Tuesday, June 28, 2022

[Ichthyology • 2022] Rhonciscus pauco • A New Species of Deep-sea Grunt (Lutjaniformes: Haemulidae) from Puerto Rico

Rhonciscus pauco 
 Tavera​, Schärer-Umpierre & Acero P., 2022

A fourth species of the genus Rhonciscus (Lutjaniformes: Haemulidae) is described from various specimens collected by small-scale fishers from the insular upper slope of western Puerto Rico. The new species was molecularly recovered as sister to the Eastern Pacific R. branickii, to which it bears many morphological similarities. It is distinguished from other Rhonciscus species by the number of scale rows between the dorsal fin and the lateral line (7), larger and thus fewer scales along the lateral line (48–50), large eyes (9.4–10.4 times in SL), longer caudal peduncle (15.2–20% of SL), larger sized penultimate (14.7–19.1% in SL) and last (7.4–9.5% in SL) dorsal fin spines which translates to a less deeply notched dorsal fin, and its opalescent silver with golden specks live coloration. This grunt, only now recognized by ichthyologists, but well known by local fishers that target snappers and groupers between 200 and 500 m in depth, occurs in far deeper waters than any western Atlantic grunt.

Rhonciscus pauco, sp. nov. OMNH 86864, holotype, 266 mm SL,
from Tres Cerros, Rincón, Puerto Rico.

Rhonciscus pauco, sp. nov. Underwater photograph taken at 218 m depth in western Puerto Rico.
 Image: NOAA NCCOS 2022.

Rhonciscus pauco sp. nov. 
Opalescent Grunt
(Spanish name: Ronco opalescente)

Diagnosis. A species of the genus Rhonciscus with XIII, 12 (total 25) dorsal-fin rays; anal-fin rays III, 7; pectoral-fin rays 15–16, 17(1); rather elongate body, maximum depth 32–37.4% SL; convex predorsal profile; eye large, its diameter 9.4% to 10.4% SL; snout subequal to eye, its length 7.6% to 11.5% SL; very coarse serrations on angle of preopercular margin; pectoral fin long (28–32.5% SL) extending beyond the tip of pelvic fin, barely reaching anus; head length 30–37.3% SL; longest dorsal-fin spine (fifth) (12.1–19.1% SL); relatively long and much thicker second anal-fin spine (16.4–21.8% SL), long caudal peduncle (15.2–20% of SL), and a large size of the penultimate (14.7–19.1% in SL) and last dorsal-fin (7.4–9.5% in SL) spines which translate to a less deeply notched dorsal fin, eye diameter 0.5 to 0.6 times length of anal fin spine; maxilla reaching anterior border of pupil; seven scale rows between dorsal fin and lateral line; 48 to 50 lateral–line scales.

Distribution. Rhonciscus pauco is found on the deep shelf and upper slope of the western coast of the northeastern Caribbean island of Puerto Rico. We are uncertain of the species’ exact range, but fishers report capturing them exclusively in fine sediment habitats distributed between the municipalities of Rincón and Mayagüez, off western Puerto Rico (Fig. 1). No additional information is currently available.

Habitat. Collection depths range from 200–360 m in fine unconsolidated sediment or mud habitats (Fig. 5).

Etymology. The name pauco comes from the fisher’s nickname Paúco, Edwin Font, who already knew of this fish locally called burro or ronco (grunt). Mr. Font was the first to report and provided specimens to MS, although it is recognized by various fishers as a component of the deep-water catch in western Puerto Rico.

Jose Tavera​, Michelle T. Schärer-Umpierre and Arturo Acero P. 2022. A New Species of Deep-sea Grunt, Rhonciscus pauco (Lutjaniformes: Haemulidae), from Puerto Rico. PeerJ. 10:e13502 . DOI: 10.7717/peerj.13502