Culture
of Mysid shrimp and Bivalve trochphores (veligers)
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sponsor of this column
For
one reason or another, there is no single perfect food
organism for the culture of marine larval fish. Each species
of fish has its own constellation of ecological and feeding
requirements during its larval stage and is adapted for
best survival in inshore or offshore waters with a particular
combination of dominant ecological, physical, and chemical
factors. It’s absolutely amazing, and a testimony to the
resiliency, vigor, and adaptability of these tiny marine
creatures that we can culture any of them in little glass
boxes so far removed from the expanses of the open sea.
Of course the intelligence and determination of the human
species has a lot to do with it also.
In
this months offering, Martin and I assist in feeding those
finicky fry by providing two additional microfoods; one
large -mysid juveniles and one small invertebrate veligers.
These microfoods are supplements that one can add to your
menu of assorted size food items to feed difficult fry.
Both microfoods are on the advanced side of culturing,
but if you can make it to the end of the column and you’re
not lost, you should have sufficient background and experience
to easily culture these food items!
Possum
Shrimp (Mysis sp.)
Background:
Mysids are small shrimp-like crustaceans with a heavy
carapace covering their thorax and can grow to 1 cm in
length (Reitsema & Neff 1980) [Fig1]. Adapted to life
in estuaries, these tough, hardy crustaceans can withstand
a wide range of salinities and temperatures. Mysids inhabit
estuarine waters from Florida, USA, to the East Coast
of Mexico (Bowman 1964). According to Price (1976), Mysidopsis
almyra is the dominant mysid species in the estuaries
surrounding Galveston Island, Texas, USA, comprising 82%
of the mysids collected. Mysids (primarily Mysidopsis
almyra or Mysidopsis bahia) have been used
extensively as indicator species in water toxicity tests
(Miller 1990) for many years and are commonly reared or
cultured in the laboratory (Reitsema & Neff 1980).
Before the advent of lab culturing, Mysids were routinely
collected via dip netting (McKenney 1996). Mysidopsis
species are omnivorous and cannibalistic, feeding on diatoms
and small crustaceans such as copepods (Mauchline 1980).
Life
cycle
These crustaceans
are commonly called possum shrimp because the females
carry their developing young in a bulging pouch or marsupium
formed by at the base of their legs. Females can carry
broods of up 30 fry in their pouches, although 6 or
7 is the normal brood size. The young mysids are not
released until they are well-developed juveniles. Each
fry is approximately 4-to-5 times bigger than newly-hatched
Artemia nauplii (baby brine shrimp). Females produce
young continuously, refilling their pouch with eggs
as soon as their latest brood is released. The juvenile
Mysids will reach their adult size of 1 inch (1.25 cm)
in about 3 weeks, creating a new generation every 30
days. Male mysids are slightly larger than female mysids
and are readily identifiable by their conspicuous absence
of the white brood pouch. Laboratory strains of tank-raised
Mysids are available that have been selected for resistance
to disease and are pre-adapted to aquarium life (see
additional reading and online suppliers).
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Fig
1. Drawing of a typical Mysid –female click
figure for full-size image
Fig1a
- A photomicrograph of Mysidopsis Bahia.
Photo courtesy of www.calacademy.org click
figure for full-size image
Fig
2. Diagram of a static mysid culture system. The two
top tanks (culture trays) were used for holding broodstock,
the two middle tanks (hatchling trays) were used for
the hatchlings, and the bottom tank was the biological
filter tank, containing a particle filter, activated
carbon filter and a submerged, oyster shell biological
filter. Water drained through the screened cores in
the culture and hatchling trays into the biological
filter tank. It was then drawn from below the crushed
oyster shell media, and pumped back into the culture
and hatchling trays through the supply lines. click
figure for full-size image
Fig
3 Mysid mass culture setup. 30 gallon tanks line this
Laboratory culture room where many mysids and artemia
are raised.
Husbandry
Despite
their widespread use as pollution bio-assay organisms, Mysids
are remarkably undemanding in terms of water quality (as
long as the values remain within a reasonable range). According
to Hemdal, no unusual mortality was noticed in tanks even
when the ammonia concentration approached 1 ppm. Mysid density
in a culture tank affects reproduction. According to Lussier
et al. (1988), a culture that is overcrowded will cease
reproduction, resulting in high proportion of females with
empty brood sacs. The above authors indicated that the optimal
densities were 15 adult mysids/ L in a flow-through system
and 10 adult mysids/ L in a static culture [Fig 2]. The
ability to culture mysids in large numbers at low cost enables
the successful aquaculturist to raise several unique marine
species, including leafy sea dragons and cephalopods (Hanlon,
Turk & Lee 1991).
Average
water quality for mysid culture tanks (according to Hemdal):
Enrichment
has been shown to be an effective way to ensure nutritionally
sufficient Mysid juveniles. The easiest way to enrich Mysids
is to feed them fortified Artemia nauplii (Kuhn et al. 1991).
Experiments in static (closed) systems indicate that enriched
Artemia nauplii are the best food item for mysids (Domingues
et al. 1998). Therefore, it is highly recommend to enrich
both adult and hatchling mysids with Artemia nauplii fortified
with marine fatty acids (such as phytoplankton-enriched
or Selco® enrichment) for 12 h prior to feeding (see
Breeder's Net column). As a reminder, Artemia cysts
are hatched for 24 h under intense fluorescent light at
temperatures of 28 °C with salinity between 18 and 22,
and are then collected on a 53um mesh screen. Enrichment
of the newly hatched Artemia nauplii is accomplished by
soaking the animals in a solution of Selco® and seawater
at 0.25 g Selco® /L sea water for 12 h.
Culturing
of Mysids
The
following culture instructions are based on a method used
by Lewis (Lewis, 2000) to raise Mysids on a commercial basis
at Aquatic Indicators (see online suppliers list). It should
be stressed that culturing Mysids is a fairly labor-intensive
project; however mysid culture can be accomplished by anyone
who is willing to put in the time and effort.
First,
utilizing a 20-gallon tall or larger all-glass aquarium,
add a standard undergravel filters at either end, but leave
the center of the tank bare (no U.G.s) to facilitate collecting
the Mysids. As an example, if you're using a 30-gallon culture
tank, install U.G. filter plates designed for a 10-gallon
aquarium at both ends of the culture tank, but leave bare
glass at the bottom in between the 2 filter plates. Adjust
the specific gravity to about 1.022 and set the temperature
at 75-78F.
Once
the tank has cycled and the biofiltration is established,
introduce 20-30 adult Mysids to get the culture started.
Establish a photoperiod of 16 hours of light and 8 hours
of darkness (Mysids mate at night), and perform 15-20% water
changes weekly. Feed you new Mysid culture with newly-hatched
Artemia nauplii at least twice a day. Keep an eye on the
wate rquality in the Mysid tank and ensure that almost all
of the Artemia nauplii are comsumed with each feeding. To
maximize growth and reproduction, maintain a density of
approximately 10 brine shrimp nauplii/ml of water. (You
should already have your brine shrimp production up and
running from our previous Breeders net columns).
One of
the keys to raising Mysids is to prevent cannibalism by separating
the adults from the young. For laboratory studies, mysid separation
is done manually by isolating the adults, transferring ovigerous
(egg-bearing) females to a culture dish, and removing the juveniles
with a pipette.
A better
method can be devised that will automatically separate the juveniles
from the adults, if you are willing to set-up a separate tank
just for the adults alongside the main culture tank. Keep the
top of this isolation tank exactly even with the top of the culture
tank, and position an air lift tube in a corner of the adult's
tank so that it returns water to the main culture tank, while
a siphon tube in the opposite corner maintains the water level
(see diagram) between the tanks. The air-lift tube should be sheathed
with plankton netting or nylon screen with a mesh size (800 microns)
that will restrain the adults while allowing the larvae to pass
through unimpeded. Likewise, the end of the siphon tube should
be covered with 500 mM plankton netting that will allow newly-hatched
brine shrimp to pass through but not the juvenile mysids. Adjusting
the air lift so it produces a slow, gentle, steady flow of water
will automatically deposit the juvenile shrimp in the main culture
tank while keeping the adults isolated in the adjacent tank, thereby
eliminating cannibalism.
It is best to let the population of mysids build up for a couple
of generations to increase your brood stock before you begin harvesting
regularly. Meaning you should start your cultures about 6-8 weeks
before you need the shrimp. As an example, when your brood stock
numbers equal approximately 400-500 adults, you should be able
to harvest about 200 Mysis juveniles per day to feed your fish
fry without concern for depleting the mysid reserves.
Harvesting
Mysids
To
harvest the shrimp, sweep a net through the water column
over the bare glass at the center of the tank, and select
the Mysids that are the best sized for your fish fry. Using
nets with progressively larger mesh will allow you to gather
larger Mysis nauplii that are the perfect size for your
fish fry, or conversely by using smaller net mesh sizes
will allow the capture of smaller Mysids. Be sure to leave
at least 20% of each generation of Mysids behind to ensure
your culture is self-sustaining.
One of the biggest
obstacles to raising Mysids at home is obtaining a supply
of shrimp to start a culture. Aquatic Indicators (see online
suppliers) is one of the few companies that sell live Mysis
shrimp. One large order includes approximately hundred Mysidopsis--enough
for several starter cultures.
Hints and Tricks
(according to Hemdal):
* Various hydroids and other "pests" can show
up in the brood tank and need to be removed by stripping
down that tank. These pests compete with the Mysids for
food, and may actually consume juvenile Mysids.
* When productivity is low, start up a new rearing tank
after seven days. The reasoning is that if there is more
than a one week age difference, the older Mysids will prey
upon the newly added ones.
* Surplus adult Mysids can be frozen for later feeding,
or added live to a large holding aquarium, as sort of a
"rainy day fund".
* The best way to remove larval Mysids from the brood tanks
is by siphoning them out. With practice, an aquarist should
be able to siphon out the babies at a rate of better than
20 per minute. The trick is to avoid wasting time trying
to siphon out three or four day old babies, they are just
too fast. Focus on the smaller one or two day old ones that
are positioned on the glass of the aquarium. Free-floating
babies are able to escape the siphon in any direction, making
them harder to capture. Mysids crawling along the glass
can only escape along a 180 degree plane, away from the
siphon.
* Although time consuming, productivity in the brood tanks
can be enhanced by selectively removing most of the male
Mysids. This reduces predation of the larva as well as the
amount of Artemia needed as food for the breeders. With
a small net, capture the majority of the Mysids which do
not show the female's white brood pouch. You may remove
some non-breeding females with this method, but the majority
will be males. Even a 10:1 ratio of pouched to non-pouched
mysids will produce many offspring.
* Some public aquariums have developed an easy larval separation
technique: Separate mysids based on size using different
mesh size net material. In most cases, this simply consists
of capturing the entire contents of a brood tank in a standard
fine mesh white aquarium net. This material is then rinsed
through a standard green mesh aquarium net into an empty
rearing tank. The adult mysids remaining in the green net
are returned to the original brood tank, and this process
is repeated every few days.
Bivalve
larvae
The basic reason
for the success of brine shrimp and rotifers as food organisms
for larval marine fish is that it is possible for the fish
farmer (or hobbyist) to produce these organisms rapidly
in incredible numbers at relatively little expense and effort.
Additionally, these food organisms can be nutritionally
enriched, which makes it possible to adjust their nutritional
value to suit the needs of many different species. Copepods
are a better choice, however, because they are the natural
food organism with the nutritional profile and digestive
characteristics best suited to most marine fish species.
Copepods are not well suited to contained culture because
of their relatively long life cycle, several weeks, thus
are difficult to culture in the required numbers for even
a modest size fish culture installation. So are there any
other possibilities for larval food organisms? Is there
anything else that might have the essential characteristics
of proper nutritional profile, abundance on demand, and
acceptability to larval marine fish? And yes, there is.
Veliger
larva
One
of the strongest contenders are the first larval forms of
some marine invertebrates, in particular the trochphore
[Fig 4] and veliger larva [Fig 5] of bivalve mollusks: clams,
oysters, scallops, and mussels. These mollusks are produced
commercially as aquacultured food organisms and the techniques
for spawning and rearing them are well known. In fact, there
is a vast, worldwide literature on the aquaculture of bivalves,
but relatively little on use of the larval forms as food
organisms for larval marine fish.
The
negative factors associated with use of larval bivalves
in marine fish culture are that, in an inland based facility,
it requires a complete system for the culture of different
macro organism, including algae culture, just for production
of a larval food. And the swimming behavior of the trochophore
larvae is more like a rotifer than a copepod nauplius and
may not stimulate some larval fish to feed.
Fig
4-The trochophore larvae. The general characteristics
of the trochophore larvae are illustrated in this
diagram. The trochophore is the first larval stage
of chitons, scaphopods, gastropods, and bivalves.
The trochophore develops directly into the juvenile
stage of chitons and scaphopods, but gastropods and
bivalves develop through a veliger stage before metamorphosis
into the juvenile. click
figure for full-size image
Fig
5 -The veliger larvae. The veliger stage is different
in the gastropod and bivalves. The development of
the vestigial shell is different, both have a velum,
but the torsion that creates the single spiral shell
of gastropods and development of the bivalve shell
of oysters and other bivalves changes the shape and
structure of the veliger larvae of these two huge
Classes of mollusks. click
figure for full-size image
Fig
6 -Brine shrimp, rotifer, and oyster trochophore larvae.
Number 1 is the newly hatched nauplius of a brine
shrimp. Number 2 is a rotifer and number 3 is a group
of six oyster trochophore larvae. These images were
all taken from the same photomicrograph of a mixed
culture so the size of each organism is in exact proportion
to the other two organisms. click
figure for full-size image
However, there are
some strong positive aspects to this source of food organisms
for larval fish. The size of the larvae from various species of
oysters, scallops, clams, and mollusks ranges from roughly 30
to 60 mM, a range of size that is acceptable as a first food organism
for many fish [Fig 6]. Cultured oysters produce a trochophore
that at 50 mM is about one fourth the size of a rotifer and one
tenth the size of brine shrimp nauplii. Also the nutritional profile
of the trochophore larvae can be influenced by the food fed to
the adults as well as the algae fed to the early trochophore.
The larvae of cultured oysters may contain 15% 20:5n3 (EPA) and
15% 22:6n3 (DHA) fatty acids. This is better than most nutritionally
supplemented rotifers and brine shrimp since they have no low-n
fatty acids, which are not normally found in wild fish larvae.
The number of larvae that can be produced from the spawn of a
single female bivalve ranges from 15 million, for an American
oyster, to 55 million from a Pacific oyster, to 170 million from
a scallop (Tamura, 1970). The adult bivalves are relatively easily
maintained in basic closed systems, they are filter feeders so
feeding is easy although particulate filtration may be a bit labor
intensive. Most cultured species of bivalves can be spawned on
demand. Temperature manipulation and sometimes a simple chemical
shock is all that it takes to induce spawning. (I used a little
vodka once to start spawning in a tank of oysters.)
Obtaining
Bivalves
There
are three ways to obtain bivalves for spawning purposes. If one
lives near the sea, it is usually possible to collect oysters
and mussels from the shoreline, clams from the mud flats, and
scallops from the grass beds. It may be possible, depending on
seasonality and latitude, to spawn the particular species at the
time of collection, or to hold and feed the adults with cornstarch
(or an algae feed) to condition them for spawning in a few weeks
(Utting, 1993). The last possibility is to simply purchase supplies
of cryopreserved embryos and early larvae of oysters and clams,
Trochofeed (Cryofeeds Ltd., Canada. (Chao, et. al., 1995). This
method has the advantage of providing live trochophore larva at
just the right stage of development (15 hours old, ciliated and
free swimming without shell formation) at any time that they are
required. It takes the spawn of about 240 carefully cultured and
spawned oysters to produce a billion trochophore larva. The larva
are collected and processed and then frozen in liquid nitrogen
at –196oC. They are kept sealed in polyethylene straws at densities
of 15 and 50 million per straw and can be thawed and shipped at
any time
Within
a few days of the spawn the trochophore larvae become veligers
with a velum and a vestigial shell. They settle and attach to
a substrate in about 10 to 15 days. The veliger stage is not as
suitable as the trochophore for larval fish food because of the
development of the shell, but larger larvae may well feed upon
them. Under certain situations, for certain high value species,
for example, the use of trochophore larvae in marine tropical
fish culture might be quite useful.
References
Bowman, T. 1964 Mysidopsis almyra, a new estuarine mysid crustacean
from Louisiana and Florida. Tulane Studies in Zoology, 12, 15
18.
Chao,
N. H., Lin, T. T., Chen, Y. J. and Hsu, H. W. 1995 Cryopreservation
of late embryos and early larvae of oyster and hard clam. In:
Larvi’ 95 – Fish and Shellfish Larviculture Symposium. Lavens,
P., E. Jaspers, and I. Roelandts (Eds.). European Aquaculture
Society, Special Publication NO. 24, Gent, Belgium, p 46.
Domingues,
P., Turk, P.E., Andrade, J.P., Lee, P.G. 1998 Pilot-scale production
of mysid shrimp in a static water system. Aquaculture International,
6, 387 402.
Hanlon,
R.T., Turk, P.E., Lee, P.G. 1991 Squid and cuttlefish mariculture:
an updated perspective. Journal of Cephalopod Biology, 2, 31 40.
Hemdal,
Jay. Raising Mysid Shrimp as a Home Aquarium Food. Seascope 2000.
Kuhn,
A.H., Bengtson, D.A., Simpson, K.L. 1991 Increased reproduction
by mysids (Mysidopsis bahia) fed with enriched Artemia spp. nauplii.
American Fisheries Society Symposium, 9, 192 199.
Lussier,
S.M., Kuhn, A., Chammas, M.J., Sewall, J. 1988 Techniques for
the laboratory culture of Mysidopsis species (Crustacea: Mysidacea).
Environmental Toxicology and Chemistry, 7, 969 977.
Miller,
D.C., Poucher, S., Cardin, J.A., Hansen, D. 1990 The acute and
chronic toxicity of ammonia to marine fish and a mysid. Archives
of Environmental Contamination and Toxicology, 19, 40 48.
McKenney,
C.L. 1996 The combined effects of salinity and temperature on
various aspects of the reproductive biology of the estuarine mysid,
Mysidopsis bahia. Invertebrate Reproduction and Development, 29,
9 18.
Mauchline,
J. 1980 The biology of mysids and euphausids. In: Advances in
Marine Biology. Part 1. The Biology of Mysids, Vol. 18 (eds J.H.S.
Blaxter, F.S. Russel & C.M. Yonge), 1 369. Academic Press,
London.
Price,
W.W. 1976 The Abundance and Distribution of Mysidacea in the Shallow
Waters of Galveston Island, Texas. PhD Thesis, Texas A & M
University, College Station, TX.
Reitsema,
L. & Neff, J.M. 1980 A recirculating artificial seawater system
for the laboratory culture of Mysidopsis almyra (Crustacea; Pericaridea).
Estuaries, 3, 321 323.
Tamura,
T. 1970. Marine Aquaculture. National Science Foundation. Translation
from the Japanese of the revised and enlarged second edition.
1966.
Utting,
S. D. 1993. Procedures for the maintenance and hatchery-conditioning
of broodstocks. World Aquaculture, 24(3): 78-82.
Online
suppliers of Mysid Cultures:
Aquatic
Research Organisms
Mark Rosenqvist
1-800-927-1650
Chesapeake
Cultures
Elizabeth Wilkens
1-804-693-4046
C-K Aquaculture
1-318-797-8636
Aquatic
Indicators
Ray Less
1-904-829-2780
(Commercial accounts only)
