I do not like this, this exhibit looks as though it has been designed for one purpose only, to display a tight knit shoal, almost in a ball formation. Herring, historically do not do well in confinement, can't see these lasting long.
Have you seen the sardine/anchovy tanks at the Monterey Bay Aquarium Kiang? They are displayed in donut shaped tanks, and seem to do well despite being fairly tightly packed in...
There are rounded edges and corners, and a circular current (somewhat like a stronger version of a kreisel tank for jellies), which is reversed periodically. They always swim against the current. Unlikely most other herring tanks I know, which typically lack a current, the survival has been quite good. It was developed with this exact goal in mind and by my estimate contains c. 10,000 l. It's been up from the opening of the aquarium (2½ years and counting) and I doubt it'll disappear anytime soon since it already has proven that it works. There are three options for herring: Normal tank (low survival rate), a tank with rounded edges+current (good survival rate) or a very large tank (good survival rate). Either way, the motality rate goes up without a dense school, which isn't all that surprising when knowing how densely packed their schools are in the wild. The same rules apply to most other clupeid species that are kept in aquariums. They are also notably sensitive during transport, but that's another discussion.
