Draft:Omobranchus obliquus/Kayleeso

Jack Randall, Bishop Museum, Hawaii

The Omobranchus obliquus, also known as the mangrove blenny, is a small striped invasive species of a fish in the family Blenniidae. The blenny's standard length ranges 3-5 centimeters, also being sexually dimorphic. Adult males of this species usually grow slightly larger than females, also exhibiting different features such as bright yellow pelvic fins and chin, along with an electric blue spot on the posterior half of the dorsal fin, tending to display broader longitudinal bands. Identified in O'ahu in the 1950's, this species has been seen at Coconut Island in Kaneohe Bay, Hawai'i. It inhabits areas such as piers, pilings, buoys, and mangrove roots.

In 1951, the US Fish and Wildlife Service (USFWS) stocked a concrete tank located on Coconut Island in Kaneohe Bay, Hawaii, with pieces of coralline rock containing Tridacna clams and other organisms collected near the Samoan Islands. In 1953, four live specimens of Omobranchus obliquus were collected from this tank. Initially, these specimens were first misidentified as Omobranchus elongatus, but they were later correctly identified as Omobranchus obliquus by Springer and Gomon in 1975.

Taxonomy Classification

The Omobranchus obliquus has a classification of the following; Animalia (Animals), Phylum: Chordata (Chordates), Class: Actinopterygii (Ray-finned fishes), Order: Perciformes (Perch-like fishes), Family: Blenniidae (Combtooth blennies), Genus: Omobranchus, Species: Omobranchus obliquus

The name Omobranchus is derived from the Greek language, where "omo" means shoulder and "brangchia" means gill.

Moku o Loe, O'ahu

Diet and Behaviors

The Omobranchus Obliquus is a diurnal grazing herbivore. Juveniles consume a higher amount of crustaceans, primarily copepods, compared to algae. They develop a dietary shift where they first consume a higher amount of invertebrates that can include primarily amphipods, tanaids, and copepods. As adults, they do not selectively feed on invertebrates to the extent that juveniles do. Instead, adults establish their own grazeable turf.

There are also ontogenetic behavioral changes from juveniles to adults. The juveniles begin to forage more successfully than adult males, juveniles also facing more aggression from others. The size or gender had no influence on the blenny's aggressive behavior, however size asymmetry had a notable impact on the aggression. Their access to shelter is determined by a dominance hierarchy that's influenced by aggressive interactions, the largest males typically being the alpha individuals.

Habitat & Distribution

With overlapping home ranges, Omobranchus obliquus inhabit briny and marine waters up to 2 m deep close to shore, living solitary or in small groups. The species can also be found in tide pools or on muddy to sandy seabeds where eelgrass and algae grow, as well as near the fringes of mangrove swamps. The blennies tend to choose habitats that are already occupied by other individuals over unoccupied habitats.

(GARMAN, 1903)

Randall, J.E.

The species native range was found in the Indo-Pacific Region, ranging from the Nicobar Islands to Samoa, extending north to the Mariana Islands, reaching south to New Caledonia, including the Palau and the Eastern Caroline Islands.

Reproduction

The female lays demersal eggs, which the male guards in the nest. Nests are located on the surfaces of stones, abandoned worm tubes, crevices in dead coral, or empty bottles and cans. Nesting males are known to be the largest and most dominant in the population. Their behavior differs from non-egg-guarding males, as they only leave the nest briefly to feed. Nests have often been found in empty oyster shells in Kaneohe Bay's fouling communities until these eggs hatch. Nests may contain egg batches of various ages as a multiply spawning species. Their larvae are planktonic, and are often found in shallow, coastal waters.

Morphology & Anatomy

Omobranchus obliquus, 3.2 cm (Photo by Ukkrit Satapoomin)

Based on their size and lengths, Omobranchus obliquus can be considered either juveniles or adults. Known for their striped skin, the species is identified by its oblique markings. They are small blennies also characterized by a lack of crest on the head. Its body coloration ranges from white to a faint brown, with the narrow oblique brown marks on the sides, often accompanied by slanting or curved white lines between them. Below and behind their eye, there can occur a narrow blue line and a dull red spot on the operculum. Irregular black lines extend ventrally from their head to their throat. If less than approximately 1.75 centimeters in length, it can be challenging to differentiate the blennies sexually based on the external features. Upon dissection, these small fish typically exhibit minimal or no gonadal development. Juveniles lack the distinct body band coloration and the posterior half of their body is transparent, revealing their spine through their musculature.

Human use

John P. Hoover

Omobranchus obliquus has limited human use due to its small size.

Bibliography & References

• FishBase:
  • Fishbase.mnhn.fr. Omobranchus obliquus, Roundhead Blenny. Retrieved from https://fishbase.mnhn.fr/summary/SpeciesSummary.php?ID=22819&AT=Mangrove+oysterblenny.
• USGS Nonindigenous Aquatic Species Database:
  • Brown, M.E. (2023). Zebra Blenny (Omobranchus obliquus) - Species Profile. USGS Nonindigenous Aquatic Species Database. Retrieved from https://nas.er.usgs.gov/queries/FactSheet.aspx?SpeciesID=3853.
• Hawaii's Fishes:
  • Hoover, John P. Omobranchus obliquus. Hawaii's Fishes. Retrieved from https://www.hawaiisfishes.com/fishes/neatfish/omobranchus.htm.
• University of Hawaii:
  • University of Hawaii. Mangrove Blennies: Omobranchus rotundiceps. Retrieved from https://www.hawaii.edu/gk-12/evo/blennies_mangrove.htm.
• IUCN Red List of Threatened Species:
  • Williams, Jeffrey. (2009). IUCN Red List of Threatened Species: Omobranchus obliquus. Retrieved from https://www.iucnredlist.org/species/48342168/48350654.
• WoRMS - World Register of Marine Species:
  • World Register of Marine Species. Omobranchus obliquus (Garman, 1903). Retrieved from http://www.marinespecies.org/aphia.php?p=taxdetails&id=278020.
• National Museum of Nature and Science, Japan:
  • National Museum of Nature and Science, Japan. Fishes of Andaman Sea - Omobranchus obliquus. Retrieved from https://www.kahaku.go.jp/research/db/zoology/Fishes_of_Andaman_Sea/contents/blenniidae/21.html.
• Picture World:
  • Photographie, Richard. Omobranchus obliquus - (Garman, 1903). Picture World. Retrieved from https://www.picture-world.org/actinopterygien-nouvelle-caledonie-2c-omobranchus-obliquus-garman-1903.html.