While most of the larvae out there are from crustaceans and insects, larvae come from a wide variety of taxonometric groups including several groups of Chordates. Today’s animal is one of my favorite larvae of all from Belize – the Spotted Trunkfish (Lactophrys bicaudalis (Linnaeus, 1758)). My idea of a perfect day out would be to dive on the reef at Carrie Bow Cay in the early morning and then spend the rest of the day snorkeling in the mangroves nearby, looking for and at the larval forms of fish and the invertebrates. So, on to the trunkfish…
While fish don’t go through complete metamorphosis, many species do go through radical changes from birth through “settlement”. In Belize many of the larval, and post larval juvenile, forms of reef fish can be found in the mangroves including the boxfishes (Ostraciidae), a family of teleost fish which includes fish often named cowfishes and trunkfishes. On my trip to Belize I was thrilled to find some juvenile spotted trunkfish, like the one above, among the mangroves myself. The above picture however is from the Smithsonian Institution’s Larval Fish Group. The Larval Fish Group is one of several excellent resources for larval fish.
Eventually this small (~1.0cm) larvae will grow to become an up to 40cm long (~16″) adult feeding on algae and small benthic (bottom) invertebrates such as mollusks, crustaceans, tunicates, sessile tunicates, and echinoderms (sea stars, sea cucumbers and urchins). They spawn at dusk releasing large eggs (~2mm) into the pelagic ocean. After hatching the larvae will remain in the nekton. The plates that form their armor begin to develop as lumps in the early preflexion larval stages. In Gulf of Mexico sampling they were rarely found and at the pre-settlement stages there were no uniquely distinguishing characteristics to allow identification of pelagic larvae to the genus or species levels. According to William’s wonderful Early Stages of Atlantic Fishes (Marine Biology), Ostraciidae spend a short amount of time as pelagic ichthyoplankton, settling rapidly to seagrass beds and mangroves. Eventually they do recruit back to the reefs to settle and develop a fiercely guarded territory on the reef.
Here then is the adult form:
Two interesting bits about Spotted Trunkfish:
- They hunt by blowing jets of water into the sediments around the reef to uncover and dislodge the small inverts.
- Some boxfishes (Ostraciidae), including the Spotted Trunkfish (L. bicaudalis) have another form of defense beside their armor. They release a compound called ostracitoxin when stressed which can kill other fish, making members of the boxfish a poor choice for aquaria.
- Actinopterygii (Ray-finned fishes)
- Tetraodontiformes (Puffers and filefish)
- Ostraciidae (Boxfishes, Cowfishes and Trunkfishes)
- Lactophrys bicaudalis
Böhlke, J.E. and C.C.G. Chaplin, (1993) Fishes of the Bahamas and adjacent tropical waters. 2nd edition. University of Texas Press, Austin.
Richards, W.J.(ed.). (2006) Early Stages of Atlantic Fishes: An Identification Guide for the Western Central North Atlantic. Taylor and Francis, Boca Raton, FL pp. 2640.