Hey there, congrats on your new little one. Let me warn you now - for those topics which I choose to respond to, I usually do not do so in one or two sentences, dang I don't even think one or two paragraphs is normal for me, so with that warning - here goes nothing.
Ok first things first, you just recently purchased him - now, 4 days ago, so he may still be adjusting. If your little guy is smaller than 8 inches, thats definitely a new baby, so stress is a huge factor. How long did you devote to acclimation, and did you ask what the water parameters of his previous tank were? I ask because though sharks are sensitive to imperfect water conditions, if they are born into them, for the most part they can deal with them temporarily (now note that I said imperfect, not poor), and as funny as it may sound, if your water is lets say perfect, believe it or not, that can actually be a stress inducer right there for the short term. I always have a quarantine tank prepared before any new arrival, and I make sure to match as closely as possible the parameters they are exiting from in advance, or if it's a last minute deal, I test the waters they are shipped or delivered in and match it best I can, as to reduce any potential shock. If the parameters don't meet my standards, I change them slowly to what they need to be, matching those of the tank they will end up in once cleared from QT. (this can take weeks depending on the individual elements of the water). Newly acclimated pups can take a few days to get their bearings. Hopefully this one was hatched at the store you purchased him from, but if not, that is another thing you need to factor in. That means that he was hatched and acclimated elsewhere, shipped to that store, acclimated there, dealt with whatever care they provided (which sounds pretty bad by what you wrote), then was caught and bagged up and transported to your home for yet another acclimation. That's a lot of moving around for one so little.
But before we get into the "Handling the stress" section, let me just touch on this real quick - - -
What dumb*** idiot was feeding this baby goldfish!?! Please please do NOT continue to feed him those! I can't believe the level of ignorance you can encounter in such places, it's just unbelievable sometimes!! No shark should ever be consuming those, or any other freshwater fishes for that matter. Everyone is going to have one opinion or another, but if you want one that comes from someone who has been doing this for years, then keep this in mind - - - This is a little rule of thumb for all those uneducated shark keepers : If it wouldn't naturally live with the shark, Don't put it in the shark!"
Some Suitable foods for pups and adults alike are the following;
ALL FOODS SHOULD BE RAW, CLEANED, AND HIGH QUALITY...THIS MEANS EITHER PREPACKAGED BY A REPUTABLE BRAND IN THE INDUSTRY, OR FRESH SEAFOOD SUITABLE FOR HUMAN CONSUMPTION... I STRONGLY DISCOURAGE ANYONE FROM TRYING TO "CATCH" THEIR OWN SHARK FOOD. DO THAT AND YOU ARE JUST BEGGING FOR ALL THINGS BAD TO TAKE UP RESIDENCE IN/ON YOUR SHARK AND IN YOUR TANK...
PUPS:
*Brine Shrimp
*Mysis
*Krill
*Plankton
*Finely Chopped Squid
*Finely Chopped Muscles
*Finely Chopped Smelt
*Finely chopped Shrimps/Prawns
Ect.
ADULTS:
* Muscles
* Prawns (Peeled and De-Tailed)
* Shrimps (Peeled and De-tailed)
* Squid
* Clams
* Silversides
* Smelt
Etc.
Now, if your little guy is stressed, there should be tell-tale signs you can read. I will give you a quick check-list to work off of...
- Rapid Breathing (More than 40 Gill movements per minute) 30ish is normal but can vary depending on the animal and age, so don't freak if it's slightly higher than 30. If it's over 40, then you can freak. J/K, just means you need to start a process of elimination with possible contributors.
- Body posture - this is big, is your little guy scooted into a cave or under an overhang and calmly chillin, or does he seem agitated (like he can't get comfortable), and is constantly wiggling around, or does his posture seem to be more rigid? When calm and comfortable, pups will chill in their chosen locations most of the day, usually only relocating if they are disturbed or the light becomes bothersome - opting for a darker cover. Ones stressed or ill will seem cranky, like they can't get comfortable, exhibit rapid breathing, arch their backs, keep their heads up and pectorals down - supporting their weight for long periods of time, thrash about, roll on their side, "Yawn" repeatedly, and so forth. Other times, in severe cases it can be completely opposite and the animals can appear nearly dead and unresponsive to anything around them, even being touched or moved - this is usually when, without an experienced individual, the right conditions, and a lot of luck.. it's too far gone.
Try to gage your sharks state before you worry about the food. If you are convinced your little guy is settling in and is ok, just a bit rattled, then try to kick-start his little metabolism with garlic. And no, do not throw a clove in your tank. I suggest using GARLIC GUARD, nearly every SWFS worth it's weight carries it, and it's not that expensive. Garlic is a natural metabolic stimulant to many fish and sharks are no exception. You can add Garlic Guard directly to your water and watch for a response (which in an already hungry shark will illicit an almost immediate reaction of the shark starting to hunt for the source). If your little one should be hungry, but has not shown interest into what you have offered thus far, don't be discouraged, just like people, sharks can be picky. They aren't the garbage disposals most would like to believe.
I would suggest trying something on the smaller side while still in the introductory phase - try something like plankton or mysis shrimp. You can get those anywhere, pre-packaged in frozen cubes. Allow some of the cube to break apart into the water column, dispersing the oils and scents in the water (and feeding other inhabitants you may have), and then, when you have about 2/3rd's to 1/2 of the cube left in your hand, place it into the sand bed with a portion of it still sticking out. Don't place it right in front of your shark, but rather a few inches away.
Bamboo's are benthic sharks and by nature, one way in which they hunt and eat, is to extract items buried in the sand (Hence one major function of those cute little "whiskers"), they do so by either sucking these items into their mouths (if they are on top of the sand), or forcing blasts of water from their diaphragm over the top layers, quickly moving the sand out of the way so they can suck up their meal. Sand which gets taken in is shot out through the gill slits. Though my larger sharks eat from my hand, I always provide this enrichment to the smaller ones, especially babies.
If you still have trouble, try different items and pay attention to his reactions. You can also soak these foods in garlic (or for the frozen cubes, allow them to melt, drain out the water, and replace it with the garlic guard and re-freeze for later use).
Pups need to be fed 2-3 times daily, and each meal (while he is this tiny) should be no larger than a Dime in diameter. Feed too large of meals and you run the risk of digestive problems you just don't even want to know about. Feed too little and your little guys system is going to be all out of whack. Benthic sharks are snackers, so smaller, more frequent meals are always best. I hope this helps some, and please keep us updated on any progress ok!
If you need anything else, let us know!! Good luck!