Over on the Backyard Aquaponics forum, there is a thread claiming that food pretty much must be bought to feed fish, since any home grown stuff will not have the right composition; no unless one wants to buy mineral supplements, etc. In the wild, fish can feed themselves, but they have a much lower (and unprofitable) density.
What are your thoughts on this? Is there some blend of foods that would work? Of course, if growing, grinding, and mixing the food took too much time, it might be better to buy it. And that was another point of the thread.
While I don't consider myself an expert, I do have a few years experience with a 2000 gallon aquaponic system. This was a small non-commercial AP system that didn't require expensive equipment such as food mixing tanks and a pellet mill. I think it is important to understand that AP systems are not natural (although they mimic some functions of a natural system). When you place animals in such a system, the expectation is that you will need to provide everything they require to live: trace minerals, food, water oxygenation, PH balance, etc. Very few things in life can be accurately described with absolutes, such as the "need" to buy feed. If you want to get optimal results, you will likely want to provide some amount of commercial feed. not everyone is after optimal results though. A natural (non commercial) diet is fine as long as the animals are growing and well cared for.
I suspect most people opt for commercial feed because it is easy, convenient, and it provides a complete diet. Trying to regularly provide a balanced diet from other sources can become difficult and/or time consuming. It is a viable option if you have more time than money or strong beliefs about commercial feed (contents or how it is sourced). I advocate using as much locally sourced feed as possible, but i am also a realist. There will be days when you cant go dig worms and forage (such as sickness, family emergency, vacation). If someone else has to fill in for you, it is likely that they will be unaccustomed to digging worms or uncomfortable handling BSF maggots. It is wise to have a bag of commercial feed on hand for such times.
We grew duckweed that provided about half of the food required and supplemented it with bag feed, black soldier fly, worms, and offerings from the bug zapper. My method was to feed duckweed and commercial feed at the same time and carefully observe which the fish ate first and how long it took them to finish off the commercial feed (ideally no more than 5 minutes). If the fish ate the pellet food first and ignored the duckweed, i assumed they needed something that they were not getting elsewhere and adjusted the ratio. Leftover duckweed on the top of the water isn't bad, but overfeeding pelleted food can lead to serious problems.
I would also like to share a source of fish feed that I have not seen mentioned elsewhere. We had a bumper crop of acorns this year and I gathered them to reforest a few acres on the back of our property. I dumped them out on a table to sort the ones that were wormy. I put a mesh window screen down to keep them on the table and make moving them around easier. By the time i finished sorting, i noticed 30-40 small white grubs had crawled out onto the screen. they died a swift death in the jaws of our hungry fish. I left the wormy acorns out overnight and had 50-60 more grubs the following day. I would roll the acorns around on the screen daily, and come back a few minutes later to collect the grubs. this provided some easily obtained supplemental feed in the fall (around the time the duckweed growth slowed down).
Location: Poplar Hill, Ontario (near London) - Zone 6a
posted 6 years ago
I'm interested about this topic too, and considering an aquaponics setup for my as yet unbuilt earthpit/SHCS greenhouse. I'm reading Sylvia Bernstein's book Aquaponic Gardening, and can see some really great advantages to aquaponics, but the problem of what you're inputting for feed is bugging me too. I'm not comfortable with commercial feed if I can possibly help it.
I have a specific question for you Ben - about the Duckweed. I'm assuming the duckweed is in a tank not connected to the system, and has to be manually added? (I'm assuming that because I read that the fish would devour it down to the last morsel if it was in the same container as them). Approximately what size is the tank growing the duckweed to provide 40% of the feed for your 2000 gallon system? This would help me figure out what ratio I'd be looking at if I grew duckweed.
Did you dry the duckweed before feeding it, or feed it wet?
Your acorn grub idea is great. It made me wonder if the fish would eat nut fragments (ie. pulverize nuts with a sledge in a bag - the ones not great for human consumption). Shells might be a problem, as they wouldn't eat those. Seeds (like sesame) might work like that too.
Did you ever try feeding with algae blooms (ie. from chicken manure)? I'm wondering about this, but sounds like it adds a lot of complexity- 'babysitting the biomass', so to speak, since the algae can alter the water conditions quickly.
greenwater systems grow algae from fish waste, instead of going to plant beds. The benefit is that the tilapia (or suitable species) can eat the algae. This reduces the amount of feed needed to add to the system, but doesn't do without it completely. And trace minerals are a must, IMO.