RAINBOW TROUT {SALMO IRIDEUS) PRODUCED IN FINLAND 11. The effect of different food on the growth of rainbow trout Jorma J. Laine, *Kerttu Östring & Fritz P. Niinivaara University of Helsinki, Institute of Meat Technology, and *Medical Research Laboratory of Messrs. Lääke Oy., Turku. Received December 19, 1966 For practical purposes, the ocean is even today a limitless source of animal protein highly suitable for the human diet (Chapman 1966). However, production is increasing most rapidly in the tropical and subtropical seas, where large unutilized resources are known to exist. Finland is not self-supporting in fish production, and in 1962 the country imported 39.8 million kilograms of fish, of which 17.0 million kg were for human and 22.8 million kg for animal consumption (Anon. 1965). In order to reduce such imports, all the possibilities concerning economic fish cultivation in Finland should be studied. This country posseses good natural possibilities for fish cultivation, and rainbow trout has already been commercially cultivated. Rainbow trout is the sole salmonid species used for cultivation (Mann 1961). It requires water with a depth of at least 1.3 to 2 metres and a temperature under 20°C and sufficient oxygen. Feeding can consist either of the natural food production of the pond or of artificial feeds, as is the case in commercial enterprises (Mann 1961). Through a selection of rapidly growing specimens with high food conversion it has been possible to obtain, by means of intensive feeding, fish having a weight of 200 g within 15 to 18 months. The size of trout for food purposes depends upon the market demand. In Germany, for instance, the following sizes of food trout are distinguished: dinner trout 130—170 g, portion trout 200—500 g, salmon trout 500—2000 g (Mann 1961). The purpose of this study was to investigate three artificial dry foods in a feeding trial performed in trout rearing nets with trouts weighing 50 g at the beginning of the test. 24 Material and methods The trial was carried out between June 22 and September 15, 1966, at Pornainen in the lake of Vermijärvi at a depth of 2.5 metres (Fig. 1). The temperature of the water at a depth of one metre was measured daily in the afternoon. The water was also tested for pH, color, KMn04-consumption and total hardness (Haase 1954), and for coliforms using the MPN- method (Anon. 1958). The test foods consisted of three different artificial dry foods with a 5 mm pellet size Group I was given an imported floating food which was made of white fish meal, dried whey solids, soya bean meal, dried brewers yeast, grass leaf meal, dextrinised wheat flakes, preserved animal fat, cod liver oil, riboflavin, calcium pantothenate, thiamine, choline chloride, A-, D 3-, E-, C and 812-vitaminB 12-vitamin concen- trate, salt, di-calcium phosphate, mangane sulphate, magnesium oxide, cobalt sul- phate, copper sulphate, potassium iodide and sodium ferrite. The mixture contained 36 % crude protein, 4 % crude fat and 4.25 % crude fibre. Croups II and 111 received domestic, nonfloating foods, consisting of white fish meal, whale meat meal, soyabean oil meal, oat meal, wheat bran, dried brewers yeast, milk powder, A, D 3, E, C, and 812B 12 vitamins, thiamine, riboflavin, calcium pantothenate, biotine, choline chloride, salt, ferric sulphate, copper sulphate, cobalt sulphate and potas- sium iodide. The food for Group II contained 39 % crude protein, 2.5 % crude fat and 2.5 % crude fibre; the figures for the food of Group 111 were 37.0 %, 4.0 % and 5 % respectively. At the beginning of the experiment the fish weighed 50 g. and were kept at B.5°C. There were 52 rainbow trout in Groups I and 111 and 60 trout in Group 11. An approximate analysis of the composition of the fish was made at the beginning and at the end of the experiment. Each group was also tested for feed conversion, mortality, and individual and total weights. The trial was performed in trout rearing nets measuring 2.25 x 2.25 x 1.5 metres (Verkkoteollisuus, Hämeenlinna). Fig. 1. Trout rearing nets in the feeding trial 25 Results Results of the water analyses on July 18, 1966 are as follows; P H 6.65 Color (Pt mg/1) Iron (mg/1) 69 0.1 KMn04 -consumption (mg/1) Total hardness (°dH) 61.9 2,36 Total coliforms per gram 2.0 The results indicate that the total numbers of coliforms by the MPN-method did not exceed 2 per gram and the KMn0 4consumption was 61.9 mg/1. The tempe- rature of the water (Fig. 2) was exceptionally high throughout the experiment. The maximum temperature at a depth of 1 m was 26°C and remained over 20°C conti- nuously for 21 days. Approximate analyses of the whole fish were made at the beginning of the experiment. At the end of the experiment both whole and gutted fish were analyzed in each group. The results of the approximate analyses of the test fish were as follows: Water % Protein % Fat % Ash % pH Whole fish (June 22) 77.7 15.6 2.9 2.4 Group I (Sept. 15) whole fish 73.1 16.3 7.4 1.9 6.25 gutted fish 73.9 16.9 4.1 3.1 6.30 Group II (Sept. 15) whole fish 70.4 16.7 7.2 3.7 6.40 gutted fish 75.1 16.8 3.4 3.3 6.28 Group 111 (Sept. 15) whole fish 73.2 16.8 6.3 2.6 6.22 gutted fish 76.1 15.8 4.5 2.5 6.20 The greatest differences between the test groups were in feed conversion and weight (Table 1). Feed conversion per live weight was greatest in Group I and Fig. 2. The temperature of the water at a depth of one metre 26 Table 1. Feed conversion, mortality and weight in different test groups. Number of fish Feed con- At the Sample Dead At the Total Mean Min-max. version/kg start July 15 end weight, weight, weight. Group of live weight grams grams grams I 2.04 kg 52 2 3 47 6240.6 132.78 12.9—220.7 II 1.58 kg 60 2 2 56 9561.4 170.74 68.9—252.8 111 1.76 kg 52 2 3 47 7243.6 154.12 33.6—308.7 smallest in Group 11. In Group II all the fishes gained weight during the experiment In Groups I and 111, on the other hand, there were some losses of weight. Discussion The trial was relatively limited owing to the short test period and the small number of fish. The water used proved to be suitable since the mortality in the different groups was small although the temperature of the water, because of the exceptionally warm summer rose to 26°C and stayed over 20°C for a long time (Fig. 2). When the distribution of fat was studied at the end of the experiment, it was found that most of the fat was situated in the intestines of the fish. In all groups the proportion of fat was higher in the whole fish than in the gutted fish: Group I 7.4 and 4.1 % respectively, Group II 7.2 and 3.4 % and Group 111 6.3 and 4.5%. The ash content of the whole fish depended mostly upon the condition of the intestinal tract. It also depended upon such factors as the size of the fish and the weight of the bones and fins. Since a more extensive study has been made on dif- ferences in the ash content, this aspect will not be further discussed here. When comparing the feed conversion, large differences between the groups are seen (Table 1). In Group II the feed conversion was smallest, 1.58 kg food per kg of live weight; the corresponding figures in Groups 111 and I were 1.76 kg and 2.04 kg respectively. Large differences also existed in the weights of the fish (Table 1). In Group II the mean weight was 170.74 g (range 68.9—252.8 g). This was the only group where all the fishes gained weight during the experiment. In Group 111 the mean weight was 154.12 g (range 33.6—308.7 g). In this group two of the fishes had lost weight during the experiment. In Group I the mean weight was 132.78 g (range 12.9— 220.7 g), four of the fishes in this group had lost weight. Pigment formation was typical for the trout in group I (Fig. 3). In Groups II and 111 the color was too light and in Group 111 some spottiness existed. Summary Three test groups of rainbow trout were cultivated in trout rearing nets to study the feed conversion, mortality and weight development of the different 27 groups. One of the groups was fed with a floating imported food and two groups with domestic non-floating dry food. It was observed that the type of food had a distinct influence upon feed con- version and weight development. It also influenced the pigment formation of the fish but had no great effect on the chemical composition of the fish. There were some differences in the distribution of fat in the different test groups. It was also noted that when water is chemically and microbiologically of good quality, no excessive mortality occurs even when the temperature of the water for a long period exceeds the optimum temperature of rainbow trout. Recognition and appreciation is extended to the Institute of Limnology, University of Helsinki, for making the chemical water analysis in this study. REFERENCES Anon. American Public Health Association, Inc, 1958. Recommended methods for the microbial ex- amination of foods, Albany, N.Y., USA. —» Kalatalouskomitean mietintö. 1965. Helsinki. Chapman, W. M. 1966. Resources of the ocean and their potentialities for man. Food Technol. 20: 45. Haase, L-W. 1954. Deutsche Einheitsverfahren zur Wasser-, Abwasser- und Schlammuntersuchung. Verlag Chemie. G.m.b.H., Weinheim. Mann, Hans. 1961. Fish cultivation in Europe. Fish as food 1: 77. Academic Press, New York. Fig. 3. Pigment formation for the trouts in different groups (1 = Group I 2 = Group 11, 3 = Group III). 28 SELOSTUS: TUTKIMUKSIA SUOMESSA KASVATETUSTA KIRJOLOHESTA (Saima irideus) 11. Rehujen hyväksikäytöstä ja vakutuksesta kirjolohen kasvuun Jorma J. Laine, »Kerttu Östring & Fritz P. Niinivaara Helsingin Yliopisto, Lihateknologian laitos ja *Tieteellinen Tutkimuslaboratorio, Lääke Oy., Turku. Verkkoaltaissa suoritetussa kasvatuskokeessa seurattiin kirjolohen rehunkulutusta, kuolleisuutta ja painonkehitystä kolmessa eri koeryhmässä, jotka saivat ulkolaista kelluvaa ja kahta kotimaista ei - kelluvaa kuivarehua. Havaittiin, että kotimaisilla koerehuilla näytti olevan selvästi edullisempi vaikutus rehunkulutuksen ja painonkehitykseen. Pintapigmentin muodostus oli kuitenkin huonompi. Kalojen kemiallisessa koostumuksessa, kuten rasvan jakautumisessa havaittiin myös pieniä eroja eri koeryhmissä. Koesarja osoitti myös, että mikäli kasvatusvesi kemiallisesti ja mikrobiologisesti on hyvä- laatuista, ei lämpötilan kohoaminen pitkäksikään ajaksi yli kirjolohen optimilämpötilan aiheuttanut kuolleisuudessa epätavallista nousua. Johtopäätösten tekemiseksi koeaika oli lyhyt ja koemateriaali pieni.