This is an anadromous (or amphidromous?) species, again acquired from Rob McAllister. The adults are collected in freshwater and live their lives happily in soft water. Males have nice pointy fins, and the females get a dramatic neon blue tummy when ready to spawn.
In my experience most Rhinogobius will spawn readily if given a cave that’s to their liking; this species spawned even more frequently and easily than the others. Perhaps this is because they’re a lower-investment parent; eggs are tiny and hatch quickly.
The fry are pelagic, and even tinier. Fortunately I had warning from Rob McAllister that the fry would require brackish water to survive, but it still took several tries to keep them healthy. I got a couple of modest successes raising a handful of fry in a 2.5 gallon brackish tank, but didn’t meet full success until years later when I had some experience with marine fish.
Treating these like marine fry worked great. I transitioned the fry fairly quickly into 20 ppt brackish water in a black tub with an existing greenwater + rotifer culture and they thrived and grew quickly. I started feeding selco-enriched bbs as soon as they were large enough to eat it.
The first few started to settle after 28 days
It took nearly another month (60 days since hatch) until the fry were all settled and I gradually replaced their brackish water with fresh.
I was warned by other keepers of this species that HUFAs (highly-unsaturated fatty acids) would be an issue. It’s standard practice when feeding bbs to marine larvae to supplement the food with HUFAs, so I enriched mine with liquid selco (a gloppy oil which sticks to the shrimp) which seemed to work fine. The thing to know about this species is that even after transitioning to fresh water they are still fundamentally a marine species on some level, and require HUFA in their diet for life. Most dried fish food is processed from marine fish so that’s not an issue, but breeders that feed their fry bbs (which is uniquely devoid of HUFAs being evolved from a freshwater organism) suffer large losses.
I kept up the selco-enriched diet for my fish post-settling and post-freshwater-transition and was able to raise a large number of healthy fish.
I haven’t come across any other anadromous Rhinogibus species other than this one. I’d like to think that my experience with this species would help me raise anadromous gobies in other species (e.g. Stiphodon) but I’ve never found a pair that would spawn regularly enough for me to experiment.