Growth and Food Intake Models in Octopus Vulgaris

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Growth and food intake models in Octopus vulgaris

Cuvier (1797): influence of body weight, temperature,

sex and diet

F. AGUADO GIMÉNEZ* and B. GARCÍA GARCÍA IMIDA – Acuicultura, Consejeria de Agricultura, Agua y Medio Ambiente de la Region de Murcia, Las

Salinas 7, Puerto de San Pedro del Pinatar, P.O. Box n o 65, San Pedro del Pinatar, 30740, Murcia,

Spain; *Author for correspondence (e-mail: [email protected]; phone: 00 34 968 184518; fax: 00

34 968 184518)

Received 11 December 2001; accepted in revised form 6 October 2002

Key words: Cephalopods, Food intake model, Growth model, Growth, Octopus vulgaris

Abstract. Multiple regression analysis was used to develop mathematical models applicable to the

growth and food intake of Octopus vulgaris. The variables considered were: body weight (Bw: 175–3,500 g), temperature (T: 13–28 °C), sex (S: male = 0, female = 1) and diet (D: bogue fish = 0, crabs =1). Growth and food intake may be succesfully expressed by means of the following equations: Ln (AGR+ 14) = −2.0135 + 0.0895 Ln Bw + 0.5087 T − 0.0142 T2 + 0.2997 D (R2 = 71.79; ANOVA p < 0.0001)and Ln (AFR) = − 5.6577 + 0.5137 Ln Bw + 0.5266 T − 0.0132 T 2 + 1.1135 D (R2 = 78.71; ANOVAp < 0.0001), where AGR: absolute growth rate, AFR: absolute feeding rate, Bw: body weight, T: tem-perature and D: diet. In our experimental conditions, sex did not affect growth or food intake. The op-timum temperature for growth (17.5 °C) and food intake (20 °C) was independent of body weight.Growth and food intake were higher with the crab diet. Nevertheless, food efficiency was better foranimals fed on fish (bogue). Maximum food efficiency was reached at 16.5 °C for both diets. When thetemperature was above 23 °C, weight losses and mortality were recorded; the temperature at which thisoccurred depending on body weight and diet, so that smaller and bogue-fed individuals were more sen-sitive to increasing temperatures. O. vulgaris growth may provide optimum economic performance from16 to 21 °C. This range is too narrow, considering the wide natural range (12–29 °C) in some Mediter-ranean areas. Therefore, O. vulgaris growth will be limited by seasonality of temperature or must be

carried out with other systems (e.g. recirculation in closed systems with temperature control) for it to beeconomically viable.

Abbreviations: Adj R2 – adjusted determination coefficient, AFR – absolute feeding rate, AGR – ab-solute growth rate, Bw – body weight, D – diet, FE – feeding efficiency, IF – ingested food, R – cor-relation coefficient, S – sex, s.d. – standard deviation, s.e. – standard error, S.E.E. – standard error of estimation, SFR – specific feeding rate, SGR – specific growth rate, t – time in days, T – temperature,Wa – average weight, Wf – final weight, Wi – initial weight

Introduction

Cephalopod growth is rapid regardless of diet composition (Forsythe and Van Heu-

kelem 1987). In general, cephalopods prey on a variety of species, mainly crusta-ceans and molluscs, and to a lesser extent on other invertebrates or fish (Nigmatu-

Aquaculture International 10: 361–377, 2002.© 2003 Kluwer Academic Publishers. Printed in the Netherlands.



lin and Ostapenko 1976; Guerra 1978; Guerra and Nixon 1987). Hanlon and Mes-senger (1996), explained that there are geographical differences in the diet althoughcrabs and/or molluscs are generally the main prey; e.g. in the Mediterranean Seaoff the coast of Catalonia (Spain), Octopus vulgaris feed 80% on crustaceans, whilein the Algarve (Portugal), they feed 80% on bivalves.

The fattening of Octopus vulgaris in captivity is a new development in Spanish

Atlantic and Mediterranean coastal waters. Experiments carried out in Galicia (NWSpain) with Octopus vulgaris have provided excellent results (Iglesias et al. 1997;Luaces and Rey 1999; Rodríguez and Carrasco 1999) using a mixed diet of crabs,mussels and fish. However, in Spanish Mediterranean coastal waters high tempera-tures have an adverse effect on growth and survival (Aguado et al. 2001), and thereare difficulties in supplying the natural diet, although there is a plentiful supply of fish of low market value, such as bogue ( Boops boops), sardine (Sardina pilchar-

dus), giltsardine (Sardinella aurita) or mediterranean scad (Trachurus mediterra-

neus).In most poikilotherm species, such as fish and molluscs, growth, survival, food

intake, etc., have an optimum temperature, which may change with age and/or size(Brett 1979; Pedersen and Jobling 1989; Jobling 1994). From an aquacultural point

of view, assessing these variables is very important not only for efficient produc-tion management, but also for determining suitable locations for rearing a particu-lar species.

Recent investigations on the fattening of Octopus vulgaris using diets of differ-ent composition (Cagnetta and Sublimi 1999; García García and Aguado Giménez2002) have revealed different growth and food intake rates. For animal breeders, anoptimum diet is one which provides all the nutritional requirements and promotesfastest growth. Since formulated diets are not available, O. vulgaris must be rearedwith natural food. The closer to its natural diet the food supplied is, the better theresults are expected. In cultured fishes, such as gilthead seabream, artificial dietshave a highly standardized composition, and growth and/or food intake modelsprovide very similar results, the only differences being the temperature and bodyweight ranges typical of each location and experimental conditions (García García

1994; Petridis and Rogdakis 1996; Lupatsch and Kissil 1998). On the other hand,natural food for Octopus vulgaris growth is not standardized and varies greatly withthe local catch. This is because growth and food intake varies so much from placeto place, as mentioned above.

The main objective of this work was to develop equations to explain O. vulgaris

growth and food intake in experimental rearing conditions in Mediterranean coastalwaters, as a function of the main variables involved: temperature, body weight anddiet. In addition, nutritional utilization and the possible effect of sex are assessed,since female growth, unlike in males, seems to be more influenced by sexual matu-ration (Smale and Buchan 1981; Cortez et al. 1995a). Such mathematical modelswill allow estimations of growth and food intake, and be of great use for produc-tion management in Mediterranean conditions, where the temperature range is very

wide and may represent a limiting factor.

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Material and methods

Octopus vulgaris specimens were captured from their natural environment in Med-iterranean coastal waters (Murcia, SE Spain) by trawling. Acclimatation took placein 4.5 m3 raceways provided with open seawater flow. Assays were carried out inindividual 400 l cylindrical tanks, because of the high degree of cannibalism and

territoriality observed in previous experiments. Furthermore, isolation allows thereliable determination of growth and food intake. The experimental period was be-tween November 1998 and November 2000. Twelve specimens were used in thefirst period (Nov. 1998 to Nov. 1999); they were fed ad libitum with bogue ( Boops

boops) once a day, in the morning. Fish were always supplied without head andtail, since these parts are not usually consumed by octopus. Each day, food wasprovided ad libitum, and any remaining food was collected the following day,drained and weighed. Ingested food was the difference between supplied food andremaining food. The food supplied was adjusted everyday according to octopus sa-tiation. In a second period (Nov. 1999 to Nov. 2000), fifty eight specimens werefed to satiation once a day with several crab species, mainly Macropipus depurator

and Calappa granulata, and in smaller proportions Squilla mantis, Dorippe lanata,

Partenope angulifrons and Homola barbata, also caught by trawling. Remainingcarcasses and food were collected on a daily basis and subtracted from the foodsupplied, to obtain food intake. Empty crab carcasses were estimated to represent30% in weight of the total food consumed. Individual octopus were sampled oncea month (wet body weight). The body weight ranged from 175 to 3,450 g duringthe experiment. Temperature and oxygen concentration in the culture water wereregistered daily, ranging from 13 °C in the winter to 28 °C in the summer, botharound 80% oxygen saturation. Photoperiod was natural (37° 50Ј N; 0° 46Ј W).For each period between sampling, the following indexes were calculated:

Absolute Growth Rate ͑ AGR͒ :Wf Ϫ Wi / t

Specific Growth Rate ͑ SGR͒ :͑ LnWf Ϫ LnWi͒ 100/ t

Absolute Feeding Rate ͑ AFR͒ : IF / t

Specific Feeding Rate ͑ SFR͒ : AFR100/ Wa

where Wf = final weight in g; Wi = initial weight in g; Wa = average weight be-tween sampling in g; t = time in days; IF = ingested food in g.

For each diet, the protein, lipid, mineral and moisture content were analyzed.The protein content was obtained by the Kjeldhal method. The lipid content wasobtained by ethylic ether extraction (SOXTEC System-HTC). The moisture con-tent was obtained by desiccation (105 ± 1 °C, 24 h) to constant weight, and min-erals by incineration (loss of organic weight: 450 ± 1 °C, 24 h). Net energy wasdetermined using the Miglavs and Jobling (1989) energetic coefficients: protein

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23.6 KJ/g and lipid 38.9 KJ/g. Accumulated mortality was calculated for each ex-perimental diet and period between sampling.

Statistical analysis

Firstly, a Partial Correlation Test was applied to ascertain the influence of each var-iable on growth and food intake. Next, a Multiple Regression Analysis involvedthe progressive elimination of independent variables according to their correlationwith dependent variables. In order to explain variations in growth and food intakeaccording to body weight (Bw) and temperature (T), several models have been de-veloped (Wooton et al. 1980; Liu and Cui 1998; Lupatsch and Kissil 1998; GarcíaGarcía and Aguado Giménez 2002) in which data have been empirically fitted toequations such as the following:

LnY ϭ Lna ϩ bLn Bw ϩ cLnT

LnY ϭ Lna ϩ bLn Bw ϩ cT

LnY ϭ Lna ϩ bLn Bw ϩ cT ϩ dT 2

LnY ϭ Lna ϩ bLn Bw ϩ cT ϩ dT 2 ϩ eT Ln Bw

A natural-log relationship between Bw and growth and food intake has been clearlyestablished for most animals. In our case, where the T range was broad, polynomicmodels of T seemed more accurate than natural-log, and so the data were adjustedto test the following models by means of the progressive elimination of variablesin a multiple regression analysis:

Љ AЉ LnY ϭ Lna ϩ bLn Bw ϩ cT ϩ dT 2eS ϩ fD.

Љ BЉ LnY ϭ Lna ϩ bLn Bw ϩ cT ϩ dT 2 ϩ eT Ln Bw ϩ fS ϩ gD.

Rearranging gives:

LnY ϭ Lna ϩ͑ b ϩ eT ͒ Ln Bw ϩ cT ϩ dT 2 ϩ fS ϩ gD.

The ЉAЉ model predicts that maximum growth and food intake will occur aroundan optimum temperature and is independent of body weight, while in the ЉBЉ model,which linearly depends on the body weight coefficient and on temperature, the op-timum temperature changes with body weight; that is, the interaction of tempera-ture and body weight influence growth and food intake. Sex and diet are qualitativevariables that were encoded as S = 0 for males, S = 1 for females, D = 0 for bogueand D = 1 for crabs. In some situations growth was negative and natural-log waserroneous. To avoid this, we added the positive number immediately above thelower observed negative growth value to all the calculated values (AGR and SGR).

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lation and adjusted determination coefficients and lower standard error of estima-tion than equations expressed in relative terms (SGR and SFR). Durbin-Watson in-dex values made sure no autocorrelation would occur. Therefore, from all thepresented models, Eqs. 5 and 17 (AGR and AFR respectively) were selected to per-form simulations which were proved useful in explaining the behaviour of growthand food intake according to Bw, T and diet:

Ln͑ AGR ϩ 14͒ ϭ Ϫ 2.0135 ϩ 0.0895Ln Bw ϩ 0.5087T Ϫ 0.0142T 2 ϩ 0.2997 D

Ln AFR ϭ Ϫ 5.6577 ϩ 0.5137Ln Bw ϩ 0.5266T Ϫ 0.0132T 2 ϩ 1.11

Figure 1 shows a simulation of AGR for our T range and Bw of 500 and 2,000 g,

Table 1. Overall data of observations for considered variables

Male Female Total

Bogue-fed 43 48 91

Crab-fed 63 82 145

Total 106 130 236

Body weight range 301–3,450 g 175–3,050 g 175–3,450 gTemperature range 13–28 °C

Table 2. Macronutrient composition of each diet (% wet substance ± s.d.)

Crabs (edible portion) Bogue

Crude lipid 0.79 ± 0.01 5.94 ± 2.56

Crude protein 19.00 ± 0.66 18.48 ± 1.11

Ash 8.59 ± 1.35 3.29 ± 0.05

Moisture 66.88 ± 2.01 70.52 ± 3.60

N-free extractable matter 4.74 0.00

Gross Energy GE (kJ/100 g food) 558.29 667.19

Protein/energy ratio P/E (g protein/MJ) 34.03 27.70

Table 3. Results of Partial Correlation Test of all factors for AGR and AFR

AGR AFR

Body weight 0.1378 0.5789

p < 0.05 p < 0.0001

Temperature 0.5574 0.5256

p < 0.0001 p < 0.0001

Sex − 0.0090 0.0540

n.s. n.s.

Diet 0.4053 0.8258

p < 0.0001 p < 0.0001

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in which it can be seen that a crab diet promoted faster growth than bogue. As wasexpected, the largest animals had higher AGR than the smallest (the opposite wastrue with SGR) regardless of diet. Weight losses occurred earlier in smaller indi-viduals than in bigger ones and in bogue-fed than in crab-fed animals. Figure 2show simulations of AFR. In similar fashion to what occurred with AGR, food in-take was higher using crabs than bogue, and the largest animal fed more thansmallest (the opposite was true with SFR). All these differences were statisticallysignificant (Table 3). Temperature, body weight and diet have an important influ-

ence on AGR and AFR. Nevertheless, FE was better for bogue-fed than crab-fedoctopuses (Figure 3) although at extremes of the T range, FE was higher in crab-fed ones.

The estimated optimum temperatures from the selected equations were 17.5 °C,20 °C and 16.5 °C for AGR, AFR and FE respectively. Above these temperatures,the values of these factors decreased and above 23 °C, weight loss and negative FEwere observed, firstly in bogue-fed animals regardless of size and then in thesmaller animals of both groups. Mortality started at 19 °C and was very high above25 °C (Figure 4). Statistically significant differences in mortality were not observedbetween diets (

2, p > 0.05).

Table 4a. Results of progressive elimination Multiple Regression Analyses for AGR and SGR (a–g:coefficients; s.e.: standard error; SEE: standard error of estimation; D.B.: Durbin-Watson index)

a b c d e f g R ANOVA

s.e. s.e. s.e. s.e. s.e. s.e. s.e. R2adj F D.B.

Eq. p-level p-level p-level p-level p-level p-level p-level SEE p-level

1 −1.9527 0.0866 0.5059 −0.0142 0.3013 −0.0262 0.74490.5327 0.0426 – 0.0501 0.0012 0.0446 0.0433 54.52% 57.35 1.37

0.0003 0.04 0.0001 0.0001 0.0001 n.s. 0.3263 0.0001

2 −1.8619 0.0730 0.0008 0.5006 −0.0142 0.3023 −0.0263 0.7449

2.0433 0.2976 0.0178 0.1266 0.0012 0.0491 0.0435 54.32% 47.58 1.37

n.s. n.s. n.s. 0.0001 0.0001 0.0001 n.s. 0.3270 0.0001

3 −2.0535 −0.3066 0.5469 −0.0149 0.3103 −0.0078 0.7293

0.5879 0.0470 – 0.0553 0.0013 0.0492 0.0478 52.18% 52.29 1.54

0.0005 0.0001 0.0001 0.0001 0.0001 n.s. 0.3601 0.0001

4 0.9752 −0.7588 0.0274 0.3684 −0.0153 0.3416 −0.0108 0.7320

2.2454 0.3270 0.0196 0.1391 0.0014 0.0540 0.0478 52.37% 44.08 1.54

n.s. 0.02 n.s. 0.01 0.0001 0.0001 n.s. 0.3594 0.0001

Eq. 1: Ln( AGR + 14) = Lna + bLn Bw + dT + eT 2 + fD + gS

Eq. 2: Ln( AGR + 14) = Lna + bLn Bw + cT Ln Bw + dT + eT 2

+ fD + gS Eq. 3: Ln(SGR + 1,3) = Lna + bLn Bw + dT + eT 2 + fD + gS

Eq. 4: Ln(SGR + 1,3) = Lna + bLn Bw + cT Ln Bw + dT + eT 2 + fD + gS

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Discussion

Octopus grow quickly, presumably due to their lack of a complex skeletal system,high food intake, efficient digestion and assimilation, direct embryonic developmentthat does not imply metamorphosis transformation and semelparity. The fact thatOctopus vulgaris females reproduce only once emphasizes the need for them todevelop fast. Smale and Buchan (1981) noticed this higher growth rate and foodintake in females, while Cortez et al. (1995a) observed that with Octopus mimus

inmature males and females grew equally, but the growth was higher in mature fe-males than in males. García García and Aguado Giménez (2002) observed fastergrowth in O. vulgaris males than in females, although no statistical differences werefound, while food intake was higher in females. Wells and Wells (1959) andMangold (1963) described the greater growth and food intake of O. vulgaris males.Forsythe and Hanlon (1988) observed high growth in O. bimaculoides males at 18°C but higher in females at 23 °C. Our results show no differences in growth andfood intake between males and females. Sexual maturation in females involves dif-ferent needs for nutrients and energy, since females have higher reproductive coststhan males for egg formation (O’Dor and Wells 1978). Higher food intake in fe-males would represent an anticipatory response to sexual maturation since somatic

growth stops and aminoacids are mobilized from muscle proteins to supply the de-

Table 4b. Results of progressive elimination Multiple Regression Analyses for AGR and SGR after sexelimination (a–f: coefficients; s.e.: standard error; SEE: standard error of estimation; D.B.: Durbin-Wat-son index)

a b c d e f R ANOVA

s.e. s.e. s.e. s.e. s.e. s.e. R2adj F D.B.

Eq. p-level p-level p-level p-level p-level p-level SEE p-level

5 −2.0135 0.0895 0.5087 −0.0142 0.2997 0.7444

0.5224 0.0423 – 0.0498 0.0012 0.0444 54.64% 71.79 1.36

0.0001 0.03 0.0001 0.0001 0.0001 0.3258 0.0001

6 −1.9757 0.0838 0.0003 0.5065 −0.0142 0.3000 0.7444

2.0319 0.2966 0.0178 0.1260 0.0012 0.0489 54.45% 57.18 1.36

n.s. n.s. n.s. 0.0001 0.0001 0.0001 0.3266 0.0001

7 −2.0178 −0.3057 0.5477 −0.0149 0.3098 0.7293

0.5761 0.0466 – 0.0549 0.0013 0.0490 53.19% 65.63 1.53

0.0003 0.0001 0.0001 0.0001 0.0001 0.3593 0.0001

8 0.9283 −0.7544 0.0272 0.3708 −0.0153 0.3407 0.7320

2.2313 0.3257 0.0196 0.1384 0.0014 0.0537 52.57% 53.10 1.53

n.s. 0.02 n.s. 0.005 0.0001 0.0001 0.3586 0.0001

Eq. 5: Ln( AGR + 14) = Lna + bLn Bw + dT + eT 2

+ fDEq. 6: Ln( AGR + 14) = Lna + bLn Bw + cT Ln Bw + dT + eT 2 + fD

Eq. 7: Ln(SGR + 1,3) = Lna + bLn Bw + dT + eT 2 + fD

Eq. 8: Ln(SGR + 1,3) = Lna + bLn Bw + cT Ln Bw + dT + eT 2 + fD

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mands of vitelogenesis (O’Dor and Wells 1978). Final female maturation seems tobe partially reached at the expenses of the body muscles and the digestive gland(Cortez et al. 1995b). The observed differences in growth and/or food intake be-tween males and females mentioned above were not reflected in our results, prob-ably because the data were taken altogether. To separate the growth and food in-take data related to sexual maturity is practically impossible, due to the lack of external morphological features that made it clear. If we had been capable of sepa-

rating these data, we would probably have found some differences because of sex.Furthermore, the physiological and environmental conditions of the experiment(captivity and isolation in individual experimental tanks) had some influence.

Unlike differences in sex, diet is a very influential factor in growth and foodintake. Diet digestibility and nutrient assimilation ultimately determine the nutri-tional value of a particular food. A diet rich in nutrients is not practical if the nu-trients cannot be adequately assimilated and utilized (Lee 1994). At a macronutri-ent level, crabs offer a similar protein source to bogue but are poorer in lipids(Table 2). Only a few data exist concerning digestibility, assimilation and nutrientutilization in cephalopods. Lee (1994) pointed to a 96% protein and 46% lipid di-gestibility for O. vulgaris. O’Dor et al. (1983) indicated low lipid digestibility anda poor capacity to oxidize it. It seems clear then that this strictly carnivorous spe-cies has capacity to digest and assimilate protein rapidly. Both diets used in thiswork have similar protein levels, although the P/E ratio was higher in crabs. This,

Table 4c. Results of progressive elimination Multiple Regression Analyses for AGR and SGR after sexand diet elimination (a–e: coefficients; s.e.: standard error; SEE: standard error of estimation; D.B.:Durbin-Watson index)

a b c d e R ANOVA

s.e. s.e. s.e. s.e. s.e. R2adj F D.B.

Eq. p-level p-level p-level p-level p-level SEE p-level

9 −2.2778 0.1441 0.5185 −0.0146 0.6830

0.5687 0.0453 – 0.0543 0.0013 45.96% 67.64 1.12

0.0001 0.0016 0.0001 0.0001 0.3557 0.0001

10 −7.1700 0.8731 −0.0448 0.8079 −0.0138 0.6937

1.9877 0.2876 0.0174 0.1249 0.0013 47.23% 53.59 1.20

0.0003 0.002 0.01 0.0001 0.0001 0.3515 0.0001

11 −2.3449 −0.2493 0.5578 −0.0152 0.6716

0.6208 0.0494 – 0.0593 0.0014 44.39% 63.54 1.30

0.0002 0.0001 0.0001 0.0001 0.3883 0.0001

12 −4.9698 0.1418 −0.0240 0.7131 −0.0148 0.6743

2.1934 0.3174 0.0193 0.1378 0.0015 44.53% 48.16 1.34

0.05 n.s. n.s. 0.0001 0.0001 0.3878 0.0001

Eq. 9: Ln( AGR + 14) = Lna + bLn Bw + dT + eT 2

Eq. 10: Ln( AGR + 14) = Lna + bLn Bw + cT Ln Bw + dT + eT 2

Eq. 11: Ln(SGR + 1,3) = Lna + bLn Bw + dT + eT 2

Eq. 12: Ln(SGR + 1,3) = Lna + bLn Bw + cT Ln Bw + dT + eT 2

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together with the low lipid digestibility, shows that protein is the main energysource for O. vulgaris. The better growth obtained with crabs may be explained bythe dominance of amino acid metabolism and its use for energy. In this way, Lee(1994) suggested that the P/E ratio might not be accurate for establishing the en-ergetic requirements in cephalopods. A better way would be to ascertain the aminoacid balance. This might provide information as to which amino acids are best forobtaining energy for routine metabolism (proline, aspartate, arginine) and thosewhich are essential for protein synthesis. Therefore, the differences in growth and

food intake observed in this work might be related to the diet lipid content, proteinquality and amino acid composition. This, together with the greater intake of crabs,might explain the lower FE values obtained with crabs than with bogue, eventhough the former led to higher growth, together with a higher food intake forcrab-fed octopuses. This greater preference for crabs compared to fish could be ex-plained by differences in pre-ingestional (size, shape, texture, flavour) and/or post-ingestional (digestibility, assimilation or energetic benefit) stimuli (Lee et al. 1991;Castro et al. 1993). Interestingly, García García and Aguado Giménez (2002) ob-tained better growth results with bogue than with sardine (19.64% lipid; 15.02 P/Eratio for sardine), using the same methodology employed in this work. DeRusha etal. (1989) found that in general octopuses grew better with fresh shrimps than fro-zen shrimps and better with shrimps or crabs than fish (Nixon 1966). Cagnetta and

Sublimi (1999) obtained similar results feeding with crabs, fish and tattler. Growthin octopuses is not linear but exponential with the initial faster growth and higher

Table 5a. Results of progressive elimination Multiple Regression Analyses for AFR and SFR (a–g: co-efficients; s.e.: standard error; SEE: standard error of estimation; D.B.: Durbin-Watson index)

a b c d e f g R ANOVA

s.e. s.e. s.e. s.e. s.e. s.e. s.e. R2adj F D.B.

Eq. p-level p-level p-level p-level p-level p-level p-level SEE p-level

13 −5.6669 0.5141 0.5270 −0.0132 1.1133 0.0039 0.88920.5998 0.0480 – 0.0564 0.0014 0.0502 0.0488 78.62% 173.83 1.03

0.0001 0.0001 0.0001 0.0001 0.0001 n.s. 0.3676 0.0001

14 −8.8963 0.9963 −0.0393 0.7173 −0.0128 1.0799 0.0071 0.8903

2.2897 0.3334 0.0200 0.1418 0.0014 0.0550 0.0487 78.72% 145.93 1.07

0.0001 0.001 n.s. 0.0001 0.0001 0.0001 n.s. 0.3664 0.0001

15 −1.0615 −0.4858 0.5270 −0.0132 1.1133 0.0039 0.8564

0.5998 0.0480 – 0.0564 0.0014 0.0502 0.0488 72.77% 126.61 1.03

n.s. 0.0001 0.0001 0.0001 0.0001 n.s. 0.3673 0.0001

16 −4.2908 −0.0036 −0.0292 0.7173 −0.0128 1.0799 0.0070 0.8578

2.2897 0.3334 0.0200 0.1418 0.0014 0.0550 0.0487 72.90% 106.38 1.07

n.s. n.s. n.s. 0.0001 0.0001 0.0001 n.s. 0.3664 0.0001

Eq. 13: Ln( AFR) = Lna + bLn Bw + dT + eT 2 + fD + gS

Eq. 14: Ln( AFR) = Lna + bLn Bw + cT Ln Bw + dT + eT 2

+ fD + gS Eq. 15: Ln(SFR) = Lna + bLn Bw + dT + eT 2 + fD + gS

Eq. 16: Ln(SFR) = Lna + bLn Bw + cT Ln Bw + dT + eT 2 + fD + gS

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food intake being followed by slower growth (Forsythe and Van Heukelem 1987;Forsythe and Hanlon 1988). In each phase, nutritional requirements are different.Since in natural conditions octopuses select their prey according to environmentalconditions, resources availability, season, time of the day, body weight, sex andmaturation (Nigmatulin and Ostapenko 1976; Cortez et al. 1995a), a mixed dietwould adjust better to the nutritional requirements in each growth phase and bringbetter results than a monodiet (Smale and Buchan 1981; Cagnetta and Sublimi

1999).Body weight and temperature are the main variables that influence growth andfood intake. As in many other cultured species, growth and food intake are propor-tionally higher in small individuals (García García 1994). Temperature dependencewas high and the optimum ranged between 16–21 °C for commercially viablegrowth. Above and below this range, growth and food intake decreased, whileabove 23 °C weight loss and mortality were recorded. Smaller individuals weremore sensitive to temperature than bigger, and lost weight earlier. Bogue-fed speci-mens were also more sensitive to high temperature and began to lose weight before(23.5 °C) crab-fed animals (25 °C) (Figure 1). This may have been due to the higherfood intake and greater P/E ratio in crab-fed octopuses, which were capable of re-sisting the temperature effects for a longer period of time. Aguado et al. (2001)described the marked influence of temperature on survival during capture, transportand maintenance, and found a highly significant relationship between survival and

Table 5b. Results of progressive elimination Multiple Regression Analyses for AFR and SFR after sexelimination (a–f: coefficients; s.e.: standard error; SEE: standard error of estimation; D.B.: Durbin-Wat-son index)

a b c d e f R ANOVA

s.e. s.e. s.e. s.e. s.e. s.e. R2adj F D.B.

Eq. p-level p-level p-level p-level p-level p-level SEE p-level

17 −5.6577 0.5137 0.5266 −0.0132 1.1135 0.8892

0.5877 0.0476 – 0.0560 0.0014 0.0500 78.71% 218.23 1.03

0.0001 0.0001 0.0001 0.0001 0.0001 0.3666 0.0001

18 −8.8655 0.9934 −0.0291 0.7157 −0.0127 1.0805 0.8903

2.2752 0.3311 0.0199 0.1411 0.0014 0.0548 78.81% 175.86 1.07

0.0001 0.003 n.s. 0.0001 0.0001 0.0001 0.3657 0.0001

19 −1.0524 −0.4862 0.5266 −0.0132 1.1135 0.8564

0.5877 0.0476 – 0.0560 0.0014 0.0500 72.88% 158.94 1.03

n.s. 0.0001 0.0001 0.0001 0.0001 0.3657 0.0001

20 −4.2602 −0.0065 −0.0291 0.7157 −0.0127 1.0805 0.8578

2.2752 0.3321 0.0199 0.1411 0.0014 0.0548 73.01% 128.20 1.07

n.s. n.s. n.s. 0.0001 0.0001 0.0001 0.3657 0.0001

Eq. 17: Ln( AFR) = Lna + bLn Bw + dT + eT 2

+ fDEq. 18: Ln( AFR) = Lna + bLn Bw + cT Ln Bw + dT + eT 2 + fD

Eq. 19: Ln(SFR) = Lna + bLn Bw + dT + eT 2 + fD

Eq. 20: Ln(SFR) = Lna + bLn Bw + cT Ln Bw + dT + eT 2 + fD

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temperature. Nevertheless, no statistical differences were found between mortalityand diet in this work. Within survival temperature range, O. vulgaris responded totemperature rises by increasing food intake and growth (Mangold 1983). Octopus

vulgaris culture then must be restricted to seasons or areas in which temperaturedoes not surpass critical survival point.

Wells et al. (1983) and O’Dor et al. (1983) pointed to great individual variationsin growth, food intake and nutritional use in Octopus vulgaris. Such variations were

even higher when octopuses were held together, when territorial interactions andeven cannibalism occurred. In fish, it is usual to work with large experimentalgroups, which minimize the effect of widely scattered data. This great variabilitymay be the cause of our lower adjusted determination coefficients (R 2adj) whenrelative indexes (SGR and SFR) were considered. In some of our equations, thetemperature–body weight interaction coefficient was not significantly different fromzero, for either growth or food intake models. Alternatively, standard errors of es-timations or coefficients were higher and adjusted determination coefficient werelower than in selected equations. In fish, findings concerning the joint effect of fishsize and temperature on growth and food consumption vary greatly (Liu and Cui1998). Imsland et al. (1996) found a significant influence of the interaction of bodyweight and temperature on growth and food intake in Scophthalmus maximus. Inother fish like Pomatomus saltatrix (Buckel et al. 1995), Channa ar gus (Liu andCui 1998) or Sparus aurata (García García 1994), this interaction was significant

Table 5c. Results of progressive elimination Multiple Regression Analyses for AFR and SFR after sexand diet elimination (a–e: coefficients; s.e.: standard error; SEE: standard error of estimation; D.B.:Durbin-Watson index)

a b c d e R ANOVA

s.e. s.e. s.e. s.e. s.e. R2adj F D.B.

Eq. p-level p-level p-level p-level p-level SEE p-level

21 −6.6394 0.7165 0.5631 −0.0144 0.5847

1.0371 0.0826 – 0.0991 0.0024 33.34% 40.18 0.38

0.0001 0.0001 0.0001 0.0001 0.6487 0.0001

22 −27.5680 3.8354 −0.1920 1.8011 −0.0111 0.6650

3.3843 0.4897 0.0297 0.2127 0.0023 43.26% 45.79 0.71

0.0001 0.0001 0.0001 0.0001 0.0001 0.5984 0.0001

23 −2.0341 −0.2834 0.5631 −0.0144 0.4023

1.0371 0.0826 – 0.0991 0.0024 15.10% 14.93 0.38

n.s. 0.0007 0.0001 0.00014 0.6487 0.0001

24 −22.9629 2.8354 −0.1920 1.8011 −0.0111 0.5382

3.3843 0.4897 0.0297 0.2127 0.0023 27.73% 23.55 0.71

0.0001 0.0001 0.0001 0.0001 0.0001 0.5984 0.0001

Eq. 21: Ln( AFR) = Lna + bLn Bw + dT + eT 2

Eq. 22: Ln( AFR) = Lna + bLn Bw + cT Ln Bw + dT + eT 2

Eq. 23: Ln(SFR) = Lna + bLn Bw + dT + eT 2

Eq. 24: Ln(SFR) = Lna + bLn Bw + cT Ln Bw + dT + eT 2

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only for growth. On the other hand, this interaction was not significant either forgrowth or temperature in Gasterosteus aculeatus and Phoxinus phoxinus (Wooton

Figure 1. Estimation of AGR (Eq. 5) according to experimental temperature range and body weight, forboth types of diet and for individuals of 500 and 2,000 g Bw.

Figure 2. Estimation of AFR (Eq. 17) according to experimental temperature range and body weight,for both types of diet and for individuals of 500 and 2,000 g Bw.

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et al. 1980) and Siniperca chuatsi (Liu and Cui 1998). In fish, the influence of theinteraction between body weight and temperature on growth implies that optimum

temperature decreases as body weight increases (Pedersen and Jobling 1989; Fonds

Figure 3. Estimation of FE (from Eqs. 5 and 17) according to experimental temperature range and bodyweight, for both types of diet and for individuals of 500 and 2,000 g Bw.

Figure 4. Mortality according to diet and accumulated mortality.

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et al. 1992; Imsland et al. 1996; Liu and Cui 1998; Jonassen et al. 1999). Accord-ing to our results, optimum temperature for growth and food intake in Octopus vul-

garis did not depend on body weight. The optimum temperature for growth was17.5 °C and 20 °C for food intake, while maximum food efficiency was achieved ata lower temperature, (16.5 °C). These results reflect those obtained with many cul-tured fish, in which food intake increases with temperature until a maximum value

is reached, decreasing afterwards; this temperature is usually higher than the opti-mum growth temperature and even higher than the optimum temperature for foodefficiency. This later decreases while body weight increases when temperature isconstant (Elliott 1975; Jobling 1994; Koskela et al. 1997). The fact that optimumtemperature for growth and food intake do not depend on body weight in Octopus

vulgaris may be related to its short life cycle and because it behaves as an estheno-therm species.

The growth and food intake equations obtained in this work reveal the influenceof key factors (e.g. temperature and diet) for commercial culture success, and pro-vide an overall vision of the evolution of O. vulgaris growth under Mediterraneanenvironmental conditions.

Acknowledgements

This project has been supported by Planes Nacionales de Acuicultura (JACUMAR),Spain.

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Growth and Food Intake Models in Octopus Vulgaris

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