first one longest. Anal fin with two unbranched rays, the first shorter than the second, followed by eight branched rays; first branched anal-fin ray slightly longer than unbranched rays; posterior margin of anal-fin slightly convex. Fleshy cover at base of anterior dorsal and anal fin rays extended. Pectoral fin with two unbranched and 15 branched rays; shape of extended pectoral fin almost triangular. Pelvic fin with one unbranched and eight branched rays; origin at vertical through base of first or second branched dorsalfin ray. Adipose fin elongate, length approximating three dorsal scales; origin at vertical through base of first or second branched anal-fin ray. Caudal fin with 10 principal rays; rays heavily ramified in adults; lobes blunt with rounded margins.

Lateral line scales: 42-43 (43 in lectotype). All lateral line scales pored, including those over caudal-fin rays; sixteen regular scale series around caudal peduncle just posterior to adipose-fin insertion in all specimens including lectotype. Four major scale rows dorsal to lateral line and 4 to 4.5 below lateral line at dorsal fin origin (lectotype 4/I/4); incomplete series of scales on base of dorsal and anal fins; predorsal scales 11-12 (11 in lectotype); scales in preanal series 33-35 (35 in lectotype); circumpeduncular scales series 16 (including the lectotype).

Color in alcohol. Overall ground color brown dorsal to lateral line between opercle and caudal peduncle, light yellowish beginning one or two scale series ventral to lateral line, abdomen and lower caudal peduncle especially pale. Dorsal surface of head brown; ventral surface of head, gular region and branchiostegal membrane yellowish. Sides with four distinct inclined dark brown vertical bars; intensity of dark brown coloration varies among specimens, but number of bars always four. First bar about five scales anterior to dorsal-fin insertion; second bar ventral to dorsal-fin insertion; third situated between end of dorsal-fin base and adipose-fin origin; fourth ventral to adipose fin insertion. First and fourth bars three or four scales wide, second bar two scales wide, third bar two or three scales wide. Opercle brown with hyaline fleshy flap. Unbranched rays of anal, pectoral and pelvic fins occasionally with dark melanophores; fins otherwise hyaline, including adipose fin. Caudal fin with superior lobe slightly brown and inferior lobe conspicuously brown.

Geographic distribution. Schizodon dissimilis is known from Parnaíba, Poti, Mearim and Jaguaribe rivers in Ceará, Piauí and Maranhão states of northeastern Brazil ( Fig. 4 ).

Designation of lectotype. The Thayer Expedition (1865–66) collected 12 specimens from the rio Puty (= Poti), Parnaíba basin, Piauí state, Brazil that were described by Garman (1890) as Anostomus dissimilis without indicating a holotype. One of the largest and better preserved of the syntypes, MCZ 19383, 264.6 mm SL, is herein designated the lectotype. The remaining specimens are consequently paralectotypes: MCZ 19381, 5 specimens (3 measured, 152.0, 225.0 and 260.0 mm SL); MCZ 19382, 2 specimens (1 measured 252.5 mm SL); MCZ 19384, 1 specimen (not measured) and the USNM 120238, 3 specimens (166.0, 172.0 and 211.0 mm SL) .

Non-type material: Brazil: Ceará: ANSP 69491, 3, 40.0–80.0 mm SL, Russas, rio Jaguaribe, R. von Ihering, 1936; ANSP 69494, 1, (c&s), Russas, rio Jaguaribe, R. von Ihering, 1936; MZUSP 55143, 4, 196.0–220.0 mm SL, rio Jaguaribe, 8 Dec 1998, F. A. Bockmann & P. M. Araujo; MZUSP 55144, 1, 155.0 mm SL, Lima Campos, rio Jaguaribe, creek São João, downstream of Lima Campos dam, 7 Dec 1998, F. A. Bockmann, P. M. Araujo; MZUSP 35763, 4, 195.0–292.0 mm SL, Ceará State, Jul 1983, Departamento Nacional de Obras Contra as Secas (DNOCS). Maranhão: MZUSP 21386, 4, 141.0– 249.0 mm SL, Pedreiras, 5 Jan 1955, P. E. Vanzolini; MZUSP 5074, 1, 272.0 mm SL, Barra do Corda, rio Corda, 16 Jun 1966, Expedição Departamento de Zoologia; MZUSP 3558, 1, 185.0 mm SL, dam at riacho Sangue, Solonópolis, 22 Oct 1944, R. S. Menezes; MNRJ 51527, 1, 181.0 mm SL, rio Mearim, no date, DNOCS (n/c 15); CPDOL 98287, 10, 155.0–187.0 mm SL, Ilha das Pedrinhas, Lago de Viana, rio Pindaré-Mearim system, 8–14 Aug 1998, N. Piorski & L. Pereira; MNRJ 51528, 1, 201.0 mm SL, municipality of Coroatá, rio Itapecuru, 1976, A. Barros (n/c 24); MNRJ 51529, 1, 274.0 mm SL, rio Mearim, no date, DNOCS (n/c102); MNRJ 51530, 1, 215.0 mm SL, rio Mearim, no date, DNOCS (n/c116). Piauí: LISDEBE 6976, 2, 221.0–229.0 mm SL, municipality of Aroazes, rio Tábua, tributary of rio Parnaíba, 1 Sep 1994, J. P. J. Filho; MZUSP 5101, 4, 61.0–114.0 mm SL, Teresina, rio Parnaíba, 16 Jun 1966, Expedição Depto de Zoologia; MCP 24967, 1, rio Pindaré, tributary of Mearim, West from Santa Inês, on the road Pará-Maranhão (BR 316), 24 Jul 1998, R. Reis, J. P. Silva, E. Pereira & J. Montoya.

Figures

Fig. 2. Schizodon dissimilis, MCZ 19383, Lectotype 264.6 mm SL, rio Poti, Piauí state.

Fig. 3. Schizodon species. (a) Schizodon dissimilis, MZUSP 55143, 220.0 mm SL, rio Jaguaribe, Lima Campos, Ceará state; (b) Schizodon fasciatus, LISDEBE 6981, 275.0 mm SL, rio Solimões, lake Janauacá, Amazonas state; (c) Schizodon borellii, LISDEBE 6977, 245.0 mm SL, Ilha Taiamã, rio Paraguay, Mato Grosso state; (d) Schizodon intermedius, LISDEBE 6984, 233.0 mm SL, rio Jacaré Guaçu, Tietê river basin, São Paulo state.

Fig. 4. Location of the lots containing the studied species: Schizodon dissimilis (red, orange star marks the typelocality), S. fasciatus (dark blue), S. borellii (yellow) and S. intermedius (white); each symbol may represent more than one sample.

Tables

Tab. 3. Morphometrics of Schizodon dissimilis and S. fasciatus expressed as percentages of SL and HL. Meristic data with numbers of specimens with each count in parenthesis. All lectotype data in millimeters.

			Schizodon dissimilis (n= 26)			Schizodon fasciatus (n= 28)
	Lectotype MCZ 19383	Range Mean Min Max		SD	Range Mean Min Max		SD
Standard length (mm)	264.6	141.0	292.0 205.6	41.477	110.0	275.0 172.6	56.879
Percents of SL
Head length	62.1	21.79	26.06 23.92	1.2923	21.25	26.91 24.16	1.7086
Trunk length	202.5	73.94	78.21 76.18	1.2055	73.09	78.75 75.75	1.7710
Body depth	62.7	19.88	29.03 25.41	3.0317	21.15	27.22 24.26	1.7799
Predorsal length	112.4	39.97	44.51 42.60	1.2893	40.00	48.00 43.27	2.1021
Caudal peduncle depth	27.4	9.21	12.97 10.93	1.2262	9.40	12.34 10.12	0.7300
Percents of HL
Snout length	25.4	34.30	44.00 41.27	2.6247	38.57	42.36 40.63	0.9773
Interorbital width	31.1	44.28	58.84 53.84	4.3804	47.42	54.90 50.16	2.2812
Orbital diameter	13.3	19.45	26.59 23.09	1.7282	19.44	28.21 23.70	3.1309
Meristics			Schizodon dissimilis (n=26)			Schizodon fasciatus (n=28)
Lateral-line scales	43		42 (8) - 43 (17) - 44 (1)			44 (23) – 45 (5)
Transverse scales	4/I/4		4/I/4 (23) - 4.5/I/4 (3)			4/I/4 (all)
Predorsal scales	11		11 (19) – 12 (6) – 13 (1)			12 (all)
Preanal scales	35		33 (7) – 34 (11) – 35 (8)			35 (4) – 36 (20) – 37(4)
Circumpeduncular scales	16		16 (all)			16 (all)
Teeth counts (pmx/dentar)	4/4		4/4 (all)			4/4 (all)