Families: 2 - Elopidae (“ladyfish”) and Megalopidae (“tarpon”)
Anatomy: fusiform (tapering spindle shaped), silvery body; large eyes with adipose eyelids; broad mouths with prominent lower jaws; swim bladder can be used as an accessory respiratory organ; eel-like leptocephalic (flat and transparent) larvae (image 4)
Diet: smaller fish and crustaceans; stage-one larvae absorb nutrients from surrounding seawater
Habitat/Range: coastal throughout tropical and subtropical regions, occasionally venturing into temperate waters; spawns at sea but can be found in brackish and freshwater
Evolved in: Elopiformes in the Middle Jurassic; the families Elopidae and Megalopidae in the Early Cretaceous
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Propaganda under the cut:
Elopiformes are known from many widespread fossil species, but today the order contains only two genera and nine species
Most Ladyfish have not been evaluated for conservation status, but as they use estuarine areas and hypersaline lagoons; changes in the quality of these habitats may affect their population dynamics, and they may be adversely affected by development and urbanization.
The habitats of Tarpon vary between their developmental stages. Stage one, or the leptocephalus stage, is completed after 20–30 days. Stage-one larvae are usually found in clear, warm, oceanic waters, relatively close to the surface, where they feed by absorbing nutrients from the seawater. The leptocephalus shrinks as it develops into a larva; the most shrunken larva, stage two, develops by day 70. This is due to a negative growth phase followed by a sluggish growth phase. Stage-two and -three larvae are found in salt marshes, tidal pools, creeks, and rivers, where they feed on zooplankton, insects, and eventually small fish. These habitats are characteristically warm, shallow, dark bodies of water with sandy mud bottoms. By day 70, the juvenile growth phase (stage three) begins, and the fish grows rapidly until sexual maturity. Tarpon commonly swim upriver into fresh water. As they progress from the juvenile stage to adulthood, they often return to the ocean's open waters, though may remain in freshwater habitats. Adults are strictly carnivorous and feed on midwater prey, hunting nocturnally and swallowing their food whole.
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Young tarpons may ride stormwater into remote, semi-landlocked ponds, where they will stay from one to three years. These ponds, some of which are brackish or freshwater, often become so low in oxygen that Tarpons (and Snooks) are the only fish able to survive in these environments, due to their swim bladders allowing them to breath air from the surface. The juveniles face fewer competitors and predators in these environments, but need to breathe atmospheric oxygen to survive. These fish are obligate air breathers and will die without sufficient access to the surface.
Tarpon can grow to about 1.2–2.4 m (4-8 ft) long and weigh 27–127 kg (60–280 lb). They are considered some of the greatest saltwater game fishes, prized not only because of their large size but also because of their fight and spectacular leaping ability. Numerous tournaments are focused on catching Tarpon, though Tarpon meat is not desirable, so most are released after being caught.
This larval Elopiform seen in Texas by saraj is our Observation of the Week!
Sara Jose is the Recreation Coordinator at the Oso Bay Wetlands Preserve & Learning Center in Corpus Christi, Texas, and the Learning Center itself will be opening to the public this week. She and her colleagues, including iNat user @justinquintanilla were using a seine net to catch fish and other organisms for the Learning Center’s freshwater tank, “meant to highlight our local freshwater species.” (They have an Educational Display Permit to do so.) After collecting specimens of interest for the tank, Sara and a park technician were returning stranded fish to the water when this tiny, transparent larval fish caught her eye - she thought it could be a larval eel. “I recently attended the Texas Academy of Science conference and knew that researchers in the central part of the state were beginning to do eel research, specifically larval eels and were hoping people in coastal areas would begin contributing sightings.” After taking some photos, she returned the larva to the water.
Once Sara posted her photo on iNaturalist, Dr. John Friel (@friel on iNaturalist), Director of the Alabama Museum of Natural History, was able to help her ID it as an Elopiform, which he says includes “ tarpons, tenpounders and ladyfishes with a total of 9 species worldwide…[they] are closely related to bonefishes, halosaurs, and true eels, and evidence for this includes the fact that all these fishes have a unique larval form known as a leptocephalus.”
So what the heck is a leptocephalus? Leptocephali are the larvae of Elopomorpha, and are transparent due to their insides consisting of clear, jelly-like substances, and due to their lack of red blood cells. They won’t gain red blood cells until they enter the “glass eel” stage of metamorphosis. Oh, and at this point they lose the sharp fang-like teeth they have has leptocephali.
The aquatic world is where Sara got her start in science and studied marine biology in college, intending to do research. However, she says that “by the end of my four years I realized that I enjoyed sharing science with the public more than spending time in the lab. I began learning more about local, native species as I took environmental education jobs that required me to share this information with the public.”
Sara found out about iNaturalist through her colleague Colleen Simpson (@colleenm on iNaturalist) and together they started a project to document the life of the Oso Bay Wetlands. Colleen has taught iNaturalist to educators in Texas, and Sara plans to incorporate it into public programs at the Learning Center there. “iNaturalist has encouraged me to look for more ‘small stuff’ on the trails,” she says. “Since I know that the members of iNaturalist can help me ID insects, bugs, and flowers I am more inclined to pause and check out those life forms these days.”
- by Tony Iwane
- Here are two awesome videos of leptocephali swimming - one a presumed moray larva off of Bali, and the other an ophichthid with green chromatophores, swimming off of Hawaii.
- Photos of leptocephali were also used as part of a “scary” meme, which purported them to be giant water parasites.
- Sara is a Windows Phone owner, and while there is no official iPhone app for Windows Phone, iNat user @coachbenson created the iNaturalist Observer app for Windows Phone. It’s a cool use of our open API.
Order Elopiformes includes the tarpons, ten-pounders, and ladyfish. These large, active predators are efficient and streamlined, and typically inhabit shallow tropical and sub-tropical waters. While members of this order may outwardly resemble large herring, they are actually more closely related to eels. Like eels, these species are catadromous (meaning they live in freshwater but migrate to marine areas to spawn). They also begin life as leptocephalus larvae; these thin, leaf-life planktonic larvae are a uniting characteristic of infraclass Elopomorpha, to which both the Elopiformes and all extant orders of eels belong. PIctured: Atlantic Tarpon.
