29 observations on the spawning development and rearing of the south african abalone haliotis midae linn

South African Journal of Marine Science

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Observations on the spawning, development and
rearing of the South African abalone Haliotis midae
Linn.
A. B. Genade , A. L. Hirst & C. J. Smit
To cite this article: A. B. Genade , A. L. Hirst & C. J. Smit (1988) Observations on the spawning,
development and rearing of the South African abalone Haliotis�midae Linn., South African Journal
of Marine Science, 6:1, 3-12, DOI: 10.2989/025776188784480465
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S. Afr. J. mar. Sci. 6: 3-12
/988

3

OBSERVATIONS
ON THE SPAWNING, DEVELOPMENT
AND REARING
THE SOUTH AFRICAN ABALONE HAL/OTIS MJDAE LINN.

A. B. GENADE*, A. L. HIRST*t

AND

OF

c. J. SMIT*

A description is given of the first successful controlled breeding of the South African abalone Ha/iotis midae.
Gametes of ripe abalone were obtained from spontaneous spawnings as well as by subjecting animals to
spawning stimuli. The larval period is five days at 20°C and seven days at 17,5°C. The first respiratory pore is
completed at a shell length of2,3 mm and the first shell ridge can be observed at approximately 2~ mm ..Benthic
diatoms on fibreglass plates served as food for post-larval stages to a length of 5-8 mm. Larger Juveniles were
fed the seaweeds Plocamium spp. and Ulvafasciata. Shell pigmentation is affected by the food consumed.
Variable growth rates for individuals from the same spawning were observed.
'n Beskrywing word gegee van die eerste suksesvolle gekontroleerde
te1ing van die Suid-Afrikaanse
perlemoen Haliotis midae. Gamete is van ryp perlemoen deur spontane kuitings sowel as kuitprikkels bekom.
Die larwale periode is vyf dae teen 20°C en sewe dae teen 17,5°C. Die eerste respiratoriese porie word voltooi
op 'n skulplengte van 2,3 mm, terwyl die eerste skulprifby ongeveer23 mm waarneembaar is. Bentiese diatomc
op veselglasplate is as voedse1bron vir postlarvale stadia tot ongeveer'n lengte van 5-8 mm aangewend, waarna
die seewiere Plocamium spp. en Ulvafasciata gevoer is. Die pigmentasie van die skulp word deur voeding
beinvloed. 'n Groot variasie in groei is vir individue afkomstig van dieselfde kuitgroep waargeneem.

Of the six South African abalones (Muller 1986),
only Haliotis midae (locally known as perlemoen)
occurs in quantities sufficiently extensive to warrant
commercial exploitation. It contributes substantially
to the inshore fisheries and the present whole mass

quota is 660000 kg (Chief Directorate Marine Development 1986). Strict conservation measures were
implemented from 1965 to curb overfishing, peak
production of 2,28 million kg being recorded in that
year. Because the present supply cannot meet the
demand, commercial industry has shown an intense
interest during recent years in the possibilities for
controlled culture of H. midae. This need has been
stimulated further by the advancement in abalone
cultivation techniques overseas.
Japan is at present the acknowledged leader in
developing techniques for the mass production of
juveniles especially for restocking. The number of
seed abalone released from hatchery-produced
seed
in Japan has increased from 200 000 in 1970 to 10,7
million in 1978 (McCormick and Hahn 1983). Efforts
to culture this economically valuable shellfish are
now undertaken world-wide and, since the major
contribution
made by Ino (1952), research and
development projects have been launched and production facilities established in Australia, the United
Kingdom, Canada, Chile, France, Mexico, Taiwan
and the United States (Ebert and Houk 1984).
Whereas the production of juveniles so far has been
aimed at augmenting the supply of natural seed,
abalone producers in the United States are now
investigating a market for small or cocktail abalone

for the restaurant trade (Chew 1984).
Various aspects of the biology of H. midae of

importance to fisheries management have been researched by Newman (1966, 1967a, b, 1968, 1969),
and they cover mainly the migration, reproduction,
growth and distribution of natural populations. No
successful rearing of H. midae has been recorded to
date, whereas most of the commercially important
species in other countries have been cultured and
larval and post-larval development documented (lno
1952, Leighton 1974).
The purpose of this preliminary investigation is to
demonstrate that spawning, larval development and
further growth of H. midae can be achieved under
controlled and semi-controlled conditions. Facilities,
which were mainly utilized for bivalve culture, at the
Aquaculture
Unit of the Fisheries Development
Corporation of South Africa Ltd at Knysna (Cape
Province) were used for this study. Knysna is about
500 km east of the main commercial exploitation
area of abalone, Cape Hangklip to Quoin Point
(Fig. I).

MA TERIALS

AND METHODS

Collection and transport
Mature H. midae larger than 110 mm shell length
were collected during August and September 1981
and May and June 1985 from the exploitation area

• Formerly Fisheries Development Corporation Aquaculture Unit, P.O. Box 346, Knysna 6570, South Africa
t Sea Fisheries Research Institute, Private Bag X2, Rogge Bay, 8012, South Africa - to whom all correspondence
Manuscript

received: March 1986

should be addressed


1988

South African Journal of Marine Science 6

4
S
290
300
310

320
0

33

340
0

35

nG?01

Intensive exploitation

0

36

0

16

0

17

0

18

o

22

o

0

31

23

o

32

E

Fig. 1: The laboratory site and main area of commercial exploitation of Haliotis midae

(Fig. I). The animals were removed either by knocking off by hand those which had raised part of the
foot (the method used by abalone for capturing
drifting fragments of kelp) or by the conventional
levering-off method used by commercial divers. The
captured animals were sexed by inspecting the colour
of the gonad, which is dark green in females and
cream in males. Collection took place between IOhOO
and I3hOO.
Immediately after delivery to the boat by SCUBA
divers, each abalone was placed in a 10-1 plastic bag
filled to one-third with seawater and inflated with
oxygen before being sealed off. The sex was recorded
on the bag, which was then put into a polystyrene
cool-box for the six-hour journey to the laboratory.
Animals collected during 1981 were placed 10 per
aerated
1 600-1 tank at ambient temperature
(± 17°C), and those collected in 1985 were put in
shallow tanks with 19°C water filtered to 3 ~m
flowing at a rate of 1 1 per minute per animal. In all
cases the sexes were kept separate. The tanks used for

the 1985 groups were lined with clear plastic sheeting
to facilitate subsequent removal of the animals.

Spawning
The groups obtained during 1981 were not exposed
to any additional stimulus, but those collected in 1985

were subjected to a stimulus procedure, more or less
corresponding to that described by Chen (1984), the
following morning. These abalone were first exposed
to air for one hour and then placed in tanks with
flowing, 17°C seawater previously exposed to ultraviolet light (2,537 A) and filtered to 3 ~m. Sexes were
still kept separate. The water temperature was then
increased by 1°C per hour for three hours, and then
decreased over the same period to the original
temperature. Once spawning had commenced, the
waterflow was reduced.

Fertilization and larval cultivation
Spawned ova were collected by siphoning into 15-1
round fibreglass containers to a density that, when
spread out, the ova would form a single layer on the
bottom. Because of their higher specific gravity than
seawater, the ova would settle within approximately
10 minutes. Siphoning was then easily accomplished.
The ova were fertilized by adding freshly released
sperm (± I hour after spawning) at a concentration of
± 120000·ml-1 to the container after microscopic
examination of their activity. After gentle mixing, the
ova were exposed to the sperm for 15 minutes, after

which the water was topped up to 15 1. Decanting to
remove the excess spenn,and debris began after most
of the ova had settled. Refilling with fresh seawater


1988

Genade et at.: Laboratory Spawning, Development and Rearing of Abalone

and decanting was then repeated ten times, approximately every ten minutes. After the final wash the
ova were transferred to 240-t tanks for further
development at either 20°C or ambient temperature
(± 17,soC).
As the larvae of the Haliotidae are lecithotropic
(Leighton 1974), no food was added to the cultures
until the settlement stage was reached. Also, there
was no water-flow or aeration during larval development. The water was changed once per day after
siphoning the larvae onto a 45-~m net. Development
stages were recorded according to the classification
Leighton (op. cit.).
To test the effect of "GABA" (')I-aminobutyric
acid), a neurotransmitter,
on the settling rate of
advanced veligers, the following experiment was
designed, as used by Morse et al. (1979) for H.
rufescens: 15 X 4-t Pyrex beakers were placed in a
waterbath at 20°C, in 5 groups of 3 beakers each. All
the beakers were filled to 4 t and treated with
penicillin at 33 ppm. "GABA" was then added to each
group at increasing concentrations,

i.e. 3 with no
addition (control), 3 at 10-6 molar, 3 at 10-5 molar, 3
at 10-4 molar and 3 at 10-3 molar. Some 3 000
advanced larvae (digitate cephalic-tentacle
stage)
were added per beaker and the reaction of the larvae
was recorded 2 and 18 hours later.
Settlement and juvenile cultivation
Benthic diatoms scraped from the bottom of the
outflow channel of the oyster nursery in the same
laboratory were used to seed corrugated fibreglass
plates of 25 X 30 em, which had been matured
previously in seawater for three weeks. A slurry was
made after washing the diatoms (± 70 per cent
Navicula) through a 50 ~m net. The cleaned settling
plates were suspended overnight in the diatom
mixture, and the next morning, covered with a thin
film of benthic diatoms, they were placed on the
bottom of the 240-t tanks with advanced larvae.
"GABA" was added to the tanks at 10-6 molar.
After settlement, the plates were left in the tanks
for a further five days, during which time the tanks
received constant lighting, slight aeration and a daily
water exchange. To encourage further diatom growth,
the plates were periodically removed and resuspended in a section of the oyster nursery which
received a constant water flow. No temperature
control was administered, but regulating natural light
by occasional screening with a shade mesh was
necessary to control diatom growth.
At an approximate length of 5-8 mm, the seed

abalones were transferred to tanks 2,0 m long X
0,5 m wide X 0,25 m deep, into which chopped pieces
of seaweed about 1,0 cm2 were introduced daily at

5

17hOO.Initially, pieces of Plocamium sp., which was
collected at low springtides on the coast and stored in
a freezer, were used, but because of the distance from
the nearest source, the feed was changed after a few
months to Viva fasciata. This species could be
obtained easily from close to the laboratory. Shelters,
in the form of halved 100-mm PVC and ceramic
pipes, which covered approximately 50 per cent of
the bottom of the tanks, were also introduced into the
tanks.
Unfiltered seawater of salinity 30-35 X 10-3 and
ambient temperature (1O-27°C) was supplied at a
flow rate of 61·min-l·tank-1 or 24 m£·min-1·animat'.
The tanks were also aerated. Stocking density was ±
250 animals·m-2 (bottom surface) at a shell length of
approximately 20 mm.
The outlets were screened with an appropriate
mesh to prevent animals from escaping during night
migration. Food residues and faeces were siphoned
off every second day. At no stage was any attempt
made to grade the abalones to prevent competition.

RESULTS
Collection and transport

Specimens knocked off by SCUBA divers experienced little or no damage, but the foot of those
levered from the substratum was injured in more than
40 per cent. In intact abalone, mortality was less than
5 per cent two weeks after transfer. Injured animals
showed signs of extreme stress and more than 50 per
cent mortality within the same period. No injury was
caused to the abalone when removed from the plastic
bags because of the ease with which the plastic could
be released from the adhering foot. On arrival,
oxygen concentration in the bags varied between 8,0
and 12,0 ppm and pH between 7,2 and 7,6.
Spawning
Natural spawning had commenced in the 1981
groups before 08hOO the morning after transfer and
continued, in the August group, sporadically until
IOh30. The temperature at spawning for the August
group was 13,5°C and that of the September group
17,0°C, in both cases the ambient temperature.
Because of the number of abalone in each tank, no
accurate estimate of the number that spawned could
be made, though probably in excess of 80 per cent of
both sexes spawned spontaneously.
The two groups collected during 1985 responded
to stimulation as follows:
May group

-

40 per cent of the females reacted at

South African Journal of Marine Science 6

6
Table

I: Times
at which
developmental
stages
(after
Leighton
1974) of H. midae larvae were first
observed at 20°C

Stage

When achieved after
fertilization

Description

Hours
I
2
3
4
5
6

7
8
9
10
II

--

Hatching
Free-swimming trochophore
Cap-shell, early veliger'
Infiatc-shell veliger, torsion
Early operculate veliger,
pre-eyespot
Incipicnt cephalic tentacle, operculate veligcr
Mid-formed cephalic tentacle
Digitate (branched) cephalic
tentacle
Crawling, settling
Total metamorphosis (loss of
cilia, but no mouthparts or
feeding yet observed)
Peristomial growth

June group

-

14
22

24
31

±

Days

46

2

51
86

3

97
1/8

4
5

145
169

6

7

Ejaculation of ova and sperm occurred mainly

through the first four respiratory pores. In contrast to
the ova, which settled to the bottom within a few
minutes, the sperm stayed in suspension.
Egg counts were made of two females 150 mm long
in the June spawning. Both animals still had a
substantial reserve after spawning and released I 245
X 106 and 0,750 X 106 ova respectively. The spherical
ova (Fig. 2), which are enveloped by a relatively thick
gelatinous membrane, varied in diameter between
212 and 222 J.lm (x
214 J.lm), and the yolk varied
between 172 and 192 J.lm (x
181 J.lm).

Fertilization

II: Achieved

stages of development
of H. midae larvae
at different ambient temperatures

Stage of development

Day on which stage achieved
17,5°C

20°C

5

6

3
4

7

5

M idformed cephalic tentacle
Digital cephalic tentacle
Crawling and settling

I

least slightly only after five hours.
All ova were prematurely released.
No males responded.
20 per cent of the females reacted
within three hours and produced
well formed "mature" ova similar to
those obtained during 1981.

=

Table

1988

=

and early development

A high rate of fertilization (± 80 per cent) was'
obtained for the naturally spawning groups of August
and September 1981. However, the June 1985 group
showed a relatively low percentage, ranging from 11
to 25 per cent. The addition of excess sperm to this
group, ova of which already showed cleavage, did not
improve the percentage successfully fertilized but
rather resulted in the rupture of many egg membranes.
The progress in larval development is summarized

in Table I. No specific differences in larval features
from those recorded by other authors for haliotid
embryology (Ino 1952, Leighton 1974) could be
observed (Fig. 2b-f). The green pigmentation of the
egg yolk is retained by the trochophores and veliger
larvae. This phenomenon has also been recorded for
other species by Leighton (1972). The behaviour of
trochophores and veligers is also typical of Haliotis.
Trochophores tend to concentrate at the surface of
containers (negative geotaxis), and healthy veligers
congregate in vertical columns, then tumble to the
bottom where they scatter and regroup again to form
new columns. This cycle is repeated every few
minutes. Trochophores
measure approximately
164 J.lm X 190 J.lm just after hatching and fully
developed veligers 207J.lm X 265 J.lm.

Development from cleavage through to settlement
at the two temperature regimes, 17,5 and 20,0°C,
appeared to be quite normal. A marked difference in
rate of development was, however, recorded as
shown in Table II.
Settlement and juvenile cultivation
Settling of larvae was advanced and stimulated by
addition of "GAB A ", as shown by the results in Table
III. Settlement was on the sides as well as at the
bottom of the beakers.
Larvae held at 17,5°C in 240-£ tanks reacted well to
the addition of "GABA" only on Day 7, with a
maximum settlement of l·cm-2 on Day 8. However,
many larvae were still swimming actively at this stage.
Complete settlement was observed on Day 9 (Fig. 2g).

Table

III: Percentage
settlement
in 4-1 beakers at 20°C after
addition of "GABA" to 4-day-old larvae

Time
After 2
hours
After 18
hours

10-3 molar

10-· molar

0

10

10

0

0

40

80

80

50

50

Control

IO-l molar

10-6 molar

.

1988

Genade et al.: Laboratory Spawning, Development and Rearing of Abalone

Fig. 2: Developmental stages of Haliotis midas (a) fertilized eggs of ± 214 Ilm, sperm attached to membrane; (b)
freshly hatched trochophore larva of 164 X 190 Ilm; (c) cap-shell veliger larva; (d) inflate-shell veliger
(torsion) of 207 X 2651lm with retractor muscle; (e) operculate veliger (pre-eye spot); (f) operculate veliger
(pre-eye spot) with retracted velum; (g) crawling and settling stage; (h) peristomial growth; (i) circular-shell
post-larva of ± 600 Ilm; (j) whole shell pink with no respiratory pores; (k) juveniles showing dietary
pigmentation; (I) juveniles of approximately 1 year of age

7


South African Journal of Marine Science 6

8
30

Vl
UJ

1988

o

25

C>::

0
0-

>- 20

C>::

~
C>::

c: 15

Vl

0

UJ

C>::

0

•

10

C>::
UJ

a:l

~

::::l

Z

~

5

•

~~

"~

Open pores
Closed pores

~

• •

~ ~

~

•

•

Fig. 4: Radial

5

10
LENGTH

Fig. 3: Relationship

15

20

on the shells of H. midae
specimen ± 36 mm)

(largest

(mm)

between length and number of pores

An extremely variable pattern of settlement took
place over the plates.
Some features of post-larval development after
transfer from the settling tanks and at different
ambient temperature are given in Table IV. Peristomial growth (Fig. 2h) was apparent the first day

after transfer to substrate with benthic algae. At a size
of 600 ~m, one juvenile could clear algae from an area
of up to 16 mm2 in 24 hours and could move 1,0 cm.
At 700 ~m, the shells were fully round with a pink tint
(Fig. 2i, j) and movement of 2 cm in 6 hours was
recorded under nursery conditions. At this stage they
were already extremely light-sensitive and would
immediately move away from a bright stereo-microscope light.
In H. midae, the notch stage is reached at a size of
2,1-2,2 mm and completion of the first pore at
2,3 mm, similar to that of the American west coast
pink abalone H. corrugata, but larger than for some

Table IV: Post-larval

ridges

25

other Baliotis species (Table V). The effect of
temperature on growth (and pore formation) at this
early stage was quite clear. The August 1981 group
took 65 days (I2-17°C ambient temperature) and the
September 1981 group 48 days (I7-22°C ambient
temperature) to display this feature.
Respiratory pores are continuously being formed
and previous ones sealed off as growth advances (Fig.
3). The first sealing off already starts at a size of
3 mm, where just two of the three pores are functional. At 25 mm a total of 27 pores would have been
formed but only five of these were open for respiration. A definite difference in pore formation in H.

midae from that of the smaller Japanese H. diversicolor supertexta (Oba 1964) can be observed after a
length of some 15 mm (Fig. 3).
Although the effect of light intensity on growth
was not tested at any stage during development, it
was observed that juveniles (2-3 mm long) on plates
receiving less light were generally larger (by up to 50
per cent) than those exposed to brighter light.
The shell colour is affected by the food consumed.
For instance, when feeding on benthic algae, a

development features after transfer to
ambient temperature

Description of stage

Time taken to achieve
stage (days)
12-I7°C

Virtually fully round, length up
to 600 11m
Fully round, pink tint to shell, 700 11m
Whole shell pink, no respiratory pore
Development of first respiratory pore
2,1-2,3 mm
Two respiratory pores ± 3,0 mm

17-22°C

22

26
40
65
79

48
55

Table V: Shell length of post-larval Haliotis spp. at formation
of first respiratory pore

Species
H. rufescens
H. corrugata
H.fulgens
H. sorenseni
H. diversicolor supertexta
H. midae

Shell length
(mm)

Source

1,5-1,8
2,0-2,5
1,7-2,0
2,0-2,1
1,8-/,9
2,1-2,3

Leighton (1974)
Leighton (1974)
Leighton (1974)
Leighton (1974)
Dba (1964)
This paper


Genade et al.: Laboratory Spawning. Development and Rearing of Abalone

1988

9

n=300
50
25

40
20

30
UJ

;:)
'" 15

'«
'"

UJ

"'"

~

20

UJ
I-

10

~
>
u
~

'.

.•....
..•...

Average

10

0"

Maximum

-

"'--4

Minimum ., .... '.
50

5

(b)

n=300

;:)

9
'"

u..

40

MAMJ

J

ASOND

MONTH

Fig: 6: Average monthly temperature of the nursery section
of the aquaculture unit

30

20

10
.:.:-:.:.:.:.:.
:-:.:.:.:.:.:-:

=

~??~~)
10

20
30
SHELl LENGTH (mm)

specimens, the shell surface would have an irregular
corrugated surface, as described by Day (1974), as a
result of the moulding of these ridges.
The size frequency (length) after one and two years
is given in Figure 5. From this Figure it is clear that a
wide variation in growth rate, originating from a
specific spawning group, can be expected under
culture conditions. After 12 months a size range
of 5-30 mm was recorded (x

Il,8 mm), and at
an age of 24 months the range was 10-45 mm
(x
34,4 mm). Another notable feature was the
stunted growth displayed by certain animals.
These results vary from those obtained by Newman (1968, 1969) for natural populations at Stony
Point near Cape Hangklip (estimated growth rate of
21,7 mm per annum) and Port Elizabeth (28,8 mm).
Newman (1969) attributed this difference to variations in the mean annual temperature at the two
sites, 15,8°C at Stony Point and I7,4°C at Port
Elizabeth. The mean monthly temperature (recorded
by thermograph for the semi-closed nursery system
used for ongrowing) is given in Figure 6. The
recorded mean for the II months February-December is identical to the annual mean for Port Elizabeth

40

Fig. 5: Size frequency of H. midae at (a) one and (b) two
years of age

turquoise pigmentation was produced, but when fed
mainly on Plocamium spp., a brick-red colour was
apparent (Fig. 2k, I).
The formation of radial ridges, which are formed
parallel to the growing margin and are most probably
used for shell strengthening, can be observed at a
length of 23-24 mm. Ridges are continuously being
added thereafter, so that an abalone of 36 mm would
have approximately five of these (Fig. 4). In mature

=


South African Journal of Marine Science 6

10

1988

1.25

35

1.0

>-

:r:
Ij

30

w
3
~
~

0.75

UJ

i13 0.5
25
0.25
E
E
:r:

20

>Ij

15

~
:j
w

20

SHELL LENGTH

25

30

( mm)

15

:r:

Fig. 8: Relationship between shell length and shell weight
of juvenile H. midae


10

5

5

10
15
SHELL BREADTH (mm )

Fig. 7: Relationship between shell length and shell breadth
for juvenile H. midae

given by Newman (1969). A difference of 5-IO°C
between the maximum and minimum within a single
month, mainly caused by changing air temperatures,
was recorded.
The relationship between shell length and shell
breadth for juveniles is given in Figure 7, and it
mirrors the linear relationship determined by Newman (1968) for abalone 20-40 mm shell length in the
wild. However, the relationship between shell length
and shell weight is exponential for juvenile H. midae
(Fig. 8).

DISCUSSION

If mature animals are to be collected for further
keeping and specific studies on maturation, the
conventional method of levering off is not recommended because of the injuries that can be inflicted

especially to the foot. Although infection can be
treated by soaking in an antibiotic solution such as
penicillin, such treatment probably only adds additional stress and may influence results.
The reaction to spawning stimuli and successful
fertilization depends mainly on the state of ripeness.
Basically, all methods used throughout the world
(Morse et al. 1979, McCormick and Hahn 1983,
Chen 1984) encompass a form of stress to stimulate
gamete release (e.g. temperature shock, air exposure,
ultra-violet irradiation, addition of hydrogen peroxide, or a combination of these).
The results indicate that the stress caused by the
duration and mode of transport is adequate to bring
on spawning by ripe H. midae. Although the August
1981 group spawned while the temperature in the
tanks was declining, the September 1981 group were
not exposed to much temperature fluctuation and
also spawned spontaneously. It is doubtful whether
the high concentration of oxygen during transportation could have stimulated spawning, but this aspect
needs further clarification.
Although specific stimuli were only applied to
groups collected in May and June 1985, it is concluded that this method should be adequate for
abalone with more advanced gonads which are
approaching the natural spawning period of October-December, as established by Newman (l967b).

The addition of hydrogen peroxide (Morse et al.
1978) as a spawning inducer was not used, although
H. midae is listed by Morse (1984) as one 'of the
species which reacts to this stimulus. To ensure the


1988

Genade et al.: Laboratory

Spawning,

availability of ripe animals for longer periods,
methods for out-of-season conditioning should be
investigated for H. midae. These methods could
include inter alia saturation-feeding (Morse et al. op.
cit.), temperature control plus adequate nutrition
(Uki and Kikuchi 1984) and photoperiods.
The importance of dense, natural spawning populations is emphasized by the observation that spawned
ova stay in suspension for only a few minutes. The
chances of contacting viable sperm in nature will be
substantially reduced where populations
are too
sparse.
This investigation also confirms the speculation by
Newman (1969) that the planktonic larval stage of
H. midae should be more or less within the time
confines of that of other abalone species. Because of
the short free-swimming period, the distribution of
H. midae is expected to be fairly limited. Prevailing

inshore currents and water temperature
will be
important factors in determining the possible areas
for settlement. When establishing abalone reserves,
this fact should be taken into consideration.
No reliable data were obtained on larval mortality
during the course of the experiments. Effective water
and culture management, which would include the
combating of contamination,
are considered to be
essential for successful rearing. The transfer of weak
and dead larvae during water changes should be
prevented and, as in all culture programmes, weak
larvae should be eliminated.
Settlement and subsequent cultivation
The most critical stage in the life history of benthic
organisms is recognized to be the availability of
suitable substrates for settling larvae. The complexity
of the metamorphic process and the factors which
regulate settlement response are discussed by Hadfield (1984). It is generally accepted that both physical
and chemical characteristics of substrates playa role
in settlement. Because it is convenient from a culturist's point of view to have synchronous settling and
metamorphosis, the only chemical thus far known to
achieve such synchrony, -y-aminobutyric acid (Morse
et al. 1979), was used. Although a positive settlement
response was recorded, the effect on metamorphosis
in H. midae is still unknown. Future work should
include detailed studies of both aspects.
The observation that shell colouration is affected
by diet can be applied to distinguish cultured from

natural abalone or to identify cultured groups by
biological colour-coding.
Although no specific attention was given to the
causes of mortalities during rearing of juveniles,

Development
observations

and Rearing of Abalone

1/

were made on:

(i) excessive losses, mainly inflicted by micropredators during the first two months after settlement;
(ii) mortalities just after handling of plates or individuals;
(iii) predation by polyclads.
It is concluded that all these factors can be eliminated
by proper management techniques.
The slower growth recorded under culture conditions when compared with the results obtained by
Newman (1969) could have been due to a combination of food availability and type, or to competition or fluctuations in light intensity and temperature.
The effect of these parameters on growth has been
illustrated by many authors for other species, e.g.
Leighton (1974), Cken (1984), Ebert and Houk
(1984). Variable growth rates for individuals of a
specific spawning were also recorded by Leighton
(1974), who documented this tendency for four
Haliotis species with identical parentage, age and
environment.

ACKNOWLEDGEMENTS
The authors thank the management of the Fisheries Development Corporation of South Africa Ltd
for their encouragement during the course of this
study. The technical assistance from former colleagues Messrs B. A. Andrews and D. J. Krebser is
also gratefully acknowledged.

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