16 NOVEMBER/DECEMBER 2015
In July 2012, a group of accomplished scientists across the spectrum of bio- logical disciplines met to discuss the
neurobiological substrates of conscious
experience in human and non-human
animals. They concluded that human
and nonhuman animals are sentient—but
never mentioned fish. This may have
been because fish are cold-blooded,
because they don't appear to have facial
expression or emotion, or because they
shine with a splendid palette … or it may
have been because of just about anything
else. But, fish simply didn't come up.
Of course, the exclusion made plain the
case: how could fish not experience the
vagaries of existence—changes as they
occur in such as weather and temperature
and pain, yes; but, even more to the point,
utter departure from the natural habitat.
Looking back, this was a remarkable
omission and portentous. It allowed for
widespread recruitment of zebrafish into
studies across the biomedical spectrum
despite an absence of knowledge about
zebrafish behavior in the wild. Only
anecdotal tidbits about their behavior in
the lab existed, and virtually no attention to welfare or enrichment was given.
Little by little, scientists are gathering
facts and creating a rich picture of zebrafish
life and of the zebrafish as a living system.
With any luck, we'll soon have a compendium on zebrafish natural behavior that will
inform welfare and enrichment. Frankly,
we believe the field is long overdue for a
gap analysis: that is, what we know about
zebrafish basic needs and how we organize
and manage their living conditions in the
lab. With such a gap analysis at hand, scientists could routinely provide for zebrafish
ease just as they now do for laboratory
rodents, rabbits, primates—and lately, birds.
At last some scientists say that zebrafish feel pain. And as a result, scientists are
taking steps to determine which end of life
practice is euthanasia—a painless death.
Specifically, the chemicals that cause
the fish distress are replaced in some EU
countries (but not the UK) with clove oil
or rapid chilling of water to between 2 and
4°C. This is the first major step in developing welfare and enrichment standards and
practices for zebrafish.
That is a good start but not nearly
enough. In this article, we summarize
highlights of what's known about zebrafish behavior—principally behavior
observed in the lab—that may inform
welfare and enrichment plans in the
Noam Miller, Assistant Professor, Department of Psychology at Wilfrid Laurier
University in Ontario, Toronto, shared his
experiences with us, and exclusive text
from Noam can be found online. And we
spoke with Carole Wilson, Head of the
Fish Facility at University College London,
about how more knowledge about zebrafish behavior in the wild would help her
create a welfare and enrichment program
for her many charges. Both contributed
generously to our understanding, and
their knowledge informs the text.
A SKETCH OF THE FISH ITSELF
A zebrafish measures about three centimeters in the wild, four to six centimeters in
captivity. The male has predominant blue
and lesser gold stripes; the female is blue
and silver. Both exhibit nuptial coloring.
All are highly predated from above and
below, but not such easy prey, being dark
on the top and very light on the bottom.
There are many strains and each shows
a unique behavior profile. All strains live
for about three years in the lab; it is not
known how long they live in the wild.
The zebrafish, Danio Rerio, is a
minnow. Danio is a Bengali word that
means of the rice paddies, and the fish is
aptly named. The natural habitat is small
shallow Himalayan pools that tend to
measure 1/2 to 2 meters wide and 50 cm
deep—quite small and typically inhabited
by a few dozen fish.
Residential pools tend to be near
river banks and rice paddies, but these
cyprinids are adaptable. As farmers flood
the paddies and weather changes the
nature of tide pools, the fish stay steady
in the shallower areas. They can thrive as
the seasons change the level and composition of the water. They can easily
survive in ditches, canals, and stagnant
pools. There are no rocks and little sunlight. Puberty is affected by fat content of
the diet, by the individual's size, and by
sunlight. Zebrafish eat mostly insects that
fall on the surface of the water, and they
spawn in the early hours of dawn.
Zebrafish are highly social creatures and
welcome additions to any group. They
have individual personalities and there
are distinct behavioral differences across
strains. By and large, they are not jealous
creatures since they don't pair bond.
In general, Danio Rerio are calm in a
group of 20 to 30, become uneasy with
fewer than eight, and distressed when
alone. They are rarely territorial, and they
are family oriented, showing a strong
preference for swimming and shoaling
with those they know. In fact, when they
consistently swim with familiars, they
grow 15% larger than those who have
no choice but to swim in non-kin groups,
So many zebrafish—so little welfare
Discovering the enrichment and care needs of this