Detail of just-laid, bright red and featureless Clark’s Clownfish eggs at
C-Quest hatchery. Note uniformity of placement.
is then attached to a standpipe or fixed in a vertical position within the
rearing tank. The top of the basket should extend above the surface of the
water. An airstone is placed within the basket along with the egg mass and
allowed to flow at a strong rate. It is a good idea to secure a few cable ties
to the inside so as the loose strands protrude to the center of the basket. In
this way the egg mass will become trapped on the tie and will be effectively
agitated by the airflow. Near 100-percent hatch rates can be achieved with
this method. If hatch rates are low, increasing the flow from the airstone
will usually help. At hatching, the larvae are freed from their egg shells by
the aeration and escape further mechanical harm caused by the bubbles
by exiting the basket through the perforations. The water motion created
by the rising bubbles causes water to rise from the bottom and spread as it
reaches the surface. It is this action that spreads the larvae throughout the
whole of the rearing chamber.
Many problems, both predictable and unique, can rise during the
incubation and hatching of marine fish eggs. Stumbling blocks surrounding
the propagation of marine fishes are frequent and most often attributed to
the early larval stages and the developmental stages near metamorphosis.
When artificial incubation must be employed it adds a whole new challenge.
Many of the hindrances associated with incubation and hatching are due
to inadequate water circulation through the egg mass, but other problems
Problem 1: Bright Light
Inexperienced breeders commonly use small flashlights to observe new
spawns within the dark confines of spawning caves. When the beam of
light is concentrated on newly spawned egg masses, little harm is done to
the developing embryos. At a later stage of development, after the eyes have
pigmented, beams of light can do great harm to unhatched larvae.
Many years ago I took great joy in witnessing the hatching of dottybacks.
After the lights had gone out, I would use a small blue incandescent light
to provide dim, diffuse illumination in the room. In this lighting, I could see
silver streaks of newly hatched larvae darting from the hatching container.
Other times I used a small flashlight to check the progress of the egg mass.
After coming under a strong beam of concentrated light, very few eggs
would hatch for me. I observed that a bright light shined on the egg mass
before hatching can prevent any larvae from hatching out. If I shined no
direct or strong light on the egg mass, most or all hatched out. Rules of
Eight-day-old Ocellaris Clownfish eggs with clearly visible dark eyespots
that are telltale signs of the approach of hatching.
elimination suggested the beam of light as the culprit.
Problem 2: Parasites
Invasions of parasites and pests are common problems during artificial
incubation. Bacteria and fungus often attack eggs quickly and without
warning. These are not large predators visible to the naked eye. Unfertile
eggs quickly turn white. The fouled eggs of substrate spawners that deposit
single rows of eggs are easily removed with a small syringe or tweezers.
The tangled egg mass of dottybacks makes the extraction of a few
fungused eggs extremely difficult. It is best to dip the egg mass in a fungus-preventative solution prior to artificial incubation. Malachite green in low
dosages, acriflavine, hydrogen peroxide ( 2 mL for every 1 L) or formalin
( 2 mL of 37-percent solution for every 1 L of treated water) work well for
this purpose. The eggs go into short-term baths of 15 minutes using rearing
tank water kept at the same temperature. Antibiotics should not be used
routinely in tank water during incubation.
A far less common problem affecting eggs are larger pests such as copepods
and ciliates. Within most conventional incubators with slow-moving water
driving the rotation of the eggs or egg mass, these organisms can gain a
foothold and consume many eggs, leaving very few larvae to hatch out.
The best strategy against such intrusion is the use of formalin dips prior to
incubation and an effective artificial incubation device designed to strongly
Problem 3: Water Quality
Under artificial conditions, water quality plays a crucial role in the success
of incubation. Without the male actively partaking in brood-care duties,
the eggs are vulnerable to many maladies and foes.
High levels of organic and nitrogenous wastes restrict the development of
the larvae within the egg membrane and they often perish before hatching.
Incubation should take place in clean water. The most effective method
of artificial incubation involves the use of newly mixed synthetic seawater
that has been aged. Chlorinated natural seawater filtered down to several
microns also works effectively. The water must be kept as clean as possible
with minimal amounts of decaying matter.Artificial incubation taking
place in a broodstock tank or central filtration system is rarely successful
due to the high waste levels. D
The Complete Illustrated Breeder’s Guide to Marine Aquarium
Fishes (TFH/Microcosm Professional Series, 2007) is available at www.
petbookexpress.com, as well as at aquatics and book retailers nationwide. For
additional information, visit us online at www.tfh.com.