C. brienzii Selz, Doenz , Vonlanthen & Seehausen, 2020

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 : 113-116

C. brienzii Selz, Doenz, Vonlanthen & Seehausen sp. nov.

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

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

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

Coregonus sp. "Balchen 2": Dönz et al. 2018 (see also synonymy of C. steinmanni )

Material examined.

Holotype. NMBE-1077126 , Switzerland, Lake Brienz (46°43'N, 7°57'E), 223 mm SL, female.

Paratypes. NMBE-1077116-1077125 , NMBE-1077127-1077128 , Switzerland, Lake Brienz (46°43'N, 7°57'E), N = 12, 118-226 mm SL.

Diagnosis.

Coregonus brienzii is a medium-sized whitefish with moderate pigmentation of all fins and body; light to dark 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; stout caudal peduncle; short head; moderately large eye with a moderately thick and triangular shaped eye socket.

Differential diagnosis.

Coregonus brienzii occurs only in Lake Brienz and we therefore compare the characters of this species specifically with the species of Lake Brienz. Differential diagnoses against C. albellus , C. alpinus , and C. fatioi are given under those species’ accounts.

Description.

General appearance is shown in Figure 8. Morphological and meristic characters of both sexes can be found in Table 7 and Suppl. material 1: Table S6 and first- and second-best ratios for both sexes combined can be found in Table 11 . The description is valid for both sexes.

Shape: Moderately deep bodied with greatest body depth anterior of the dorsal fin. Dorsal profile moderately arched compared to ventral profile. The dorsal profile from the tip of snout to the anterior origin of dorsal fin is moderately convex, whereas the ventral profile is slightly arched such that is almost straight or slightly convex from the interorbital area to the pelvic fin origin. In some specimens the ventral profile and dorsal profile are similar and only slightly arched. Head moderately short. Mouth is rather thin (i.e., width of upper and lower jaw), moderately short and terminal to sub-terminal. The snout can range from almost equally wide as deep to wider than deep, and is only moderately pronounced, since the tip of the snout can sometimes be fleshy and roundish. Moderately large eye. The eye-socket is thick and triangular (i.e., sickle-shaped). Pectoral fin moderately tapered. The anterior unbranched ray of the erected dorsal fin is almost vertically straight with an approx. 70-80° angle to the body axis and is only bent slightly posteriorly at the end of the ray. Caudal peduncle is moderately stout and short. Caudal fin forked and sometimes slightly asymmetrical with the dorsal part being longer. Unbranched ray of anal fin mostly straight and only sometimes slightly bent posteriorly. Anal fin longest anteriorly and progressively shortening posteriorly with the outer margin of the anal fin mostly slightly concave and only rarely straight.

Meristics: Many gill rakers that are moderately long.

Colour: Pigmentation of fins and body overall moderate in live specimens. The pectoral fin is mostly translucent and only rarely moderately pigmented at the median to distal parts of the fin. The dorsal, adipose, pelvic, anal, and caudal fins are moderately pigmented. Silvery appearance along the flanks with moderate to many pigmented small dots on the scales. The dots are found along the flank and the dorsum. 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 (as can be found for the species of C. alpinus and C. fatioi from both lakes and C. steinmanni from Lake Thun). 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 is moderately pigmented. The snout around the nostrils is moderately pigmented with 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. 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 brienzii is found in Lake Brienz (46°43'N, 7°57'E) which is connected with Lake Thun through the river Aare at Interlaken. Our previous genetic work ( Dönz et al. 2018) suggested that C. brienzii is the same species as C. steinmanni and that it together with the other three species, C. alpinus , C. fatioi , and C. albellus , is present in both lakes. All four species displayed the same genetic relationships in both lakes (i.e., the same hierarchical grouping into distinct genotypic clusters and similar extends of genetic divergence). However, recent analyses of whole-genome data (De-Kayne et al. unpublished) revealed, that specimens of C. steinmanni from Lake Thun do not group with those of C. brienzii , whereas those of the other three species from both lakes do cluster together. Instead the whole genome data suggests that C. steinmanni clusters closer to C. alpinus from Lake Thun - as has previously been shown with genetic data ( Dönz et al. 2018) - and that C. brienzii clusters closer to C. fatioi from Lake Brienz. Interestingly, we also find morphological relationships to differ between the lakes; in Lake Thun C. steinmanni groups in morphospace with C. alpinus , whereas in Lake Brienz C. brienzii groups in morphospace with C. fatioi .

Coregonus brienzii most likely feeds on a mix of benthic prey and zooplankton (stomach content: Maurer and Guthruf 2005; Müller et al. 2007; isotopic signatures: Selz 2008; Hudson 2011) and has a moderatly fast growth rate ( Müller et al. 2007). It has to be noted that the work by Kirchhofer (1995), Maurer and Guthruf (2005) and Müller et al. (2007) did not distinguish between all species in Lake Brienz and thus lumped different species together into few groups. 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 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 ). Also, the isotopic work by Selz (2008), and Hudson (2011) did not yet differentiate between C. fatioi and C. brienzii . The relative species abundances in the pelagic and benthic habitat from a habitat-stratified random sampling of Lake Brienz (mid-September 2011: Vonlanthen et al. 2013) shows, that C. brienzii is absent from the benthic habitat and is present in the moderately deep pelagic waters (30 m; N = 1) ( Dönz et al. 2018). It is to note that the habitat-stratified random sampling data only covers a short period of time (one month in late summer) and it is thus not clear how the species is distributed spatially through the rest of the year. Coregonus brienzii resembles phenotypically C. fatioi . The average size (total length) at 3 years of age for specimens in this study is 254 + 14 mm (N = 8) (Suppl. material 1: Figures S5, S6). The size at 3 years of age of C. brienzii is similar to that of C. fatioi , slightly smaller than that of C. alpinus and consider ably larger than that of C. albellus (Suppl. material 1: Figure S6). Coregonus brienzii has a short spawning season in late December (Suppl. material 1: Figure S3; Dönz et al. 2018). Coregonus brienzii spawns mostly in moderately shallow waters of 10 m down to 60 m and rarely to 100 m (Suppl. material 1: Figure S3; Bittner 2009; Dönz et al. 2018). The spawning season and depth of C. brienzii overlaps largely with that C. fatioi .

Etymology.

The specific epithet brienzii is the genitive of Brienz. We name this species after Lake Brienz, as it is the only endemic whitefish species known for Lake Brienz.

Common name.

None. We suggest the German name "Brienzer Kleinbalchen"