Lancetfish on the (Long) Line

You’ve probably heard of fish such as bigeye tuna and mahi mahi, but what about lancetfish?  Hawaii’s longline fishery catches lancetfish at about the same rate at tuna, but lancetfish aren’t very tasty so they don’t make it back to shore and on to your plate.  They’re pretty interesting fish, though.  Scientists at PIFSC are working with colleagues form the University of Hawaii at Manoa (UH Manoa), the Monterey Bay Aquarium Research Institute (MBARI), and Stanford University to answer several questions about lancetfish.

How many species of lancetfish are there in the North Pacific?

Until recently, we thought the only lancetfish in the North Pacific was the long-nose lancetfish (Alepisaurus ferox).  However, recent work has shown that lancetfish seem to come in two distinct sizes (shown below), which has us thinking there might be a second species present, too.  We’ll be examining 100 lancetfish collected for us by the PIRO Observer Program to see whether this is the case.  To determine the actual species of each fish, we look at a number of characteristics.  For example, we note the shape and size of their fins and measure where on the body the dorsal fin starts.  We also look at the pattern of spots, or melanophores, on the fishes’ skin and take tissue samples for DNA analysis.

What can lancetfish teach us about the ecosystem?

One pretty amazing thing about lancetfish is their stomach contents.  Unlike what you might find in a human or tuna stomach (unrecognizable mush), the contents of a lancetfish’s stomach is largely undigested.  This means we can open up their stomachs and see exactly what kind of fish and other marine organisms they’ve been eating.  By looking at enough stomachs, we can get an idea of what lancetfish, and other fish like tuna, are eating.  Knowing what fish eat helps scientists understand the ecosystem as a whole and project how it might change in the future.  We’re also studying the tissues in lancetfishes’ digestive tracts to learn more about how they digest their prey (see below).

Why do there only seem to be two sizes of lancetfish?

Most species of fish caught by the longline fishery span a range of sizes.  This is because fish grow larger as they get older.  Oddly, the lancetfish seem to fall into two distinct size groups.  Even if this is because there are two different species of lancetfish, it still leaves us with questions about how quickly they grow, how big they get, and how long they live.  We’ll be looking at their ear bones, or otoliths, to help answer these questions.  Otoliths have rings in them that scientists can use to age fish, similar to how you might count the rings in a tree to see how old it is.  Unlike trees, though, otoliths are tiny.  Lancetfish otoliths are about the size of a grain of sand.

This blog post is brought to you by Team Lancetfish: Phoebe Woodworth-Jefcoats (PIFSC – ESD), Anela Choy (MBARI), Jeff Drazen (UH Manoa), Joe O’Malley (PIFSC – FRMD), Elan Portner (Stanford), and Jenn Wong-Ala (NOAA Hollings Scholar).  Want to know more about lancetfish?  Send your questions to Phoebe.Woodworth-Jefcoats@noaa.gov.  We’ll answer them in future blog posts as our lancetfish work unfolds.

lancet1

Lancetfish seem to come in two sizes, bigger fish about 4 feet long (left) and smaller fish about 2 feet long (right).

 

lancet2

Clockwise from top left: One characteristic we use to identify specific species is the shape of the dorsal fin.  We also note which dorsal fin ray is the longest and how far back on the body the dorsal fin starts.  The size, coloration, and number of melanophores on the skin are another characteristic we examine.  Muscle tissue is used for DNA analysis.

 

lancet3

Jeff Drazen (UH Manoa) and Anela Choy (MBARI) work on removing a lancetfish’s digestive tract for further study.

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