I
began rearing the common clownfish, Amphripion
ocellaris in relatively large numbers in late 1972. This
was the first actual commercial scale culture of a tropical
marine aquarium fish. Soon after the success with clownfish I
wanted to broaden the numbers of species under culture and the
neon goby was an excellent candidate. It was a small species,
very easy to maintain, spawned very easily in a small tank,
and was in some demand in the then rather small, marine
aquarium hobby. It was important to inform hobbyists of these
developments and so over the years I usually wrote a short
article on each new species that we brought under culture. At
the time, the most prestigious marine aquarium magazine (out
of the two then in print) was The Marine Aquarist published by Dr. John Miklosz (Terry Siegel, was
the co-editor). I wrote a number of articles for this
magazine, including the following one on propagating the neon
goby. This article, recently updated, contains some
information originally reprinted from the February 1975 issue
of The Marine Aquarist.
The
neon goby, Gobiosoma oceanops, is one of the largest species of the genus and
probably the most common goby in marine aquariums. It is a
cleaner species and even though of small size (2 to 3 inches
as adults) the neon goby does well in a community tank. It
will engage in cleaning behavior with Pacific as well as
Atlantic marine fishes. We often keep them with large
clownfish and frequently observe symbiotic cleaning behavior.
The clownfish assumes a head up position and slowly flutters
its fins while the neon goby swims with rapid, jerky movements
over the fins and sides of the clownfish looking for
parasites. A quick shake and resumption of normal swimming
posture by the clownfish breaks the cleaning pattern and sends
the goby on its way. The neon and its close relative, the
shark-nosed or gold lined goby, Gobiosoma evelynae, make an interesting and colorful addition to any
marine tank and even benefit the occupants through their
parasite cleaning behavior.
As
the neon gobies mature, they begin to pair for mating and this
can cause great problems in the close confines of an aquarium.
Once a pair is established they forcibly reject any others of
their species and even a 100- gallon tank is not big enough
for three neon gobies. However, if six to eight or more gobies
are present in a tank, pairing and aggressive behavior is
muted, and aside from a few minor squabbles, the fish can
co-exist.
Once
a pair is identified, they can be easily induced to spawn by
providing a suitable spawning habitat. The neons, like other
gobies we have worked with, are secretive spawners. They
select an overturned shell, small pipe or inside of an
aquarium ornament as a spawning site. Spawning has always
occurred on the underside of a surface and the attached eggs
extend downward into a restricted cavity. Spawning usually
takes place in the early morning hours, although I have
observed it to occur in afternoon and early evening hours as
well. Itis difficult to observe the actual deposition of eggs because of
the secretive spawning site, but there seems to be several
periods of egg deposition by the female followed by
fertilization by the male. Both sexes twitch and wiggle side
by side under the shell during the spawning process. The
female leaves the site after spawning and only infrequently
visits the eggs during the incubation period.
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The
male neon goby aerates the eggs and guards the developing
embryos.
A
close up shot of neon goby eggs after 7 days of
incubation. The well-developed eyes indicate that hatching
is close. The eggs are about 2 mm long and hatched soon
after the photo was taken.
This
newly hatched neon goby is only 4 mm long and retains a
remnant of the yolk sac that will provide energy for early
development.
The male spends much time caring for the
eggs during incubation by moving his body and fins over the egg
patch at frequent intervals. He readily leaves the eggs for
short periods to feed and explore, but soon returns and rests
upside down underneath the egg mass. The female often rests
above the shell at the entrance to the nest cavity or cruises
about the general vicinity. The shell containing the spawn can
be removed for examination and replaced without any harm to the
eggs or disruption of the male's incubation behavior. The male
cares for the eggs throughout the incubation period, which,
depending upon the temperature may be between 6 to 8 days.
A large female at the height of
reproductive activity may lay 500 to 600 eggs, but the usual
spawn size is about 250 eggs. The egg capsule is about 2 mm long
and 1 mm in diameter and is completely transparent. The entire
development of the embryo, from the first division of the
blastodisc through to hatching, can be observed through the
transparent chorion, or egg “shell” casing. The attachment
of the egg consists of a mass of fiberous threads extending from
the base of the egg capsule to a sticky pad that adheres to the
substrate. The eggs are placed very close to each other and the
newly laid spawn has the appearance of, an undulating patch of
clear globules. After the eyes become pigmented, the patch takes
on a silvery appearance. The embryo begins development with the
head pointed towards the base or attached end of the egg
capsule. The embryo turns around in the egg capsule on about the
third day of development and completes incubation with the head
developing within the stelate, distal end of the capsule
Feddern (1967) and Valenti (1972) both describe
embryonic development of neon goby larvae and these papers
should be consulted for technical details on larval development.
Valenti states that larvae that do not reverse in the egg
capsule at 50 hours, but complete development with the head at
the base of the capsule, do not hatch. Our experience has shown
that hatching takes place regardless of the position of the
larvae. At hatching, the capsule ruptures by the head of the
larvae wherever it happens to be positioned, and the larvae
forces itself out the opening. I have never observed a larvae
fail to hatch because of a reversed position.
(Note:
At first, the larvae were recovered similar to recovery of
clownfish larvae in a large tank. The light from a flashlight
was aimed at a corner of the tank shortly after hatching
occurred at night. The larvae were attracted to the light and
concentrated in that corner where they could be siphoned out
into a bucket and then transferred to the rearing tank. This was
too laborious a method for commercial culture however, and we
soon discovered that the shell or pipe section that contained
the egg mass could be removed on the day that the hatch was
expected and hatching could be stimulated manually. This was
done by exposing the nest to a relatively bright light and then
gently stroking the eggs with a feather from a sea gull. Within
a few minutes of stimulation with the feather if the eggs were
ready, they would begin to hatch en mass and the larvae would
pop off the nest like popcorn. We could determine when the eggs
were due to hatch by counting 7 days from the spawn and also by
the size of the eye of the embryonic larval fish compared to the
size of the residual yolk sac in the embryo. The embryo was
ready to hatch when the size of the yolk sac was about the same
size as the eye of the embryo. This seems to hold true for
clownfish as well.)
In
one instance that I was fortunate enough to observe through the
microscope, a malformed goby larva was completely encased in a
normal egg capsule. The larvae appeared to be missing a portion
of the notochord and the body wall about the gut was completely
absent leaving the gut and yolk sac exposed within the egg
capsule. This condition was observed shortly after hatching of
the spawn and this larva had eroded the egg capsule in the
vicinity of the gut instead of at the head. These observations
indicate that hatching occurs as a result of the release of some
substance, probably a proteolytic enzyme, originating in the
vicinity of the gut and released at the mouth, that breaks down
the egg capsule in the area of the head.
(Note:
In nature, and sometimes in marine aquaria, neon gobies nest in
small, deep holes with only a tiny opening just large enough to
allow passage of an adult goby. I have no idea how the tiny
larvae get from the hatched egg, entwined deep in the nest with
other eggs, to the open waters of the tank, but they do. Perhaps
the male helps as I have seen a male neon goby appear at the
entrance of his nest, open his mouth, and then release a tiny,
new-hatched larvae that then swam up into the water column. Not
once, but twice did I see this!)
The
larvae are quite small (4 mm long) upon hatching and usually
carry a residual yolk. Feeding usually begins about 12 hours
after hatching, depending upon the state of development at the
time of hatching. Small living organisms are required as a first
food. The larval stage of the neon goby is rather prolonged.
First metamorphosis into the adult coloration and behavior
pattern occurs at about 18 to 20 days, although it may extend to
40 days under adverse conditions. The larvae are reared under a
carefully simulated pelagic environment.
(Note: At
the time that this article was written, late 1974, great secrecy
surrounded the culture of marine tropical fish. There were only
two commercial, marine tropical fish hatcheries at that time,
Aqualife Research, and Neptune’s Nurseries. Aqualife Research
was my own small, struggling company and Neptune’s Nurseries
was a sister company of the rich and powerful Aquarium Systems
that had recently entered the field with my old friend Frank
Hoff at the helm. Although the technology for rearing marine
tropical fish was relatively simple, especially at that time, it
was a new application of a fledgling technology and it held the
promise and potential for a new and lucrative industry. There
was a tendency to make it appear that we were in possession of
special secrets worthy of protection from industrial spies and
that our problems were less significant than those of the other
participants in this new endeavor. Therefore I took pains in
writing my articles to document our success in rearing various
species without describing the “carefully simulated pelagic
environment.” In those days, a bare 75-gallon tank surrounded
with black plastic sheeting, with a two bulb fluorescent fixture
resting on the top of the tank and two air stones spaced
centrally in the tank. Rotifers, brine shrimp, and water changes
completed the picture. Actually not a whole lot has changed in
30 years.)
The early
juveniles take up a benthic mode of life shortly after the first
color appears on the transparent larvae. A faint blackening of
the sides quickly becomes a bright sliver of electric blue and
the cupped pelvic fins attach the early juvenile to the tank
substrate. Growth is rapid after this point in development is
attained and sub-adult size is reached within 3 months. The
young gobies can be paired at this time although first spawning
is still 2 or 3 months in the future.
We have
spawned about ten pairs of tank-reared gobies to date and have
noted no obvious difference between wild and tank-reared fish,
either in morphology or reproductive success. Growth continues
after spawning commences and when the fish are ten months to a
year old, they are full adult size and are at the height of
reproductive activity. Spawning takes place every 10 to 12 days
depending on temperature, and we have had pairs spawning in
every month of the year. The spawning period in nature is
February to April (Feddern, 1967); however, we have been able to
spawn neon gobies every month of the year in the laboratory.
A neon goby larva at 16 days
old, not far from metamorphosis into a bottom dwelling
juvenile. The late larva is still transparent and lives
above the bottom in the open water.
An
early juvenile transformed overnight into a benthic living
goby with dark blue and black coloration.
Tank reared neon gobies can
be held in large numbers in grow-out tanks. The two month
old neon gobies in this 75 gallon tank were reared from
two spawns.
References
Feddern,
H. A. 1967. Larval Development of the Neon Goby, Elacatinus oceanops,
in Florida. Bull. Mar. Sci. Vol. 17, No. 2, pp 367-375.
Valenti,
R. J. 1972. The Embryology of the Neon Goby, Gobiosoma oceanops. Copea,
1972, No. 3. pp 477-482.
