22 Comparative studies on the nutrition of two species of abalone, Haliotis tuberculata L. and Haliotis discus hannai Ino. IV. Optimum dietary protein level for growth

Aquaculture 252 (2006) 225 – 233
www.elsevier.com/locate/aqua-online

Effect of diatom diets on growth and survival of the abalone
Haliotis discus hannai postlarvae
Nurit Gordon a, Amir Neori a,*, Muki Shpigel a, John Lee b, Sheenan Harpaz c
a

Israel Oceanographic and Limnological Research, National Center for Mariculture, P.O. Box 1212, Eilat 88112, Israel
b
Department of Biology, City College of City University of New York, New York, NY 10031, USA
c
Department of Aquaculture, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel
Received 12 January 2004; received in revised form 17 June 2005; accepted 20 June 2005

Abstract
Growth and survival of postlarval abalone Haliotis discus hannai Ino fed different diatom diets were examined for one
month from settlement. Two diatoms, Amphora luciae Cholnoky and Navicula cf. lenzii Hustedt, supported high postlarval
growth and survival, especially when supplied in combination. A third species, Nitzschia laevis Hustedt, did not support
survival for more than two weeks as a unialgal diet and had limited value in mixed diets.
Diatom mixtures were superior to single-species diets as of the first week after settlement. The mixture of N. cf. lenzii and A.
lucia supported the highest survival, up to 50%, and growth rate up to 36Am of shell length per day, reaching a size of 1.4mm
30 days after settlement. The three diatom species contained high levels of total lipids (6.4%–14.5% of dry weight) and fatty
acids (16%–22% of lipids); from 39% to 48% of fatty acids were polyunsaturated (PUFA). The three diatoms were richer in n-3
PUFA than in n-6 PUFA. The content of the essential fatty acid 20:5n-3 (EPA) was highest among the PUFAs and higher,
though not significantly, in the two diatom species A. luciae and N. cf. lenzii that produced the better results. Among the free
amino acids, arginine was dominant in N. laevis, proline in N. cf. lenzii, and both free amino acids plus glutamic acid were
equally dominant in A. luciae. The suitability of A. luciae and N. cf. lenzii for enhancing growth and survival of postlarvae was
attributed to their complementary balanced nutritional properties.
D 2005 Elsevier B.V. All rights reserved.
Keywords: Abalone; Postlarvae; Biochemical composition; Growth; Survival; Diets; Diatoms; Fatty acids; Amino acids

1. Introduction

* Corresponding author. Tel.: +972 8 6361445; mobile: +972 50
5993746; fax: +972 8 6375761.
E-mail address: (A. Neori).
0044-8486/$ - see front matter D 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.aquaculture.2005.06.034

Benthic diatoms are the principal food source for
postlarval abalone in hatcheries (Kawamura, 1996,
Kawamura et al., 1998a). In spite of the increasing
number of studies on the nutrition of newly settled
abalone larvae (Kawamura and Takami, 1995; Kawa-


226

N. Gordon et al. / Aquaculture 252 (2006) 225–233

mura, 1996; Kawamura et al., 1998a,b; Daume et al.,
1999, 2000; Roberts et al., 1999; Searcy-Bernal et al.,
2001), growth and survival rates during the early
postlarval stages as reported in the literature are variable and generally low (Searcy-Bernal et al., 1992).
Poor and unpredictable performance is related to
variability in food (different diatoms and their composition), as well as to abalone species and the growing conditions in hatcheries (Kawamura et al., 1998a).
To improve growth and survival of abalone postlarval
stages in a specific growing system using specific
diatom species, a better understanding of their basic
diet requirements is necessary. Cell density, digestion

efficiency, ingestibility, extra-cellular products, and
associated bacteria are known to affect food value of
diatoms in early postlarval stages (Kawamura and
Takami, 1995; Kawamura et al., 1995, 1998a,b;
Roberts et al., 1999; Searcy-Bernal et al., 2001).
The biochemical composition of algal cells is another
important factor (Dunstan et al., 1994), but its effect
has been examined mostly in juvenile abalone (Mercer et al., 1993; Mai et al., 1994, 1995a,b, 1996) rather
than in newly settled postlarvae.
The biochemical composition of the diet is most
important once the postlarvae acquire the capability
to digest and benefit from diatom cell content (Kawamura et al., 1998a). According to them, the diatom diet
has little impact on growth rates during the first two
weeks after settlement. Diet-dependent postlarval
growth rates diverge at 800 Am SL, when the postlarvae
begin digesting and utilizing the cell content. According to Daume et al. (1999), differences in growth rates
by postlarvae fed different diatoms can already be
observed earlier, a week following settlement.
The nutritional value of microalgae as a feed is
influenced to a great extent by the fatty acid composition of their lipids (Brown et al., 1997; Renaud et al.,
1999) and to a lesser extent by sugar composition
(Chu et al., 1982). The protein amino acid composition of microalgae is generally conserved (Brown et
al., 1996) and is unlikely to account for major differences in the nutritional value of a particular species
(Brown, 1991; Brown and Jeffrey, 1995; Brown et al.,
1997). Free amino acids (FAA) may constitute a significant proportion of the total amino acids in the algal
cell (Dortch et al., 1984; Brown, 1991) and their
composition does vary among algal species (Derrien
et al., 1998). FAA are easily absorbed by postlarvae

(Manahan and Jaeckle, 1992), a fact that is especially

important in very early life stages, before the complete
development of the gut enzymes involved in protein
digestion (Takami et al., 1998). For this reason the
diatom composition phase of the present study has
focused on FAA and fatty acids.
Diatoms, as a class, offer high levels of lipids and
PUFAs, especially the essential PUFA 20:5(n-3)
(Dunstan et al., 1994; Brown et al., 1997), and therefore may fulfill the nutritional requirements of abalone
postlarvae better than other algae. Polyunsaturated
fatty acids (PUFA) of both n-3 and n-6 families are
essential for growth of juvenile Haliotis discus hannai
(Mai et al., 1996). Their primary function is considered to be structural (Mai et al., 1995a; Floreto et al.,
1996). Among PUFAs, 20:5(n-3) seems to contribute
the most to faster growth of juvenile H. discus hannai
(Mai et al., 1996).
The aim of this research was to investigate growth
and survival of H. discus hannai postlarvae fed different diets of diatoms (including local species), which
had previously been shown to induce larval settlement
(Gordon et al., 2004), and verify whether these could
be correlated to the diatoms’ nutritional quality.

2. Materials and methods
2.1. Preparation of abalone postlarvae
Larvae of H. discus hannai were obtained from an
indoor abalone hatchery in Eilat (Red Sea, Israel).
Adults were induced to spawn using ultraviolet light
(Kikuchi and Uki, 1974). Fertilized eggs were collected
and transferred into 20-L aquaria at a concentration of
12 eggs/ml. To control bacterial growth, an antibiotic
(Rafamycin) was added at a concentration of 1.5 mg/L.

Larvae were kept at 22 8C with a 12 L:12 D photo cycle
(60–70 Amol photons mÀ 2 sÀ 1), for 4–5 days, until
reaching competence. Larval competency on day 5 was
assessed by observing the swimming behavior, as
described by Seki and Taniguchi (1996). Competent
larvae were used for the growth experiments.
2.2. Diatom cultures
Benthic diatoms were isolated from the Red Sea
(Eilat, Israel) and from the Atlantic Ocean (Massachu-


N. Gordon et al. / Aquaculture 252 (2006) 225–233

setts, USA) (Table 1). Axenic cultures were prepared
as described in Gordon et al. (2004). The diatoms
were cultured in 1-L Erlenmeyer flasks filled with
f/2 medium (Guillard and Ryther, 1962), enriched
with silica (Na2SiO3) and aerated with CO2. Temperature was maintained at 22 8C and light intensity was
60–70 Amol photons mÀ 2 sÀ 1 throughout the growth
experiment.
2.3. Growth experiments with abalone postlarvae
Competent larvae of 280 F 12 Am in size were
transferred to 90-mm petri dishes, filled with 32 ppt
Red Sea water (diluted with DDW from 40 ppt). To
reduce handling damage to the larvae, the number of
larvae transferred was calculated according to samples
taken from culture bottles. Each petri dish was
stocked with 82 F 17 larvae. Settlement was induced
by adding 1 AM gamma-amino butyric acid (GABA)
(Morse, 1992), to petri dishes, whose media included

50 mg/l (each) penicillin and streptomycin (Sigma)
(Morse and Morse, 1984). This approach was preferred over natural settlement induction by the diatoms, to obtain a better reproducibility of larval
settlement across diatom treatments. After 24 h,
GABA was rinsed out of the dishes and algae, as
monocultures or mixtures, were added (Table 1).
Five replicate dishes were made for each diet. Algal
cell concentration was adjusted to obtain a similar cell
volume rather than cell number throughout all the
experiments. Water in the dishes was exchanged
daily, and algae were replaced with fresh cultures
once a week. During the week algae were added to
each dish once clear patches (consumed diatoms)
developed around the postlarvae, to keep them supplied. Larval survival was measured as a percentage of

227

postlarvae surviving from all the larvae introduced
into the petri dishes at the beginning of the experiment. Larval shell length (SL) was measured once a
week for all postlarvae that were on the bottom of the
dish, with the aid of a calibrated ocular micrometer,
and then averaged. Daily growth rate (DGR) was
calculated according to the formula: L f À L i / t, where
L f = final shell length (Am), L i = initial shell length
(Am) and t = time in days. The duration of each experiment was 31 days.
2.4. Biochemical analysis of algal cells
Fatty acid analysis was carried out for the three
algal species (Nitzschia laevis, Amphora luciae and
Navicula cf. lenzii) on batches harvested during the
late logarithmic growth phase. Centrifugally concentrated algal cells were lyophilized and the lipids were
extracted (Folch et al., 1957). The lipid extracts were

then transmethylated to fatty acids methyl esters
(FAME) by acidified methylation overnight at 50 8C
in 2% H2SO4 in methanol. The resulting FAME was
concentrated in hexane and injected into an on-column Chrompack CP9001 gas chromatograph (Koven
et al., 2001).
For free amino acid analysis, late logarithmic phase
cells from the three diatom species were centrifuged
and homogenized with an ultrasonic cell disruptor
(Microson) for 5 min. Cell disruption was confirmed
microscopically. Free amino acid analysis was carried
out with an HPLC (Biotronik LC-5000 Amino Acid
Analyzer) as described by Moor and Stein (1951).
Dry matter was calculated from weight loss after
drying for 24 h at 105 8C. Crude protein was calculated
from Kjeldahl nitrogen multiplied by 6.25. Crude lipid
was measured gravimetrically after 5 min homogeniza-

Table 1
Details of the diatoms in the seven diets used in this study
Diet #

Species

Source

Cell dimensions
Length (Am)

Width (Am)

1
2
3
4
5
6
7

Navicula cf. lenzii
Nitzschia laevis
Amphora luciae
Mixture 1 + 2 + 3
Mixture 1 + 2
Mixture 1 + 3
Mixture 2 + 3

Sediment pond, IOLR, Eilat, Israel
Sediment pond, IOLR, Eilat, Israel
Lake Tashmoo, Martha’s Vineyard Island, MA, USA

24
8–10
10

5
5
5

Initial density
(total cells/cm2)

5.3 Â 103
2.5 Â 104
1.9 Â 104
1.2 Â 104
1.3 Â 104
9.7 Â 103
1.2 Â 104


N. Gordon et al. / Aquaculture 252 (2006) 225–233

tion of the sample in chloroform-methanol (2:1),
separation and vacuum drying (Folch et al., 1957).
Ash content was calculated from weight loss after
incineration of samples in a muffle furnace for 24 h
at 550 8C. Carbohydrates were calculated as:
Carbohydrates ¼ dry matter
À ðcrude protein þ lipid þ ashÞ:
2.5. Statistical analyses
The data were compared using ANOVA (one way)
with Duncan’s multiple range tests. The results, in
percentages, were arc-sine transformed prior to
ANOVA analysis to homogenize variances (Sokal
and Rohlf, 1969).

3. Results
3.1. Survival of abalone postlarvae
Survival of larvae/postlarvae during the first month
(Table 2) varied from as low as 4% when fed on a diet
of N. laevis (diet 2) to a high of 49% when fed on a

diet of N. cf. lenzii and A. luciae (diet 6). Survival of
postlarvae with a diet of N. laevis was significantly
lower than with all the other diets ( P b 0.05); these
postlarvae were excluded from later data analysis.
3.2. Growth of abalone postlarvae
With the exception of the diet based on N. laevis,
the postlarvae grew steadily on all the diets offered.

Diets
1 N. cf. lenzii
2 N. laevis
3 A. luciae
4 Mix 1+2+3
5 Mix 1+2

1500
Shell length (microns)

228

6 Mix 1+3
7 Mix 2 + 3

1000

a
a

b
c

b
c

d
e

d

500

0

12
24
36
Time from larval introduction (days)

Fig. 1. Growth of postlarval shell length (SL F SE) during 31 days
post settlement. More information on the diets is provided in Table
1. Significant differences (ANOVA, Duncan’s multiple range test,
p b 0.05) between data points are letter-labeled only on days 24 and
31, to reduce clutter.

The highest growth rates of postlarvae were obtained
on a mixture diet of N. cf. lenzii and A. luciae (diet 6)
and a mixture of the three diatoms (diet 4). After one
month in culture, the postlarvae fed these diets reached
mean SL of 1.4 mm and 1.3 mm, respectively (Fig. 1).
Growth rates in these treatments were significantly

higher ( P b 0.05) than in all the other diets. The SL
of the postlarvae increased by an average of 35.5 F 1.1
Am dayÀ 1 on the diet of A. luciae and N. cf. lenzii and
33.2 F 2 Am dayÀ 1 on the diet of the three algae
combined. In the first 12 days, postlarvae grew faster
when fed the two-diatom mixture of A. luciae and N.
laevis (diet 7) than those fed most other diets (Table 2).
Diet 7 also supported the largest ( P b 0.05) postlarval

Table 2
Survival rates and daily growth rates (DGR based on shell length) of the postlarvae fed the seven different diets of diatom listed in Table 1
DGR, % dayÀ 1 F SE (*)

Diet #

Initial individuals
per dish (# F SD)

Survival rate at
31 days (% F SE*)

1–12 days

13–24 days

Total 31 days

1
2
3

4
5
6
7

69 F 16
84 F 30
66 F 7
74 F 15
70 F 4
103 F 24
109 F 17

39.8 F 4.75a
4.4 F 1.9b
42.6 F 5.5a
39.6 F 10.8a
42.4 F 5.2a
49.2 F 6.1a
31.4 F 14.1a

19.8 F 1.4d
15.0 F 1.4e
23.2 F 1.1cd
25.5 F 1.2bc
20.1 F 0.5d
28.4 F 1.9ab
32 F 1.5a

23.8 F 2c

–
30.4 F 3.1bc
48 F 4.9a
26 F 2.9bc
45.4 F 1.7a
34 F 2.8b

20.6 F 0.9c
–
23.7 F 1.3bc
33.2 F 2a
22.8 F 2.8bc
35.5 F 1.1a
27.3 F 2b

* Data with the same letter indicate treatments that are not significantly different from each other within columns (ANOVA, Duncan’s multiple
range test, critical p = 0.05).


N. Gordon et al. / Aquaculture 252 (2006) 225–233

SL for the first 2 weeks (Fig. 1). However, later, diet 6
and diet 4 became the significantly better diets with
respect to both DGR and SL of the postlarvae, while
the performance of diet 7 deteriorated by day 24 and
became even worse by day 31 (Fig. 1). Growth of the
postlarvae on the single alga N. laevis (diet 2) was
worst ( P b 0.05) of all diets after the first week (Fig. 1).
The diet of A. luciae (diet 3) was best of the singlediatom diets, yet significantly ( P b 0.05) inferior to all
but one of the mixed-diatom diets.

3.3. Lipid content and composition of diatoms
Lipids comprised between 6.4% and 14.5% of the
dry weight of the diatoms analyzed (Table 3). Polyunsaturated fatty acids (PUFA) constituted the largest
fraction (between 41% and 47%) of the total fatty
acids (TFA). The proportion of the various PUFAs
varied among the diatom species. Although all of the
analyzed diatoms had significant quantities (between
14% and 21% of TFA) of 20:5n-3 (EPA), N. laevis
had slightly lower percentages of this fatty acid and
higher quantities (9.7% of TFA) of 20:4n-6 arachidonic acid (AA). Shorter chain PUFAs, 16:2n-4 and
16:3n-4, were also present in significant quantities
(4.2–8.5% of TFA) in all three diatoms (Table 4).
3.4. Amino acid content and composition of diatoms
The three diatoms varied in their total free amino
acid (TFAA) composition (Table 5). Proline was the
main free amino acid (2.8 fmol cellÀ 1, 49% of TFAA)
in N. cf. lenzii but only a minor constituent (0.13 fmol
cellÀ 1, 8% of TFAA) in N. laevis. The proline content
of A. luciae was intermediate (0.8 fmol cellÀ 1, 30% of
TFAA). The share of arginine in the TFAA fluctuated
even more than proline among the analyzed species.
In N. laevis arginine was the main free amino acid
(0.7 fmol cellÀ 1, 43% of TFAA), while in N. cf. lenzii
it was only 0.18 fmol cellÀ 1 (3% of TFAA). In A.

229

Table 4
The content of specific fatty acids as fractions of total fatty acids
(TFA) in the three diatoms used in this study (n = 4 in a, n = 2 in b)

Type of fatty acid

Diatom species
N. laevis a
(% F SD)

A. luciae a
(% F SD)

N. cf. lenzii b
(% F SD)

Saturated
14:0
15:0
16:0
18:0
Sum

6.0 F 0.4
0.9 F 0.5
14.7 F 0.5
1.4 F 1.5
23.0 F 1.3

10.4 F 2.5
0.9 F 0.3
13.7 F 0.9
1.6 F 1.8
26.6 F 1.9

2.5 F 0.0
0.5 F 0.1
13.9 F 0.1
2.4 F 0.5
19.3 F 0.4

Monounsaturates
15:1n-8
16:1n-7
16:1n-9
18:1n-7
18:1n-9
Sum

0.3 F 0.3
22.4 F 1.6
2.7 F 0.9
1.0 F 0.7
2.7 F 2.6
29.1 F 3.7

0.1 F 0.2
18.4 F 2.4
2.8 F 0.3
0.8 F 0.8
3.6 F 2.6
25.7 F 0.7

0.0 F 0.0

18.8 F 0.4
3.5 F 0.1
1.5 F 0.2
4.5 F 0.0
28.2 F 0.3

Polyunsaturates
16:2n-4
18:2n-6
16:3n-4
18: 3n-3
18:3n-4
18:3n-6
18:4n-3
20:2n-6
20:3n-3
20:4n-6 (AA)
20:4n-3
20:5n-3 (EPA)
22:1n-9
22:5n-3
22:6n-3 (DHA)
Sum PUFA
Sum n-3 PUFA
Sum n-6 PUFA

4.2 F 0.2
1.7 F 0.7
8.1 F1.7
0.6 F 0.4

0.3 F 0.4
0.8 F 1.1
0.0 F 0.0
0.4 F 0.5
0.3 F 0.6
9.7 F 1.3
0.0 F 0.0
14.3 F 3.5
0.0 F 0.0
0.4 F 0.5
1.6 F 0.2
42.4 F 3.4
17.2 F 2.9
12.6 F 0.9

4.2 F 0.6
3.4 F 0.1
5.4 F 0.9
0.5 F 0.2
0.1 F 0.3
0.8 F 1.2
1.1 F 0.9
0.5 F 0.7
0.0 F 0.0
5.0 F 1.4
0.3 F 0.4
18.5 F 2.9
0.0 F 0.0
0.8 F 0.2
0.5 F 0.6

41.2 F 2.6
21.7 F 3.2
9.7 F 3.1

5.6 F 0.4
1.5 F 0.1
8.5 F 0.5
0.9 F 0.6
0.0 F 0.0
1.8 F 0.0
0.0 F 0.0
0.7 F 0.1
0.5 F 0.1
2.8 F 0.1
0.0 F 0.0
21.2 F 0.2
0.7 F 0
0.85 F 0
1.8 F 0.9
46.6 F 1.1
25.1 F1.9
6.8 F 0.1

luciae arginine appeared in between these extremes
(0.5 fmol cellÀ 1, 22% of TFAA). The content of
glutamic acid in N. laevis was lesser in the other
two species but it contained glutamine, which was

Table 3
Biochemical composition of the three diatoms used in this study

Diatom

Protein (% in DW)

Lipids (% in DW)

Nitzschia laevis
Navicula cf. lenzii
Amphora luciae

38.32
32.00
32.65

11.25
14.55
6.43

a

A missing value (technical reason).

Fatty acids (% in Lipids)

Carbohydrates (% in DW)

Ash (% in DW)

16.48

17.55
25.09
19.36

32.88
28.36
41.56

a

21.6


230

N. Gordon et al. / Aquaculture 252 (2006) 225–233

Table 5
The content of free amino acids (FAA) in cells of the three diatoms
used in this study
Amino acid

Diatom species
N. laevis
fmol
cellÀ 1

Aspartic
acid
Glutamic

acid
Glutamine
Proline
Glycine
Alanine
Valine
Ornithine
Lysine
Arginine
Total FAA

A. luciae
%

fmol
cellÀ 1

N. cf. lenzii
%

fmol
cellÀ 1

%

0.12

7.11

0.21

9.56

0.59

10.43

0.21

12.69

0.45

20.14

1.08

19.24

0.24
0.13
0.02
0.16
0.02
0.01
0.04
0.71
1.66

14.21

7.87
1.02
9.90
1.27
0.76
2.28
42.89

0.00
0.68
0.02
0.21
0.04
0.06
0.06
0.50
2.24

0.00
30.38
1.02
9.56
1.71
2.73
2.73
22.18

0.00
2.79
0.10

0.66
0.10
0.07
0.07
0.18
5.63

0.00
49.46
1.80
11.69
1.80
1.26
1.26
3.24

not found in the other species. The protein content
was the same in N. cf. lenzii and A. luciae (32% of
DW) and higher in N. laevis (38% of DW) (Table 3).
The carbohydrate content was lowest in N. laevis
(18%) and highest in N. cf. lenzii (25%). The ash
content was highest in A. luciae (41%).

4. Discussion
4.1. Growth and survival of abalone postlarvae
The growth experiments with H. discus hannai
postlarvae fed the different diatom diets, together
with biochemical analysis of these diatoms, established that those diatoms that are attractive for the
larval settlement usually also support postlarval
growth and survival. In our previous study (Gordon

et al., 2004) we found that the three diatom species
used in this research, N. laevis, N. cf. lenzii and A.
luciae, induced settlement of H. discus hannai larvae.
We examined the suitability of these diatoms to support early postlarval growth, concurring with other
studies, where conditions that induced a good larval
settlement were usually followed by high growth rates
and survival of the settled postlarvae (Daume et al.,
1999). However, in the present study, the three
dsettlement-inductiveT diatoms differed greatly in

their nutritive value. A. luciae and N. lenzii were
indeed highly nutritious. A. luciae was the best
among unialgal diets and, combined with N. cf. lenzii
in a two-diatom diet, supported the best postlarval
growth and survival in this study. On the other
hand, N. laevis, the preferred species for settlement
(Gordon et al., 2004), was unsuitable as a sole diet for
early postlarval growth or survival. This finding is
reminiscent of the results with the diatom Cocconeis
scutellum var. parva, when fed to postlarvae of H.
discus hannai by Takami et al. (1997). Both diatoms
induced good larval settlement, but were poor food for
newly settled postlarvae. The latter authors attributed
their observations to the scarce mucus secretion and
the highly adhesive strength of C. scutellum var.
parva. These properties made it an unsuitable diet
for the postlarvae, which eventually starved. In contrast, N. laevis, being small, poorly silicified and
attached only weakly, is probably more easily edible.
Yet it did not support growth, and 96% of the postlarvae began to avoid the algae after several days and
eventually died within 2 weeks. This observation

suggests that the abalone postlarvae do not like N.
laevis as a sole food for extended periods, for reasons
yet to be determined. It could be that N. laevis secretes
unfavorable or toxic substances that gradually accumulate in the dishes (Wen and Chen, 2002).
A good growth of the postlarvae was apparently
related to a wholesome diet, as indicated by the
synergism between the two bbestQ diatoms, A. luciae
and N. cf. lenzii, in the sustenance of the fastest
growth rates and largest SL when administered
together in this study, as also suggested by Epifanio
(1979). However, Kawamura et al. (1998a) showed
the benefit of a good diet is not necessarily steady and
sustained, as we have shown with the mixture of A.
luciae and N. laevis. An inconstant nutritional value
of this mixture may reflect a dual function, wherein N.
laevis apparently provides the postlarvae feeding stimulation right after settlement, while A. luciae provides the required balanced nutrition for more
sustained growth. This diet combination could therefore support the best growth only for the first 2 weeks
after settlement. Afterwards, however, the same reasons that caused the postlarvae to avoid feeding on a
uni-algal N. laevis diet after several days apparently
came into play, making this mixture unsuitable for
further growth.


N. Gordon et al. / Aquaculture 252 (2006) 225–233

Nutritional developments with postlarval age seem
to include increases in the rate and efficiency of
feeding and digestion, leading to the acceleration in
the postlarval growth rates with most diets during
days 13–24 post-settlement; this phenomenon was

already noted by other investigators (Martinez-Ponce
and Searcy-Bernal, 1998; Kawamura et al., 1998a;
Roberts et al., 1999). The reduced postlarval growth
rates in the fourth week of the experiment, when they
were already over 1 mm long, probably resulted from
excessive biomass densities (Kawamura et al., 1998a)
reached in the petri dishes.
4.2. Nutritional value of diatoms to abalone
postlarvae
The three diatoms contained protein levels that
were deemed optimal for juvenile abalone (Mai et
al., 1995b). They were probably also similar to each
other in their high protein quality (Brown and Jeffrey,
1995). Since the diatoms were grown under similar
conditions (nutrients, light and temperature) and harvested in the same phase of growth, it can be
assumed they had similar nutritional value with
respect to their amino acid profiles (Brown and Jeffrey, 1995; Brown et al., 1997). Conversely, as in
Martin-Jezequel et al. (1988), De Roeck-Holtzhauer
et al. (1993) and Derrien et al. (1998), the composition of free amino acid (FAA) varied between the
diatoms and was dominated in each diatom by different FAAs.
In A. luciae, our bbestQ unialgal diet, three predominant FAAs (proline, arginine and glutamic acid)
were in equal amounts. In N. cf. lenzii, which supported moderate yet steady growth of the postlarvae,
proline was predominant. Proline is considered an
essential amino acid for molluscs (Harrison, 1975)
and a major component in the FAA pool in the tissues
of early developmental stages of abalone (Litaay et
al., 2001). However, arginine, an often limiting essential amino acid for abalone postlarvae (Mai et al.,
1994), was the predominant FAA in N. laevis,
which was not as good a diet as the other two species.
Good lipid complements also contribute to the

nutritional value of a diatom. In the three diatoms
studied, total lipid content was about double the
value reported to be required for maximal growth of
juvenile abalone (Uki et al., 1986; Mai et al., 1995a).

231

The relative PUFA content in our three diatoms was
high in comparison to diatoms of similar size (Volkman et al., 1989; Renaud et al., 1999) and so was the
ratio of n-3 to n-6 PUFA. Both of these fatty acid
groups are considered essential for the growth of H.
discus hannai juveniles (Uki et al., 1986; Mai et al.,
1996). The essential fatty acid 20:5n-3 (EPA) was the
predominant n-3 PUFA in the diatoms studied here, as
in other diatoms (Dunstan et al., 1994). This PUFA is
reported to promote a fast growth in H. discus hannai
juveniles (Mai et al., 1995a, 1996; Dunstan et al.,
1996). Indeed, our two dbetterT diatoms, N. cf. lenzii
and A. luciae, contained larger fractions of n-3 PUFA,
especially EPA, than N. laevis (though the latter still
had a higher EPA content than other Nitzschia species
reported for instance by Renaud et al., 1999). On the
other hand, in our worst diatom, N. laevis, PUFAs
were dominated by n-6 and particularly by arachidonic acid 20:4n-6; these PUFAs are important for larval
stages of fish but have no special reported importance
in abalone. The fatty acid 22:6n-3 (DHA), which is
low in abalone tissue and therefore presumed of a
lesser quantitative importance (Dunstan et al., 1996;
Fleming et al., 1996; Mai et al., 1996), was also low in
the three diatoms studied here.

Carbohydrate content in our three diatoms was
high compared to other studied diatoms (Brown and
Jeffrey, 1995; Renaud et al., 1999; Simental-Trinidad
et al., 2001) and within the range needed for juvenile
abalone diet (Mercer et al., 1993).
The fact that no gross composition nor single
chemical component (fatty acid or free amino acid)
could be decisively correlated with postlarval growth
or survival was, as suggested by others (Chu et al.,
1982; Mai et al., 1996; Brown et al., 1997), probably
due to the multitude of components that determine the
nutritional value of a diatom.

5. Conclusions
Carefully controlled, mixed and administered diets
of selected diatoms have provided consistently good
growth and survival of abalone postlarvae during their
most critical stage of life, when mortalities are highest. The results presented here substantiate the nutritional basis proposed for low performance of abalone
postlarvae in their natural habitat and in certain arti-


232

N. Gordon et al. / Aquaculture 252 (2006) 225–233

ficial settings; the biochemical composition of the
diatoms has been shown to affect their suitability as
feed for abalone postlarvae. Differences in n-3 PUFA
and in FAA composition of diets used in this study
can partly explain differences in diatom nutritional

value, as reflected in postlarval growth and survival.
The results can be of practical help in the reproduction
of abalone in culture.

Acknowledgements
This work was supported by the Israeli Ministry for
National Infrastructures (N.G., M.S. and A.N.), by
several grants from the European Commission (M.S.
and A.N.) and NIH /NIGMS 08168-22 (J.J.L.). We
are grateful to E. Chernova, D. Malka, B. Koven, H.
Krogliak, I. Lupatsch, R. Weiss, and V. Zlatnikov for
their help during the experiments; to M. Ben-Shaprut,
A. Colorni and several anonymous reviewers for help
in preparation of the manuscript and bringing it to its
final form.

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