Pacific Beakfish

Oplegnathus insignis is a fish of the family Oplegnathidae ^[1]. It lives close to the bottom on the rocky shore of the eastern Pacific, from the Galápagos Islands in Ecuador to northern Chile, and in Chile it is called San Pedro ^[2],[3]. Juveniles are yellow with black stripes, and adults are dark brown ^[2]. Its global IUCN Red List category is Data Deficient ^[4].

The body has an anal fin with three spines and a dorsal fin that is continuous or deeply notched, rarely divided in two parts, and usually has seven or more spines. The teeth of the jaws are fused into one continuous plate that forms a beak ^[2].

The colour changes a great deal with age. Juveniles have a yellow background and six overlapping black stripes; in adults the body is dark brown ^[2]. A 326 mm juvenile caught in Chile showed black and yellow vertical bands, which the authors say give way to a reticulated pattern in the adult ^[2].

Documented records run from the Galápagos Islands in Ecuador, through Peru, to Antofagasta in northern Chile ^[2]. Adults are demersal. Juveniles occasionally visit littoral pools, mostly in autumn and winter, and both juveniles and adults are relatively common in kelp forests (Lessonia) at 3 to 30 m depth in northern Chile ^[2].

In November 2022 a 326 mm juvenile was caught incidentally at 3 m depth in an artisanal net off Chañaral, Chile, which pushed the known limit about 370 km further south ^[2]. The authors suggest it may reflect warmer water linked to El Niño, although no El Niño conditions were reported that month, or else escapes from nearby experimental cultures ^[2].

It is an omnivorous fish that feeds mainly on macroalgae and small invertebrates ^[2]. Another study describes it as omnivorous while it lives in the intertidal zone and carnivorous once it moves to the subtidal ^[3]. In captivity it has accepted live brine shrimp, crustaceans and shellfish, and can gradually get used to commercial dry feed for marine fish ^[2].

In the laboratory, oxygen consumption was measured at 13, 18 and 23 °C in four groups of hatchery-reared juveniles, with mean weights from 9.5 g to over 500 g. At the same temperature, consumption per kilogram fell as fish weight rose, and at the same weight it rose with temperature ^[5]. The authors mention preliminary growth studies, still unpublished, in which it grows better in warmer water, so they propose rearing it above 19 °C, and they say that, from preliminary observations, it is very sensitive to a lack of oxygen ^[5].

In northern Chile juveniles pass through littoral pools and adults are associated with kelp forests, so the species uses different habitats over its life ^[2]. Its diet changes with that move, from omnivorous in the intertidal zone to carnivorous in the subtidal ^[3]. The colour change with age is shared with other coastal fishes of the same region, such as Scartichthys viridis, Scartichthys gigas and Nexilosus latifrons ^[2].

The global IUCN assessment lists it as Data Deficient ^[4].

In Chile, Méndez-Abarca and colleagues regard it as a species of conservation concern, because of threats from fishing and because the status of its population on the northern coast is unknown ^[2]. They recall that after spearfishing was introduced in the 1950s it went from a recreational pastime to an important commercial activity, with overexploitation of inshore fishes, and that reliable data on artisanal and recreational fishing are lacking ^[2]. Another study notes that it does not appear in national fishing statistics and that its extraction has fallen considerably ^[3].

In northern Chile it is a species of fishing interest, with firm flesh and some demand, and it has been studied as an aquaculture candidate ^[3],[6]. In a trial with captive-bred fish, keeping them tightly crowded for 90 minutes raised plasma cortisol from 24.9 ng/mL at rest to 120.7 ng/mL at 10 minutes; it reached 225.3 and 243.7 ng/mL at 20 and 60 minutes, and fell to 56.1 ng/mL at 90 minutes ^[6].

To make feeding cheaper, diets in which 30 % of the fishmeal was swapped for other proteins were tested on 180 juveniles of 295.6 g and 450 days after hatching. Total digestibility was 68.0 % with fishmeal, 67.1 % with mollusc meal, 64.1 % with quinoa meal and 62.7 % with soybean meal ^[3].