The Reproductive Biology and Spawning of Zebrafish in Laboratory Settings - Zebrafish: Methods for Assessing Drug Safety and Toxicity - page 7

tube into separate collection screens by means of pressurized air directed into the
funnels, allowing eggs to be collected without disturbing the fish. The units also have
the capability to be run on altered photoperiods via the use of an attached light cycle
dome with a programmable light cycle dimmer.
The MEPS system capitalizes upon several attributes of the general in-tank

breeding approach, including consistent water quality and minimal handling of
animals, with the added benefits of reduced labor input and increased space efficiency.
When used properly, this technology is capable of supporting high-level egg
production on the order of tens of thousands of embryos per event, and is therefore
well suited for experimental applications requiring large numbers of time-staged
eggs. However, this approach is not without its limitations and specific challenges.
For example, its use is limited to experiments where the individual identity of parents
is not necessary, which excludes it frombeing used for certain types of genetic screens,
which are an important component of the zebrafishmodel system. The performance of
fish in this type of breeding unit is also very dependent upon management. Detailed
understanding of reproductive behavior and biology of the fish is imperative to
maximize efficiency, and therefore the MEPS

may be less suitable for newly
established zebrafish laboratories where such expertise is not available.

1.3.2 Static Tank Strategies

The alternative to in-tank breeding strategies is to remove fish from holding tanks and
to spawn them in off-system or “static water” breeding chambers. This general
approach, which is utilized in the great majority of zebrafish breeding facilities,
adheres to the following general principles: a small (typically 1 L) plastic mating

cage or insert with a mesh or grill bottom is placed inside a slightly larger container
that is filled with water. Fish (pairs or small groups) are then added to the insert in the
evening. When the fish spawn, the fertilized eggs fall through the “floor” of the insert
and are thereby protected from cannibalism by adults (Mullins et al., 1994).
This technique has proven to be generally effective and, consequently, deriva-
tions of the static tank design are manufactured by a number of aquaculture and
laboratory product supply companies. Available products vary slightly in size, shape,
depth, and total volume, as well as adjustability of inserts in the static spawning
chamber (Fig. 1.2c). A very small number of studies have explored the effects of
variations of these parameters on reproductive success and spawning efficiency. Sessa
et al. (2008) showed that fish set up in crossing cages in which spawning inserts were
titled to provide a deep to shallow water gradient showed statistically significant
increases in egg production when compared with fish set up in cages in which the
inserts were not titled (no gradient). Fish that were set up in chambers with titled
inserts displayed both a preference to spawn in shallow water and specific breeding
behaviors that were limited to the tilted physical configuration. Indeed, this behavior
is the basis of a newly developed approach for collecting large numbers of devel-
opmentally synchronized embryos from groups of fish in a static breeding vessel
(Adatto et al., 2011).

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