Coregonus alpinus Fatio, 1885

Selz, Oliver M., Doenz, Carmela J., Vonlanthen, Pascal & Seehausen, Ole, 2020, A taxonomic revision of the whitefish of lakes Brienz and Thun, Switzerland, with descriptions of four new species (Teleostei, Coregonidae), ZooKeys 989, pp. 79-162 : 96-102

Coregonus alpinus Fatio, 1885

Coregonus "Albock": Rufli 1978, 1979; Kirchhofer and Tschumi 1986; Kirchhofer 1995 (see also synonymy of C. steinmanni and C. acrinasus )

Coregonus balleus : Fatio 1885

Coregonus "Balchen", "THU2": Douglas et al. 1999, 2003; Douglas and Brunner 2002 (see also synonymy of C. steinmanni )

Coregonus "Balchen": Heuscher 1901; Surbeck 1917 (see also synonymy of C. steinmanni )

Coregonus "Felchen": Kirchhofer 1990; Kirchhofer 1995 (see also synonymy of C. fatioi and C. brienzii )

Coregonus "Large type": Maurer and Guthruf 2005; Müller et al. 2007 (see also synonymy of C. fatioi and C. brienzii )

Coregonus lavaretus natio arurensis, oekot. litoralis: Steinmann 1950

Coregonus lavaretus natio arurensis, oekot. primigenius: Steinmann 1950 (see also synonymy of C. fatio and C. steinmanni )

Coregonus schinzii alpinus : Fatio 1885

Coregonus schinzii helveticus : Fatio 1890

Coregonus schinzii helveticus var. Thunensis : Fatio 1890

Coregonus sp. "Balchen": Hudson et al. 2011, 2013, 2016; Ingram et al. 2012; Vonlanthen et al. 2012, 2015; Lundsgaard-Hansen et al. 2013; Roesch et al. 2013; Vonlanthen and Périat 2013 (see also synonymy of C. steinmanni and C. brienzii )

Coregonus sp. "Balchen 1": Dönz et al. 2018

Coregonus "Albock", "Uferalbock": Steinmann 1950 (see also synonymy of C. steinmanni and C. fatioi )

Material examined.

Lectotype. MHNG-717.045 , Switzerland, Lake Thun (46°40'N, 7°46'E), 283 mm SL, sex unknown.

Non-types. NMBE-1077241-1077261 , Switzerland, Lake Thun (46°40'N, 7°46'E), N = 21, 210-364 mm SL; NMBE-1059817 ; 1059821 ; 1077134 , NMBE-1077110- 1077115 , Switzerland, Lake Brienz (46°43'N, 7°57'E), N = 9, 147-290 mm SL.

Diagnosis.

Coregonus alpinus is a large whitefish with strong pigmentation of all fins and the body; greenish blue colour on the flanks above the lateral line; moderate to many pigmented small dots on the scales along the flank and the dorsum; deep bodied; truncated blunt snout; short head; sub-terminal mouth; small eye with a thick and triangular-shaped eye socket; short and stout caudal peduncle; few and short gill rakers.

Differential diagnosis.

Differential diagnosis against C. albellus is given under that species account. The total number of gill rakers of 25 to 34 with mode-values of 28, 29, and 30 distinguishes C. alpinus from all other six whitefish species of lakes Thun and Brienz, by either having more gill rakers than the species C. profundus (total GR: 15-27, mode = 21) or fewer gill rakers than C. fatioi (total GR: 32-43, mode = 38), C. albellus (32-44, mode = 38), C. steinmanni (30-35, mode = 31), C. brienzii (32-39, mode = 37) and C. acrinasus (30-40, mode = 36) (Suppl. material 1: Table S6). The contemporary gill raker range is congruent with the historical gill raker range (23-27) given in Fatio (1890).

For specimens in Lake Brienz smaller than 163.5 mm SL C. alpinus can be distinguished from the other three whitefish species by a larger "length of the depressed anterior part of the dorsal fin / lower jaw length" ratio (DFAd/LJ: 2.57-2.58 vs. 1.6-2.1). For fish larger than 163.5 mm SL, C. alpinus can be distinguished from C. brienzii and C. fatioi by a larger "length of the erected anterior part of the dorsal fin / upper jaw length" ratio (DFAe/UJ: 3.28-4.1 vs. 2.58-3.19). With the full-size range (100-290 m) of Lake Brienz specimens, C. alpinus can be distinguished from the other three whitefish species by a larger "length of the erected anterior part of the dorsal fin / upper jaw length" ratio (DFAe/UJ: 3.25-4.1 vs. 2.14-3.19) (Table 11 ).

Coregonus alpinus - Coregonus fatioi

The specimens from lakes Thun and Brienz of C. alpinus can be distinguished from those of C. fatioi by having a shorter under jaw (24.3-30.1% HL, mean = 27.4 vs. 27.6-34.1% HL, mean = 30), and a shorter longest gill raker (10-15.2% HL, mean = 11.9 vs. 12.3-22.6, mean = 15.6).

In Lake Brienz C. alpinus can be distinguished from C. fatioi by having a shorter caudal peduncle (11.3-13.9% SL, mean = 12.5 vs. 13.1-16.1% SL, mean = 14.2) and a shorter and narrower lower jaw (lower jaw length: 33.8-39.4% HL, mean = 38.2 vs. 37.6-48.4% HL, mean = 42.6; lower jaw width: 7.3-10.6% HL, mean = 8.8vs. 8.6- 13.3% HL, mean = 11.6). For fish from Lake Brienz larger than 163.5 mm SL, C. alpinus can be distinguished based on ratios from C. fatioi by having a larger "length of the erected anterior part of the anal fin / upper jaw length" ratio (AFAe/UJ: 1.96-2.5 vs. 1.66-1.96) and a larger "head length / upper jaw length" ratio (HL/UJ: 3.55-3.93 vs. 3.13-3.55). With the full size range (100-290 mm) of Lake Brienz specimens, C. alpinus can be distinguished from C. fatioi by having a larger "length of the erected anterior part of the dorsal fin / upper jaw length" ratio (DFAe/UJ: 3.25-4.1 vs. 2.14-3.19) (Table 11 ).

In Lake Thun C. alpinus can be further distinguished from C. fatioi by having a shorter postdorsal length (38.3-43.9% SL, mean = 42.7 vs. 41.6-50.7% SL, mean = 44.9) and a thicker eye socket (3.4-6.3% HL, mean = 5.1 vs. 1.7-5.9% HL, mean = 3.6). Based on ratios C. alpinus can be distinguished from C. fatioi by having a larger "caudal peduncle depth / postdorsal length" ratio (CD/PostD: 0.17-0.21 vs. 0.14-0.17) (Tables 4 , 5 , 10 ).

Coregonus alpinus - Coregonus brienzii

C. alpinus from Lake Brienz can be differentiated from C. brienzii by having a shorter caudal peduncle (11.3-13.9% SL, mean = 12.5 vs. 12.2-15.8% SL, mean = 13.8), a shorter upper and lower jaw (upper jaw: 25.4-29.1% HL, mean = 26.8 vs. 27.1-32% HL, mean = 29.5; lower jaw: 33.8-39.4% HL, mean = 38.2 vs. 40.5-45.7% HL, mean = 42.2), a narrower snout (14.6-17.6% HL, mean = 15.7 vs. 15.7-20.2% HL, mean = 17.8), a narrower lower jaw (7.3-10.6% HL, mean = 8.8 vs. 10.1-14.1% HL, mean = 11.5) and shorter gill rakers (middle gill raker length: 8.3-11.2% HL, mean = 9.8 vs. 10.9-15.1% HL, mean = 13.5; longest gill raker length: 10-12.3% HL, mean = 10.8 vs. 12.1-16.8% HL, mean = 14.7). For fish larger than 163.5 mm SL, C. alpinus from Lake Brienz can be distinguished based on ratios from C. brienzii by having a larger "caudal peduncle depth / snout width" ratio (CD/SW: 2.25-2.64 vs. 1.82-2.04), "length of the erected anterior part of the dorsal fin / length from the adipose fin to the caudal fin base" ratio (DFAe/PAdC: 1.11-1.32 vs. 0.96-1.16) and by having a smaller "lower jaw width / upper jaw width" ratio (LJW/UJW: 0.33-0.44 vs. 0.45-0.55). With the full size range (100- 290 mm) of Lake Brienz specimens, C. alpinus can be distinguished from C. brienzii by having a larger "length of the depressed anterior part of the dorsal fin / lower jaw width" ratio (DFAd/LJW: 9.84-14.82 vs. 6.05-8.91), "dorsal head length / lower jaw length" ratio (DHL/LJ: 1.84-2.22 vs. 1.63-1.82), "head depth / lower jaw width" ratio (HD/LJW: 6.72-9.39 vs. 5.23-6.66), "head length / lower jaw length" ratio (HL/LJ: 2.54-2.96 vs. 2.19-2.47) and a smaller "length of the pectoral fin 2 / length of the depressed anterior part of the dorsal fin" ratio (PecF2/DFAd: 0.74-0.85 vs. 0.85-1.03) (Tables 4 , 7 , 11 ).

Coregonus alpinus - Coregonus profundus

Coregonus alpinus from Thun differs from C. profundus by having shorter pectoral fins (pectoral fin 1 length: 13.6-18.7% SL, mean = 16.2 vs. 16.6-21% SL, mean = 18.4; pectoral fin 2 length: 15.3-19.7% HL, mean = 17 vs. 17.7-23.2% SL, mean = 20.2), a deeper caudal peduncle (7.6-8.9% SL, mean = 8.2 vs. 6.5-7.9% SL, mean = 7.3), a shorter head (12.6-15.6% SL, mean = 14.2 vs. 15.5- 18.4% SL, mean = 16.4) and longer gill rakers (middle gill raker length: 9.3-15.2% HL, mean = 11.3 vs. 7.6-11.7% HL, mean = 9.2; longest gill raker length: 10.6-15.2% HL, mean = 12.3 vs. 7.8-12.4% HL, mean = 10.1). Based on ratios C. alpinus can be distinguished from C. profundus by having a larger "caudal peduncle depth / dorsal head length" ratio (CD/DHL: 0.54-0.62 vs. 0.4-0.49) (Tables 4 , 8 , 10 ).

Coregonus alpinus - Coregonus acrinasus

Coregonus alpinus can further be differentiated from C. acrinasus by having a shorter lower jaw (36.6-41.4% HL, mean = 38.6 vs. 38.6-47% HL, mean = 40.9). Based on ratios C. alpinus can be distinguished from C. acrinasus by having a larger "caudal fin length / maxilla length" ratio (CF/M: 5.55-6.55 vs. 4.4-5.57) (Tables 4 , 9 , 10 ).

Description.

General appearance is shown in Figure 5. Morphological and meristic characters of both sexes can be found in Table 4 and Suppl. material 1: Table S6 and first- and second-best ratios for both sexes combined can be found in Tables 10 , 11 . The description is valid for both sexes and both lakes; differences between the populations of lakes Thun and Brienz are mentioned.

Shape: Generally deep bodied with greatest body depth anterior of the dorsal fin. Dorsal profile strongly arched compared to ventral profile such that the dorsal profile from the tip of snout to the anterior origin of dorsal fin is moderate to strongly convex. Ventral profile slightly arched such that almost straight or slightly convex from the interorbital area to the pelvic fin origin. Head short. Mouth thin (i.e., width of upper and lower jaw), short and sub-terminal. Rostral plate pronounced and almost equally wide as deep resulting in an almost square shape. Tip of the snout often blunt. Small eye, which is less pronounced in specimens from Lake Brienz. Eye-socket thick and triangular (i.e., sickle-shaped). Pectoral fin moderately tapered. Dorsal fin long with the anterior unbranched ray of the erected dorsal fin approx. 60-70° angle to body axis and only slightly bent posteriorly at the end of the ray. Caudal peduncle stout and short with the caudal fin forked and sometimess lightly asymmetrical with either the ventral or dorsal part being longer. Unbranched ray of anal fin slightly bent posteriorly. Anal fin longest anteriorly and progressively shortening posteriorly with the outer margin of the anal fin mostly straight and only rarely slightly concave.

Meristics: Few short gill rakers, which are shorter for specimens from Lake Brienz.

Colour: Pigmentation of fins and body over all strong in live specimens. In specimens from Lake Thun the pectoral fin is moderately to strongly pigmented. Dorsal, adipose, pelvic, anal and caudal fins are strongly pigmented. In specimens from Lake Brienz all fins are less pigmented. The pectoral fin is sometimes yellowish and ranges from translucent to moderately pigmented at the median to distal parts of the fin. Dorsal, adipose, pelvic, anal, and caudal fins are moderately pigmented. In both lakes fish have a silvery appearance along the flanks with few to many pigmented small dots on the scales along the flank and the dorsum (as can be found for the species of C. fatioi , C. steinmanni , C. brienzii ). The distribution of the dots is bound to the scale patterning such that the dots are found at the edge of the scales or at the boundary point of two scales. Dorsally above the lateral line the silvery appearance changes to a light (e.g., RGB (135, 236, 179)) or darker greenish blue colour (e.g., RGB (7,168,125)). The dorsal part of the head of specimens of Lake Brienz is moderately pigmented, whereas that of specimens from Lake Thun is strongly pigmented. The snout around the nostrils is moderately (Lake Brienz) to strongly (Lake Thun) pigmented. Specimens in Lake Brienz have a gap of very weak pigmentation posteriorly of the nostrils up to the height of the middle of the eyes. The pre-operculum and operculum are silvery with one black dot on the lower margin of the pre-operculum. In some specimens of Lake Thun, the pre-operculum and operculum has some pigmented dots, similar to those found on the scales and extending also to the dorsal part of the head. For a comparison to the main colouration found in the other species see Suppl. material 1: Figure S8. Preserved specimens are pale in colouration with similar pigmentation as described for live specimens. The silvery, translucent, not coloured or unpigmented parts of the body become brown-yellowish (e.g., RGB (239, 210, 40)), whereas the pigmented parts are conserved and the coloured parts (dorsally above the lateral line) become brownish (e.g., RGB (186, 140, 100)).

Distribution and notes on biology.

Coregonus alpinus is found in the lakes Thun (46°40'N, 7°46'E) and Brienz (46°43'N, 7°57'E) that are connected through the river Aare at Interlaken. Coregonus alpinus feeds predominantly on benthic prey and parts of the year on zooplankton (stomach content for Lake Brienz: Maurer and Guthruf 2005; Müller et al. 2007; isotopic signature for both lakes: Selz 2008; Hudson 2011; Ingram et al. 2012) and has a rapid growth rate (Lake Brienz: Müller et al. 2007; both lakes: Kirchhofer 1995; Bittner et al. unpublished). It has to be noted that the stomach content and isotopic work did not distinguish between all species in lakes Thun or Brienz and thus in some cases lumped different species together into few groups. The stomach content work by Maurer and Guthruf (2005) and Müller et al. (2007) differentiated between "small-type" and "large-type" whitefish based on cohort-specific threshold values for length-at-age. Based on morphology and ecology Kirchhofer (1995) differentiated in Lake Thun between "Albock" (comprising most likely of C. alpinus , C. steinmanni and C. acrinasus ), "Brienzlig" (comprising most likely of C. albellus and C. fatioi ) and "Kropfer" ( C. profundus ) and in Lake Brienz between "Felchen" (comprising most likely of C. alpinus , C. fatioi and C. brienzii ) and "Brienzlig" and "Winter-Brienzlig" (comprising of summer- and winter-spawning specimens of C. albellus ). Finally, Selz (2008), Hudson (2011) and Ingram et al. (2012) did not yet differentiate between C. alpinus and C. steinmanni in Lake Thun, which were most likely both grouped under C. "Balchen". The gill raker number and length of C. alpinus (few and short gill rakers) suggests, based on the functional properties of the number of gill rakers experimentally tested with specimens of this species and other whitefish species from lakes Thun and Lucerne ( Lundsgaard-Hansen et al. 2013; Roesch et al. 2013), that C. alpinus feeds more on benthic prey and less on zooplankton. However, this assumption needs to be verified with stomach content analysis that distinguish between the different species within a lake.The relative species abundances in the pelagic and benthic habitat from a habitat-stratified random sampling of Lake Thun (mid-October 2013: Vonlanthen et al. 2015) and Brienz (mid-September 2011: Vonlanthen et al. 2013) shows, that C. alpinus can only be found in shallow water in the benthic habitat (first 15 m; N = 1 each for lakes Thun and Brienz) and is completely absent from the pelagic habitat in Lake Thun, while in Lake Brienz it can be also found in the very shallow waters (approx. first 5 m; N = 2) of the pelagic habitat ( Dönz et al. 2018). It is noteworthy that the habitat-stratified random sampling data for both lakes only covers a short period of time (one month in late summer) and it is thus not clear how the species are distributed spatially throughout the rest of the year. In Lake Thun C. alpinus resembles phenotypically C. steinmanni and to some extent C. acrinasus . The average size (total length) at 3 years of age for specimens in this study is 321 ± 20 mm (mean and standard deviation, N = 8) and 273 + 14 mm (N = 4) for lakes Thun and Brienz respectively (Suppl. material 1: Figures S4-S6). The average size at 3 years of age for the specimens of C. alpinus from Lake Thun from this study are similar to those for the years 1969-1970 (333.8 ± mm, N = 13) and 2004-2005 (342.8 ± 21 mm, N = 14) (Bittner et al. unpublished; Vonlanthen et al. unpublished). In Lake Thun the size at 3 years of age of C. alpinus is similar to that of C. steinmanni , larger than that of C. acrinasus and considerably larger than that of C. albellus , C. fatioi and C. profundus (Suppl. material 1: Figure S6). In Lake Brienz the size at 3 years of age of C. alpinus is larger than that of C. fatioi and C. brienzii and considerably larger than that of C. albellus (Suppl. material 1: Figure S6). However, the size-at-age comparisons should be treated with some caution since the sample size for C. alpinus is rather small. Coregonus alpinus has a short spawning season in late December and spawns mostly in very shallow water (1-2 m) and to a lesser extent down to 10 m and very seldom down to 30 m or more (Suppl. material 1: Figure S3; Bittner 2009; Dönz et al. 2018). Coregonus alpinus spawns earlier in Lake Brienz than in Lake Thun ( Fatio 1890; Dönz et al. 2018). The spawning season and depth of C. alpinus overlaps largely with that of C. acrinasus , C. fatioi and C. steinmanni in Lake Thun and with that of C. fatioi and C. brienzii in Lake Brienz.

Kottelat (1997) has designated a lectotype as C. alpinus which is incongruent with his description of the species (with the common name "Kropfer": Kottelat (1997) and Kottelat and Freyhof (2007)). Fatio (1885, 1890) was unaware of this species (the "Kropfer") as it is not considered in his compendium of the Swiss fauna ( Fatio 1890) nor in his earlier work on the Swiss whitefish ( Fatio 1885). The lectotype designated by Kottelat (1997) to C. alpinus clearly and correctly resembles the description given by Fatio ( Fatio 1885, 1890) for the species-group Coregonus schinzii alpinus (Fatio, 1885) and later Coregonus schinzii helveticus (Fatio, 1890), known then and today by its local name as "Balchen". Fatio (1890) describes the "Balchen"-type whitefish as a relatively large whitefish,with few and short gillrakers, a short and stout head with a thick and squared snout, mouth inferior and often subterminal especially for specimens from Lake Thun, a more or less small eye, caudal peduncle short and stout, long pectoral fin, all fins more or less strongly pigmented, colour of live specimens generally olive or grey-olive with greenish or blueish reflections on the back, head more or less strongly pigmented, black pigmented dots more or less abundant on the dorsum, and on the margins of the scales, spawning season in winter (November-December) and spawning depth rather shallow at the shoreline over boulders or stones ( Fatio 1885: Page 663, Tables 1 , 2 ; Fatio 1890: Pages 222-234). This description is very clearly and accurately that of a "Balchen", and very different from "Kropfer". We thus identify C. alpinus as the species from lakes Thun and Brienz known under the common name "Balchen". The description of C. alpinus in Kottelat (1997) and Kottelat and Freyhof (2007) and the photograph in Kottelat and Freyhof (2007) does not describe and depict "Balchen" but C. profundus , the species from Lake Thun known by the common name "Kropfer".

Common name.

Balchen.