Is there a gap in fish depths?

Factual Questions
1

So, some fish* live near the surface or in shallow waters, some live in really deep waters (where there’s no light and minimal plant life).

Are there fish living at every depth between those two extremes? Or are there certain layers that are largely unpopulated?

  • I’m including whales, sharks, and the like in this group, even though they’re in completely different orders/families. Basically, if it has a (mostly) streamlined body and swims (propels and steers) by moving it’s fins it’s included in this query. Squids and octopii are also included even though they don’t have fins.
2

I think what you’re asking about is the mesopelagic zone.* Sure, it’s the home of animals like swordfish, squid, wolf eels, cuttlefish, the fluorescent chain catshark, and other semi-deepsea creatures.

*A.K.A. THE TWILIGHT ZONE!

3

I’m not confident about the answer, but I’ll venture that it’s slightly more complicated than just what levels given animals live in. Many oceanic animals migrate vertically, typically rising to the surface or near-surface at night, but descending far into the unlit depths during the day. Thus they live at different depths depending on the time of day/night.

4

Unless they’re migrating in one vertical direction throughout the day/night (so they’re never at a given depth for any length of time), I’d consider them to be living in both regions , though I’d be interested to find out that a given region is only inhabited during the day or night (whichever it happened to be).

You’re definitely on the right track, Johanna. Though that seems like just the first step in a rapidly declining (population-wise) depth. If, otoh, it had less fish than the Bathypelagic zone, it’d be the sort of situation I’m asking about. (and thanks for reminding me about eels and cuttlefish; I’m including those too. Basically, anything other than clams, corals, tubeworms, barnacles, lobsters/shrimp/crabs, and the like)

It sounds like the answer is that there isn’t a gap. Population drops off as the depth increases, and there may be a cliff (in the statistical sense) or two, but no hills or valleys.