Know your bones

Looking for a fun challenge? Got some time to kill? Why not dissect a fish and describe every bone of its skeleton?

Performing this task on the two species in the genus Xiphister was the first chapter of my dissertation.

Let me explain.

My dissertation research focused on the comparative anatomy of a family of marine fish called Stichaeidae. The goal of the dissertation was to reconstruct the evolutionary history of the family, and others thought to be its relatives, by comparing the skeletal anatomy of each genus. There are about 37 genera and 80 some odd species of stichaeids. Where does one begin to make these sorts of comparisons?

The primary literature was a good place to start. There is a lot of great fish anatomy work out there, and it’s possible to piece together a pretty good picture of the skeletal anatomy of most stichaeids just by reading previous publications. A sizable portion of my first year as a student went to familiarizing myself with that literature. I went as far as tracking down copies of the original descriptions of the two species of Xiphister, which both were published in 1858, one of which was in German.

The problem was that after months of research, while I was closer to understanding the anatomy of Stichaeidae, I was not quite where I needed to be. There were lots of discrepancies among publications. Terminology changed. Descriptions contradicted themselves. Some publications missed obvious features or ignored whole portions of the skeleton. Using the literature alone left me educated but confused.

What I really needed to do was pick a stichaeid, dissect it from head to tail, and focus on learning all the details of that particular fish. That species then would become the template for comparison of all the other species. I chose Xiphister for a few reasons. First, we had loads of them in our Nunnally Ichthyology Collection at the Virginia Institute of Marine Science, and we could easily go collect more near Friday Harbor Labs. Second, we had a good size series, meaning I could look at the development of their skeletal system. Third, they have some weird characteristics about their mechanosensory lateral-line system (discussed here) that I wanted to look at in more detail.

I used a combination of clearing and staining, whole fish dissections, and x-rays to look at their anatomy. Then, I pulled apart all of the major bits – the neurocranium, suspensorium and jaws, pectoral girdle, axial skeleton, and the like. Then, I illustrated and described every bone. It was time consuming and meticulous work. It was also incredibly effective at helping me learn the anatomy of a stichaeid.

This deep dive into the anatomy of Xiphister was the first chapter and second peer-reviewed publication from my dissertation (if you don’t count the Xiphister locomotion project that wasn’t technically part of my dissertation). In it, I was able to completely describe the anatomy of this genus, clarify points from the primary literature, and discuss their development. Even better, by working for this intimate knowledge of the anatomy of this genus, I had a basis of comparison for all of the other stichaeids and their relatives that was the main part of my dissertation.

Do you like puzzles? Have you ever thought about fish as super complex puzzles and wondered how they are put together? Let me know in the comments below or on Twitter!