TROCHUS
CULTURE
Trochus polyculture with pearl oyster spat [selection from a report
by Dr. Rick Braley in 1999]
The consultant would like to discuss the value of polyculturing trochus (Trochus niloticus) or a similar herbivorous species
of archeogastropod along with the blacklip pearl oyster spat / juveniles. Since the start of the mass culture of giant clams
in the mid-1980s, the idea of polyculture with trochus was tested in Palau, MMDC; North
Queensland, [ James Cook
University's Orpheus Island Research Station]; Solomon
Islands, ICLARM). The result was good, as long as trochus juveniles
were still small when the clam juveniles were small [trochus spawning 1-2 weeks before or
about the same time as the clams]. This
avoided any problem of trochus which were too large for the clam juveniles running over
them and damaging or killing them with their shell or radular teeth scraping algae off the
substrate. During the Asian Development Bank
project to assist the Blacklip Pearl Oyster project in Penrhyn, Cook Islands, trochus
were spawned and added to land nursery raceways with spat and juvenile blacklip pearl
oysters. The result was positive in that the
trochus helped to curtail growth of the filamentous algae growing on the sides of the
raceway and on the blacklip spat / juveniles themselves spawning and larval rearing
of trochus and other similar archeogastropods is relatively
easy in comparison with pearl oysters. Larvae
are lecithotrophic (have yolk reserves so no larval feeding necessary) and the larval
period is only about 3 days before settlement. The following information gives a
background on trochus culture to date:
The first research on
the biology of trochus was done in Palau by Japanese
biologists in the 1930s and early 1940s, and also by an Australian marine biologist, F.W.
Moorehouse (1932) on the Great Barrier
Reef. The documentation on the spawning of trochus and
rearing of the larvae to young juveniles was first accomplished in the late 1970s and
early 1980s in Palau by researchers such as Ann
Hillman and Gerald Heslinga at the MMDC (Micronesian Mariculture Demonstration Centre). Gerald Heslinga and Rick Braley successfully
spawned broodstock and reared large numbers of larvae to settlement in two 100-tonne
concrete tanks at the MMDC in mid-1979. This
was the stimulus for MMDC to become committed to improving the culture of trochus during
the 1980s. During the 1980s, Mr. G. Heslinga
reared the larvae and juveniles of Trochus
niloticus in concrete raceway tanks [8m x 1.5m x 1m] and the juveniles were
polycultured with juvenile giant clams (family
Tridacnidae). The trochus were spawned about 3
weeks – 1 mo. before the spawning of the clams, so that when the juvenile trochus
were about 3-4 mo. of age they could be collected and added to the tanks with 90 day old
juvenile clams. The juvenile trochus would
then eat filamentous algae and diatoms from the bottom of the clam tank and also clean off
algae which would grow on the clam shells or over them.
The MMDC regularly produced 1000s of trochus juveniles in each spawning
throughout the year. These were almost all
used in the above-mentioned polyculture system.
During the ACIAR-James Cook
University (JCU) International giant clam project, Rick Braley and other project staff
cultured trochus juveniles similar to the protocol in Palau for use with the giant clam
juveniles. After that
project ended in 1992 the trochus research work at JCU continued with the then
PhD-candidate researcher, Laura Castell. Her
work involved small-scale rearing in Australia with
re-seeding experiments in both Australia and Vanuatu. Results from the experiments of releasing cultured
juvenile Trochus niloticus onto coral reefs
indicated that after 3 days, 20-40% of the juveniles are missing. Predation was deemed to be the main cause of
mortality. Seeding densities used were from
5-30 juveniles / m2. She suggested that seeding densities of not greater
than 10 juveniles/ m2 are advisable. The work in Australia has shown that
juveniles larger than 24mm shell diameter survive better than smaller sizes because
predation by Portunid crabs and stomatopods is minimised above 24mm shell diameter. Another ACIAR-funded project was based out of
Northern Territory University (NTU), Darwin and involved two Universities and a government
Marine Research Facility in eastern Indonesia, and the
Fisheries Department in Vanuatu. One of the products of the project was ACIAR
Proceedings No. 79 (published 1997) entitled Trochus: Status, Hatchery Practice and Nutrition. A recirculation system was developed at NTU
which involved the spawning, larval culture and nursery culture of juveniles.
In regards to private ventures involved with the
aquaculture of trochus, there have not been many yet, because the trochus resource is
still available in the sea for collection. However,
one Chinese-Indonesian businessman took the step to make the aquaculture of trochus
commercial. This consultant prepared plans for
a hatchery and nursery facility for at a pristine site near to one of his pearl oyster
hatcheries and growout farms in western Ceram Island [Maluku, eastern Indonesia]. The plans were made in 1995 and work began on the
facility by latter 1995, being essentially completed by May 1996 when this consultant
carried out training with the hatchery technicians and conducted the first spawning/larval
rearing for the facility. The owner's goal was
to be able to culture enough trochus shell that he could harvest 100 tonnes of shell per
year. The hatchery / nursery designed
included 10 concrete raceways [8m x 2m x 1m = ~ 15 tonnes seawater / raceway when filled],
12 concrete tanks [3m x 1.5m x 0.8m = ~3.4 tonne seawater / tank when filled], and other
smaller tanks, a dry lab, and an algal culture lab.
Although broodstock were not very common locally, the initial large spawning was
successful and the consultant was informed after 12 mo. that there were still ~1,000,000
trochus juveniles in the large raceway tanks from the initial spawning and settlement
(about 40% survival). These averaged about 20
mm shell base diameter, though many were larger than 25 mm.
As this was the first commercial trial, future details of the culture protocol can
be improved to produce more optimal faster growth and higher survival. I advised the owner that they should try growing
out juveniles in concrete intertidal ponds, in plastic-lined non-tidal ponds, and in
intermediate hanging basket culture. I am not
aware if they have trialed these methods of growing juveniles but they had ideal
conditions at his pearl oyster farm because workers, boats, rafts, longlines, etc. were
all available at the site
Table
1 below shows an approximate survival of trochus at various stages in their aquaculture
life history.
Table 1:
Approximate survival of trochus at different stages in the hatchery and nursery
culture. Weight of trochus shell at ~52 mm
basal shell diameter (bsd) = 100 grams. Therefore,
1 tonne would require about 10,000 shells.
Stage
Number
surviving % survival
between stages Comments
Spawned
Hatchery
Eggs
8,819,320
100
tank
Veliger
Hatchery
Larvae
5,291,560
60
tank
1 mo.
Settlement
juvenile 1,587,390
30
tank
4
mo.
Settlement or
juvenile
793,690
50
Nursery tank
8 mo.
Nursery tank;
juvenile 476,190
60
can move to
pond
1.5 yr.
Pond, ocean
juvenile 142,850
30
nursery, or
cages
2.5 yr.
Pond, ocean
juvenile
nursery, or
(52 mm bsd) 100,000
70
cages; ready
This estimate (Table 1) would produce about 10
tonnes of shell in about 2.5 yr. The survival
of trochus juveniles from 1 mo. old juveniles to harvest-size shell is just 8.4% but this
type of percentage is not unrealistic for molluscs. The
survival would hopefully be better but only the trial will prove this. These number of spawned eggs could be
obtained in 2 or 3 spawnings.
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A related archeogastropod
with aquaculture potential:
The
Ass's Ear Abalone, Haliotis asinina
(written
in 2002)
The first aquaculture work
on the tropical abalone Haliotis asinina, the
donkey’s ear abalone, was done in Thailand in 1989.
It has since been given attention as a new target species for coastal
aquaculture. This work has been taken up by
some researchers at CSIRO, Cleveland [Dr. Nigel Preston] and more recently by a PhD
student at University of Queensland (Dept. of Zoology), Regina Counihan.
The published research on
the larval and juvenile culture of Haliotis asinina appears
to be quite similar to that of trochus. The
same facility used for trochus would work for the donkey’s ear abalone. Spawning is monthly in the lower latitude tropics. Number of eggs spawned per female per night varied
from 3000 to 609,800 and it was a preliminary conclusion that matured H. asinina of 50-80 mm SL spawn 200,000-600,000
eggs in a spawning day under favourable conditions. A
paper on the growth rate of this abalone species in Thailand inside culture tanks
reconfirmed that the species has significant potential as a new target species for
aquaculture. Hatchery reared H. asinina grew well in 2.5-tonne tanks fed with
the diatom Nitzschia sp. And seaweed, Gracilaria salicornia. They reached 42.7 mm SL in one year,
“which is probably the fastest early growth result recorded among abalone
species.” The survival of H. asinina from 1 mo. to 1 yr. of age was estimated
at 93.3%.
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Updated 22 November 2009; Copyright © Aquasearch