This is a little backwards from my experience and research.
Basically the older the fish the slower its metabolic rate/activeness, also water temperature plays a role as warmer water increases the metabolic rate and the thus the hunger of the fish!
*Piranhas 1"-3" (babies/juvies) should be fed 2-3x daily, this also depends on aggression in the tank and size of the tank. Temperature should be around 78°-80° but ime higher temps equate to aggression so at that size if your experiencing cannibalism within the shoal more feedings, lower temp, more current and perhaps more hiding spots or a larger tank will help!
*Piranhas 4"-6" (teens) should be fed 4-6x per week or about 1x per day, again depending on temp/tank size and aggression! Temps of 78° are relatively good at that size!
*Piranhas 7"-8"+ (adults 1 year + & sexually mature) should be fed 1-3x per week again dependent on all the above! One should note aggression/chasing/fin nipping dulls down after or during the teen stage!
-juvies can eat flakes/pellets/various worms/chunks of whitefish/various frozen cubes/small healthy live food (quarantining store bought fish like guppies should take a minimum of 3-4weeks always avoiding goldfish!)
-teens can eat the same although smaller worms like bloodworms can be messy and impractical for a larger tank, fish fillet/frozen cubes and pellets are a good choice with healthy live.
-adults can eat the same as teens however I prefer to cut up the fish fillets into chunks as my shoal has incurred injuries due to 6 blood thirsty piranhas all going after 1 fillet!
<If your tank is 70-76° their metabolic rate is slower thus less feeding can be managed given little to no cannibalism in some instances!
<if your tank is large and not overstocked (generally 20-25gal per fish) they have more territory and swimming room thus increasing their metabolic rate so you can feed more! Footprint is more important then gallons, width/depth are more important then height!
<if you have a high current tank with adequate space containing a good sump or canister with 6-10x turnover + a nice circulator/ph (about 200gph for every 20gallons) setup the right way so they can exercise when they want and relax as well that will bump up energy used/metabolic rate so feeding should be more often.
•All in all a fishes metabolism depends on many factors, a warm tank (78°-84°) will make the fish hungrier and with piranhas given their age perhaps even more aggressive towards each other so watch carefully! Note that oxygen levels decrease as temperatures increase! Aeration can aid with oxygen!
•Energy/calories spent needs to be replaced so the food also makes an impact (lower quality food in most cases equates to low quality ingredients thus more feedings required) as fish only intake about 50% of available nutrients in the food! I prefer supplementing whitefish like talapia/smelt/catfish with a good quality pellet ensuring they get all the necessary nutrients!
I know a lot of mummble jummble! Clean water, adequate space, efficient current and filtration with stable 78° or so temps will 99% of the time create a very healthy and active shoal that will give you years and years of enjoyment, not only for you but for them as well!
" Since fishes are poikilothermal animals, they differ fundamentally from ourselves in that they have increased metabolic rate as the temperature rises and are hungriest when warm. Another factor influencing the metabolic rate is activity. A resting fish consumes less energy than an active fish. The higher the temperature, the more energetic a fish tend to be so that an elevated temperature acts doubly in causing greater energy consumption."-
http://hpfisheries.nic.in/aqua.htm
But with piranhas (pygos) just remember at younger ages and even older this can increase aggression. A lot of other fishes (like cichlids and catfish for example) grow fast and healthy with high temps of 84°+ & more food & their metabolic rate is fast but piranhas are a special kind of fish where a delicate balance is needed to sustain a healthy/active shoal with little to zero casualties along the way! There's no need to crank up temp and cram food into the tank to try to get them to grow faster!
http://monsterfishkeepers.com/forums/showthread.php?t=306686
For my shoal of 6 red belly piranha adults (7-10") in a 125gal 76° with fx5 & 1400gph hydor circulator they get NLS jumbo fish formula about 2x per week and 1 cut up talapia fillet every Sunday! Aggression is low and health is great!
https://www.youtube.com/watch?v=pMlTNLAYG8E&feature=youtube_gdata_player
This same trait most often applies to all piranha species (obviously solo's there's no need to worry about cannibalism!)
To really know if you need more flow what type of piranha do you have, filtration, tank size, water parameters and temp would help!
×Go S. Vettel #1 Infiniti Redbull! 4x WDC!!! Congrats on another flawless title and 9 wins back to back in 1 season (record!) See you next year in Australia boys!×
__________________________________________________________________
Cheap way to decrease nitrates and keep your fish healthy:
http://monsterfishkeepers.com/forums/showthread.php?t=504763
