Adult threadfin jack are large, stocky, deepwater fish and rarely seen. Juvenile threadfins aren’t seen often either, even though they spend their time in shallow waters. One reason for this is that they don’t appear in great numbers. Another is that they’re easy to miss in the often stirred-up shallows. When they are seen, many people see their long, wavering filaments and think they’re jellyfish (I did the first time I saw one).

If the juveniles are to be seen, this is time of year for it. I’ve been looking out for them for a few weeks without success. Then, a few days ago, my wife saw one. A couple of days later, in the same area, we got in the water and saw one, then another, then a third. The water was quite murky and the threadfins quickly shimmied off among the rocks.

I managed to snap a couple of photos, but wasn’t sure the fish were even in the frame because they were hard to see on the camera screen. So I was thrilled that one of the photos had captured these two as they swam by. Hopefully, they’ll be around a few more weeks before they head out to deeper water, so I’ll get to see them again.

These are another of those fish that look quite different when they catch the light, with blue highlights standing out. They also look different as they age. The top photo is a large adult, the other two, a small younger adult.

These fish are big time predators, eating many other species of fish. I find this interesting because I often see bluefin trevally when I’m in the water. I see them pass by other fish and I’ve never seen them strike or seen other fish particularly bothered by their presence. One day …

In my attempts to identify what I see in the water, I use John P. Hoover’s book The Ultimate Guide to Hawaiian Reef Fishes, Sea Turtles, Dolphins, Whales, and Seals. His website is hawaiisfishes.com.

This little diamond-shaped fish is probably my favorite to see on the reef. The first time I saw one I thought it was a jellyfish, shimmering along with its long filaments wavering behind it. I got a little closer and realized it was actually an extraordinary fish.

The juvenile gives no hint of what it will look like as an adult. It grows to four feet in length, becomes stocky, loses the filaments entirely, and ends up looking like a nightclub bouncer.

It’s always a thrill to see one of these, its little tail thrashing back and forth, hauling the long filaments behind it as it putters through the water.

In my attempts to identify what I see in the water, I use John P. Hoover’s book The Ultimate Guide to Hawaiian Reef Fishes, Sea Turtles, Dolphins, Whales, and Seals. His website is hawaiisfishes.com.