Cryptopsaras couesii is one of the most commonly collected ceratioid anglerfishes. The ceratioid anglerfishes are a group of 11 families with representatives distributed around the world below a depth of about 300 meters (they may sometimes be found at much shallower depths as well, e.g. see Cryptopsaras couesii in Stewart and Pietsch 1998). They are most strikingly characterized by having an extreme sexual dimorphism in which males are dwarfed and, in some species, become parasitically attached to the body of a relatively gigantic female. The males of most species (but not C. couesii or its sister taxon, Ceratias) are equipped with large nostrils, apparently for homing in on a female-emitted, species-specific pheromone (Pietsch 2005). Normal jaw teeth are lost during metamorphosis, but are replaced by a set of pincher-like denticles at the anterior tips of the jaws for grasping and holding fast to a prospective mate. In some forms (including Cryptopsaras couesii) attachment is followed by fusion of epidermal tissues and, eventually, by a uniting of the circulatory systems so that the male becomes dependent on the female for blood-transported nutriment, while the female becomes a sort of self-fertiliizing hermaphroditic host (Pietsch 1976; Pietsch and Orr 2007 and references therein). A Cryptopsaras couesii female may have as many as eight males attached to various parts of her body (Pietsch 2005). Attached C. couesii males are almost invariably found facing anteriorly, as if they approached their mates from behind (Pietsch 2005).
Most ceratioid anglerfishes, including Cryptopsaras couesii, have a bacterial bioluminescent bait or lure (known as an "esca"), the structure of which is extremely useful (at least to humans) in distinguishing species (Pietsch and Orr 2007). Remarkably, at least in C. couesii luminescence is not limited to the caruncle and esca. In shipboard experiments, Young and Roper (1977) found that this species is luminescent over most of its body, with the glow apparently emanating from its skin (except where damaged). In their experiments the fish varied its luminosity to match varying levels of overhead illumination, achieving both lateral and ventral countershading that made it nearly invisible.
See Pietsch (1986) for a technical diagnosis.
Cryptopsaras couesii has a wide distribution between 63°N and 54°S, although it appears to be absent from the western South Atlantic ocean (Stewart and Pietsch 1998).
Pietsch (1986) described the distribution as follows: Occurs in all three major oceans of the world [Atlantic, Pacific, and Indian Oceans] between approximately 63°N and 43°S. Throughout North Atlantic, ranging as far north as Iceland and from the Gulf of Mexico to the African coast. In the Pacific, ranges from the Philippine and Molucca Islands to the Eastern Tropical Pacific and between Hokkaido, Japan and Monterey Bay, California, to New Zealand and off northern Peru. In the Indian Ocean, this species is known from more than 60 specimens (primarily larvae and males) taken mainly from localities that appear to be associated with continental margins (but which in reality coincide with the route of the DANA Expedition of 1928-30).
Adolescents and adults of Cryptopsaras couesii have been captured between approximately 75 and 4000 m. The majority of known specimens, however, were taken between 500 and 1250 m (Pietsch 1986).
The ceratioid family Ceratiidae contains relatively elongate, large-sized anglerfishes, easily separated from members of allied families by having the cleft of the mouth vertical to strongly oblique, the posterior end of the pterygiophore of the illicium emerging from the dorsal midline of the trunk, and two or three caruncles on the back just anterior to the origin of the soft-dorsal fin (Pietsch 1986).
Cryptopsaras couesii: Dorsal fin rays 4 or 5; anal fin rays 4; pectoral fin rays 18; caudal fin rays 8. Female Cryptopsaras couesii have three fleshy, club-shaped caruncles on the dorsal midline of the trunk, just anterior to the origin of the soft dorsal fin, the central caruncle being the largest (Stewart and Pietsch 1998).
The sexual parasitic mode appears to be obligatory for Cryptopsaras couesii. Free-living males and non-parasitized females never have well-developed gonads. Thus, it appears males either establish a parasitic association with a female within the first few months of their lives and mature, or else die without mating (Pietsch 2005). The jaws and alimentary canals of free-living males appear unsuited for feeding themselves, so males probably do not feed after metamorphosis, instead depending on parasitic association with a female for long-term survival (Pietsch 2005). Given the dependence of both sexes on sexual parasitism for reproduction, it is surprising that of the more than 600 metamorphosed females in collections, only about 6% are parasitized (Pietsch 2005).
Cryptopsaras is a monotypic genus (i.e., it includes just a single species). Its closest known relatives are the three species of Ceratias (Pietsch and Orr 2007). Together, these two genera comprise the family Ceratiidae.
The ceratioid family Ceratiidae comprises two genera, Ceratias and Cryptopsaras, the former including three species and the latter just a single species (Pietsch 1986). Pietsch and Orr (2007) have reviewed the taxonomy and systematics of the ceratioid anglerfishes.
