The Coryphopterus gobies
Published 10 February 2023
With over 2000 species around the world, the gobies may considered one of the most diverse of fish lineages. Most are small fishes that live close to the bottom of their home waters. Among the many species hewing to this line are some, but not all, species of the genus Coryphopterus.
Coryphopterus is a genus of some thirteen species of goby, most of which are found in warm, shallow waters of the western Atlantic. A single species, C. urospilus, inhabits the other side of the Isthmus of Panama in the eastern Pacific. They are small fishes, growing from about one to five centimetres in length, and are mostly pale in coloration with few darker patches or spots. Characteristic features of the genus include a body that is covered in scales except on the cheek and opercle, six dorsal fin spines with the sixth widely separated from the fifth, relatively short second dorsal and anal fins, and a fleshy ridge running from the origin of the dorsal fin to just between and behind the eyes (Thacker & Cole 2002). The majority of species are benthic, living among rocks or sand close to reefs. However, three species found in association with coral reefs are notable exceptions. The peppermint goby C. lipernes lives perched atop the coral whereas the hover gobies C. hyalinus and C. personatus form dense schools in the water column above the coral. Most Coryphopterus inhabit shallow waters with records below 40 metres being somewhat unusual, but the recently described C. curasub of Venezuela lives deeper than any of its congeners with a depth range from 70 to 80 metres (Baldwin & Robertson 2015).
Coryphopterus species are also noteworthy among gobies as protogynous hermaphrodites. They begin their adult lives as females, only later potentially developing into males. Not that their adult lives are necessarily that long. Growth rings in the otoliths (ear bones) of C. kuna reveal that while individuals may spend up to two-and-a-half months as pelagic larvae, they mature rapidly after settling with post-settlement lives topping out at about two months (Victor et al. 2010). The length of time spent as males vs females varies from individual to individual (for those that develop into males at all, of course). Studies of sex ratios in C. personatus by Allsop & West (2004) found that, when population densities were relatively low, individuals tended to develop into females relatively late. As a result, males were large and able to maintain harems of females. But when populations on leeward-facing reefs became denser, individuals were more likely to transform into males earlier and at smaller size. These smaller males would then attempt to sneak matings with unguarded females. Early male development may be more advantageous at such higher densities because larger harems are harder to guard. However, males tended not to develop earlier in windward-facing reefs, perhaps because the difficulty of travelling from one patch of habitat to another in high-energy environments negates the advantages of sneaking tactics. When everyone is gathered close together, they become easier to keep an eye on.
References
Allsop, D. J., & S. A. West. 2004. Sex allocation in the sex-changing marine goby, Coryphopterus personatus, on atoll-fringing reefs. Evolutionary Ecology Research 6: 843–855.
Baldwin, C. C., & D. R. Robertson. 2015. A new, mesophotic Coryphopterus goby (Teleostei, Gobiidae) from the southern Caribbean, with comments on relationships and depth distributions within the genus. ZooKeys 513: 123–142.
Thacker, C. E., & K. S. Cole. 2002. Phylogeny and evolution of the gobiid genus Coryphopterus. Bulletin of Marine Science 70 (3): 837–850.
Victor, B. C., L. Vasquez-Yeomans, M. Valdez-Moreno, L. Wilk, D. L. Jones, M. R. Lara, C. Caldow & M. Shivji. 2010. The larval, juvenile, and adult stages of the Caribbean goby, Coryphopterus kuna (Teleostei: Gobiidae): a reef fish with a pelagic larval duration longer than the post-settlement lifespan. Zootaxa 2346: 53–61.