Longspine Squirrelfish
Holocentrus rufus
Taxonomy
Kingdom Animalia
Phylum Chordata
Subphylum Vertebrata
Class Actinopterygii
Order Beryciformes
Family Holocentridae
Abstract
Longspine squirrelfish are members of the family Holocentridae
The family Holocentridae is made up of ray finned fish that can be divided into two subfamilies the Myripristinae (Soldierfish) and the Holocentridae (squirrelfish). Squirrelfish can be best seen at night since they are nocturnal carnivorous feeders. These medium sized fish are a brightly colored red with large rough scales, sharp spines, and small teeth. They are known for their large eyes, sound producing capabilities, and the spines coming off its operculum. The sharp spines can secrete a poison. Holocentrus rufus is found near the bottom in tropical shallow reef waters.
Habitat
H. rufus is found in the warm tropical waters of the western Atlantic Ocean from the Southern United States to Northern South America and lives in coral and rocky reefs at depths of up to 100 meters (Woods, 1955). Typically H. rufus can be seen in waters less than 50 meters deep (Shcultz, 2003). Since it is a nocturnal fish, H. rufus spends most of the daylight hours hiding in a hole or cave formed by the reef structure. The preferred characteristics of a shelter shown to be ones that are higher up and embedded in a steep surface, like an overhang (Menard et al., 2008). Longspine squirrelfish are territorial of their micro territories, and do not share them among conspecifics. They are defended against members of the same species and against predators of a slightly larger size. Some individuals defend multiple shelters that could possibly be used as a reserve shelter (Menard et al., 2008). Often, they are seen in a small group of about 8 to 10 individuals (Schultz, 2003). At night H. rufus moves off of the reef and into sea grass beds and sandy areas to hunt its prey. The carnivorous diet is a wide variety of various small arthropods such as crab and shrimp, gastropods, and brittle stars (McGinley, 2008). The squirrelfish have little teeth that restricts their prey size, since they have to swallow them whole.
Reproduction and life cycle
Squirrelfish, like many other marine organisms reproduce by external fertilization and do not provide any parental care. They typically have two breeding seasons per year. H. rufus life cycle is complex, with pelagic and benthic life stages (Bowen et al., 2006). The members of the family Holocentridae have a diagnostic post larval life stage known as rhynchichthys (Tyler et al., 2003). The morphological characteristics of the pelagic rhynchichthys are the presence of five different spines at the rostral, in front and at the operculum, and at the supraoccipital bone (Coad and McAllister, 2010). The body length is estimated to be an average of a 25mm at this stage (Tyler et al., 2003). The organism progresses from the rhynchichthys stage to the next pelagic stage, often called meeki. At this stage the distinguished spines become less prominent as the body takes a more streamlined shape (Tyler et al., 2003). The color remains a silverfish and the average size is about 55mm (Tyler et al., 2003). This extension of the pelagic level is not seen in many others. It allows the H. rufus to have a quick transformation into the benthic juvenile life stage when the conditions are right (Bowen et al., 2006). They turn a red orange color at the juvenile stage. Some are able to change their body color from silver to a red orange overnight (Tyler et al., 2003). Squirrelfish are slow in developing and have a fairly long life span (anonymous). The average length on an adult is about 20 cm (Froese and Pauly, 2011).
Recent Research
Some fish are able to produce grunting sounds, including squirrelfish. Sound is production is controlled by the nervous system and is caused by muscles that make the ribs vibrate around the swim bladder (Winn and Marshall, 1963). The sounds are a low frequency and produced throughout the day, but with far more at night (Luczkovich and Keusenkothen, 2007). Currently research is being done to investigate the meanings of the sounds. Studies show that H. rufus use sounds in agnostic behaviors and alarm calls between conspecifics (Luczkovich and Keusenkothen, 2007). Also, it has been shown that H. rufus is able to judge a predator’s threat by the sound it produces.
The effects of major hurricanes and the destruction they cause to reef habitats is a growing topic of research. Population numbers and distribution of the squirrelfish, their predators, and prey are being observed in the years following a major disturbance. The comparison of the data sets is showing the effect that storms have in species distribution and habitat erosion in coral reefs (Kaufman, 1983).
Economic Impacts
Squirrelfish are not of huge commercial importance to humans. They are edible and have been called flavorful but, due to their small size and ability to survive in traps for long periods of time, they are not commonly eaten (Chapman et al., 1980). The majority of their commercial value is being sold for aquariums around the world. H. rufus are wanted for their bright color and large eyes. Their small size relative to other squirrelfish makes them a better fit for aquarium owners.
Personal Interest
The bright colors and organisms that are unique to coral reef habitats makes it one of the most interesting aspects of marine biology to study. Snorkeling in Thailand and Mexico allowed me to see the environment first hand and come in to contact with some of the species. I chose the squirrelfish because they can produce sound and a toxin which sets them apart from other reef species.
Literature Cited
Please note that the following references may have either been removed or relocated by the webpage owners since the time this student report was created.
Bowen, B., Bass A., Carlin, J. and Robertson, D. 2006. Phylogeography of two Atlantic squirrelfishes (Family Holocentridae):
exploring links between pelagic larval duration and population
connectivity. Marine Biology 149:889-913.
Chapman, S., L. Hale, and L, Ng. 1980. A Preliminary Study of the Edibility Characteristics of Southeastern Finfish. Texas A&M University. Available http://fshn.ifas.ufl.edu/seafood/sst/AnnPdf/5th_148.pdf.
Coad, B. and McAllister, D. 2010. The dictionary of Icthology [online]. Available http://www.briancoad.com/dictionary/introduction.htm.
Froese, R. and D. Pauly. 2011. Holocentrus rufus. FishBase [online]. Available www.fishbase.org.
Kaufman, L. 1983. Effects of Hurricane Allen on Reef Fish Assembelages near Discovery Bay, Jamaica. Coral Reefs 2:43-7.
Luczkovich, J. and M. Keusenkothen. 2007. Behavior and Sound Production by Longspine Squirrelfish Holocentrus rufus During Playback of Predator and Conspecific Sounds. Rubicon Research Depository [online]. Available http://archive.rubicon-foundation.org/dspace/bitstream/123456789/7000/1/AAUS_2007_14.pdf.
Mcginley, M. 2008. Coral reef fish feeding behavior in the Caribbean. The Encyclopedia of Earth [online]. Available: http://www.eoearth.org/article/Coral_reef_fish_feeding_behavior_in_the_Caribbean#gen6
Ménard, A., Turgeon, K., and Kramer, D. 2008. Selection of diurnal refuges by the nocturnal squirrelfish, Holocentrus rufus. Environmental Biology of Fishes 82:59-70.
Schultz, H. C. 2003. But They Don't Look Like a Rat with a Fuzzy Tail: The Family Holocentridae. Reef Keeping 2:11.
Tyler, J., Johnson, G., Brothers, E., Tyler, D., and Smith, L. 1993. Comparative Early Life Histories of Western Atlantic Squirrelfish (Holocentridea): Age and Settlement of Rhynchicthys, Meeki, and Juvenile Stages. Bulletin on Marine Science 53:1126-50.
Winn, H. and J. Marshall. 1963. Sound-producing organ of the squirrelfish Holocentrus rufus. Physiological Zoology 36:34-44.
Woods, L. P. 1955. Western Atlantic species of the genus Holocentrus. Proceedings of the Linnean Society of New South Wales 37: 91-119