Fun with Fishes!

April 5, 2019


Fishes do much more than swim! Some fishes cling to rocks so they don’t get pushed around by waves and currents. Others fly through the air so get away from predators. But the #BestFish (in my unbiased professional opinion) climb waterfalls! My name is Kelly Diamond, and currently I am a PhD candidate in  Rick Blob’s lab. I study how waterfall-climbing fish called gobies migrate from the ocean to freshwater habitats.

I am taking a selfie in front of a wall of lava in Hawai'i

I get really excited about being in the field, especially when I get to study the o’opu!

Goby fishes are one of the largest groups of fishes in the world (currently 1842 species!). Most of these species live their whole lives in the ocean. But some species migrate from the ocean to freshwater streams, where they live as adults. This type of life cycle is called amphidromy. The Hawaiian name for these fish is o’opu (pronounced oh-oh-poo). There are five species of o’opu found only in Hawaii (lucky fish I know!) In early spring the baby o’opu, or hinana (hin-na-nah), migrate from the ocean upstream to freshwater habitats.

life cycle illustration of the o'opu

The life cycle of the o’opu. Adults live in freshwater and babies develop in the ocean, and then migrate back upstream by avoiding predators and climbing waterfalls!

There are 2 measures of performance we collect from these hinana. The first is escape performance because hinana must avoid other fish trying to eat them! To measure escape performance we simulate a predator attack. These fish use their lateral line system (a series of pores along the body) to detect differences in water flow caused by the predators. The lateral line system in the water is analogous to the hair on our bodies. We can tell which direction a breeze is blowing because the wind hits the hairs on one side of the body slightly before the hairs on the other side of the body. The pores on the body of a fish work the same way as our hairs! We simulate an escape response by squirting a jet of water at the fish, which they think is a predator. We record their responses with high speed video! From these videos we can measure a bunch of things, including how fast the fish escapes and at what angle.

The other measure of performance we collect is climbing performance. These fishes climb waterfalls as part of their life cycle! To measure climbing performance we have made artificial waterfalls! One waterfall is Plexiglas (to record the belly side of the fish), the other is a rain gutter (to record the back side of the fish). We record the fish climb and measure how fast the o’opu climb.

This year we had three major projects we were working on. The first looks at how performance may differ among the Hawaiian islands. The second examines how water temperatures may influence performance. For the third, we measured how performance may change of the course of the migration period. For updates on all these projects stay tuned, and check out my website or follow me on twitter (@DiamondKMG)!

I am standing in a giant green tank with 5 white trash cans serving as experimental chambers in the background

Here is the set up for our temperature experiment! Each bucket contains a predator-prey trial sitting in a giant water bath to maintain constant temperature!

Outside of data collection, working in Hawaii has some major perks! The weather is wet but warm! The field sites are beautiful! There are some great hikes to explore in the evenings! And as a #HERper (a lady that likes to search for reptiles and amphibians) there is always something fun to do in our free time!

I am in a wetsuit holding a chameleon lizard

A female Jackson’s chameleon found at one of our field sites

Thanks for the read! I love talking with people about fishes (especially gobies) and science in general. Please fell free to reach out if you have any questions or just want to chat about some cool fish!





  • Johnnie Perkins says:

    Hi Kelly, my names is Mrs Johnnie I’ve been interested in this fish for years.
    I’m interested in the changes the Climbing Goby Fish goes through.
    They are pushed out to sea as seeds
    Then they become little fry (look like adults)
    Then Juveniles
    Then Adults–They return
    At what point do they decide to leave the sea?

    • kmdiamo says:

      Hi Mrs. Johnnie,
      The short answer to your question is that the gobies leave the ocean and migrate upstream to adult habitats during the juvenile life stage.

      Adults lay their eggs in freshwater streams. Once the eggs hatch, the larval fish are swept out to the ocean where they stay for 3-6 months depending on the species of goby. Larval fish have a yolk sac that they use for nourishment. As with most other fish, once the yolk sac is depleted, the larvae must metamorphose into a form that allows the fish to feed itself. The yolk sac is not pictured in the illustration in the post because to be completely honest, we don’t know exactly what a larval goby looks like! They are too small and transparent to see!

      For these gobies only the larvae can survive in the salt water. Once they metamorphose into their juvenile form, their gills can no longer handle the salty ocean water. This means the larvae will enter a stream estuary (where the stream meets the ocean) and metamorphose into the juvenile form. The juveniles look like tiny adult fish, except that the juvenile sucker is bigger relative to the size of their body. This is similar to how babies have larger heads compared their body size. The concept that different body parts grow at different rates is a concept known as allometry! Having a larger sucker-to-body-size ratio gives the juveniles an advantage for climbing as they have more relative sucker surface area and less body mass to heave up the waterfall! Once the juveniles migrate upstream they will grow to their adult form and live upstream for approximately 3-5 years.

      However, we still don’t know exactly how the larvae decide when to enter the estuary. How do they know when their yolk reserves are depleted? How do they search for freshwater? We believe the plumes of freshwater that are pushed out into the ocean from streams during floods help to attract larvae to streams, but we still haven’t figured out a way to test this, any ideas are always welcome!

      Thank you for the question! Please reach out if you have any others!
      Best Fishes!

      PS Since posting this blog I have graduated and my new contact information is feel free to reach out with any future fish questions!

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