Scales along lateral line 127 to 156. Head 25.1 to 30.5% of standard length. Snout 30.2 to 34.5% of head length, eye diameter 16.0 to 21.0%, and interorbital 21.5 to 28.4%. Scales on nasal membrane, lacrimal, lower part of cheek, and preopercular; no scales on lower part of interopercular. Gillrakers on first branchial arch 8 (10) 12, 1 to 3 on upper arm and 7 to 9 on the lower. 1D 8 (10) 11 rays; 2D 35 (38-39) 40 rays; A 36 (38) 40 rays. Pectoral fins with 10 (14) 15 rays, length 14.1 to 18.7% of standard length, tips of pectoral fins reaching to level of anal-fin origin in small fish (less than 20 cm standard length). Ventral fins 14.0 to 19.1% standard length. Posterior caudal-fin margin usually truncate, becoming progressively concave with growth. Vertebrae 49 (51-52) 54, 5 or 6 being cervical with 3 or 4 ribs.
Colour: dark silvery grey on back, lighter on the sides, white on belly; rainbow-hued on some specimen. No submandibular mark.

Part of the material used by Inada (1981b), attributed to the trinomen Merluccius merluccius smiridus, correspond to nine specimens from a Tunis (Mediterranean) market. The other part (USNM 219331, 219332 and 219333) originated from the Atlantic, as the longitudes and latitudes indicated correspond to a series of geographical points west of San Vicente Cape (Portugal).
Maybe this is the reason why the entity labelled by the trinomen Merluccius merluccius smiridus Rafinesque, 1810 possesses characters specific to both Atlantic and Mediterranean subspecies.
Two, possibly three, subspecies can be distinguished in the western Mediterranean:

Merluccius merluccius merluccius (Linnaeus, 1758)
(European Atlantic, Bay of Biscay, Portugal, north of Morocco and southwestern Mediterranean)
Pectoral fins larger than ventral fins
1D. 9 (10) 11; 2D. 35 (38-39) 40; A. 36 (38) 40; P. 10 (14) 15; V. 7; Gr. 8 (10) 12; L.L. 127-156; TV. 49 (51-52) 52; CV. 6; CC. 4

Merluccius merluccius smiridus Rafinesque, 1810
(northwestern Mediterranean)
Pectoral and ventral fins of equal size
1D. 8 (10) 11; 2D. 35 (38-39) 40; A. 36 (38) 40; P. 10 (14) 15; V. 7; Gr. 8 (10) 12; L.L. 133-143; TV. 49 (51-52)-54; CV. 6; CC. 4

One of the specimens examined (MNHN 1966-0435) coming from the Red Sea (20°00’N – 39° 00’E), is the first record of Merluccius in this sea; thus it would be antilessepsian. The trinomen Merluccius merluccius lessepsianus is therefore proposed here, despite there being only one specimen, as it is the only one with pectoral fins smaller than the ventral fins.

Eastern Atlantic, from the coast of Norway and Iceland to the Mauritanean coast (Cape Blanc, 21°N), where it is quite rare. There are 3 specimens (MNHN 1956 0019) from the Azores in the Muséum National d’Histoire Naturelle de Paris, which we have not examined. The species shares its distribution area along the coast of Morocco with M. senegalensis.

A demersal and benthopelagic species. Lives on muddy or mud-sand grounds on the continental shelf and slope, in depths between 50 and 370 m, although it can also be found in depths of 30 m as well as 1 075 m. In the north and northeast of the Iberian Peninsula (Galicia and Bay of Biscay), M. merluccius feeds on crustaceans and fish. Specimens smaller than 15 cm feed mainly on euphausiacids, which are present in 85% of stomachs. Larger specimens gradually feed more on fish, mainly blue whiting (Micromesistius poutassou), which are present in all stomachs of specimen more than 50 cm in length. In the Mediterranean and especially in the Adriatic, juveniles of 13-cm length consume mainly Amphipoda, Mysidae, Pomatoschistus, and decapods of the genus Processa; adults feed mainly on clupeiforms. In Atlantic populations, age/size relation to sexual maturity is 57 cm and seven years for females, 40 cm and five years for males. In the Mediterranean females reach maturity at 36 to 40 cm and males at 26 to 27 cm. The spawning period is long and varies according to population; four or five spawnings occur without an ovary resting period, with approximately 20% of the ooctyes per emission. Small ooctyes remain after the last emission and degenerate when the ovary enters the resting period. In the Mediterranean, spawning fluctuates between December and June; from February to May in the Bay of Biscay; from April to July in Iceland; and from May to August to the west of the British Isles. In the western Mediterranean, there are two recruitments per year, in the spring and in autumn at between 50 and 250 m depths, with relatively stable oceanographic conditions. Fecundity is estimated at between 2 and 7 million ooctyes per female.

Maximum recorded length in the Atlantic is 140 cm and 15 kg, rarely exceeds 100 cm and 10 kg; minimum size in Mediterranean 89 cm and 6 kg, common up to 60 cm.