THE ROLES OF BACTERIA AND MICRO AND MACRO ALGAE IN ABALONEAQUACULTURE: A REVIEW SABINE DAUME Research Division, Department of Fisheries Western Australia, PO Box 20, North Beach, WA 6920
Trang 1BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research
THE ROLES OF BACTERIA AND MICRO AND MACRO ALGAE IN
ABALONE AQUACULTURE: A REVIEW
Author(s): SABINE DAUME
Source: Journal of Shellfish Research, 25(1):151-157.
Published By: National Shellfisheries Association
DOI: http://dx.doi.org/10.2983/0730-8000(2006)25[151:TROBAM]2.0.CO;2
URL: http://www.bioone.org/doi/full/10.2983/0730-8000%282006%2925%5B151%3ATROBAM
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Trang 2THE ROLES OF BACTERIA AND MICRO AND MACRO ALGAE IN ABALONE
AQUACULTURE: A REVIEW
SABINE DAUME
Research Division, Department of Fisheries Western Australia, PO Box 20, North Beach,
WA 6920, Australia
ABSTRACT Abalone aquaculture is dependent on cultured algae to induce larval settlement and as a food source for the early life
stages of abalone until formulated feed or macroalgae such as Macrocystis sp., Porphyra sp and Ulva sp are introduced into the
growout system In the natural environment, abalone larvae settle on coralline red algae, which provide one of the strongest and most consistent settlement cues available for abalone larvae However, propagation of coralline red algae is not practical commercially.
Abalone farms in Japan successfully settle abalone larvae (Haliotis discus hannai) on the green alga Ulvella lens U lens also proved
to be suitable to enhance settlement of cultured southern Australian abalone species (Haliotis laevigata, H rubra) Most abalone farms
in Australia are now growing U lens for that purpose U lens is easy to culture, no specific facilities are needed and the alga can be grown on PVC settlement plates in commercial nursery tanks However, U lens has limited value as a feed for young postlarvae.
Instead, cultured diatoms can be added after larvae successfully settle and start feeding Juvenile abalone (>3 mm in shell length) can
consume U lens and grow rapidly on this alga Diatom cultures and biofilms developing on settlement plates are not axenic and the
role of bacteria in early postlarvae feeding is poorly understood It has been suggested that bacteria may perform metabolic activities
in the undeveloped gut of young postlarvae At later stages of the nursery phase it becomes increasingly difficult to maintain adequate feed on the plates and this is still regarded as a significant bottleneck for the abalone aquaculture industry Recent investigations have
indicated that sporelings of macroalgae like Ulva sp or diatoms that can provide more biomass may provide a suitable additional food
source for juveniles (>3 mm in shell length).
KEY WORDS: abalone, abalone eggs, antibiotics, algae, bacteria, diatoms, growth, larval quality, lipids, settlement, Ulva sp., Ulvella
lens
INTRODUCTION
Abalone fisheries (Haliotis spp.) produce high value,
export-orientated products with about 50% of the world supply being
provided by Australian fisheries in 1999 (Gordon & Cook 2001)
The worldwide catch from abalone fisheries has declined by about
30% over a 10-year period from ca 14,000 mt in 1989 to 10,000
mt in 1999, and consequently the interest in aquaculture products
has increased substantially The world production of abalone from
aquaculture in 1999 was approximately 7,775 tonnes (Gordon &
Cook 2001) Future production from the numerous farms and sites
established, under construction or approved in several countries
including Australia, could be even more substantial if the
technol-ogy is improved
In an aquaculture environment, abalone larvae are produced by
spawning recently collected wild broodstock, or wild or farmed
abalone broodstock that have been held in conditioning systems
for extended periods The nonfeeding larvae have a short larval
phase (e.g., 7 days at 17°C for Haliotis rubra Leach and Haliotis
laevigata Donovan) When larvae are ready for settlement they
actively seek a suitable surface In the natural environment,
aba-lone larvae settle on coralline red algae (Shepherd & Daume
1996); however on farms the surface is typically vertical, spaced
plastic plates that have been colonized by a variety of different
algal species Abalone aquaculture in most countries is dependent
on cultured algae at least for the early life stages, to induce larval
settlement and as a food source for postlarvae and juveniles, until
formulated food is introduced into the growout system As
provi-sion of algal supplies decline, the juveniles may be weaned onto
formulated foods They can be transferred to various land-based
tanks or sea-based systems (Freeman 2001) In several countries
around the world (e.g., South Africa) even the growout depends
solely on algae; macroalgae that are harvested from the ocean are fed to the abalone in specialist growout systems A large compo-nent of the cost of producing juveniles is the provisioning of live food in a manner suitable for a grazing herbivore This review examines the roles of bacteria, micro and macroalgae during the nursery phase of abalone aquaculture and emphasizes research
conducted by the author with postlarval and juvenile H laevigata and H rubra in Australia It complements earlier reviews by
Rob-erts (2001) on larval settlement and by Kawamura et al (1998c) on postlarval growth and survival by highlighting the applicability of bacteria and algae for commercial abalone hatcheries and nurser-ies Their roles are considered in the context of the main areas of research undertaken to improve juvenile production efficiency: (1) presettlement larvae quality; (2) larval settlement; (3) dietary re-quirements for postlarvae and juveniles
Pre-settlement Larvae Quality
Previously wild abalone broodstock that feed on a range of macroalgae have been the main source of gametes for commercial abalone hatcheries Selection of broodstock is mainly based on gonad size and appearance (Litaay & De Silva 2001), with abalone judged to be ready for induced spawning and have mature eggs based on the amount of swelling of the gonad However, animal selection based on these criteria shows variable results in spawning success and produce offspring with large variability in larval and postlarval survival More recently there has been greater commer-cial and research interest in conditioning captive and farmed broodstock using macroalgae or formulated foods (Grubert & Ritar
2003, Daume & Ryan 2004a, Freeman et al this volume) Lipids and protein in abalone eggs are known to fuel the de-velopment and metamorphosis of the larvae (Jaeckle & Manahan 1989a, 1989b, Litaay et al 2001) Nelson et al (2002) demon-strated that variations in lipid content and fatty acid profile of the digestive gland coincided with variation in their macroalgal diets Corresponding author E-mail: sdaume@fish.wa.gov.au
151
Trang 3and are related to seasonal temperature fluctuations Biochemical
variation in the diet may affect the composition of the eggs and
ultimately larval performance However studies of changes in
bio-chemical composition such as fatty acids in abalone eggs are
scarce Litaay et al (2001) demonstrated changes in biochemical
composition during larval development Recently, Daume and
Ryan (2004a) showed high variability in proximate biochemical
composition and fatty acid profiles of abalone eggs between
batches derived from conditioned and wild broodstock as well as
between two consecutive spawning seasons The relative
propor-tions of some PUFAs in the broodstock diets were reflected in the
eggs and varied between batches of conditioned and wild
brood-stock, indicating that formulated diets designed to maximize
growth rates are not necessarily adequate to maintain viable, high
quality eggs and larvae from captive broodstock
Other factors that can influence the quality and success of
larval culture are opportunistic pathogenic bacteria that can bloom
and cause deformities in and collapse of whole larval batches
under potentially stressful commercial growing conditions Many
abalone hatcheries are using antibiotics like oxytetracycline
pro-phylactically Similarly they may be used in research projects
Roberts (2001) suggested using antibiotics to eliminate bacterial
interference in settlement assay systems Apart from the general
problem of development of antibiotic resistant strains of bacteria in
hatcheries, problems have been reported with certain antibiotics
when used with abalone during larval rearing or settlement assays
Streptomycin at low doses of 5 g mL−1 was toxic to Haliotis
diversicolor (Bryan & Qian 1998) Emitine caused abnormal loss
of velum that could have been confused with metamorphosis
(Fenteany & Morse 1993)
An experiment conducted to assess the effect of two antibiotics
(Ampicillin and Kanamycin at 50g mL−1) on the settlement of
H rubra revealed no difference in settlement rate between treated
and untreated settlement substrate (Table 1) In this experiment 3
algal settlement substrata were tested (Navicula cf jeffreyi, Ulvella
lens, Sporolithon durum) and compared with a negative control
(plastic square of commercial settlement plate without any algal
growth) all with and without antibiotics The ratios of settlement
rates between treated and untreated substrates did not change over
time In addition, the difference in settlement preferences between
specific substrates remained the same regardless if antibiotics were
used or not The antibiotics were initially effective as indicated by
the higher survival of swimming larvae (in water column) in
con-trol jars treated with antibiotics However, the settlement rate was
not higher in the antibiotic treatment, indicating that unfit larvae might survive if treated with antibiotics but they do not settle successfully This result questions the need and usefulness of an-tibiotics in abalone hatcheries Further studies are needed to assess the effects of other antibiotics and earlier treatment with antibiotics (e.g., during larval rearing) However, alternatives like probiotics should be investigated to enhance larval survival safely Many antibiotics, including Kanamycin and oxytetracycline, work by inhibiting or interfering with the protein biosynthesis by targeting the bacterial ribosomes The close similarity between bacterial and mitochondrial ribosomes makes the latter (present in all cells of the “treated” organisms) a potential target (Hart 2004) Inhibition of mitochondrial protein synthesis or injuries in mito-chondria of the treated organism have occurred and can lead to various dysfunction; any cell type or tissue with a high aerobic energy requirement is more likely to be affected when this or-ganelle is injured (Hart 2004) The effects of antibiotics on abalone larval settlement and postlarval performance however are not well understood The knowledge we have from other systems, however, warrants extreme caution and highlights the danger of introducing other, potentially detrimental factors These may not be obvious initially but may manifest themselves at later stages of larval or postlarval development
Larval Settlement
The term “settlement” in this review describes the permanent attachment of abalone larvae to the substrate after shedding of the velum to complete metamorphosis In the natural environment, abalone larvae, like many other invertebrate larvae, settle on cor-alline red algae Daume et al (1999a) revealed that settlement of
Haliotis laevigata larvae in response to three nongeniculate
cor-alline red algae is species-specific In that study the frequency of occurrence of epiphytic bacteria and diatoms was assessed on all coralline red algal species tested However, no significant corre-lation was found indicating that the settlement induction is algal in origin The authors concluded that bacteria and diatoms may in-fluence the settlement response of abalone larvae but they are not the main driving force Roberts (2001) referred to some of his unpublished work and stated that bacteria can induce abalone lar-val settlement but that the response is slow, taking 1 week to reach 50% metamorphosis In contrast, very rapid settlement was re-ported in small-scale laboratory experiments through the use of the
coralline red alga, Sporolithon durum, with the maximum rate
TABLE 1.
Percentage settlement of Haliotis rubra on different settlement substrates (Ulvella lens and Navicula cf jeffreyi and a negative control), with and without antibiotics, as well as Sporolithon durum (positive control) after 24, 48 hours, % settled and survived up to 1 week and % of
larvae in water column after 1 week (n = 6 ± SE) Data are from Daume (2003).
Species Antibiotics
% Settlement
24 Hours
% Settlement
48 Hours
% Survival Up
to 1 Week
% in Water Column After 1 Week
Ulvella lens − 30 ± 8.1 a 35 ± 7.6 a 12 ± 1.5 0 ± 0
Ulvella lens + 22 ± 4.4 a 36 ± 5.3 a 17 ± 1.1 5 ± 1.6
Navicula cf jeffreyi − 5 ± 1.4 b 3 ± 2.0 b 4 ± 1.2 8 ± 3.5
Navicula cf jeffreyi + 0.3 ± 0.3 b 1 ± 0.3 b 2 ± 0.3 30 ± 4.2
Sporolithon durum − 39 ± 3.7 50 ± 4.6 16 ± 2.6 0 ± 0
* Means with different superscript letters are significantly different (P < 0.05).
152
Trang 4being reached after 24 h (Daume et al 1999a) indicating that
nongeniculate coralline red algae are strong settlement inducers
This result coincides with disproportional high numbers of recruits
found on S durum in the natural environment (Shepherd & Daume
1996)
Historically, benthic biofilms, consisting of bacteria and mixed
diatom species growing on PVC settlement plates, have been used
in abalone hatcheries worldwide to induce larval settlement
Dia-toms, brought in by the incoming seawater, colonize clear plastic
sheets arranged in commercial nursery tanks This process is
un-predictable and larval settlement rates can be low (1% to 10% of
larvae) (Daume 2003) In both experimental and commercial
sys-tems, to achieve more control and consistency, films dominated by
single algal species can be generated (Daume et al 2000, Daume
& Ryan 2004b) H rubra did not respond to films of any diatom
species tested, but settled on the nongeniculate coralline red alga
Phymatolithon repandum (Daume et al 1999b) In contrast, H.
laevigata settled comparably well on the diatom Navicula
ramo-sissima and on the coralline S durum Roberts (2001) reviewed
data on settlement cues including diatoms and other biofilms
Overall it is apparent that coralline red algae provide more
con-sistent and reliable settlement cues, whereas settlement on diatoms
can be highly variable However, propagation of coralline red
al-gae is not practical at a commercial scale
Abalone hatcheries in Japan successfully settle abalone larvae
(Haliotis discus hannai) on the green alga Ulvella lens (Takahashi
& Koganezawa 1988) U lens is also suitable for enhancing
settle-ment of both cultured southern Australian abalone species (H.
rubra and H laevigata) (Fig 1) Most abalone farms in Australia
are now growing U lens for that purpose (Daume et al 2000,
Daume et al 2004, Daume & Ryan 2004b) The earlier study
established settlement preferences of H rubra for U lens at
labo-ratory scale whereas the later studies focused on commercial scale
experiments Both species (H rubra, H laevigata) showed a clear
preference for older rather than for younger U lens (Table 2, Table
3) even with similar percentage cover, indicating that the
devel-opmental stage of the alga and not percentage cover per se is
important in settlement induction (Table 3) Settlement was also
significantly higher in the combined U lens treatments (old and
young) compared with 2 diatom treatments (Navicula cf jeffreyi
and Cocconeis sp demonstrating the suitability of U lens to
im-prove the settlement of Haliotis laevigata larvae on commercial
scale (Table 3) No significant difference between high and low
larval release densities was found with H rubra in the nursery
(Table 2) confirming earlier findings at laboratory scale with H.
laevigata larvae that settlement of abalone larvae is not gregarious
when tested with larvae of the same batch (Daume et al 1999a) In
contrast, settlement was found to be gregarious in response to
conspecific postlarvae as young as 7 days (Daume et al 1999a)
and older conspecific juveniles and adults and their grazing mucus
is believed to be responsible (Seki & Kan-no 1981, Slattery 1992)
Recently alternative systems, to replace live algae as a means of settlement and growing postlarvae, have been proposed in Japan
for H discus discus and H diversicolor (Stott et al 2002, 2003,
2004a, 2004b) In the earlier studies, an alginate gel solution con-taining micro particulate diets was pasted onto settlement plates In more recent studies settlement plates are sprayed with a solution of
agar and one of the following: dried algal powder (Spirulina pla-tensis, Chlorella vulgaris, Undaria pinnafifida), dried natural
dia-tom powder, formulated diet and two different concentrations of
␥-aminobutyric acid (GABA), each with and without antibiotics, and compared with negative (clean plates) and positive (living natural diatom biofilms) In both recent studies there was no sig-nificant difference in settlement rates between the microalgae powder treatments and the living natural biofim but both supported significantly higher rates when compared with the negative control and GABA treatments (Stott et al 2004a, 2004b) The authors demonstrated that pregrazing of plates by conspecific juveniles covered with microalgal powder/ agar solution enhanced larval settlement significantly (85% vs 30% on grazed and ungrazed plates respectively) This system shows some potential, however mechanized and cost-efficient ways of spraying the plates need to
be developed before it becomes viable commercially
Dietary Requirements
Post-larval abalone feed on benthic diatoms (Kawamura et al 1995) and the diatom film on plates also provides the food for growing postlarvae in commercial abalone nurseries Commercial farms traditionally rely on mixed species of diatoms as a food source throughout the nursery period (settled larvae to 8–10 mm) The film is maintained through passive seeding (new cells are brought in with the incoming seawater), adding nutrients and ma-nipulating the light intensity through shading Without much con-trol over composition and density of the biofilm species, the results are very inconsistent and often very poor Isolating particular dia-tom species and growing them in monoculture before inoculating settlement tanks in the nursery affords greater control This how-ever has not been embraced by the industry and further investiga-tions are needed to assess the effectiveness in larger scale systems However, a significant bottleneck experienced by industry is the inability to maintain adequate food (both quantity and quality) on the plates particularly at later stages of the nursery phase Growth rates of juveniles are influenced by the availability, digestibility and nutritional composition of the algae (Kawamura et al 1998b, Roberts et al 1999, Daume et al 2003)
The Role of Bacteria in Postlarval Nutrition
Diatom cultures and biofilms developing on settlement plates are not axenic and the role of bacteria in early postlarvae feeding
Figure 1 Sequence from settlement cue to potential food items
pro-posed for Australian temperate abalone species, in commercial
farm-ing systems, as they grow.
TABLE 2.
Percentage settlement (±SE) of Haliotis rubra in the nursery 3 days after larval release (n = 32) Data from Daume et al (2004).
Larval Density Ulvella lens
Per U lens
Treatment
Total per Tank
High Old (18 days 31% cover) 31.9 ± 7.5 53.6 ± 5.8
Young (4 days 57% cover) 21.7 ± 6.8 Low Old (18 days 31% cover) 44.0 ± 7.3 70.4 ± 8.7
Young (4 days 57% cover) 26.4 ± 7.6
Trang 5and growth is poorly understood Newly settled postlarvae ingest
diatoms but are often not able to digest the cell contents This
suggests that bacteria and the extracellular material produced by
the diatoms, present in the biofilm, are a significant source of
nutrition for postlarval abalone (Fig 1) Garland et al (1985)
reported that postlarval H rubra ingested bacteria growing on the
surface of coralline red algae It has been suggested that bacteria
may perform metabolic activities in the undeveloped gut of young
postlarvae and are able to enhance the digestion efficiency of the
host by supplying polysaccharolytic enzymes (Garland et al 1985,
Erasmus et al 1997) Polysaccharolytic enzyme activity has been
reported in day 17 H discus hannai postlarvae (Takami et al.
1998) Sawabe et al (2003) detected the bacteria Vibrio halioticoli
in the gut of H diversicolor aquatilis and suggested that this
bacterium may play a crucial role in converting alginate to acetic
acid As part of the alternative systems proposed by Stott et al
(2002, 2003, 2004a, 2004b), the authors observed that the growth
of postlarvae H diversicolor aquatilis fed a formulated diet was
reduced when antibiotics were added and suggested that bacteria
that assisted in digestion became limiting In a later study they
discovered that 5–10 times more bacteria (including Vibrio spp.)
were present on plates sprayed with the agar/formulated diet
so-lution These bacteria could have provided a substantial food
source to early postlarvae, which may have contributed to the
significantly better growth rates on these plates 1 week after
settle-ment (Stott et al 2004b) The authors suggest that for recently
settled postlarvae, bacteria might be a superior food source
com-pared with diatom and abalone grazing mucus All these studies
indicate that bacteria are ingested and play an important role in
early postlarvae nutrition and health, but further studies are needed
to elucidate their role and contribution
Food Preferences for Postlarval Abalone
Worldwide, several studies have examined postlarval feeding
and growth on different algal species (Ohgai et al 1991, Ishida et
al 1995, Kawamura et al 1998a, Roberts et al 1999) Studies
devoted to examining their feeding preferences and growth
(Kawa-mura & Kikuchi 1992, Kawa(Kawa-mura & Takami 1995, Kawa(Kawa-mura et
al 1995, Matthews & Cook 1995, Kawamura 1996, Takami et al
1997, Daume et al 2000, Takami & Kawamura 2003) have shown
that food requirements change as abalone grow (Fig 1) Two to
three weeks after settlement, postlarvae become responsive to the
“digestibility” of the diatom strains and grow more rapidly on
effectively digested strains (Kawamura et al 1998a, 1998b)
Post-larvae 0.8–2 mm in shell length grow ca 40–60 m day−1 on
“digestible” diatoms and only ca 15–30m day−1on
“indigest-ible” diatoms (Kawamura et al 1998b) In addition, the diatom cell
size, attachment strength, frustule’s strength and postlarval size
can influence digestion In a feeding trial covering the whole
post-larval period, Roberts et al (1999) showed that different diatom
food species affected survival and growth After day 17, postlarvae
grew faster on Cocconeis scutellum and Cylindrotheca closterium.
Both species were most efficiently digested Transitions in post-larval feeding preferences and growth performances on different algal species are reviewed in Kawamura et al (1998c)
Alternative Food Sources for all Stages of Nursery Culture
The green alga U lens has limited value as a food for growing
postlarvae Instead, cultured diatoms can be added after larvae successfully settle and start feeding Seki (1997) reported that
growth rates of postlarvae on U lens were improved by the
in-oculation of cultured diatoms
Recent studies showed that plates with a low cover of young
germlings of U lens could be used for settlement induction of Australian abalone species (H rubra, H laevigata) and followed with inoculation of the cultured diatom Navicula cf jeffreyi to
ensure sufficient food for the growing postlarvae (Daume et al
2000, 2004, Daume & Ryan 2004b) The former study provided
crucial information on early development of H rubra and
estab-lished that growth rates on several diatom species are significantly
higher than on U lens at laboratory scale (Fig 2) In the more
recent study, at commercial scale, the type of substrate on which larvae settled, light (which affected the food density) and the den-sity of postlarvae all had very marked effects on growth (Daume et
al 2004) The results also suggest that early growth is important in determining later performance Daume and Ryan (2004b) investi-gated settlement, growth, survival and size variability of the
aba-lone H laevigata on commercial scale Both growth rate and size
variability increased over time until juveniles reached approxi-mately 5 mm in shell length Whereas postlarval abalone do not
grow well on U lens (Fig 2), juvenile abalone (>3 mm in shell length) can consume U lens and grow rapidly (80–110m day–1)
on this alga (Table 4)
TABLE 3.
Percentage settlement (±SE) of Haliotis laevigata 3 days after larval release (n = 3) when given a choice between 4 substrates Data from
Daume and Ryan (2004b).
Treatments
Old U lens
(8 weeks–97% cover)
Young U lens
(6 weeks–82% cover) Navicula sp Cocconeis sp.
Total per Tank
Figure 2 Early growth of H rubra postlarvae feeding on different algal species Vertical bars indicate standard error; n = 4 Data from
Daume et al (2000).
154
Trang 6At later stages of the nursery phase (>5 mm in shell length), it
becomes increasingly difficult to maintain adequate food on the
plates and this is still regarded as a significant bottleneck for the
industry Recent investigations have indicated that sporelings of
macroalgae like Ulva sp may provide a suitable food source for
juveniles (see Strain et al this volume) (Fig 1) Alternatively,
chain forming diatoms, like Delphineis, offer a 3-D structure
com-pared with the 2-D structure of nonchain forming prostrate
attach-ing species, like Navicula spp and thus providattach-ing more biomass
for the growing juveniles (Fig 1) Kawamura et al (1995) reported
growth rates of 48m day−1of H discus hannai juveniles 1–2 mm
in shell length, when feeding on the diatom Achnanthes longipes,
which has a 3-D structure More recently, Takami and Kawamura
(2003) found that juveniles 2.8–2.9 mm in shell length grew 100
m day−1on this diatom species, which was comparable to growth
rates achieved on juvenile sporophytes of the macroalga
Lami-naria japonica.
Biochemical Composition and Nutritional Value of Algal Diets
The biochemical composition of microalgae, and therefore their
nutritional value to herbivores varies between species (Brown et al
1996) and is greatly affected by harvest stage, light intensity
(Thompson et al 1993, Brown et al 1996), nutrient concentrations
(Fábregas et al 1996, Fábregas et al 1998) and culture methods
(Otero & Fábregas 1997) It is known that the biochemical
com-position of algae can be altered by changing the growing
condi-tions (e.g., Otero & Fábregas 1997, Thompson et al 1993, Brown
et al 1996) When microalgal cultures are grown in
nitrogen-limited media, the protein content of the cells decreases (Enright et
al 1986, D’Souza & Kelly 2000, Daume et al 2003) Daume et al
(2003) showed previously that juvenile H rubra grew faster when
feeding on the diatom Navicula cf jeffreyi that was cultured in a
higher nitrate medium Searcy-Bernal et al (2003) found that
re-cently settled H fulgens postlarvae grew and survived better under
low light (6E) conditions, whereas a lower number of cells of the
diatom Navicula incerta were available in the lower light
treat-ment The authors suggested that oxygen supersaturation in the boundary layer, particularly in high-density diatom films at high light levels (75 E), could have caused high mortality in this treatment In another study, the influence of light intensity on two
diatom species (Navicula cf jeffreyi, Cocconeis sp.) as a food for juvenile H laevigata (3–4 mm in shell length) was tested (Watson
et al 2004) In contrast to N cf jeffreyi, growth of Cocconeis sp.
was not inhibited at lower light levels making it a good candidate for culture in shaded nursery systems Light was more influential
in juvenile grazing behavior (photophobic) than food availability Watson et al (2005) examined the combined effect of manipula-tions in light intensity and nitrate concentramanipula-tions on the nutritional
value of the diatom Navicula cf jeffreyi when fed to juvenile abalone (H laevigata) Under high light conditions Navicula cf jeffreyi was lower in protein and higher in carbohydrates and fat.
Juveniles grazed larger numbers of diatom cells when the protein content was low, possibly compensating for the lower protein lev-els The authors reported elevated pH levels in higher light treat-ments and suggested that this could have caused high mortality These studies indicate that changes in light intensity and nitrate concentration, under which the diatom species are cultured, can have a dramatic effect on growth, grazing rates and particularly survival of postlarval and juvenile abalone This emphasizes the need for selecting the right light and nutrient level to achieve high value food and conditions for optimal growth and survival of ju-venile abalone in commercial nurseries
This study reviewed three main areas of abalone research as-sociated with abalone hatchery and nursery production Further studies are needed to find alternatives, such as probiotics, to the use of antibiotics in abalone hatcheries Alternative cost effective foods, for broodstock and for the latter stage of the nursery still need to be found that will increase larval quality and allow abalone farmers to keep animals on the plates longer and thus reduce weaning mortality
ACKNOWLEDGMENTS
The author thanks Stephen Ryan, Sylvain Huchette, Ben Long, Peter Crouch, Anton Krisnich, Sascha Brand-Gardner, Rob Day and Bill Woelkerling who were involved in various parts of the
work on H laevigata and H rubra and Greg Maguire for many
useful comments
LITERATURE CITED
Brown, M R., G A Dunstan, S J Norwood & K A Miller 1996 Effects
of harvest stage and light on the biochemical composition of the diatom
Thalassiosira pseudonana J Phycol 32:64–73.
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Biol Ecol 223:39–51.
D’Souza, F M L., & G J Kelly 2000 Effects of a diet of a
nitrogen-limited alga (Tetraselmis suecica) on growth, survival and biochemical
composition of tiger prawn (Penaeus semisulcatus) larvae Aquaculture
191:311–329.
Daume, S 2003 Early life history of abalone (Haliotis rubra, H
laevi-gata): settlement, survival and early growth Final report for FRDC
project 1998/306 Department of Fisheries Western Australia
Fisher-ies Research Contract Reports 3:1–110.
Daume, S., S Brand-Gardner & Wm J Woelkerling 1999a Settlement of
abalone larvae (Haliotis laevigata Donovan) in response to non-geniculate coralline red algae (Corallinales, Rhodophyta) J Exp Mar.
Biol Ecol 234:125–143.
Daume, S., S Brand-Gardner & Wm J Woelkerling 1999b Preferential settlement of abalone larvae: diatom films versus non-geniculate
cor-alline red algae Aquaculture 174:243–254.
Daume, S., A Krsinich, S Farrell & M Gervis 2000 Settlement, early
growth and survival of Haliotis rubra in response to different algal species J Appl Phycol 12:479–488.
Daume, S., B M Long & P Crouch 2003 Changes in amino acid content
of an algal feed species (Navicula sp.) and their effect on growth and survival of juvenile abalone (Haliotis rubra) J Appl Phycol 15:201–
207.
TABLE 4.
Daily growth-rates (µm day −1) of juveniles (Haliotis rubra) on plates
52 days after settlement and shell length (mm) 114 days after
settlement (mean ± SE) Data from Daume et al (2004).
U lens
Daily Growth Rate (µm day −1 )
Shell Length (mm)
114 Days 52–64 Days 64–94 Days 94–114 Days
Old 79.4 ± 7.7 107.4 ± 4.2 82.8 ± 4.2 6.9 ± 0.2
Young 94.9 ± 8.4 115.3 ± 14.8 87.8 ± 8.2 7.4 ± 0.2
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