Catarina scallop

Argopecten ventricosus is a scallop (a bivalve of the family Pectinidae) of the eastern Pacific known in English as the Pacific calico scallop or Catarina scallop ^[1]. Its range runs from California to northern Peru, where it reaches 5.9° S, in Piura ^[2]. In Peru it shares only a short stretch of coast with Argopecten purpuratus, and unlike that species it is not exploited at large scale ^[2]. Most of what is known about its biology comes from Mexican populations ^[3],[4].

The genus Argopecten is recognised by well-marked disc flanks and auricle margins, a deep byssal notch, a ctenolium (a row of small teeth beside that notch) present throughout its development, and wide variation in shell colour ^[2]. The same source warns that identifying scallops from external shell traits alone can lead to errors, because valve shape can converge and the sea erodes the shells ^[2].

In the literature the species also appears as Argopecten circularis and Pecten ventricosus, which are disused synonyms. These names make it hard to match its distribution with the fossil record: for example, Argopecten circularis of Sowerby I is also a disused synonym of an Atlantic subspecies of Argopecten irradians ^[2]. The thesis illustrates the species with a 32 mm specimen from Ecuador, an image taken from WoRMS ^[2].

Similar species

• Argopecten purpuratus: These are the only two species of the genus in the eastern Pacific and they overlap only between 5.1° S and 5.9° S, in Piura; Argopecten purpuratus continues south to Chile and lives at 5 to 40 m depth ^[2].

Argopecten ventricosus is distributed from California to Bayóvar, in northern Peru (5.9° S), with occasional records up to Monterey Bay ^[2]. Another source gives a wider southern limit, to the southern coast of Peru, which does not match the thesis ^[5]. In Peru it coexists with Argopecten purpuratus between 5.1° S and 5.9° S, at the northern edge of the Humboldt current system ^[2].

It has been recorded between 1.5 and 136.5 m depth, on rocky, sandy, sandy-mud or mud bottoms, and associated with brown algae, coralline algae or gorgonians ^[2]. In the Gulf of California it reaches high densities in rhodolith beds, made of loose, branching coralline algae ^[4].

It is a short-lived species, of 2 to 3 years ^[3], and a suspension feeder that filters particles from the water ^[5]. In the Mexican field study, individuals spawned twice, whereas in the laboratory all of them died after the first spawning ^[3]. Another review reports two spawning peaks a year and a maturity that takes between 8 months and 1 year in the wild, with no clear link to temperature ^[2].

Larvae reach the juvenile stage at 25 to 27 days in captivity ^[2]. In the experiment by Guerra and colleagues, a temperature 5 °C above the field one sped up growth and gonad production but raised mortality ^[3]. Its vertical distribution seems limited by temperature: it withstands down to 16 °C in deep parts of Magdalena Bay ^[2].

Larvae settle far more often on live rhodoliths than on sediment. In the field, settlement on Lithophyllum margaritae rhodoliths was 30 to 35 times higher than on non-carbonate sediment, and in the laboratory it was 3.3 times higher on whole live rhodoliths than on dead ones ^[4]. More complex rhodoliths also favoured a larger size after settlement ^[4].

The presence of predators changes how energy is shared out: with predators, individuals invested more in muscle than in gonad, delayed spawning and lived longer ^[3]. In Peru there are no studies of how sea conditions influence its distribution, behaviour or ecology ^[2].

The thesis consulted notes that the status of the species' populations has not been re-evaluated in the United States ^[2]. Off California its disappearance since the 1980s was described and attributed to overexploitation ^[2].

Not medical advice. For a sting, a poisoning or an allergy, seek medical care.

In a laboratory experiment with juveniles fed the dinoflagellate Gymnodinium catenatum, a producer of paralytic shellfish toxins, about 60 % of the scallops were paralysed at 15 h ^[5]. The only toxins detected before hydrolysis in the dinoflagellates and in the scallops were C1 and C2, most abundant in the mantle and then in the digestive gland, and no biotransformation was seen in that short trial ^[5].

The authors recall that in Mexico (1970-2004) human poisonings from shellfish were mostly associated with bivalves that had ingested Pyrodinium bahamense and Gymnodinium catenatum ^[5].

On the Baja California peninsula there is a local commercial fishery for this scallop, of interest to aquaculture ^[5]. Up to 2013, its culture in Mexico supplied 1.5 % of Latin American scallop aquaculture output, while Argopecten purpuratus accounted for 68.2 % of Latin American production ^[2]. In Peru it is not marketed at large scale ^[2].

Genetic and physiological studies, focused on aquaculture, have been done mostly in Baja California (Mexico) and in Panama ^[2].

The Peruvian literature consulted, a 2022 thesis, gives as its current distribution in Peru the Piura strip between 5.1° S and 5.9° S, up to Bayóvar, and gives no observation sites or behaviour data there ^[2]. Its known depth range is 1.5 to 136.5 m ^[2].