Optimal Proportions of Crabs and Fish in Diet for Common Octopus

7/27/2019 Optimal Proportions of Crabs and Fish in Diet for Common Octopus

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Optimal proportions of crabs and fish in diet for common octopus

(Octopus vulgaris) ongrowing

Benjamn Garca Garca*, Jesus Cerezo Valverde

I.M.I.D.A.Acuicultura, Consejera de Agricultura y Agua de la Region de Murcia. Puerto de San Pedro del Pinatar, Apdo 65,

30740 San Pedro del Pinatar, Murcia, Spain

Received 3 January 2005; received in revised form 18 April 2005; accepted 20 April 2005

Abstract

Although the ongrowing of Octopus vulgaris shows great economic potential, to date, no commercially available diet exists

so that trawled fish species of low economic value, which would otherwise be discarded, are used. Crustaceans form an

important part of the diet of natural populations of O. vulgaris and, in captivity, they seem to be equally important for growth

and survival. However, both the availability of crustaceans and their price seriously affect the profitability of O. vulgaris

farming, particularly in the Mediterranean area. In the present study, we look at the optimal percentage of crabs and fish in the

O. vulgaris diet, and different patterns of food distribution, taking into account biological and economic factors. For this, we

used five experimental groups of octopus (only males), each of which followed a distinct pattern of feeding, representing five

different diets: (i) crab provided every day (Group C); (ii) crab provided on 3 consecutive days followed by bogue for 1 day

(Group 3C1B); (iii) crab and bogue provided on alternate days (Group 1C1B); (iv) crab provided on 1 day, followed by bogue

for 3 days (Group 1C3B); and (v) bogue provided every day (group B). According to the macronutrient composition of the diet

supplied and the quantity of crab and/or bogue consumed by each individual octopus, the mean macronutrient consumed each

day was calculated, along with the gross energy and P/E ratio. The protein content of each diet was similar, 1920% (wet

substance), while the lipid content varied linearly from 0.79% in Group C to 6.11% in Group B. The optimal diet was reached in

group 1C1B, with a growth rate of 1.98F0.30% and a feeding efficiency of 39.35F4.40%. The diet had a 2.65% lipid content

and a P/E ratio of 31.68 g protein/MJ. However, from an economic point of view, the feeding strategy of group 1C3B seems to

be the most adequate with a conversion index of 3 /kg of octopus produced.

D 2005 Elsevier B.V. All rights reserved.

Keywords: Octopus vulgaris; Ongrowing; Diet; Feeding and nutrition

1. Introduction

Octopus vulgaris presents a series of characteris-

tics which make it an interesting proposition for ma-

rine culture. These include a high reproductive rate

0044-8486/$ - see front matterD 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.aquaculture.2005.04.055

* Corresponding author. Tel./fax: +34 9 68184518.

E-mail address: [email protected] (B. Garca Garca).

Aquaculture 253 (2006) 502511

www.elsevier.com/locate/aqua-online


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with 100,000500,000 eggs per female (Mangold,

1983; Iglesias et al., 1997), rapid growth of more

than 5% body weight per day (Mangold, 1983; Igle-

sias et al., 1997; Aguado and Garc a Garca, 2003), ahigh feed conversion rate, 3060% of ingested food

being incorporated in its own weight (Mangold and

von Boletzky, 1973; Mangold, 1983; Aguado and

Garca Garca, 2003).

A few companies in Galicia (NW Spain) have used

floating cages for intensive ongrowing for several

years (Rama-Villar et al., 1997; Rey-Mendez, 1998;

Luaces-Canosa and Rey-Mendez, 1999; Tunon et al.,

2001, 2002), the estimated production in 1998 and

1999 being around 32 tonnes/year (FAO, 2001, 2002).

However, the technology available is still underdevel-oped. At present O. vulgaris culture is based on

catching individuals weighing about 750 g from the

sea, keeping them in floating cages and feeding with

by-catch from trawling until they reach their commer-

cial size (2.53.5 kg). The profitability of this activity

is low (Garca Garca et al., 2004), since it depends

basically on the supply of subadults and because no

commercial diet is available (Vaz-Pires et al., 2004).

The techniques for producing subadults in the hatch-

ery have still to be perfected despite the efforts of

several research groups (Itami et al., 1963; Imamura,

1990; Villanueva, 1995; Iglesias et al., 1997, 2000,

2004; Carrasco and Rodrguez, 1999; Navarro and

Villanueva, 2000, 2003; Villanueva et al., 2002,

2004; Carrasco et al., 2003); while, although various

diets have been tried experimentally for feeding sub-

adults cephalopods, including cuttlefish and octopus,

the results have always been inferior than those

obtained with natural diets (Lee et al., 1991; Castro

et al., 1993). Nevertheless, once the necessary tech-

nology is in place, as it already is for Sparus aurata

and Dicentrarchus labrax, there is no need for this

sector to be any less profitable (Garca Garca et al.,2004).

With a natural diet (which is basically composed of

different species of crustaceans and fish), growth and

feed efficiency in O. vulgaris can vary widely,

depending on the exact species of the diet (Cagnetta

and Sublimi, 2000; Garca Garca and Aguado, 2002;

Tunon et al., 2002; Aguado and Garca Garca, 2003).

The best results are obtained with a diet composed

entirely of crustaceans (Aguado and Garca Garca,

2003) or, at least, when these form a major part of

mixed diets (Cagnetta and Sublimi, 2000; Tunon et

al., 2002). A diet solely of fish, on the other hand,

leads to comparatively poor growth (Nixon, 1966;

Tunon et al., 2002; Aguado and Garca Garca,2003), the lipid content plays an important role

since octopus fed bogue (6% lipid, wet substance)

provides better growth than sardines (20% lipid). It

has also been suggested that a diet totally lacking in

crustaceans leads to higher mortality (Tunon et al.,

2002). In the Mediterranean region the availability of

low priced crustaceans from trawling is low (Garca

Garca and Aguado, 2002), while in Galicia, although

companies use them for feeding O. vulgaris, it is to be

expected that their price will rise as O. vulgaris

production increases. This inevitable increase in feed-ing costs will mean that crustaceans will become a

limiting factor in the profitability of O. vulgaris

ongrowing installations (Garca Garca et al., 2004).

The conclusion, then, is that a diet based exclusively,

or even mainly, on crustaceans is not a commercially

viable proposition.

It is for this reason that the present study set out to

ascertain the optimal proportion of crab and bogue for

the growth and conversion rates of ongrowing O.

vulgaris to be as satisfactory as possible. In addition,

knowing the macronutrient composition of the species

used, interesting data will be made available for future

research into a commercial diet for O. vulgaris.

2. Material and methods

The octopus (O. vulgaris) were caught at sea

(Murcia, S.E. Spain) and kept in 3500-l tanks in the

laboratory. The experiment began when the octopus

had acclimatised (2 weeks) and were feeding on the

amount of feed calculated according to the ingestion

equations of Garca Garca and Aguado (2002) andAguado and Garca Garca (2003). Bogue (Boops

boops) and crab (Carcius mediterranus) were sup-

plied on alternate days before the experiment started.

For this, 20 male octopus weighing 388660 g were

placed in individual 450-l tanks, containing PVC

tubes as shelters and with an open flow-through sea-

water system. We rejected females in order to avoid

reproductive processes, such as gonad maturation,

which might have had a negative effect on growth.

These were divided into five groups of four octopus,

B. Garca Garca, J. Cerezo Valverde / Aquaculture 253 (2006) 502511 503


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each group representing different diets composed of

both frozen crab and bogue: (i) Group C (crab pro-

vided every day); (ii) Group 3C1B (crab provided on

3 consecutive days followed by bogue for 1 day); (iii)Group 1C1B (crab and bogue provided on alternate

days); (iv) Group 1C3B (crab provided on 1 day,

followed by bogue for 3 days); and (v) Group B

(bogue provided every day) (Table 1). Food was

provided ad libitum every day and uneaten food was

withdrawn the following day to calculate by differ-

ence the exact amount of food eaten (Garca Garca

and Aguado, 2002; Aguado and Garca Garca, 2003;

Cerezo and Garca Garca, 2004). Bogue and crabs

were supplied with head and legs, respectively, and, in

the case of crabs, the edible fraction was estimated as50% including legs. The experiment lasted 57 days

(March to May). The water temperature varied be-

tween 15 and 18 8C (16.5F1.0 8C), which is within

the optimal range of temperatures for this species

(Aguado and Garca Garca, 2003), while salinity

remained practically constant at 37x and dissolved

oxygen was maintained at above 90% saturation, so

that this factor was not limiting (Cerezo and Garca

Garca, 2005).

The body composition was analysed (moisture,

protein, fat, ash and nitrogen-free extractable matter)

in three octopus of similar weight to those used in the

experiment and in all the octopus at the end of the

experiment. To do this, the whole animals including

visceral mass were ground and mixed three times

consecutively until a homogenous sample was

obtained. A 1-g sample (in the case of moisture,

protein and ash) or 2-g sample (in the case of lipid)

were used for analysis purposes, which were carried

out in triplicate. The composition of the food was also

analysed. In the case of crab, complete animals and

the remains left after being consumed by the octopus

were homogenised. The percentage of macronutrientsof the edible portion was calculated as:

%IC %RC =2 %WhC;

so%IC 2T%WhC %RC;

where %IC is the nutrient percentage of ingested crab;

RC is the percentage of nutrient in the left-over

(remaining) crab; and %WhC is the nutrient percent-

age of the whole crab.

Protein content was determined by the Kjeldhal

method using a conversion factor of 6.25. The lipid

content was obtained by ether extraction (SOXTEC

System-HTC). Moisture was obtained by drying

(105F1 8C, 24 h) until constant weight was reached

in a drying chamber (KOWELL, D2 NOVA), and

ash by incineration (loss in weight: at 450F1 8C, 24

h) in a MUFLA oven (HOBERSAL, HD-230). Net

energy was estimated using the Miglavs and Jobling

(1989) energy coefficients: protein 23.6 kJ/g and

lipid 38.9 kJ/g.

From the composition of the food (Table 2) and

from the quantity of crab and/or bogue consumed by

each individual, the mean macronutrient compositionof the diet intake by each octopus was calculated

(Table 3), as was the gross energy and the protein

energy ratio (P/E in g/MJ).

All the samples were weighed at the outset (Wi=

initial weight in g) and at the end of the experiment

(Wf=final weight in g). The following indices were

calculated: absolute feeding rate: AFR = IF/t; abso-

lute protein feeding rate: APFR=IP/t; absolute lipid

feeding rate: ALFR= IL/t; specific feeding rate:

SFR = AFR100/ Wa; absolute growth rate: AGR =

Table 1Initial experimental conditions

Experimental

group

Percent of days

crab provided (%)

Specimen

number

Average weight

FS.D. (g)

Group C 100 4 491F26a

Group 3C1B 75 4 517F116a

Group 1C1B 50 4 526F133a

Group 1C3B 25 4 507F77a

Group B 0 4 491F46a

C, crab every day; 3C1B, crab 3 days followed by bogue 1 day;

1C1B, crab and bogue on alternate days; 1C3B, 1 day crab followed

by 3 days bogue; B, bogue every day.

Table 2

Feed composition expressed as a percentage of wet substance

Bogue Whole

crab

Left-over

crab

Crab edible

fractiona

Crude protein 20.10 12.89 6.78 19.00

Crude lipid 6.11 0.44 0.09 0.79

Ash 4.51 23.48 38.37 8.59

NFEb 0.00 6.54 8.34 4.74

Moisture 69.95 56.65 46.42 66.88

GE (kJ/100 g) 712.04 430.54 302.79 558.29

P/E (g protein/MJ) 28.23 29.94 22.39 34.03

a Calculated from whole and left-over crab.b Nitrogen-free extract.

B. Garca Garca, J. Cerezo Valverde / Aquaculture 253 (2006) 502511504


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(Wf Wi)/t; specific growth rate: SGR = (LnWf

LnWi)100/t; feed efficiency: FE=(Wf Wi)100/IF;feed conversion ratio: FCR = IF/ (Wf Wi); proteinproductive value: PPV = 100 (Retained protein / IP);

and Lipid productive value: LPV = 100 (Retained

lipid/ IL); where Wf= final weight in g; Wi= initial

weight in g; Wa=average weight between sampling

in g; t= time in days; IF ingested food in g; IP ingested

protein in g and IL ingested lipid in g.

From the SGR values obtained with the five dif-

ferent diets, the time necessary for the octopus to

reach 3500 g from an initial weight of 500 g was

calculated. Based on the percentage of crab and/or

bogue consumed in each case and the price of 0.34 /kg

(bogue) and 1.13 /kg (crab) for the Mediterranean

coast of Spain, the economic feeding conversion rate

(cost of producing 1 kg of octopus was calculated,

EFCR=o/kg).

An analysis of variance (ANOVA) for a Pb0.05

was carried out, complemented by a multiple range

analysis of LSD; a Neperian logarithmic transforma-

tion of the indices and percentages was made before the

ANOVA. A correlation analysis between these vari-

ables and the percentage of crab in the diets was made.

3. Results

Survival in all experimental groups was 100%. As

can be seen from Table 2, the edible portion of both

crab and bogue contained similar percentages of pro-

tein (19.00% and 20.10%, respectively). However,

bogue had a greater gross energy content (712 kJ)

than the edible portion of crab (558 kJ) and a lower P/

E ratio due to its higher fat content.

Table 3 shows the percentage of the crab edible

fraction and bogue intake by the different groups.Also shown is the mean macronutrient composition

of each diet. The protein content was similar in all

cases, varying between 19% and 20%. The lipid

content, however, varied lineally with the increasing

proportion of bogue: from 0.79% (crab only) to 6.11%

(bogue only). This different lipid content was also

responsible for the differences seen in the gross ener-

gy content, which decreased with increasing propor-

tions of crab, accompanied by an increasing P/E ratio.

No significant differences were observed among

the AFR and APFR values of groups C, 3C1B and

1C1B but there were significant differences (Pb0.05)

between these groups and the other two (1C3B and

B), (Table 4). On the other hand AFR and APFR were

significantly and positively correlated with the per-

centage of crab in the diet. However, no significant

correlation was observed between ALFR and the

percentage of crab consumed, although there were

significant differences among the mean values

obtained in groups C and 3C1B (0.48 and 0.67,

respectively) and groups 1C1B, 1C3B and 1B, with

values of 1.26, 1.29 and 1.15, respectively. The SFR

was positively and significantly correlated with thepercentage of crab consumed and, in general, signif-

icant differences existed among the different groups.

Therefore, the amount of food intake increased line-

ally with the percentage of crab in the diet.

Wf and growth measured as AGR and SGR var-

ied significantly among groups due to the ways in

which the diets were distributed and, consequently, to

different compositions of the diets (Table 4). The

percentage of crab in the diet was positively and

significantly correlated with Wf, AGR and SGR

Table 3

Composition of each diet (percent wet substance)

C 3C1B 1C1B 1C3B B

Percent crab intake (%) 100 89F3 65F5 46F5 0Percent bogue intake (%) 0 11F3 35F5 54F5 100

Crude protein 19.00F0.00 19.12F0.03 19.38F0.05 19.60F0.05 20.10F0.00

Crude lipid 0.79F0.00 1.36F0.17 2.65F0.24 3.67F0.26 6.11F0.00

Ash 8.59 8.15F0.13 7.17F0.19 6.38F0.20 4.51

NFEa 4.74 4.23F0.15 3.09F0.22 2.17F0.23 0.00

Moisture 66.88 67.21F0.10 67.95F0.14 68.54F0.15 69.95

GE (kJ/100g) 558F0 575F5 612F7 642F7 712F0

P/E (g protein/MJ) 34.03F0.00 33.26F0.22 31.68F0.28 30.55F0.27 28.23F0.00

a Nitrogen-free extract. Data represent the meanFS.D.



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(Table 4). However, no significant differences were

observed among the Wf values of groups C, 3C1B

and 1CIB, while they were significant between these

groups and the others (1C3B and B). As regards to

the growth indices measured (AGR and SGR), no

significant differences were observed among C,

3C1B, 1C1B and 1C3B, while the difference be-

tween these groups and B was significant. It seems,

then, that growth was not modified in C, 3C1B and

1C1B, while it diminished slightly in 1C3B, and

more so in B. Therefore, there was a significant

decrease in growth when bogue alone was fed to

the octopus, at least when the feeding strategies used

in this experiment are applied.

The FCR decreased with decreasing percentages of

crab, and so FE tended to increase, although no

significant correlation was established. However the

mean values changed to a statistically significant ex-

tent as a function of the food provided, the highest

FCR values being obtained with groups C and 3C1B.

The PPV was not significantly affected by thefeeding strategy and although it tended to increase

with decreasing percentages of crab, no significant

correlation was observed. The LPV fell with decreas-

ing percentages of crab although no significant corre-

lation existed. However, the mean values were

significantly affected, the highest value being

obtained in 3C1B and the lowest in 1C3B and B.

The body composition of the samples at the end of

the experiment was not significantly affected by the

different feeding strategies (Table 5) and neither was it

correlated with the percentage of crab in the diet,

except in the case of lipids, which were significantly

higher in 3C1B, 1C1B and 1C3B. There was no

significant difference in lipid content between the

octopus at the outset of the experiment and those

fed with crab alone (group C), but there was between

the initial specimens and those fed a partial or total

diet of bogue (groups 3C1B, 1C1B, 1C3B and B).

Based on the SGR values obtained for the different

experimental groups (Table 4), it was estimated that

the time needed for octopus to grow from an initial

weight of 500 g to 3.5 kg was as follows: group C, 95days; 3C1B, 99 days; 1C1B 98 days (in which growth

Table 4

Mean valuesFS.D. for every index of each experimental group

C 3C1B 1C1B 1C3B B

Wi (g) 491F26a 517F116a 526F133a 507F77a 491F46a

Wf (g) 1546F160a 1537F154a 1560F167a 1366F375b 922F177c

AFR (g/day) 60.13F1.93a 49.25F5.97a 47.33F5.85a 34.87F7.41b 18.88F5.79c

APFR (g/day) 11.42F0.37a 9.42F1.15a 9.18F1.14a 6.83F1.46b 3.79F1.16 c

ALFR (g/day) 0.48F0.02a 0.67F0.15a 1.26F0.22b 1.29F0.32b 1.15F0.35b

SFR (%) 5.92F0.37a 4.79F0.11b 4.56F0.36b,c 3.77F0.61c 2.63F0.40d

AGR (g/day) 18.83F3.13a 18.21F3.22a 18.47F1.37a 15.33F5.72a 7.69F2.38b

SGR (%) 2.04F0.26a 1.97F0.42a 1.98F0.30a 1.74F0.34a 1.11F0.19b

FE (%) 31.30F5.02a 37.20F6.88a,b 39.35F4.40b 43.43F9.72b 40.76F2.57b

FCR 3.26F0.56a 2.76F0.54a,b 2.56F0.27b 2.42F0.67b 2.46F0.16b

PPV 27.99F4.60a 30.61F8.04a 33.15F5.67a 37.16F8.24a 36.48F2.87a

LPV 12.17F3.82a 18.0F5.84b 10.86F3.04a 6.43F3.39c 3.30F0.64c

Values on the same line and different superscripts are significantly different ( Pb0.05). Wi, initial weight; Wf, final weight; AFR, absolute

feeding rate; APFR, absolute protein feeding rate; ALFR, absolute lipid feeding rate; SFR, specific feeding rate; AGR, absolute growth rate;SGR, specific growth rate; FE, feed efficiency; FCR, feed conversion ratio; PPV, protein productive value; LPV, lipid productive value.

Table 5

Wet body composition of whole O. vulgaris (including visceral mass) fed five diets composed of different proportions of crab and bogue

Initial specimens C 3C1B 1C1B 1C3B B

Crude protein 15.52F0.52a 16.52F0.34a 15.63F0.95a 16.06F1.08a 16.30F0.20a 16.62F0.35a

Crude lipid 0.21F0.08a 0.28F0.06a,b 0.50F0.12b 0.55F0.10b 0.45F0.23b 0.34F0.02b

Ash 2.41F0.05a 2.24F0.04b 2.31F0.02a,b 2.26F0.08b 2.22F0.12b 2.23F0.03b

Moisture 80.30F0.52a 78.55F0.37b 78.85F0.62b 79.06F1.32b 79.16F0.64a,b 79.76F0.34a,b

Data represent the meanFS.D. Values on the same line and different superscripts are significantly different ( Pb0.05).



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was not modified significantly) followed by groups

1C3B (112 days) and B (175 days) (Fig. 1). The

EFCR (economic feeding conversion rate) diminished

lineally and sharply with the percentage of crab form-

ing the diet since this is by far the most expensive

component. In the first three groups, where the time

needed for growth was least, the EFCR was high,

varying from 7.37 to 4.07 /kg, while in groups

1C3B and B it was 2.96 and 0.84 /kg, respectively.

4. Discussion

The growth obtained with the monospecific diets

(crab or bogue) and the feed efficiency were within

the normal range observed previously for this species

in the experimental conditions described and for the

initial weight of the specimens (Aguado and GarcaGarca, 2003). In addition, the growth rates were

within the range of those obtained in ongrowing

cages using similar water temperature, initial weights,

duration and diets (including crustacean and fish)

(Luaces-Canosa and Rey-Mendez, 1999; Tunon et

al., 2001, 2002). The feeding efficiencies indices

were generally very high and also within the range

previously observed for this species (Mangold and

von Boletzky, 1973; Mangold, 1983; Aguado and

Garca Garca, 2003). In absolute terms, the speci-

mens fed exclusively on crab were practically double

the weight of those fed exclusively on bogue, al-

though in the latter the feeding rate was lower. Con-

sequently the FCR of octopus fed with crab was

higher (3.26) than in those fed with bogue (2.46),

results which coincide with those of Aguado and

Garca Garca (2003).

Growth was not significantly affected in groups C,

3C1B and 1C1B, in which crab represented 100%,

89% and 65%, respectively, of the diet. However, this

last group showed a significantly lower FCR com-

pared with the other two groups, which also showed

the most favourable PPV (33%). In principle, then, it

seems that the feeding strategy provided in group

1C1B, that is alternate days of crab and bogue,

would offer the best performance. Above this percent-

age, growth and ingestion tended to diminish as the

percentage of bogue rose, and the FCR did not varysignificantly (Pb0.05). Some authors have main-

tained that a mixed diet of crustaceans and fish may

better cover the nutritional requirements of O. vul-

garis than monodiets to guarantee high growth rates

(Smale and Buchan, 1981; Cagnetta and Sublimi,

2000).

The feeding strategy used with group 1C3B, that is

1 day of crab followed by 3 days of bogue (bogue

representing 54% of the diet), also provided good

results even though growth was slightly lower. Eco-

0

20

40

60

80

100

120

140

160

180

200

C 3C1B 1C1B 1C3B B

Feeding strategy

Durationofongrowing(days)

0

1

2

3

4

5

6

7

8

EFCR(Euros/kg)

Duration of ongrowing

EFCR

Fig. 1. Variation in ongrowing duration and EFCR (economic feeding conversion rate) as a function of feeding strategy followed (C: crab

provided every day; 3C1B: crab provided on 3 consecutive days followed by bogue for 1 day; 1C1B: crab and bogue provided on alternate days;

1C3B: crab provided on 1 day, followed by bogue for 3 days; and B: bogue provided every day).



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nomically, however, it is perhaps the most advanta-

geous strategy. When we look at the time needed for

ongrowing, based on the values obtained for the SGR,

it can be seen that group 1C3B would take only 15days longer to reach optimal weight than groups C,

3C1B and 1C1B (Fig. 1). In these three groups, the

time needed is practically the same (about 97 days).

However, the cost of providing food falls from 7 /kg

of octopus produced to 4 as the percentage of crab

decreases. If we bear in mind that the wholesale price

for specimens weighing 33.5 kg is 79 , it is clear

that the margin existing to cover other production

costs (acquisition of subadults, labour, amortization,

etc.) is so low that it is difficult to see how any

reasonable benefit can be obtained. However, if the1C3B strategy is followed, the cost falls to 2.96 and

the 15 extra days needed for the ongrowing cycle will

not have such a significant effect on production costs,

perhaps justifying the initial investment.

In terms of the macronutrient composition, the

greatest difference among the different diets was the

lipid content, which at the same time implies changes

in the P/E ratio. If this was the limiting factor we

could conclude that for levels of 0.79% to 2.65%

(Table 3), growth will not be significantly affected

(Table 4), but when lipids reach 2.656.11% growth

decreases. Lipid digestibility is low in cephalopods

(ODor et al., 1984; Lee, 1994), since their capacity to

metabolise them is limited (Ballantyne et al., 1981;

Mommsen and Hochachka, 1981). Furthermore Gar-

ca Garca and Aguado (2002) found that O. vulgaris

growth is lower when the lipid content is high. These

authors studied the growth, feeding rate and feed

efficiency in specimens fed bogue (18.48% protein

content and 5.94% lipid content) and sardines

(17.77% protein and 19.64% lipids). Growth was

significantly higher in the octopus fed bogue, al-

though food intake was greater in those fed sardines,the latter therefore having the lower FE of the two

groups. ODor et al. (1984) suggested that the low and

inefficient digestion of lipids in O. vulgaris is due to

the absence of emulsifiers in their digestive tract.

Indeed, the group fed sardines produced fatty and

floating faeces (Garca Garca and Aguado, 2002).

The higher ingestion recorded in octopus fed sardines

may have been due to the fact that the quantity of fat

in the digestive tract contributed to a lower absorption

of amino acids so that the O. vulgaris would attempt

to compensate for the lower protein digestibility by

increased food intake.

The lipid requirement of cephalopods is low but

nevertheless important to guarantee high growthrates. Their use is probably restricted to cell membrane

structure, cholesterol and steroid hormones (Lee,

1994), although in recent years the importance of 3-n

PUFA in the first stages of cephalopod nutrition has

been emphasised (Navarro and Villanueva, 2000,

2003; Koueta et al., 2002). However, the lipid reserves

stored principally in the digestive gland may be mobi-

lised in fasting situations (ODor et al., 1984).

The high feeding rates observed in this study

(group C) and in that made by Aguado and Garca

Garca (2003), when the diet was composed entirelyof crab, or when crab was the principal component of

the diet (group 3C1B), may be due, amongst other

factors, to the fact that the lipid content was low and

that the octopus compensate for this by increased

food intake. The highest LPV values were obtained

with a lipid content of 0.792.56 in the diets (C,

3C1B and 1C1B), while the values tended to decrease

with higher lipid contents (Table 4). On the other

hand, the FE of group 1C1B (2.65% lipid content)

was significantly better than that of group C (0.79%

lipid) and not significantly different from that of the

group fed entirely on bogue (6.11%), although

growth was much greater in this last group (B) and

equal to that of group C. It seems therefore that the

optimal lipid content in the diet, if the content of the

different types of lipid is not limiting, is 23%. Such

a quantity would, on the one hand, cover the nutri-

tional requirements of octopus and, on the other, not

interfere with protein absorption. However, the high

feeding rates observed with the crab-rich diets are

probably not only due to a deficiency in some lipid

component, but also to some, so far unidentified,

nutritional deficiency.As the percentage of bogue in the diet increases, so

does the FE, while the PPV reaches a maximum of

54% in 1C3B (Tables 3 and 4). In principle these

results suggest a more suitable amino acid balance

in bogue than in crab; however, growth is lower. Such

a decrease in growth as a result of a diet composed

entirely of fish has been described by several authors

(Nixon, 1966; Garca Garca and Aguado, 2002;

Tunon et al., 2002; Aguado and Garca Garca,

2003). In natural O. vulgaris populations, the diet is



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6280% composed of crab, while fish may only rep-

resent 1230% (Nigmatullin and Ostapenko, 1976;

Guerra, 1978). In captive conditions, too, octopus

show a preference for crustaceans rather than fish(Guerra, 1978). Ghiretti and Violante (1964) related

octopus growth with the copper content of the natural

prey, while Castro et al. (1993) suggests that high

mortality in cuttlefish may be due to copper deficien-

cy. Copper is needed for the synthesis of haemocya-

nin, the oxygen-carrying pigment in cephalopod and

crustaceans blood. Dietary restriction has been seen to

cause a significant decrease in copper levels in the

haemolymph but not in the mantle or digestive gland

tissue (Castro et al., 1993). It seems, then, that octopus

need a certain level of this element and that crusta-ceans are a good source, while fish, which contain

iron in their haemoglobin, do not provide the mini-

mum levels needed.

Whatever the case, a copper deficiency or the

nutrient provided by crab and not by bogue, could

be related with the increased aggressiveness and can-

nibalism (and consequent mortality) observed in other

studies (Aguado et al., 2001; Tunon et al., 2002). In

our case, survival was 100%, even in the group fed

exclusively on fish, reflecting the results of Garca

Garca and Aguado (2002), who studied individual O.

vulgaris fed a mono diet of bogue or sardine, when

the survival exceeded 90%. Aguado et al. (2001), on

the other hand, in an experiment to study O. vulgaris

ongrowing, in which the animals were kept jointly in

the same tanks, registered high levels of mortality

when fish alone formed the diet; similarly, Tunon et

al. (2002), using floating cages in which the octopus

were kept jointly, suggested that survival was lower

with a fish diet. On the other hand, in experiments in

which octopus were kept jointly in tanks but were fed

a mixed crustacean-fish diet, survival was seen to

exceed 90% (Iglesias et al., 1997; Otero et al., 1999;Garca Garca and Cerezo, 2004). In our own installa-

tions, we have observed how octopus kept jointly in

tanks and fed exclusively on fish show aggressiveness

and resort to cannibalism (Aguado et al., 2001), while

this behaviour abates and survival reaches more than

90% when crab is included in the diet (Garca Garca

and Cerezo, 2004). In short, a monodiet of fish is

deficient in some nutrient that limits growth, while

lack of this nutrient (or perhaps another) induces

aggressive behaviour and cannibalism.

The great difficulty, then, in approaching the many

questions raised in this article and others related with

the nutritional requirements of O. vulgaris, is the

preparation of an experimental diet which will beaccepted and totally ingested by octopus. The dry

and semi-humid diets successfully used in experimen-

tal fish studies are not valid in the case of O. vulgaris,

since they disintegrate when manipulated. This is one

of the first aspects to be considered before we can

carry out the studies necessary to formulate the opti-

mal diet for the industrial scale ongrowing of this

species.

Acknowledgements

This work has been financed by JACUMAR Span-

ish Nationals Plans for Aquaculture.

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Optimal Proportions of Crabs and Fish in Diet for Common Octopus

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