Feeding fry

[Mugwump]

  I know everyone has their own way of feeding fry. The when, what, and how is likely different dependent on the species, the preferred food, and method of introduction.
  Example: I feed angel fry after they all have been free swimming about 12hrs+. I know that some egg sac is left, and as a result I feed very lightly because of two things 1) to make sure that they're eating it at all 2) and because I want a minimum of waste, from not eating it, and/or over feeding period.
  What are your preferred foods? When do you transition to other foods? How do you introduce these other types of food?
  What are your ways of approaching this? Be species specific when necessary.

[BillT]

One of my favorite topics.

What I do is largely based upon lab procedures for zebrafish I have used in the past. This approach is a bit labor intensive, but if done properly works well. A genetically good line of fish (not harboring any lethal genes that might result in dead fish for genetic reasons) should have about 80-90% survival to adult from starting at a fertilized (as opposed to unfertilized) egg.

The old lab way was to collect eggs, put them in a beaker in a defined pond water solution, clean them.
Check them each day, remove dead eggs/embryos. The fish hatch out (depending upon temperature) at about 3 days post fertilization (dpf), but as John said, they don't feed immediately. They usually they stick the sides of the beaker and digest their yolk. In about a day, they inflate their swim bladder and start cruising around looking for something to kill. This is when they start feeding. In labs, they used to be fed a very large species of paramecium (parameciium multimacronucleatum) cultured in the lab. The usual strategy is flood the beaker with the paramecia which stay alive and provide a continuous source of food. 

The fish are fed this way until they are large enough to transition to BS nauplii. Unlike many labs, I also feed Walter worms before the brine shrimp. I can easily produce and collect 30 mls of Walter worms a day. Walter worms are similar to microworms, but they stay alive for days in the water. The adult worms are barely large enough to see and sink to the bottom, but the baby Walter worms are microscopic. The adult worms lay round eggs that are smaller than their body's diameter. The baby worms are curled up in the eggs. Microworms are considered a carbohydrate rich diet but less good for fatty acids. In tests I have done survival went up and the transition to BS occurred earlier when Walter worms were add.

I like to introduce a few of their first (or next size up) prey items to them before they are really be able to eat them so that they can form a search image of it prior to their actually feeding on the food. This is something I can up with from reading some behavior article about the development of predator hunting behaviors. Don't really know if it applies here though. On the other hand the paramecia (or rotifers) will eat bacteria.

Eating paramecia, the ZF will be able to eat BS in about 10 days (at about 83˚F). This is the most difficult period of raising ZF and much of the problem has to do with the difficulty of raising and collecting enough paramecia to supply high concentrations of them to the baby fish. Paramecia are also somewhat limited nutritionally and they can not be effectively gut loaded prior to being eaten because they don't really have a gut.

The more modern method is to feed rotifers at the first stage instead of paramecia. They are much easier to raise on large amounts and easier to collect because most paramecia cultures and very gloopy. When eating heavily, they get gut loaded (usually with nutritious algae). The aquaculture industry depends to a large extend on rotifers for raising baby fish.

Many people I know have tried freshwater rotifers (there are two major groups) but they are much more difficult to raise than the salt water ones. Most people doing this now use salt water rotifers. Some salt water rotifers are too large for newly hatched baby zebrafish to eat, but I have a small species (S-type as opposed to L-type) which zebrafish can use as a first food. Salt water rotifers, like brine shrimp, don't do to well in  freshwater.  These work well for me.

I keep the larval fish in elevated salt, at a density of 1.006 gms/ml (1.00 is pure water) or about 11,500 ?S (or 11.5 mS). This is a brackish level of salinity. The fish don't die in this, it also keeps the salt water rotifers alive and the baby brine shrimp alive when I add them at later stages of development. The Walter worms also survive. As a result the both the rotifers and brine shrimp stay alive for days and provide a continuous source of food, plus they don't die as much so the water stays nicer.

I keep my fish in little plastic cups rather than beakers (more expensive) until they are eating brine shrimp. Then I put them in tanks on a recirc rack with the same salt levels until they get bigger.

This has worked well for all the Danionins that I have been able to breed.
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I am now also starting to raise Nothobranius furzeri killifish. They hatch out large and can eat brine shrimp. I also feed them Walter worms and black worms when they are big enough. When they are eating the black worms they grow incredibly fast. This is a research animal and one of the vertebrates with the shortest life span and shortest generation times.
There is still a lot for me to learn about raising these guys.

[PaulineMi]

Interesting reading Bill.  That species of killifish is a beauty from pictures I saw when I looked them up.  A lifespan of 3-6 months....are you going to collect eggs and raise new batches of them?

[PaulineMi]

My angel fry get fed after a full day of free swimming. I hatch out bbs 24 hours apart to rotate for fresh bbs feedings each day. The bbs are in separate containers with saltwater and an airstone in each container and heat from lightbulbs set near the containers. The fry are in a 4 gallon tank at this time. When they have full bellies I siphon out excess bbs.

When the fry start looking like little angels I mix a tiny amount of crushed flake food in with the bbs at their morning feeding. That's when they seem hungriest. When they eat flakes and bbs they get moved to a 10 gallon. I slowly wean them off bbs to straight flake foods.

[wsantia1]

I start feeding my angel fry bbs about 24 hours after the last one starts free swimming.   At about 21 days old I start feeding finely ground up flake first thing in the morning followed by bbs. I move them into a 29 gallon tank of there own once they have been eating the flake for about a week.  I continue to feed both flake and bbs until they are about dime size and then I move them into a 55 gallon grow out and feed mostly flake with an occasional bit of bbs. Of course this is subject to change depending on the size of the spawn.

[b125killer]

I feed there first feeding when most are free swimming. it's a lite feeding because I know that not all are ready to eat. I do that because most of the time they all start free swimming when I'm not able to feed. I start doing 90% water changes when they become wigglers so I don't foul the water. I only feed twice a day. working 12 hour shifts don't allow me to feed three or more times. To compensate I feed a little heavy. When the fry spike I move them to a 10 gallon. then I start feeding them small amounts of crushed or powdered foods. I have been feeding Captain Bob's Brand X to them lately. I slowly feed more crushed flake or powdered until they out grow the ten gallon then they move to the 90 gallon at that point it mostly flake or some other dry foods. I still feed bbs in small amounts after they stop eating bbs I'll start feeding frozen blood worms or frozen brine shrimp. 

[LizStreithorst]

With Discus I start BBS on day 4 of free swimming.  Until then their mouths are not big enough.  They feed from their parents.  With Angles I start feeding BBS late in day one or early day two.  Their next food is live CBWs.  Even little bitty fry can pick at them until they're eaten.  After that I introduce small pellets to Discus and smushed up flake to Angels.

[BillT]

Interesting reading Bill.  That species of killifish is a beauty from pictures I saw when I looked them up.  A lifespan of 3-6 months....are you going to collect eggs and raise new batches of them?

Yes I am. I have collected a few eggs and should be getting a bunch more soon. It keep them going i will have to keep breeding them fairly quickly. I have been told that the line I have should be dead at 11 months and ideally would be bred by about 4 months.

It seems there are several strains of Nothobranchius furzeri with different growth and maturation rates, different lifespans, and differing in whether they go through diapause or not. Normally in the wild they grow fast in a flooded plain area, lay eggs in the dirt and then die when things dry up. Therefore their is no selection for a longer lifespan, but a strong selection for rapid growth and breeding.
Some of the strains (some of which seem to be inbred) do not have to go through diapause and can just develop "fast" in the water. One of these strains can go from being an egg to making eggs in 1-2 months. This is useful for genetics. People are studying them in labs to figure out how the length of lifespan is controlled and how the diapause works.

When the fry start looking like little angels I mix a tiny amount of crushed flake food in with the bbs at their morning feeding.

Something I find very interesting about these stages of fish are these changes.
A fish in an egg is considered an embryo. After it hatches it is a larval fish. This stage looks quite different from an adult. To me it has a lot of similarities to tadpoles. They then metamorphose into juveniles (or sub-adults I guess, or a variety of other names). Then they get larger and eventually mature to an adult that may (or may not) breed.

The changes in fish when they metamorphose include:
1) development of the pelvic fins (pectoral fins are present early)
2) the change of the larval fin fold (which goes along the midline from behind the anus, around to back of the tail and up to the top of the body) into the anal, caudal, and dorsal fins. The folds in between these adult fins "go away".
3) Changes in pigmentation patterns from the larval to a more adult pattern.
4) Changes in the body shape from the blobby larval shape to themore adult shape.
This is also the time when flounders flop over on one side and one of their eyes migrates around the head to the top side.

It is well worked that metamorphosis of tadpoles to frogs/toads is triggered by the Thyroxin-T4 hormone (Thyroxin protein with 4 iodines bound to it).
The same hormone is highly conserved in all vertebrates and is thought to control fish metamorphosis.
Some people think that the changes that occur in humans around the time of birth are the human (or mammalian) equivalent of metamorphosis. Thyroxin rises and significant changes occur such as changes in blood vessel connections to and from the umbilical cord to support the different blood flow required for the baby to survive using its lungs rather than getting its oxygen from the mother via the placenta. this stuff is rather obscure but I think its really cool.

Thyroxin has lots of other functions at other times also. It not a single purpose thing.