I aqquired 1 banggai from a member of a local fish society; its really big.  I purchased another from a LFS, its smaller.  I watched them carefully for the first couple hours; they seemed to get along.  Now its been a couple weeks, and they do like eachother. 

My question:  How do you know if they will mate?  I'm thinking the big one may be too old to spawn, but have no way of telling its age.  Is there a normal time period for banggai to mate once placed in a new tank?

They are in a 40g tank with some LR, but no other fish.

I'm trying to decide if I should give up on the large one, and buy another small one.

Scott, my suggestion on this is simple. If they're getting along, you have good odds of a pair. So check that off your list for the time being.

Banggais have reportedly short reproductive primes..i.e. females only produce good routine clutches for a couple of years, after which they fall off. The natural lifespan is realtively short for a marine fish too...6 years max.

As with any breeding, old specimens can sometimes make poor broodstock, so your hunch may be well founded. However, I wouldn't give up just yet. Afterall, what if the issue is not that your larger fish is too old, but perhaps that your smaller fish is not yet ready?

I'd give them a few months and pump them full of quality foods, especially PE Mysis in this case, before switching things up. Also, know that if you swap the large one for a small one, you only have a 50% chance of getting a pair....one of the extra things to consider with banggais is the need for extra tanks while you figure out which fish are what sex and who will get along and breed with who :)

Good luck - we need more CB Banggais!

Matt

Could you elaborate a little on proper feeding of Banggai?

Looking at your other post, I assume you mean adult / broodstock nutrition. Basically, Piscene Energetics Mysis (aka, PE Mysis) is a freshwater mysis that is heavily enriched (i.e. with HUFAs) and in many cases is cited as a great base for fish like Mandarins and Cardinalfish. Of course, there is always the possibility of feeding too much fatty foods and causing fatty liver disease, so I'm always inclined to feed a myriad of foods even if people are feeding one item exclusively (like PE). So, I'd offer PE, but also other types of mysis. "Plankton", basically mini-krill type foods, won't hurt either. Enriched Adult Brine Shrimp (i.e. especially Spirulina enriched) won't hurt (and with the Spirulina enrichment, at least a tiny bit of "vegetable matter" is getting into the diet). I LOVE the new Seachem Shrimp - the red shrimp may prove a big bite for a Banggai, but my Serranus annularis take 'em down without issues - you might have to chop 'em up for Banggais. Some of the scientific literature points to the use of livebearer fry as an exceptional food for conditioning Banggais, so you might do well to maintain a colony of "saltwater mollies" to produce treats for your Banggais. Of course, some Banggais will take mixed frozen diets / chopped foods like pieces of shrimp / squid etc. Again, my premise is to always feed a varied diet even if the need for one is not readily apparent. Cardinalfish are all micro-predators, so that's where the diet should start. Again, with all predators, we often neglect to think about the gut contents of what they are feeding on, and that is often where small amounts of plant matter can come into play. So if you can get them to eat something like chopped up chunks of a frozen diet (i.e. a Dwarf Angel diet or Formula 2), it may not hurt to occasionally supplement that into the diet once in a blue moon.

Yes, in the end, it's a little bit of a shotgun approach, and you may find that you might do better off feeding exclusively PE mysis. Again, fundamentally, I worry about the mono-diet having deficiencies and overages in the nutrition that can cause problems, so in the long term, mix it up.

FWIW,

Matt