I don't suppose your baby goldfish are up to reading clocks yet and probably just have a daily cycle driven by daylight. Why don't you use the same simple approach to feed them? You can detect whether it's daylight using a quid's worth of LDR and a line of code - much easier and cheaper than connecting up an RTC and getting the code working to read/set it.
Then just use a trivial change to the 'blink without delay' sketch to feed at whatever interval you want during daylight.