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Sat Oct 30 08:01:00 EST 2004
One of the best ways to know whether you are reasonably optimal on your
diet is to compare the performance of your diets with natural live diets.
At the very low densities of only 5 to 7 fish/l, feeding a tank almost
anything will produce enough live bacterial / algal slimes, live
protozoans, etc. to balance out a poor diet. Depending upon the size of
the fish, you are only talking about biomass densities in the few mg/l
range as larva, which is a few tens of kg/ha which is less that the
production you get with pig manure in a pond. Unless you went to extreme
cleaning, you can't say your diet worked only that your protocol worked
with the natural
contamination in your system. Most larval fish do very well on live
single cell protein (organic slimes), which gets into the whole
aquaculture pro-biotic black magic game and hetrotrophic system games
(where you add carbohydrate to the system to grow bacteria and remove
ammonia while providing supplemental feed to the animals being produced).
Considering that you stated that it took 120 days to get good breeders
when, with live food and a better diet than tetramin, it should only take
47 days at 28ºC. Even at 22-24ºC at densities of 50+/l the fish will
start breeding at 70 days. Zebra fish in ponds in Florida, including
transgenic fish, are mature in 60 to 80 days, depending upon the
temperature. At pond densities, you can get by with cheap "pond" feeds
where you depend upon live material to balance the diet.
The primary impact of the leutine is to color the fins on the males with a
golden shade, but not females, and make the the long fin gold strain gold
instead of white. Several years ago, we did a comparison between a diet
with a mixture of pigments (leutine, and astaxanthan) with a diet without
the pigments on zebra fish and guppies. Guppies had better survival,
growth rate and food conversion without pigments, but zebra fish (like
salmon) did better with pigment. Hence, our zebra diet contains the
pigments. The effect was small, but we kept track of a lot of tanks to
get a valid result.
The research community needs to keep in mind that the business of rearing
larval fish and shrimp is a multi-billion dollar world wide business.
This business is highly dependent upon live feeds, including wild
harvested artemia cysts and everyone wants to get away from the problems
associated with live feed. Even with these half a billion dollar
incentives and very high cost per gm for live feeds (net cost into the
tank), there is nothing that is considered a real 100% replacement for
live feeds for larval fish/shrimp. The only species which can be started
without live food have very large fry, such as trout, salmon, catfish,
etc. which have well developed digestive systems and large mouths. Zebra
fish are not in that category.
Some aquaculture nutrition researchers like "Dr. Lou D'Abramo"
<ldabramo at cfr.msstate.edu> have some good experimental larval diets, but
it is not optimal for zebra fish, but would probably work better that
anything available on the market. Frederic Barrows <rbarrows at mcn.net>
has also been working on some larval diets and has done a lot of good
research. The type of research needed for zebrafish can be found for
other species in the books on fish/shrimp nutrition and in journals like
Aquaculture Nutrition, Aquaculture, etc. Scientists such as Rick Barrows
consult with feed mills who actually produce the diets on a commercial
scale. If we had more and better knowledge of the nutritional
requirements of zebra fish, that information would become incorporated
into the formulation of my diets custom manufactured by Silver Cup in
Murray Utah. That would then put the formulations into by customers
Note that feed mills such as Silver Cup (aka Murray Elevators) produce
product for most of the distributors of fry/larval and ornamental fish
feeds. Minimum batch sizes are usually a ton or more.
Another good measure of how close to optimal you are on a diet is to look
at the FCR (food conversion ratio = dry wt of feed/ wet wt of fish
growth). My diets are running about 1.0 to 1.2 for young zebra fish. One
kg of diet will produce almost a kg of live zebra fish. With live
rotifers, I can go from swim-up to eating second instar artemia in 4 days
or rotifers to dry feed at 20 days or just rotifers to maturity.
The question that needs answering is what impact does nutritional stress
have on research results?
Dallas E. Weaver, Ph.D.
5542 Engineer Dr.
Huntington Beach, Ca 92649
deweaver at surfcity.net
PS: For this type of discussion, I always assume that all the water
quality variables are fully under control and not an issue. With well
designed systems and protocols, it shouldn't be an issue.
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