How Do You Know if Copepods are Dead?

If you just bought a jar of new copepods and can’t see
movement within, you might be wondering: How does one know if their copepods
have died?

The first thing to understand is that copepods are very,
very tiny animals. Especially if you don’t have excellent vision, it is quite
difficult to see them, whether or not they’re moving! For instance, say you
just bought a jar of pods such as EcoPods, which contains multiple species in
various life stages. There might be several thousand individual pods in the package.
Yet, if you hold the jar to bright light and squint a little--maybe turn the
jar in such a way that it magnifies the contents--you might see a few Tigriopus (the largest species in the product). As to the other species, however, which
are smaller, you might not even be able to see the adults. Regardless of
species, you definitely won’t see the nauplii (i.e. copepod larvae) as they are
microscopic.

Funny thing is, sometimes it’s easiest to see the dead ones.
This is because they quickly settle to the bottom of the package and (if
they’ve been dead long enough) may take on a milky discoloration. Seeing a few
dead pods in a shipment can be extremely misleading. Especially if you can
hardly see live ones--but there are clearly dead ones--it can lead to an
assumption that the package “went bad.” In most of these cases, nothing could
be further from the truth!

First of all, when you’re shipping literally thousands of
specimens of a species that have a short lifecycle, you can certainly expect
some natural mortalities in transit. Given that the majority of these
mortalities will be older (i.e. larger) individuals, they will be rather
conspicuous. If you see any live pods at all in the package, it’s probably just
fine.

If your pods are all dead, you’ll know it. There will
be a conspicuous layer of whitish/greyish sediment at the bottom of the
package. Upon opening, the water won’t just smell a little bad (which is
normal) but really bad. As copepods are extremely hardy and ship quite
well, this typically only occurs after a very late delivery or if the package
has been subjected to very extreme temperatures. If you suspect your culture
may have crashed in transit, let us know (but don’t throw them out just yet)!