On the contrary, the paper says that the captive triggerfish are better at some tasks. They have four tests:
1. They introduced new objects to the tank and tested if the fish bites them to explore what they are, or hides from them. Long-term captive fish bite less than wild-caught and take longer for their first bite. However, they also show no fear while some wild fish hide when confronted with a 3D printed seaweed (but not other objects).
2. The fish were given a puzzle box to solve. All wild fish succeeded, as did all captive fish that tried the apparatus, but three declined to engage with the toy.
3. The fish were locked in a box within their tank and tested to see how fast they emerge once the door was opened. Captive fish emerged faster.
4. The fish were trained to swim through a cylinder in various configurations, with the ultimate test involving their capacity to go around a transparent cylinder for a treat (as opposed to rushing in and bumping into it). Captive fish that tried the experiment were more successful, but some didn't try (and their tanks apparently had a different design that might've given them an advantage, since the captive fish were usually moved to the side of the tank while giving them access to the test area, which let them approach the puzzle at an angle). Wild-caught fish all tried the experiment but failed.
Overall, I think the message here is less "captive fish become dull" and more "captive fish understand that they'll be fed consistently and refuse to play along with the researchers' games". Them being faster to exit the box and less fearful of new objects also suggests that they're more relaxed with their environment.
Still, I do think that providing enrichment for fish is a good thing, mostly because coming up with fish toys is also entertaining for the keeper. I've previously tried putting bloodworms in a dog toy and seeing if my adonis pleco would shake them off by pushing the toy around, but it ended in failure because the toy was too floaty.
link.springer.com
