Coregonus intermundia, Selz & Seehausen, 2023

Selz, Oliver M. & Seehausen, Ole, 2023, A taxonomic revision of ten whitefish species from the lakes Lucerne, Sarnen, Sempach and Zug, Switzerland, with descriptions of seven new species (Teleostei, Coregonidae), ZooKeys 1144, pp. 95-169 : 95

Coregonus intermundia sp. nov.

Figs 4 , 14

Coregonus sp. 'benthic intermediate’: Hudson et al. 2016.

Coregonus sp. ‘Schwebbalchen’: Vonlanthen et al. 2012; Alexander et al. 2017a (see also synonymy of C. suspensus ).

Material examined.

Holotype. Contemporary specimen (year: 2007): NMBE- 1078097, 274 mm SL, male; Switzerland: Lake Lucerne . Paratypes. All from Switzerland, Lake Lucerne: Contemporary specimens (year: 2007): NMBE-1078076, NMBE-1078077, NMBE-1078078, NMBE-1078084, NMBE-1078086-1078090, NMBE-1078093-1078096, N =13, 232- 278 mm SL .

Diagnosis.

Coregonus intermundia is a medium-sized whitefish (standard length at 3 years of age: range = 243-300 mm, mean = 273) with moderate pigmentation of all fins and the body; greenish blue colour on the flanks above the lateral line; moderate number of pigmented small dots on the scales along the flank; short head (19.1-21.5% SL, mean = 20.3); sub-terminal mouth; thick (3.4-5.7% HL, mean = 4.4) and triangular-shaped eye socket; rather short and stout caudal peduncle (caudal peduncle depth: 7-8.3% SL, mean = 7.5; caudal peduncle length: 11.6-14.4% SL, mean = 12.9).

Description.

Shape: Only slightly deep bodied with greatest body depth anterior of dorsal fin. Dorsal profile from tip of snout to anterior origin of dorsal fin and ventral profile from interorbital area to pelvic fin origin are moderately convex. Head moderately short. Mouth moderately long and mostly sub-terminal and rarely terminal. Lower jaw moderately wide. Rostral plate equally wide as deep, not strongly pronounced with tip of the snout often more pointed than blunt. Eye-socket thick and sickle cell-shaped. Pectoral fin moderately tapered and moderately short. Dorsal fin rather short with anterior unbranched ray of erected dorsal fin mostly 70-80° angle to body axis, almost straight and only very slightly bent posteriorly at end of the ray. Dorsal fin longest anteriorly and progressively shortening posteriorly with outer margin of dorsal fin mostly straight and rarely concave. Caudal peduncle stout and moderately short with caudal fin moderately forked. Unbranched rays of anal fin slightly bent posteriorly. Anal fin longest anteriorly and progressively shortening posteriorly with outer margin of anal fin mostly straight and only rarely slightly concave. Meristics: Moderately many and moderately long gill rakers. Colour: Pigmentation of fins and body overall moderately strong in live specimens. Pectoral fin slightly pigmented at distal parts of fin. Pelvic fin moderately pigmented at the median to distal parts of fin. All other fins strongly pigmented. Silvery appearance along flanks with moderate number of pigmented small dots (aggregation of melanophores) on scales along flank and dorsum. Distribution of dots bound to scale patterning such that dots are found at edge of the scales or at boundary point of two scales. Dorsally above the lateral line the silvery appearance changes to a pale greenish to dark greenish blue colour and sometimes with pale mustard yellow ground colour. Dorsal part of head and snout around nostrils moderately pigmented. Pre-operculum and operculum silvery with one black spot on lower margin of pre-operculum. Preserved specimens pale in colouration with similar pigmentation as described for live specimens. The silvery, translucent, not coloured or unpigmented parts of body become yellowish brown, whereas pigmented parts are conserved and coloured parts (dorsally above the lateral line) become brownish.

Differential diagnosis.

The differential diagnosis against C. litoralis and C. sarnensis are given under those species’ accounts.

Coregonus intermundia - Coregonus suspensus

Coregonus intermundia can be distinguished from C. suspensus based on having a smaller 'predorsal length / eye diameter’ ratio (PreD/ED: 9.92-10.59 vs. 10.73-11.4) (Table 10 ).

Coregonus intermundia - Coregonus nobilis

Coregonus intermundia differs from C. nobilis by having an anteriorly longer erected and depressed dorsal fin (erected dorsal fin: 16.7-19.9% SL, mean = 18.2 vs. 15.3-17.2% SL, mean = 16.3; depressed dorsal fin: 18.2-21.5% SL, mean = 19.7 vs. 16.7-18.8% SL, mean = 17.8), a shallower snout (5.2-10.8% HL, mean = 8.3 vs. 7.9-12.4% HL, mean = 10.5) and head (43.5-49.8% HL, mean = 46.4 vs. 46.2-55% HL, mean = 50.6 (Tables 3 , 5 ). Based on ratios C. intermundia differs from C. nobilis by having a larger 'caudal peduncle depth / head width’ ratio (CD/HW: 0.77-0.87 vs. 0.63-0.77) (Table 10 ).

Coregonus intermundia - Coregonus muelleri

Coregonus intermundia differs from C. muelleri by having strong pigmentation of all fins vs. none or very little pigmentation of the pectoral, anal, caudal and dorsal fin in C. muelleri , by having a deeper caudal peduncle (7-8.3% SL, mean = 7.5 vs. 6.3-7.4% SL, mean = 6.9), a shorter head (19.1-21.5% SL, mean = 20.3 vs. 20.3-23.5% SL, mean = 22), smaller eye (eye diameter: 20.4-23.3% HL, mean = 22.1 vs. 22.2-26% HL, mean = 24.1; eye cavity: 23.8-27.9% HL, mean = 25.9 vs. 26.4-31.1% HL, mean = 27.7), differently shaped eye socket (sickle cell-shaped vs. roundish), a longer postorbital length (50.2-55.8% HL, mean = 52.6 vs. 48.4-52.6% HL, mean = 50.6) and a shorter lower jaw (38.8-42% HL, mean = 39.9 vs. 40.3-45.8% HL, mean = 42.7) (Tables 3 , 6 ). Based on ratios C. intermundia differs from C. muelleri by having a larger 'caudal peduncle depth / eye diameter’ ratio (CD/ED: 1.53-1.84 vs. 1.12-1.43) (Table 10 ). Furthermore, the average standard length at 3 years of age differentiates C. intermundia (range = 243-300 mm, mean = 273) from C. muelleri (160-232 mm, 194 mm). (Suppl. material 1: table S3).

Distribution and notes on biology.

Coregonus intermundia occurs in all basins of Lake Lucerne (Fig. 2 ) except possibly in Lake Alpnach. It has been caught during the spawning season in all basins except for Lake Alpnach, where no nets were set by Hudson et al. (2016). There is no isotopic or stomach content data available for C. intermundia to infer the prey spectrum of this species. Coregonus intermundia is a medium-sized whitefish species and the size (i.e., standard length) at 3 years of age of C. intermundia is smaller than that of C. litoralis , considerably larger than that of C. muelleri and almost equal to that of C. suspensus (Suppl. material 1: table S3). We cannot compare its size to C. nobilis since only older individuals of the latter species have been caught ( Hudson et al. 2016). Coregonus intermundia has most likely a short spawning season in winter around the month of December. The spawning season lasts for approximately two weeks and the spawning depth is mostly in shallow waters (10-30 m, rarely 40 m; Hudson et al. 2016). The spawning depth of C. intermundia overlaps partially with that of C. litoralis , with the former spawning deeper than the latter ( Hudson et al. 2016).

Etymology.

The specific name intermundia means in Latin 'spaces between the worlds’. It refers to the observation that this species is intermediate to C. litoralis and C. suspensus in its ecology and in some morphological characters. A noun in apposition.

Common name.

This species was not recognised by local fisheries, fisheries authorities, researchers, or the public before the works of Lundsgaard-Hansen (2009) and Hudson et al. (2016), who named the species as Coregonus sp. ‘benthic-intermediate’ (In German: 'benthischer Schwebbalchen’).

Figures

Figure 2. Map of Switzerland with the lakes studied; 1. Lake Constance, 2. Lake Sempach, 3. Lake Zug, 4. Lake Lucerne, 5. Lake Sarnen. On the right is a bathymetric map of Lake Lucerne with the German names of each basin (modified from Alexander et al. 2017 a).

Figure 4. Coregonus intermundia, Lake Lucerne, Switzerland A holotype, NMBE- 1078097, 274 mm SL, male, freshly caught specimen, (right side, reversed) B, C holotype, NMBE- 1078097, preserved specimen D non-type, Eawag- 124308, Lake Lucerne, 316 mm SL, male. Scale bars: 1 cm.

Figure 14. Illustrations of specimens of each species of Coregonus from Lake Lucerne and Sarnen. Illustrations of Lake Lucerne species are based on several individuals. Illustration of C. sarnensis is based on NMBE- 1078159, 230 mm, male. Scale bar for C. sarnensis: 1 cm.