Rearing of turbot larvae (Scophthalmus maximus L.) on cultured food organisms and postmetamorphosis growth on natural and artificial food

Aquaculture, 23 (1981) 183-196 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands

183

REARING OF TURBOT LARVAE (SCOPHTHALMUS MAXIMUS L.) ON CULTURED FOOD ORGANISMS AND POSTMETAMORPHOSIS GROWTH ON NATURAL AND ARTIFICIAL FOOD

DIRK KUHLMANN, GERRIT QUANTZ and ULRICH WITT lnstitut Republic

fiir Meereskunde,

(Accepted

Aussenstelte

Biilk, O-2301

Xnischenhagen-Biilk

(Federal

of Germany) 13 June 1980)

ABSTRACT Kuhlmann, D., Quantz, G. and Witt, U., 1981. Rearing of turbot larvae (Scophthalmus maximus L.) on cultured food organisms and postmetamorphosis growth on natural and artificial food. Aquaculture, 23: 183-196. Turbot larvae (Scophthalmus maximus L.) were fed with mass-cultured rotifers (Brachionus plicatilis) and copepods (Eurytemora affinis and Acartia tonsa). The fish preferred copepod nauplii to rotifers. Larvae reached metamophosis between days 30 and 36 at a length of 22 mm at temperatures between 13.2”C and 17.8”C. Survival rate was about 50% from day 3 to the end of metamorphosis. Postmetamorphosis growth was examined for 38 days under comparative feeding programmes using herring meat, living mysids, pelleted trout feed and combinations of trout feed plus mysids and herring meat plus mysids. Mean growth rates varied from 4.7% x d-l (herring plus mysids) to 4.1% x d-l (trout dry feed). The addition of living mysids to the diets positively influenced the growth increase and food conversion rates.

INTRODUCTION

Based on assessments of the biological and economical factors, Purdom et al. (1972) have demonstrated the potential of the turbot (Scophthalmus maximus L.) as a species for marine aquaculture. The successful weaning on to dry diets and postmetamorphosis feeding with artificial feedstuffs for further fattening is described by Purdom et al. (1972), Rahe (1977) and Bromley (1978). The development of turbot production on a commercial scale has been impeded by difficulties in the larval rearing process. Almost all the rearing experiments used rotifers for initial feeding, followed by Artemia nauplii and adults until metamorphosis (Jones, 1972; Ringwell et al., 1977; Howell, 1979). In trials with exclusive Artemia feeding, the survival rates were found to be very low (< 10%) and the time span until metamorphosis very long (up to 70 days). Therefore a key factor, affecting successful propagation, was probably the lack of suitable larval nutrition. Recently, the feasibility of weaning early stage turbot larvae of 6-17 mm (2-3 weeks old) on

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Elsevier Scientific Publishing ChIPanY

184

to commercial salmon starter diets was demonstrated experimentally, obtaining good growth and survival rates from lo-70% during the weaning phase (Bromley, 1978). The partial replacement of Artemia by foodstuffs with variable ingredients contributed to an improvement in the rearing procedure. An alternative approach is seen in the use of different cultured planktonic invertebrates right from the beginning of larval feeding. In the aquaculture station Kiel-Biilk, experiments during recent years have aimed at the establishment of cultures of green algae (Nannochloris), rotifers (Bruchionus plicatilis), calanoid and harpacticoid copepods (Eurytemora affinis, Acartia tonsa and Tigriopus) and mysids (Neomysis integer) (Nellen et al., 1979; Witt et al., 1981). This paper deals with outdoor experiments on the rearing of one generation of turbot larvae on these cultured food organisms up to metamorphosis. Further observations on the weaning and growth of O-group fish on different artificial and natural diets in laboratory experiments are described. MATERIAL

AND METHODS

Larval rearing Eggs of turbot from the Western Baltic Sea (Langeland) were fertilized in filtered sea water (15’ loo S), with a fertilization rate of 83.5%. For incubation the fertilized eggs were spread out on a 500 pm nylon gauze that was mounted horizontally in a partly shaded 2 m3 tank. A constant water flow (300 l.h-’ ) of ambient brackish water was set with a salinity of 15.4°/oo (+ 0.3) and a water temperature of 15.5”C (+ 0.3). This temperaturesalinity combination was found to be close to the optimum for the incubation of turbot eggs of this origin (Kuhlmann and Quantz, 1980). After hatching, the water flow was stopped and the nylon screen removed. Algal suspension (Nannochloris) was added as food for rotifers and copepods. Temperature, S”/oo, pH, NH4 and NO? of the water were measured daily. Mean values and range during the experimental phase were as follows: Temperature: 15.1 + 1.4 (13.2-17.8) “C Salinity : 16.9 + 0.7 (15.6-18.0) o/‘oo pH: 8.7 ? 0.2 (8.408.92) NO* : 7.5 f 6.4 ( 6.6-20.3) c(gl-’ NH,: 67.3 f 49.5 (14.0-201.6) pg.l--’ All data on larval rearing refer to one batch of larvae, hatched in summer 1979. The larvae were measured daily for both total and standard length ‘and wet and dry weight. At the same time, the stomach content and the density of food organisms in the rearing tank were examined. Mortality rates were estimated from numbers of dead larvae regularly siphoned from the tank bottom. Feeding started 3 days after hatching when the following cultured food organisms were added to the rearing tank:

185

(1) (2) (3)

rotifers (Bruchionus pkxtilis) and harpacticoid nauplii (T&riopus) calanoid nauplii (Eurytemora affinis (80%) and Acartia tonsa (20%)) and adult calanoid copepods (E. @finis and A. tonsu) and cladocerans (Podon).

Post-metamorphosis rearing At the end of the larval rearing experiments the metamorphosed turbots were weaned on to different diets. A closed laboratory system with bypassed filtering through activated carbon was used. Four white polyethylene aquaria with a volume of 40 1 each, were connected with a 200 1 reservoir, the filter rate was 515 l*h-’ and the water flow through the holding tanks was set at 30 l.h-‘. The mean temperature was 18.0 + 0.9”C and no artificial light was used. Each holding tank was stocked with 15 turbots. One of the aquaria was divided into two departments, each stocked with 7 turbots. The foods used were: (1) herring meat, cut from frozen fish caught during spring spawning in the Kiel-Fjord, (2) trout dry feed, 1 mm and 2 mm pellets (47% protein, 8% fat), (3) living mysids (Neomysis integer) from outdoor cultures, (4) combination of 50% Neomysis and 50% dry trout feed, (5) combination of 50% Neomysis and 50% herring meat. After an adaption period of 12 days, all groups of fish accepted the diets and were fed twice daily. The daily rations were then set at 5% (dry weight) of food per total weight of fish, corresponding to 25% wet weight of foods for all wet foods and 10% of total wet weight of fish for dry foods. This was necessary to compensate for the different bulks of foods offered. The daily rations were recalculated from the daily amount of food taken up by the fish (Table IV). Food conversion was calculated as dry weight of food per gain of fish wet weight. For daily growth estimates the formula of Winberg (1960) was used:

. 100

Daily growth rate (%) = (W, + w0 )/2

WO = initial weight, wt

T

= final weight,

= time interval in days.

RESULTS

Larval rearing Growth. Larval growth until day 45 after hatching is shown in Fig. 1. The dry weights in Table I are partly measured and partly calculated from total

186

length-weight correlation formulae of Jones (1972), which correspond well with the present data. Dry weight was determined to be 20% of the wet weight. From daily growth rates (Winberg, 1960) for different periods (Table II) it can be seen that, after an initial stagnation of the weight until the start of feeding at day five, the larvae were growing very quickly during the first days with a maximum growth rate of 23.0%-d-‘. The rates then decreased slightly with the approach of metamorphosis (day 30-36). During metamorphosis the growth rate decreased to 7.2%.d-’ (Table II). This is also demonstrated by the length growth curve (Fig. 2). Food. A mixture of rotifers (Brachionus) and copepod nauplii (Eurytemora, Acartia) was offered to the larvae from the third day on. The average food concentrations were: Bruchionus 3.2 individualsml-‘, nauplii 2*ml-‘, copepodites and adults 0_7ml-’ and Podon < O.OSml-‘ . During the light phase, no distinct rhythm of food intake was observed. The number of food organisms in the stomachs of larvae sampled every 2 hours during the light phase of 3 days increased towards the evening. The same findings were reported by Last (1978) for other species of pleuronectiform larvae. It became obvious from stomach analysis (Table I), that after the 14th day larger organisms (mainly copepods) were ingested in preference to the smaller nauplii. The dry weight of stomach contents correspond well with the mean dry weights of the larvae until day 30 (4.7 t 1.85%) (Fig. 3). From day 30 to day 36 they decreased relative to the weight of the turbots (Fig. 1). In this period most of the larvae completed metamorphosis and moved to the bottom. Riley (1966) described similarly declining ingestion rates during metamorphosis for the plaice, Pleuronectes platessa. The decreased food intake resulted in a slower growth rate. Mortality. The viable hatch during the breeding period under the given temperature and salinity regimes was close to 50% (Kuhhnann and Quantz, 1980). The experiment was started three days after hatching with a batch of approximately 500 larvae in the rearing tank. In the course of the trial 200 of them were taken for stomach analysis and measurements. These larvae were taken into consideration for further calculations. Highest mortality of about 40% occurred between day 17 and 22, the time during which the swimbladder was filled (Fig. 2). At the end of this period the overall survival rate was estimated to be about 50%. No further mortality was observed. About 40% of the remaining 160 juveniles exhibited incomplete or no pigmentation, but this had no influence on their vitality and growth.

dry weight

187

mu 100

-j

10 5

1.0 0.5

0.1 0.05

0.01 0.005

0.001 3

5

10

15

20

25

30

35

40

45

days

Fig. 1. Weight growth (*-) and stomach contents (0-C) (mg dry weight) until day 30. Stomach contents are mean values of five individuals each.

% su lrvi

total

length

100

,30mm

75

50

25

0

I

I

3

5

I

lo

15

20

25

30

I

35

I

40

Fig. 2. Length growth (with SD.) and survival (a-a) tion of mortality is started at day 3.

days

until day 45 after hatching. Registra

12 29 9 25 35 7 5 5 4 5 9 5 5 5 5 4

9

Larvae invest.

-

0.1 -

-

7.8 -

0.6 -

4.5 8.8 14.0 10.8 39.8 20.0 25.0 32.5 3.0 -

-

-

0.042 0.040 0.50 0.074* 0.101* 0.116* 0.170* 0.186* 0.268* 0.484* 1.10* 3.76 11.4 20.4 26.8 31.6 70.4 0.15

10.5

-

-

-

-

Harpact

5.0 4.3

0.2 0.7 2.2 12.0 12.8 28.0 -

-

-

-

Podon

1

-

Insect larvae (Corethra)

Average

1.3 2.6 7.0 4.0 14.4 11.6 13.0 20.6 54.3 175.2 290.8 761.0 217.0 207.0 1708.0

-

stomach ‘Ontent (pg dry weight)

Dry weights of food organisms: (own measurements) Eurytemora affinis nauplii 0.3 Ilg Copepodites + adults 3.5 rg Brachionus plicatilis 0.5 /Jclg Harpacticoides 2.5 fig Podon sp. 12.0 pg Corethra (insect larva) 1260.0 Irg

0.8 0.1 0.7 1.6 0.8 0.7 6.6 8.9 39.2 121.4 62.0 42.0 106.0

-

ad. Cop.

3.38 3.51 3.59 3.82 4.10 4.20 4.56 4.63 5.02 5.70 6.90 10.66 15.32 18.52 21.5 22.6 29.4

Nauplii

(mm) Brach.

Dry weight Stomach content (n)

(mz)

TL

*Calculated after Jones (1972): In W = 4.6699 In L - 7.2446 (< 7 mm) In W = 3.0575 In L - 4.3013 (> 7 mm)

3 4 5 6 7 8 9 10 12 14 17 22 26 30 33 36 45

Days from hatching

Growth and stomach content (average number and dry weight of food organisms per larvae) of turbot larvae

TABLE I

E oc

189 TABLE II Growth

of turbot

larvae from hatching

until metamorphosis

Growth period (days after hatching)

Daily growth rates (W weight increase per day, after Winberg, 1960)

3- 4 3- 5 5-10 10-17 17-22 22-30 30-36 36-45

-4.9 a.7 23.0 20.3 21.9 17.2 7.2 8.4

larval dry weight

[pi]

100

1000

2 Ig larval

Fig. 3. Larval dry weight 0.96 lg x - 1.24.

Post-metamorphosis

is completed

dry

10000

3 weight

in relation

to stomach

content

until day 30. (P = 0.97) lg y =

growth

Weaning. During weaning the young fish accepted all new diets quickly. Even dry pellets (1 min) were consumed within one week. The number of pellets taken was less than the number of living mysids or pieces of herring meat eaten.

At the end of the weaning phase two length-groups had been established by the differences in food intake. Those being fed with natural diets started at a length of 4.6 cm (range: 4.2-5.0 cm), and those which had been fed on dry feed and the mysids + dry feed mixture started with 4.0 cm (range: 3.4-4.3 cm). Growth. The mean total lengths of the fish from the different feeding regimes are shown in Fig. 4, the corresponding data are given in Table III. The different feeding on the follow_ing 38 days resulted in significantly different final weights of the fishes (F = 29.56; Fao4s = 3.74; P = 0.01). The best growth in weight and length (Fig. 4 and Fig. 5) was obtained by feeding a mixture of herring and mysids closely followed by herring meat. Turbot fed only on artificial diets showed the poorest growth rate, while a 50% replacement by living mysids increased the average final weight significantly from 4.7 g to 6.9 g (F = 35.62; F1.17 = 8.40; P = 0.01 (Fig. 5)). The daily growth rates and food conversion over the 38 days are given in total length mysids+ herring

Clll

herrinp mysids myrids+ trout feed

trout

;

5I

101

15I

20I

25I

3011

35

4011

45

50I

feed

55I days

Fig. 4. Length increase of O-group turbot during feeding experiments at 18°C.

Length (cm) Weight(g)

Length (cm) Weight (g)

Length (cm) Weight (g)

Length (cm) Weight (g)

Length (cm) Weight(g)

13

23

30

41

51

7.9 9.7

6.9 6.1

6.2 3.9

5.5 2.9

4.6 1.7

3.4 0.8

z

4.6 1.6 5.1 2.3 5.7 3.3 6.5 4.7

0.10 0.25 0.15 0.43 0.17 0.56

4.0 1.0

3.4 0.8

z

0.10 0.24

0.10 0.22

0.12 0.20

0.09 0.12

0.08 0.05

0.05

0.05

S.E.

Group II fed with trout feed

0.12 0.16

0.07 0.09

0.04 0.05

S.E.

Group I fed with herring meat

*Days of exp. + 52 = age of fish.

Length (cm) Weight (g)

0

Days of experiment*

Length and weight data of O-group turbot during feeding experiments

TABLE III

7.8 7.6

7.1 5.9

6.3 3.9

5.6 2.7

4.6 1.6

3.3 0.8

f

0.06 0.19

0.04 0.13

0.04 0.10

0.07 0.12

0.07 0.07

0.04 0.03

S.E.

Group III fed with mysids

7.3 6.9

6.6 4.9

5.9 3.1

5.1 2.0

4.0 1.3

3.3 0.8

0.86 0.22

0.08 0.15

0.11 0.14

0.08 0.12

0.06 0.13

0.05 0.04

Group IV fed with mysids + trout feed f S.E.

8.3 10.8

7.2 6.8

6.2 4.0

5.5 2.9

4.6 1.8

3.3 0.8

0.20 0.85

0.17 0.59

0.18 0.37

0.14 0.27

0.12 0.22

0.03 0.05

Group V fed with mysids + herring meat F S.E.

mysids

WOt

+

herring

weight III

having

mysids mysids+

04 0

I

I

5

lo

,

15

,

20

I

25

,

30

trout

ford

trout

fend

8

(

I

I

I

35

40

45

50

55

dus

Fig. 5. Weight increase of O-group turbot during feeding experiments

at 18°C.

Table IV. The average daily weight increase ranged from 0.10 g*d-’ using dry trout feed up to 0.24 g*d-’ using mysids-herring mixture. Similarly, the overall weight increase was 370% of the initial weight using trout feed and 500% using the mysid-herring mixture. The food conversions were quite variable from week to week in the different feeding groups (Table IV). Relatively poor conversion rates were found for fish fed with dry pellets and the best conversion with a value of 0.54 was obtained by feeding with herring meat. DISCUSSION

The most common method for rearing fish larvae is based on the food organisms Bruchionus and Artemia nauplii. Instead of the relatively artificial food organism Artemia, we alternatively offered mass-cultured zooplankton

193 TABLE IV Daily food rations, weight increase, growth rates and food conversion of O-group turbot fed with different natural, artificial and combined foods

Daily food rations (%) Daily weight increase (g.day-’ )

Daily growth rates (%) (after Winberg, 1960)

Food conversion (food dry weight/gained wet fish weight)

Days of experiment

Group I fed with herring meat

Group II Group III fed with fed with trout meat mysids

Group IV fed with mysids + trout feed

Group V fed with mysids + herring

13-51

4.2

8.2

4.5

7.9

4.9

13-23 23-30 30-41 41-51

0.12 0.14 0.20 0.36

0.06 0.10 0.10 0.14

0.11 0.17 0.18 0.17

0.07 0.16 0.16 0.20

0.11 0.16 0.25 0.40

13-51

0.21

0.10

0.16

0.15

0.24

13-23 23-30 30-41 41-51

5.22 4.12 4.00 4.56

4.62 5.13 3.57 3.50

5.12 5.15 3.67 2.52*

4.25 6.27 4.00 3.39*

4.68 4.64 4.63 4.55

13-51

4.58

4.07

4.10

4.39

4.72

13-23 23-30 30-41 41-51

0.77 0.88 0.56 0.36

1.56 1.50 1.45 1.33

0.70 0.66 0.96 0.77

2.04 0.81 1.13 1.08

1.03 0.79 0.63 0.40

13-51

0.54

1.43

0.80

1.16

0.60

*The supply with mysids could not be kept up; the daily ration during day 45-51 at 2.5% mysids.

was set

organisms of the larvae’s natural environment. With this, possible nutritional deficiencies may best be avoided. In Japan, the food combination of rotifers and copepods is already successfully employed in the rearing of sea fish. From first feeding to metamorphosis, the turbot larvae showed clear food preferences: In spite of high concentrations, Brachionus played an insignificant, role when offered together with copepod nauplii. The cladoceran Podon, which appeared in much smaller densities, was selectively taken by older larvae. This corresponds well with observations by Last (1979) on turbot larvae caught in the North Sea and may be explained by the higher attraction the big Podon may have to the fish. The walls and bottoms of the tanks were densely colonised by harpacticoids, but these copepods were found in the stomachs only on two occasions. Comparable growth data are available from Howell (1979) and Scott and Middleton (1979), who reared turbot larvae at 17°C and 16°C respectively. Howell (1979) reported a length of 8 mm at day 17 compared with 6.9 mm

194

in our study. In Scott and Middleton’s (1979) growth experiments with different species of algae added to the food, the larvae grew to a maximum of 11.5 mm until day 31, whereas in our trial mean length was 19.6 mm at that time. Contrary to survival rates of about 50% from day 3 to the end of metamorphosis in our experiments, Kingwell et al. (1977) reported an average survival of 15.1% for the period from day 2 to day 20 and Jones et al. (1974) achieved maximum survival of 4.6% from day 7 until metamorphosis. First mortality, which occurred on days 8 to 10 (7.6%), was supposed to be due to starvation (Jones, 1972), but as the density of food organisms was high, some larvae possibly did not learn or were not able to ingest food. Mortality was highest from day 17 to 22, probably caused by difficulties in filling the swimbladder. Purdom et al. (1972) suggested that such difficulties may be due to low oxygen tension, although in our tanks a constant oxygen saturation was measured. Further studies of this phenomenon are necessary for future efforts in reducing mortality. Hatching to metamorphosis lasted 30-36 days in our experiment. This is much shorter than the period of 45-70 days found by Jones (1972) at a similar rearing temperature. The present data were gained from only one generation of turbot larvae. They do however, indicate that the chosen breeding and feeding strategies and the quality of the food organisms were responsible for the good growth and survival rates, as well as for the short time period from hatching to metamorphosis. After metamorphosis, it is no longer practicable to meet the food requirements of the ongrowing turbots by living food organisms because the fish can be weaned easily and quickly on to artificial feed or on natural diets in various forms (see also Deniel, 1976; Bromley, 1978). Owing to the voracious feeding behaviour of the turbots no great losses of food occur. As both herring meat and pelleted trout feed are available without difficulty they were chosen as the main diets. The results showed that the commercial trout feed was not as efficient for turbot nutrition as herring meat or living mysids. Although a part of the final differences in the size of the fish may be induced by the inequalities at the end of weaning the overall growth rates and the daily weight increase were markedly high in groups fed with natural diets. The partial replacement of trout feed by living mysids clearly increased the growth rates and the food conversion rates. Such an effect, though less pronounced, was also observed when herring meat was partly replaced by mysids. During the controlled feeding and growth experiments as well as over the following 3 months no mortality occurred. No comparison with available data on O-group turbot growth was possible because of variations of the feeding and temperature regimes in experiments described by other authors. Although this growth experiment lasted for 51 days only, it resulted in

195

information on the nutritional requirements of young turbots, and demonstrated the possibility of achieving good growth of the fish when fed on natural diets under controlled rearing conditions. As long as a pelleted dry feed, adjusted to the‘turbot% requirements, is not available, the diets made of fish and fish waste cannot be replaced. It was found that a small addition of living food organisms to the diets may have a measureable and positive influence on growth. ACKNOWLEDGEMENT

We wish to thank Prof. W. Nellen for his helpful discussion and review of the manuscript. The study was financed by the Federal Ministry for Research and Technology (Project “Marine Bioproduktion” MFE 0320/7). REFERENCES Bromley, P.J., 1978. The weaning of hatchery reared turbot larvae (Scophthalmus maximus L.) on a dry diet. Aquaculture, 13: 339-345. Deniel, C., 1976. Growth of O-group turbot (Scophthalmus maximus L.) fed on artificial diets. Aquaculture, 8 : 115-l 28. Howell, B.R., 1979. Experiments on the rearing of larval turbot, Scophthalmus maximus L. Aquaculture, 18: 215-225. Jones, A., 1972. Studies on egg development and larval rearing of turbot, Scophthalmus maximus L., and brill Scophthalmus rhombus L., in the laboratory. J. Mar. Biol. Assoc. U.K., 52: 965-986. Jones, A., Alderson, R. and Howell, B.R., 1974. Progress towards the development of a successful rearing technique for larvae of the turbot, Scophthalmus maximus L. In: J.H.S. Blaxter (Editor), The Early Life History of Fish. Springer Verlag, Berlin, Heidelberg, New York, pp. 731-737. Kingwell, S.J., Duggan, MC, and Dye, J.E., 1977. Large scale handling of the larvae of the marine flatfish turbot, Scophthalmus maximus L., and dover sole, Soles solea L., with a view to their subsequent fattening under farming conditions. 3rd Meeting of the I.C.E.S. Working Group on Mariculture, Brest, France, May lo-13,1977. Actes de Colloques du CNEXO, 4: 27-34. Kuhlmann, D. and Quantz, G., 1980. Temperature-salinity effects on the embryonic development and incubation time of the baltic turbot, Scophthalmus maximus L. Meeresforsch., 28 (2). Last, J.M., 1978. The food of four species of pleuronectiform larvae in the Eastern English Channel and Southern North Sea. Mar. Biol., 45: 359-368. Last, J.M., 1979. The food of larval turbot, Scophthalmus mcrximus L. from the central North Sea. J. Cons. Int. Explor. Mer., 38: 308-313. Nellen, W., Koske, P., Lenz, D., Kuhlmann, D. Quantz, G and Witt, U., 1979. Problems of energy transfer in multiple marine aquaculture systems. ICES CM 1979/F: 8, 27 pp. Purdom, C.E., Jones, A. and Lincoln, R.F., 1972. Cultivation trials with turbot (Scophthalmus maximus L.). Aquaculture, 1: 213-230. Rahe, R., 1977. Die Halterung adulter Steinbutts (Scophthalmus maximus L.) in einem rezirkulierenden System. Dipl.-Arbeit, Univ. Kiel. Riley, J.D., 1966. Marine fish culture in Britain. VII. Plaice (Pleuronectesplatessa L.) nauplii and the effects of varying feeding levels. J. Cons., 30: 204-221. Scott, A.P. and Middleton, C., 1970. Unicellular algae as a food for turbot (Scophthalmus masimus L.) larvae - the importance of dietary long-chain polyunsaturated fatty acids. Aquaculture, 18: 227-240.

196 Winberg, G.G., 1960. Rate of metabolism and food requirements of fishes. Fish. Res. Board Canada, 194: 202 pp. Witt, U., Koske, P.H., Kuhlmann, D., Lenz, J. and Nellen, W., 1981. Production of Nary nochloris spec. (Chlorophyceae) in large-scale outdoor tanks and its use as a food organism in marine aquaculture. Aquaculture, 23: 171-181.