Barbatula ommata, Calegari & Freyhof & Waldock & Wegscheider & Josi & Rüber & Seehausen, 2025

Calegari, Bárbara B., Freyhof, Jörg, Waldock, Conor, Wegscheider, Bernhard, Josi, Dario, Rüber, Lukas & Seehausen, Ole, 2025, Two new species of stone loaches of the genus Barbatula (Cypriniformes: Nemacheilidae) from Europe with a neotype designation of B. barbatula (Teleostei: Nemacheilidae), Journal of Fish Biology 107 (4), pp. 1364-1397 : 18-21

Barbatula ommata , new species

(Figures 11 and 12)

urn:lsid:zoobank.org: act:4A1BCF03-B054-41B6-8020-F34B01B13ADE

Barbatula sp. ‘Lineage I’ – Alexander & Seehausen 2021:110 – 111 [listed].

Holotype. NMBE 1105555 , 74.1 mm SL, female, Corcelles-près-Concise beach, Lake Neuchatel, Aare catchment, Rhine drainage , Canton of Vaud, Switzerland, 46 Ǫ 5003300 N, 6 Ǫ 4204200 E, 20 Jul 2023, Calegari, B. B., Wegscheider, B., Josi, D., Waldock, C.

Paratype. All from Switzerland: Rhine drainage: Aare catchment : Canton of Vaud: NMBE 1105553 – 1105554 , 2, 69.1 – 73.7 mm SL, collected with the holotype. — NMBE 1105282 – 1105290 , 9, 53.1 – 70.9 mm SL, Lake Neuchatel , 46 Ǫ 5104700 N, 6 Ǫ 5103800 E, 19 Jul 2023, Calegari, B. B., Wegscheider, B., Waldock, C., Josi, D. — NMBE 1105291 – 1105293 , 3, 56.9 – 70.7 mm SL, Lake Neuchatel, Corcelles-près-Concise beach , 46 Ǫ 5004800 N, 6 Ǫ 4205900 E, 20 Jul 2023, Calegari, B. B., Wegscheider, B., Josi, D., Waldock, C. Canton of Neuchâtel: NMBE 1105309 – 1105311 , NMBE 1105313 , NMBE 1105315 – 1105326 , NMBE 1105328 , 17, 46.8 – 57.6 mm SL (HRXCT of NMBE 1105313 ), NMB 6482 – 6483 , 2, 52.7 – 54.5 mm SL, ZFMK-ICH 135312, 1 C&S, 54.6 mm SL, Lake Neuchatel , littoral zone, 367 m alt., 47 Ǫ 008.500 N, 7 Ǫ 004000 E, 17 Jul 2022, Calegari, B. B., Wegscheider, B., Josi, D. — MHNN 89-2491 and MHNN 89-2492 , 2, 64.1 – 67.2 mm SL, Lake Neuchatel, littoral zone at camping Paradis-Plage , 46 Ǫ 5800.400 N, 6 Ǫ 52025.500 E, 16 Oct 2024, Calegari, B. B., Sudasinghe, H. Canton of Fribourg: NMBE 1105261 – 1105264 , NMBE 1105266 – 1105269 , NMBE 1105272 – 1,105,278, NMBE 1105280 , 48.7 – 66.2 mm SL, ZFMK-ICH 135309 – 135,311, 3, 62.9 – 65.6 mm SL, ZSM 49671 , 2, 53.7 – 56.4 mm SL, NMW 101169 , 2, 52.4 – 65.9 mm SL, Lake Neuchatel at Estavayer harbour , 46 Ǫ 4903100 N, 6 Ǫ 4006000 E, 28 Jun 2023, Calegari, B. B., Wegscheider, B., Josi, D., Waldock, C. Canton of St. Gallen: NMBE 1105245 – 1105249 , 5, 49.1 – 75.7 mm SL, Lake Walen, near to Quinten , 47 Ǫ 705700 N, 9 Ǫ 1103200 E, 28 Jun 2023, Calegari, B. B., Wegscheider, B., Josi, D., Reichlin, P. — NMBE 1105237 – 1105238 , NMBE 1105241 – 1,105,242, NMBE 1105244 , 6, 51.3 – 82.3 mm SL, ZFMK-ICH 135313 – 135314 , 2, 53.6 – 71.5 mm SL, Lake Walen, near to Quinten , 47 Ǫ 705200 N, 9 Ǫ 120200 E, 28 Jun 2023, Calegari, B. B., Wegscheider, B., Josi, D., Reichlin, P. — NMBE 1105250 – 1105258 , 8 + 1 C&S, 56.7 – 71.7 mm SL, Lake Walen, near to Mols , 47 Ǫ 6051.400 N, 9 Ǫ 16055.800 E, 28 Jun 2023, Calegari, B. B., Wegscheider, B., Josi, D., Reichlin, P. Canton of Lucerne: NMBE 1105219 – 1105221 , NMBE 1105224 – 1105226 , NMBE 1105228 – 1105229 , NMBE 1105231 – 1105235 , 12 + 1 C&S, 50.6 – 71.1 mm SL, MNHN 2024 – 1385 , 2, 55.0 – 63.8 mm SL, MNCN-ICTIO 298.404 and MNCN-ICTIO 298.405 , 2, 56.5 – 68.2 mm SL, Lake Lucerne at Vitznau , 430 m alt., 47 Ǫ 001400 N, 9 Ǫ 290400 E, 27 Jun 2023, Calegari, B. B., Wegscheider, B., Josi, D., Reichlin, P. Canton of Nidwalden: NMBE 1105236 , 1, 58.5 mm SL, Lake Lucerne, Beckenried , 440 m alt., 46 Ǫ 5801800 N, 8 Ǫ 2605700 E, 27 Jun 2023, Calegari, B. B., Wegscheider, B., Josi, D., Reichlin, P.

Genseq-2 coI. NMBE 1105553 (tissue tag 241420); Genbank Acession Number PQ488228. Genseq-2 coI. NMBE 1105282 (tissue tag 241424); Genbank Acession Number PQ488229. Genseq-2 coI. NMBE 1105291 (tissue tag 241441); Genbank Acession Number PQ488230. Genseq-2 coI. NMBE 1105310 (tissue tag 239503); Genbank Acession Number PQ488120. Genseq-2 coI. NMBE 1105245 (tissue tag 241280); Genbank Acession Number PQ488223. Genseq-2 coI. NMBE 1105248 (tissue tag 241283); Genbank Acession Number PQ488224. Genseq-2 coI. NMBE 1105250 (tissue tag 241286); Genbank Acession Number PQ488225. Genseq-2 coI. NMBE 1105261 (tissue tag 241392); Genbank Acession Number PQ488227. Genseq-2 coI. NMW 101169 (tissue tag 241410); Genbank Acession Number PQ488226. Genseq-2 coI. NMBE 1105237 (tissue tag 241240); Genbank Acession Number PQ488221. Genseq-2 coI. NMBE 1105220 (tissue tag 241212); Genbank Acession Number PQ488217. Genseq-2 coI. MNCN-ICTIO 298.404 (tissue tag 241214); Genbank Acession Number PQ488218. Genseq-2 coI. NMBE 1105226 (tissue tag 241218); Genbank Acession Number PQ488219. Genseq-2 coI. NMBE 1105236 (tissue tag 241228); Genbank Acession Number PQ488220.

Additional material (non-types). All from Switzerland. Canton of Bern: NMBE 1120429 and NMBE 1120489, 2, Lake Biel, 57.4 – 58.7 mm SL, 47 Ǫ 0404800 N, 7 Ǫ 11046.700 E, 20 Sep 2017, Décourcière, H. — NMBE 1120476 and NMBE 1120485, 2, 53.5 – 59 mm SL, Lake Biel, 47 Ǫ 03039.500 N, 7 Ǫ 10029.300 E, 20 Sep 2017, Décourcière, H. Canton of Fribourg: NMBE 1061957, NMBE 1061974, NMBE 1061976 – 1061978, NMBE 1061993 – 1061995, NMBE 1062005, 7 + 1 C&S, 53.2 – 76.3 mm SL, Lake Neuchatel, 46 Ǫ 52014.900 N, 6 Ǫ 52016.500 E, 3 Oct 2011, unknown collector. — NMBE 1061958, 1, 64.2 mm SL, Lake Neuchatel, at Sous la Corbière, 46 Ǫ 51056.900 N, 6 Ǫ 51050.300 E, 3 Oct 2011, Project Lac. — NMBE 1074762, 1, 52.3 mm SL, Lake Neuchatel, at Sous la Corbière, 46 Ǫ 5205.900 N, 6 Ǫ 51011.100 E, 7 Oct 2011, unknown collector. Canton of Neuchâtel: NMBE 1074763, 1, 53.6 mm SL, Lake Neuchatel, at La Grande Béroche, 46 Ǫ 5506.900 N, 6 Ǫ 48055.600 E, 7 Oct 2011, Project Lac. Canton of Lucerne: NMBE 1069200 – 1069202, 3, 54.0 – 60.3 mm SL, Lake Lucerne at Vitznau, 430 m alt., 47 Ǫ 001600 N, 8 Ǫ 290100 E, 20 Aug 2014, Vonlanthen, P. — NMBE 1066769 – 1066772, 4, 36.3 – 40.3 mm SL, Lake Zug, near to Immensee, 47 Ǫ 0603000 N, 8 Ǫ 2806000 E, 22 Aug 2013, Tourreau, G. — NMBE 1080978, 1, 59.9 mm SL, Steinibach, 47 Ǫ 1014.500 N, 8 Ǫ 17059.900 E, 9 Sep 2013, Vonlanthen, P. — NMBE 1080958 – 1080971, 14, 58.2 – 76.0 mm SL, Steinibach, Ringstrasse, 47 Ǫ 0054.500 N, 8 Ǫ 18035.500 E, 9 Sep 2013, Vonlanthen, P. Canton of St. Gallen: NMBE 1074613, 1, 69.3 mm SL, Lake Walen, near to Sargans, 47 Ǫ 0704900 N, 9 Ǫ 12016.300 E, 23 Oct 2012, Brodersee, J. — NMBE 1111831 – 111833, NMBE 1109966, 4, 32.1 – 76.1 mm SL, Rufibach River, Limmat drainage, northwest of the airport Schänis between Maseltrangen and Ussbühl, 413 m alt., 47 Ǫ 10043.700 N, 9 Ǫ 1044.800 E, 13 Sep 2022, Calegari, B. B., Wegscheider, B.; Josi, D., Sudasinghe, H. Canton of Schwyz: NMBE 1105516 – 1105530, 15, 54.9 – 88.8 mm SL, Canton of Schwyz, Hoggibach River, at side channel of Hintergraben/Linthkanal, Aare River, Reichenburg, 406 m alt., 47 Ǫ 10032.700 N, 8 Ǫ 59021.900 E, 14 Oct 2022, Calegari, B. B., Wegscheider, B., Josi, D., Waldock, C., Schmid, A., Moreau, S. Canton of Vaud: NMBE 1061953, NMBE 1061974 – 1061975, NMBE 1061992, NMBE 1062001, 4 + 1 C&S, 52.2 – 57.6 mm SL, Lake Neuchatel, at Corcelles-près-Concise beach, 46 Ǫ 50016.900 N, 6 Ǫ 42027.900 E, 3 Oct 2011, Project Lac. — NMBE 1061963 and NMBE 1061989, 2, 54.4 – 55.3 mm SL, Lake Neuchatel, at Corcelles-près-Concise beach, 46 Ǫ 5008.700 N, 6 Ǫ 42012.300 E, 3 Oct 2011, Project Lac. — NMBE 1062004, 1, 59.5 mm SL, Lake Neuchatel, near to La Poissine, 46 Ǫ 49035.100 N, 6 Ǫ 4109.100 E, 3 Oct 2011, Project Lac. Canton of Zürich: NMBE 1105329 – 1105338, 9 + 1 C&S, 36.9 – 51.6 mm SL, Lake Zurich at Linthkanal, 394 m alt., 47 Ǫ 1306.200 N, 8 Ǫ 56028.900 E, 11 Jul 2022, Calegari, B. B., Wegscheider, B., Josi, D. — NMBE 1071771, NMBE 1071774, NMBE 1071787, NMBE 1071789, NMBE 1071793 – 1071794, NMBE 1071797, 7, 36.6 – 49.8 mm SL, Lake Zurich, Richterswill, 47 Ǫ 1301000 N, 8 Ǫ 41033.300 E, 1 Oct 2014, Vonlanthen, P.

Diagnosis. Barbatula ommata is a member of a monophyletic group of species, herein designated as Western Europe clade (including B. barbatula , B. hispanica , B. leoparda and B. fluvicola ), which is diagnosed from all clade congeners, except by B. hispanica , by having a shallower head 38.4% – 46% HL (vs. 46.1 – 51.7% in B. fluvicola , 51.7 – 57.3% in B. barbatula and 51.5 – 58.3% HL in B. leoparda ). The new species differs from B. hispanica and B. fluvicola by having a larger eye 21.1% – 28.3% HL (vs. 16.8% – 22.5% and 16.1% – 19.8% HL). It is distinguished from B. leoparda and B. hispanica by having a shallower caudal peduncle 7.7% – 10.9% SL (vs. 12.1% – 13.6% and 12.1% – 13.9% SL). It is further distinguished from B. leoparda and B. barbatula by having a smaller suborbital depth 23.7% – 31.2% HL (vs. 32.2% – 36.3% and 33.1% – 36.3% HL). It further differs from B. leoparda by having a shorter lower lip 12.7% – 17.1% HL (vs. 17.4% – 21.2% HL), and ventral surface of head and area between pectoral to pelvic-fin origins without pigmentation (vs. ventral surfaces with brown to dark irregular blotches). B. ommata is further distinguished from B. barbatula by having a shorter dorsal head length 19.3% – 21.4% SL (vs. 23.2% – 25.8% SL), a shorter first dorsal-fin ray 13.5% – 19.8% SL (vs. 20% – 24.3% SL), a shorter dorsal-fin base 11.1% – 14.3% SL (vs. 14.5% – 18.6% SL), a shorter dorsal fin length 18.4% – 23.3% SL (vs. 24.1% – 25.8% SL), a shorter prepectoral length 21.3% – 25.8% SL (vs. 26.2% – 28.7% SL), a longer caudal peduncle 12.7% – 16.2% SL (vs. 11.7% – 12.7% SL), a shorter snout length 37.2% – 46.1% HL (vs. 50.8% – 52.6% HL), a weekly developed slope present between anterior nares (vs. protuberant slope from preceding area of anterior nares) and adpressed anal-fin tip reaching about middle of caudal peduncle (vs. adpressed anal-fin tip slightly anterior to end of caudal peduncle). Barbatula ommata differs from B. fluvicola , which have widely overlapping distribution ranges, by having ventral border of dentary straight (vs. ventral border of dentary curved; Figure 8), shorter coracoid, half-length of cleithrum (vs. coracoid long, occupying at least two thirds of cleithrum length; Figure 7), larger swimbladder bony capsule, occupying slightly more than half of head depth (Figure 13) (vs. smaller swimbladder bony capsule, not reaching half of head depth), and posterior border of swimbladder bony capsule rounded in ventral view (Figure 13) (vs. posterior border of swimbladder bony capsule straight in ventral view).

Description. Morphometric data and counts are provided in Table 2. Body robust and elongate, cylindrical in cross-section at trunk. Dorsal profile of trunk approximately straight descending from dorsal-fin origin to middle of caudal-fin peduncle; ascending from that point to caudal-fin origin. Ventral profile of trunk straight, except from anal fin descending towards caudal-fin end. Dorsal head profile slightly concave from snout tip to posterior border of supraoccipital. Trunk depth similar along its length slightly decreasing posteriorly dorsal-fin base towards middle of caudal-fin peduncle. Greatest body depth slightly anterior to dorsal-fin origin. Body width decreasing and gradually compressed from pectoral-fin origin towards caudal fin. Greatest body width at dorsal-fin origin.

Head cylindrical in dorsal view, longer than wide. Eyes laterodorsally positioned, located at middle of head length. Ocular capsule rounded to slightly ellipsoid. Nostrils small; anterior naris opening slightly smaller than posterior one. Anterior nostril with an elongate fleshy flap-like tube oriented laterodorsally. Posterior naris in oval shape with anterior border slightly pointed. Anterior and posterior nostril close to each other and connected by thin skin ridge.

Ventral border of gill opening attached to body at line of pectoral-fin base. Mouth ventral, arched in a semicircular shape. Mouth wide, almost equal to head width. Gape twice times longer than deep. Upper lip somewhat slim, leaving exposed middle portion of premaxilla area. Median incision usually deep, occupying approximately entire lip depth; poorly developed in some individuals. Lower lip separately at midline by a deep notch. Mesial portion of lower lip developed in a fleshy fold in inverted U-shape forming a mental lobe. Mental lobes usually separate each other at mid-line along entire length; without protrusion. Anterior border of lower lips in majority of specimens not covering anterior border of dentary, leaving this portion visible. Lateral portion of lower lip positioned inclined in 45 Ǫ angle to vertical midline, not bearing evident furrows; posterior tip without projection. Lower and upper lips rugous covered with small rounded papillae in its entire length. Barbels tapering gradually towards tips. Two pairs of premaxillary barbel of similar width. Tip of mesial premaxillary barbel reaching or almost reaching to base of maxillary barbel. Lateral premaxillary barbel tip surpassing middle of posterior naris usually reaching anterior border of eye. Maxillary barbel slightly surpassing vertical of middle of eye.

Pectoral-fin rays i,11* (31). Innermost soft ray unbranched and tiny, usually visible only in C&S specimens. Distal margin of pectoral fin truncated or convex. Principal unbranched pectoral-fin ray slightly longer than two-thirds of longest pectoral-fin ray. Pelvic-fin rays i,7* (31). Pelvic fin ellipsoid, its origin at vertical through second branched dorsal-fin ray. Pelvic fin with distal margin convex, its tip slightly anterior to vertical of end of adpressed dorsal fin. Axillary pelvic lobe present, conspicuous attached to body, in oblate ellipsoid shape. Dorsal-fin origin located slightly after middle of body; distal margin slightly convex to truncated. Dorsal fin with 3 small (6 C&S), unbranched rays, and i,7½* (30) or i,8½ (1). Dorsal fin with 9 (4 C&S) or 10 (2 C&S) pterygiophores. First dorsal-fin pterygiophore composed by what seems a supraneural and first proximal radials fused each other in a single complex structure supporting 3 shorter simple rays + a principal longest unbranched ray. Remaining 8 or 9 pterygiophores with posterior laminar bony keel, supporting their respectively branched ray, except last pterygiophore lacking any correspondent ray, and smaller in size. Ultimate 1½ dorsal-fin rays supported by the penultimate pterygiophore. Principal dorsal-fin unbranched ray shorter than the subsequent outermost three branched rays, reaching two-thirds of its length. First dorsal-fin pterygiophore inserted anterior to neural spine of 13 – 14th vertebrae (6 C&S). Distal margin of anal fin slightly concave due to longer mid-rays. Anal fin with 2 – 3 shorter simple rays (6 C&S) plus i,5½* (25) rays. Two to 3 simple rays + first unbranched principal ray supported by composed structure of at least 3 proximal radials fused in a single element; remaining branched rays supported by 5 pterygiophores; ultimate pterygiophore supporting 1½ rays. Anal-fin origin located posterior to vertical of dorsal-fin end. First pterygiophore inserted anteriorly to hemal spine of 25th or 26th vertebra (6 C&S). Caudal fin weakly emarginate (rarely truncated). Caudal-fin rays i,7 + 6,i (1), i,7 + 7,i (2), i,8 + 7,i * (23), or i,8 + 8,i (5 C&S). Procurrent rays in dorsal lobe 7, and ventral lobe with 6 rays. Procurrent rays pronounced and embedded in skin forming a dorsal and ventral adipose keels extended on up to half of caudal-peduncle length. Ventral adipose keel slightly elevated, shorter than dorsal keel. Ventral margin of caudal fin sometimes somewhat convex, while dorsal margin approximately straight in most of specimens; rarely straight in both margins. Epural reaching half-length of caudal skeleton. Upper hypural plate as a single element with hypurals 3, 4 and 5 articulated, but not fused, separate each other along entire length. Lower hypural plate with co-ossified parhypural, and hypurals 1 and 2 separated each other, forming the compound caudal centrum. Total vertebrae, 39 (3 C&S) or 40 (3 C&S); 13 pairs of ribs (6 C&S) gradually decreasing length towards caudal fin.

Body covered by embedded tiny, rounded, not overlapping scales, separated by a distance larger than scale diameter. Scales irregularly set along trunk. Scales present on flank from anterior vertical of dorsal-fin origin to caudal-fin base. Ventral portion of body with scales present only between end of pelvic-fin girdle to anal-fin origin. Scales completely absent on predorsal region and head. No evident developed dermal tubercles in any mature or juvenile individuals, even at reproductive season.

Lateral line incomplete, ending before caudal-fin base approximately at vertical of end of anal fin. Lateral line quite variable with 32 – 55 (6 C&S) canals; first three to four canals well ossified. Lateral line interrupted usually at vertical through dorsal-fin origin continuing approximately at vertical of end of anal-fin base. Lateral line canals drastically decreasing size after first half of trunk and more spaced each other towards caudal fin.

Cephalic lateral sensorial system with canals only partially ossified, between pores, sometimes weakly ossified. Infraorbital canal 11 – 12 pores (two pores + posterior-half pore of antorbital segment, and anterior-half pore + nine pores + posterior-half pore of suborbital segment). Infraorbital canal composed by the antorbital branch bearing two pores (anterior and dorsomedial) and posteriorly half-pore, close but separately from anterior-half pore of adjacent suborbital branch, followed by nine to 10 pores and ending in posterior-half pore. Posterior-half pore of suborbital segment connected to postorbital canal with anterior-half pore, plus three pores and ending in posterior-half pore connected to half pore of both supratemporal and lateral line canal. Supratemporal canal with two and half pores. Nasal canal with three pores (anterior, mid-lateral, and posterior) usually unossified (rarely weakly ossified). Frontal canal bordering orbital border, but truncated at mid-portion splitting in two branches, each one bearing three pores (anterior, lateral and posterior). Preoperculomandibular canal with eight to nine pores with anterior part located ventrally to articular and posteriorly to dentary. Trunk canal short with two pores limited by pectoral-fin girdle. Nasal canal present with three pores (Figure 1).

Colouration (in alcohol). Overall background colouration pale yellow. Body trunk covered by light to medium brown pigmentation forming irregular roundish blotches, randomly distributed (Figure 11). Pigmentation more concentrated on dorsal surface of body, with three to four brown blotches on predorsal region, and three blotches on postdorsal region, less evident in most individuals. Blotches mostly separately from each other, but coalescent. Lateral line portion usually bearing a faint brown stripe formed by coalescent blotches of pigmentation, sometimes more conspicuous and continuous at middle to end of trunk. Pigmentation fading abruptly in ventral portion of head and body, between pectoral-and-pelvic fins origins, and abdominal region. Head with more uniform dark-brown pigmentation along dorsal profile by concentration of pigmentation. Suborbital area and distal margin of opercle pale yellow to whitish with small, sparse pigmentation. Dark-brown, narrow stripe present on prenasal area, extending from snout tip to anterior portion of eye, but interrupted by nasal opening. Specimens varying in pigmentation over axillary pelvic-fin keel and at dorsal surface of pectoral-fin base, from barely present to conspicuous darker brown colour.

Pigmentation absent on maxillary barbel, but present and faded in premaxillary barbels, usually restricted to base of barbel, rarely reaching its half length: mesial premaxillary barbel more pigmented than lateral pair. Upper and lower lips deprived of any pigmentation, except by the anterior area preceding upper lips. Pectoral fin with elongate dark brown blotches over rays reaching almost entire length, except by posterior margin. Outermost six pectoral-fin rays with larger blotches, more concentrate along anterior half of fin length; fainting towards mesial portion. Concentrated dark-brown pigmentation present on dorsal-fin base and at distal portion of fin; fading at middle portion of rays. Pigmentation on dorsal-fin rays forming or not rectangular dark bars over all rays, distributed irregularly; more conspicuous on first unbranched ray. Pelvic fin with no pigmentation or rarely showing few faint pigments concentrated only on distal portion of fin. Pigmentation on anal fin mostly absent, except by distal portion with faded small pigmentation. All fins lack pigmentation on ventral surface. Caudal-fin rays covered by small irregular pigmentation over entire length, except on distal margin. Elongated dark-brown to black blotch on caudal-fin base.

Colouration in life. Similar to that observed in preserved specimens but with ground colour of body more pale yellow and mid-portion of lateral body with gold iridescent coloration in some individuals.

Distribution. Barbatula ommata is known only from the lakes Neuchatel (Figure 6b), Lucerne, Walen, Zurich, Zug, Biel and Murten, all systems of the Aare drainage in Switzerland (Figure 3). The species has been further historically reported from lakes Thun and Brienz (Figure 3), but its continued occurrence in these systems remains uncertain due to the lack of recent records, highlighting the urgent need for further surveys to confirm its persistence and presence in these lakes.

Remarks. There are four records of Barbatula in the InfoFauna database (www.infofauna.ch), dated 1988, 1998, 2001 and 2011, from two sites in Lake Thun and one record (1998) from Lake Brienz. These historical records lack accompanying photographs, voucher specimens or precise geographic coordinates, but given the ecological differences between the two new sympatric species, only B. ommata inhabits Aare lake systems. We therefore assign these historical records tentatively to this species. Despite considerable sampling efforts using electrofishing, minnow traps and nets across different seasons and years, no Barbatula specimens were observed from lakes Thun and Brienz after 2011. Given the very limited number of records, each separated by a decade or more (except for 2001), we assume that B. ommata previously inhabited these lakes but that its population has since declined drastically, likely potentially approaching local extinction. Given the limited historical records of the species from lakes Thun and Brienz and the lack of recent confirmed occurrences, a targeted search for these subpopulations is recommended to clarify their potential persistence in these lakes and assess the species' conservation status.

Additionally, only three specimens of B. ommata were recorded in Lake Murten (also known as Lac de Morat) in 2010, two of which were detected during Project Lac and one in NAWA monitoring. The InfoFauna database contains just two further records from this lake, in 1985 and 2001. A similar situation applies to Lake Zug, where there are only four specimens recorded in 2013 during project Lac. Data indicate that B. ommata is present at low abundance in Lakes Murten and Zug. Given the declining habitat quality in these lakes, we recommend systematic monitoring to assess the population dynamics and conservation status of this species. Such monitoring is crucial for developing effective conservation strategies to mitigate further habitat degradation and support the survival of B. ommata in these lakes.

Sexual dimorphism. Barbatula ommata shows epidemical tubercles in the pectoral-fin rays of adult males. The tubercles are present mostly on the innermost fourth branched pectoral-fin rays (vs. tubercles absent or not evident in females and juveniles). Difference in pectoral-fin shape is easily noticed in adults, with male showing pointed pectoral-fin tip and enlargement of outermost branched-fin rays (vs. rounded in female, and fin rays similar in width). Urogenital papilla of males small and conical (vs. urogenital in females rounded).

Etymology. Barbatula ommata from the Greek ómmata (ὄμμ ατα) for eyes, and is given in reference to the species diagnostic great diameter of its eyes. A noun in apposition.

Vernacular name. Lake Stone Loach (English), Seebartgrundel (German), Loche du Lac (French).

Ecological notes. Specimens were collected in the littoral zone of lakes. Collected on the shore down to 1.2 m water depth, most abundantly found in small pebbles substrate, and among middle-sized stones (~20 cm). Barbatula ommata and Cottus sp. are syntopic and were collected together. Few individuals dissected indicate that the species is primarily insectivorous.

Conservation status. Barbatula ommata seems endemic to Switzerland, with its distribution largely confined to lakes within the Aare catchment, including Neuchatel, Biel, Murten, Lucerne, Walen, Zug and Zurich (Figure 3). Despite extensive sampling efforts, the species has not been observed in lakes Thun and Brienz in the past 15 years, despite sporadic historical records. Assessing whether the species is approaching local extinction in these lakes is critical, as such a loss would account for 25% of its overall distribution and one entire subcatchment of the four within its original range. The Extent of Occurrence (EOO) based on the extant range of the species was estimated at 4302 km 2 by the Minimum Convex Polygon (calculated using GeoCAT tool) meeting the IUCN criteria of Endangered (B1: EOO <5000 km 2). The area of occupancy (AOO) based on IUCN methodology (2 × 2 km grid) of known records was estimated at 132 km 2 meeting the criteria of Endangered (B2: AOO <500 km 2). The AOO for the entire lake area for all lakes where the species occurs was also estimated at 490 km 2, which represents an overestimation because this species is confined to shallow littoral zones of the lakes (<1.5 m depth) requiring pebbles and small stones substrate, and it is absent from deeper areas as well as large boulders and rock faces. Barbatula ommata has a restricted distribution driven by its specific habitat requirements. Accordingly, we estimate the extent of suitable habitat within the very restricted range for the species at 26.2 km 2, considering only the shoreline areas of all lakes and excluding deeper zones where the species does not occur. We used a geospatial buffer from the shoreline to make this calculation, assuming all habitat within 50 m of the shoreline was habitable within all lakes where the species has recently been recorded (Zurich, Neuchatel, Murten, Biel, Lucerne, Walen and Zug; note that the median distance from the shoreline for B. ommata records was 13 m). The distribution of B. ommata in Swiss lakes is severely affected by urbanisation. Many areas are impacted by habitat degradation, primarily from urbanisation, pollution and the alteration of littoral zones caused by constructions, harbours, boulders and retaining walls, yet the impact degree of these modifications remains largely unknown. The loss of suitable habitats, already highly restricted (26.2 km 2), poses a significant threat to the species, which is confined to shallow littoral zones, absent from deeper lake areas and dependent on pebble and small substrate for survival. This specific habitat has currently a patchy distribution in the lakes that B. ommata occurs in, which further isolates subpopulations within the lakes of this species whose range is already naturally fragmented across lakes. Additionally, the extensive recreational use of the last natural lake shores, particularly in the summer, has potentially caused a continued decline of habitat quality and area of occupancy due to this species having its reproductive activity, feeding areas and nursery grounds in the littoral zones. Climate change is also an important factor that has been negatively impacting cold-water lakes due to the increase of water temperature in the shallow inshore zones in summer, despite it being difficult to measure the extent of impact. Barbatula ommata is naturally confined to large, oligotrophic, clear water lakes and its range is already naturally severely fragmented. Many of these lakes are surrounded by urban areas undergoing significant habitat degradation, with a notable loss of suitable habitat across multiple locations. Subpopulations in lakes Thun, Brienz, Murten, Biel and Zug are very small and have not been observed for over 12 years despite targeted collection efforts. These lakes together represent approximately 50% of the species' distribution within the lake system. The prolonged absence of B. ommata suggests a significant reduction in the AOO of the species and the population is assumed to be severely fragmented. Thus, Barbatula ommata is preliminary assessed as Endangered (EN) based on the criteria B1ab(ii,iii) + B2ab(ii,iii), according to IUCN criteria (IUCN Standards and Petitions Subcommittee, 2022).