One-day-old spotted green puffer babies.
Two-month-old T. nigroviridis fry at feeding time.
to proceed. I came across anecdotal reports of hobbyists
breeding them in captivity, and one report of a breeding
program in Southeast Asia. But none of the information
provided specific details about issues such as conditioning,
water chemistry, stocking rates, and so forth. Therefore, we
were pretty much on our own.
A local importer donated adult spotted green puffers for us to
work with, and just to be certain, we confirmed their species
using genetic analysis. Then we started trying things.
Initially, we placed pairs or trios in aquaria to see if they’d
spawn naturally. We provided various combinations of water
(fresh, brackish, or marine) and spawning substrates (sand,
gravel, vegetation, or PVC pipe). No luck there.
We were getting sperm out of the males if we lightly squeezed
them, so I decided to check it for motility in various types of
water. In fresh water it barely moved, in brackish it was sluggish,
but in full-strength seawater it was actively swimming around
looking for an egg! This told us that, in nature, spotted green
puffers spawn in marine conditions. But why would they not
spawn when mature males and females were placed in a tank?
Something—a trigger of some kind—was still missing.
There was an obvious alternative, known as induced
spawning. It’s commonly used for hard-to-breed species. You
give the females an intramuscular injection of a hormone that
induces ovulation. Then the eggs are harvested, fertilized with
sperm collected from males, and placed in tanks to develop and
hatch into larvae.
We tried this but it didn’t work, which—in my opinion—was
due to a couple of physical features that contribute to the
puffer’s signature defense mechanism. When alarmed, they
ingest water or air and swell up into a spiny ball. To facilitate
this, the puffer has unusually elastic skin and little muscle
mass—which meant that intramuscular injection often failed
to puncture the skin or caused too much stress to the female.
What happened next is a classic case of stumbling across a
good idea that was hidden in plain sight.
Circumventing the Problem
One of the preliminary steps that must be taken before
giving a female fish hormones is that a catheter must be
inserted into the ovaries via the vent so a small sample of
eggs can be removed and checked for their maturity. We
look for a migrated macronucleus, which is an indication of
mature eggs. We were doing this routinely on the puffers with
no apparent trauma to the fish, and we were finding good,
It occurred to me that if we routinely use catheters to reach
the eggs, maybe we could simply introduce the hormone with a
catheter, eliminating the need for an intramuscular injection.
The idea seemed logical enough. We set about testing the