Acta Sci. Pol., Piscaria 6 (1) 2007, 15 30

Acta Sci. Pol., Piscaria 6 (1) 2007, 15 30 REARING SEA TROUT (Salmo trutta m. trutta L., 1758) FRY FOR STOCKING FED ON ZOOPLANKTON CAUGHT IN THE OUTLETS OF NATURAL AND ARTIFICIAL BODIES OF WATER Robert Czerniawski 1, Przemys aw Czerniejewski 2 1 University of Szczecin 2 Agricultural University of Szczecin Abstract. Salmonid fishes represent an important component of the fisheries in Poland as well as in other countries. The stocks of salmonid fish in the natural waters depend to a large extent on the feeding conditions of the streams into which their larvae or fry are released. Rearing the fry on artificial diets prior to stocking, in a controlled environment, leads to a higher stocking success, primarily due to better survival rates compared with the free swimming fry. There is a hypothesis, however, that rearing the sea trout fry on a natural diet in the form zooplankton could considerably improve the chance of survival in the stream. Natural diets, contrary to the artificial ones, enhance the fry hunting instincts, which may often become a critical survival factor. This report presents the results of rearing sea trout fry on natural diets, which has been compared with artificial feeding as well. The food reservoir comprised the zooplankton collected from the outlets of an artificial and a natural water body. Key words: diet, fish larvae, rearing, sea trout, stocking, zooplankton INTRODUCTION The outlets of lakes and ponds carry large quantities of planktonic animals, whose biomass can reach several hundred kilograms per day [Szlauer 1977, Czerniawski and Czerniejewski 2003, Trojanowska et al. 2003, Czerniawski 2004, Czerniawski and Wolska 2004, Wolska and Czerniawski 2004]. According to Szlauer [1974], even small streams remove considerable biomass of zooplankton from lakes. This effect has been confirmed by the observation that large numbers of fry concentrate at the outlets to feed on their basic food, the zooplankton. The salmonid fishes have been a valued component of the fisheries for years, both in Poland and worldwide. This has been confirmed by statistics on catches and aquaculture of this particular family [Szczerbowski 1993, Steffens 2001, Füllner 2001 a, b, Bontemps 2004]. Over the recent years, the populations of salmonids have grown substantially due to intensive and regular stocking. However, the quantitative and economical success of the Corresponding author Adres do korespondencji: Dr in. Robert Czerniawski, Department of General Zoology, University of Szczecin, Z. Felczaka 3 C, 71-412 Szczecin, Poland, e-mail: czerniawski@univ.szczecin.pl

16 R. Czerniawski, P. Czerniejewski stocking is limited due to a small number of hatcheries and nursing farms, on the one hand, and by low survival rates of released fry, on the other. From the economical point of view it seems more reasonable to use a more mature form of the stocking material, reared in small streams prior to release. It seems, however, that rearing the fry in a controled environment on natural diets should allow stocking the streams with a salmonid material of a smaller size. Salmonids hatch in cold and clean waters of brooks and rivers, where zooplankton densities are extremely low. Thus, after a long period of yolk sack absorption, they are able to catch tiny invertebrates. Besides the dominant benthic organisms, psychrophilic species of zooplankton are also found in the diet [Leonard and Leonard 1946, Nilsson 1955, Ró a ska 1961]. Wojno [1961], who studied the diet of lake trout in lake Wdzydze, reported the presence of zooplankton. Szlauer [1976], who fed sea trout fry on zooplankton, observed that the fish had foraged intensely throughout the entire period of the experiment and their stomach contents were by weight dominated by typically psychrophilic Cyclops vicinus and Cyclops kolensis. Szlauer and Winnicki [1980] stated that a better stocking success can be achieved if we stock the stream with the fry reared on zooplankton rather than with non-reared fry or those fed on artificial feeds. This is linked to the adaptation of the fry to consume the natural food. Zooplankton is also a valuable source of proteins, amino acids, fat, and enzymes [Ogino 1963, Millamena et al. 1990, Munilla-Moran et al. 1990, Pillay 1990], with the level of protein reaching 54 to 65%, like in some Australian cladocerans [Kibria et al. 1999]. Yurkowski and Tabachek [1979] observed that the level of amino acids in Daphnia pulex and Diaptomus sp. is as high as that required by the fry to grow, or higher. The cited literature allows concluding how important zooplankton is in the feeding of the hatchery fry. The aim of this study consisted in indicating the usability of zooplankton in fish fry rearing as well as examining the growth rate of body length and weight and making behavioural observations of the sea trout fry as a potential stocking material, fed on either zooplankton carried from natural or artificial water bodies or on artificial diets. MATERIAL AND METHODS The experiment began on 18 March 2004, when 13 aquaria were stocked with 100 16-day sea trout larvae each. After a week, i.e. as soon as 2/3 yolk had been absorbed from yolk sacks and when the fry were observed to come to the surface, the fish were provided with their first food. The fry fed on zooplankton were placed in ten equal-size aquarium tanks. Five tanks, marked with the letter A, were used for the fry fed on the zooplankton carried from lake P o. The fry fed on the zooplankton carried from the other body of water, the second reclaimed water holding pond of the Police Chemical Plant wastewater treatment facility, were stocked in another 5 tanks, marked as B. Sea trout fry placed in the remaining three tanks represented the control group. In the two of these, marked Acta Sci. Pol.

Rearing sea trout... 17 with the letter C, the fry were fed entirely on a starter feed for salmonid fry containing 52% protein and 13% fat, produced by Dana Feed [Bontemps 2004]. In the third tank, the fry were fed on both the feed and zooplankton. The rearing cycle in all the tanks took 4 weeks. The densities applied in each tank were 2.9 fish dm 3, water volume 35 dm 3 with 25 cm water column. According to Goryczko [2001], the key to successful rainbow trout fry rearing is in everyday thorough cleaning of tanks [or ponds], i.e. removal of feed remnants, faeces, and dead fish. This rule was also obeyed in our experiment on the sea trout; 2/3 of water volume was exchanged daily and the bottom was cleaned of deposits with a plastic hose. On the first day of feeding, i.e. 25 March 2004, 100 fry were weighed and measured for length in order to estimate the mean fry total length, which was 22.6 mm, and the mean body weight, 0.0971 g. After each week of the rearing cycle, 10 larvae from each tank were caught with the hose to be measured for weight and length, which was carried out within about 10 minutes following the capture. The water was aerated throughout the experiment. Feeding with the zooplankton and/or the feed began on the date when the fry reached 24 days of age. The daily ration comprised zooplankton contained in 0.4 dm 3 water and a constant dose of feed, 1800 mg. The fry fed on both the feed and the zooplankton received 1800 mg of feed and zooplankton in 0.2 dm 3 water of the river P onia and the holding pond of the Police Chemical Plant. The weight gains of the fry were measured in subsequent weeks of the rearing cycle. The source of food for the fry consisted of the zooplankton collected once a week from the outlet of the eutrophicated lake P o [790.7 ha, according to Filipiak and Raczy ski 2000], named the river P onia and marked as st. 1, as well as in the outlet of the other body of water, the holding pond [40 ha, Piasecki 1998] located on the premises of the Police Chemical Plant, marked as ZbR 2. The zooplankton on site 1 was collected on 23 March, 30 March, 8 April, and 16 April, whereas on site 2 on 24 March, 1 April, 9 April, and 17 April. The zooplankton was caught by means of a flour mesh plankton net [50 µm mesh size, 400 cm 2 inlet area], set in the stream of each outlet for four hours. The problem of mesh cramming was solved through frequent washing of the net. Daily rations were higher than required, since the zooplankton fed on one day was still present on the following day. Fulton's (1904) condition factor was used to describe the condition of the fry: K=100 000 W/L 3 where: W total unit body weight [g], or the weight of individual fish, L tail length [l. caud.] [mm]. The resulting data on the unit weight and total length of the sea trout fry were processed statistically using Excel spreadsheet and Statistica package. The testing of the null hypothesis about equality of means followed a test of normality of the distribution of the analysed traits [we used the Shapiro-Wilk test and the Levene test for Piscaria 6 (1) 2007

18 R. Czerniawski, P. Czerniejewski homogeneity of variances]. The significance of differences was tested using Scheffe's F test [p < 0.05] and ANOVA [for many samples] [Stanisz 1998]. Additionally, to illustrate differences in selected traits between the particular groups of the zooplankton and the fish, we used Ward's hierarchical clustering method, measured with Euclidean distance calculated as follows: [x, y] = [ 1 [xi yi] 2 ] 1/2 where: x, y the object the distance between which is calculated. This parameter indicates the geometric distance [dissimilarity] in a multidimensional space. According to the prior assumption that the purpose of rearing is stocking, the fry unused in the measurements were released to previously ecologically-examined streams, a forest brook and the Sitna stream [Raczy ski et al. 2005] located in the buffer zone of the Drawno National Park. RESULTS Food source The data on abundance, biomass, and the load of zooplankton carried through the outlets in the aforementioned sites are presented in Table 1. At the first sampling site (st. 1), the total zooplankton abundance remained relatively high over the entire period of sea trout rearing, exceeding 100 indiv. dm 3 on each sampling day. The highest abundance was recorded on 8 April, 192.3 indiv. dm 3. The highest zooplankton biomass at the site 1 was observed on 30 March, i.e. 0.97 mg dm 3. The highest load of carried zooplankton at the site 1 was recorded on 30 March as well, 207.3 kg per day, whereas the lowest, 116.7 kg per day, was recorded on 16 April. At the outlet of the other water body, i.e. the treated wastewater holding pond of the Police Chemical Plant, the highest number of zooplankton specimens were noted on 24 March, 174.9 indiv. dm 3. The highest biomass of zooplanktonic organisms at this site, 0.67 mg dm 3, was observed on 24 March as well. The highest loads of zooplankton carried out of the holding pond with water were recorded also on 24 March, 20.1 kg per day, as well as on 1 April, 21.428 mg dm 3. Sea trout fry survival rate The survival rate in the tanks where the fry was fed on either feeds or feeds with zooplankton (C and D) was 100% of the initial number. The survival rate of the fry fed on the zooplankton from the river P onia (A) was 99% of the initial number, while those fed on the zooplankton collected from the holding pond (B) was 99.5% (Table 2). Acta Sci. Pol.

Rearing sea trout... 19 Table 1. Abundance [indiv. dm 3 ], biomass [mg dm 3 ], and load of zooplankton transported daily [kg day 1 ] from lake P o (st. 1) and the secondary holding pond of the Police Chemical Plant (ZbR 2) Tabela 1. Liczebno [osob. dm 3 ], biomasa [mg dm 3 ] i masa zooplanktonu wynoszonego w ci gu doby [kg doba 1 ] z jeziora P o (st. 1) oraz z drugiego zbiornika retencyjnego Zak adów Chemicznych Police (ZbR 2) indiv. dm 3 osob. dm 3 mg dm 3 kg day 1 kg doba 1 23.03. 30.03. 8.04. 16.04. 23.03. 30.03. 8.04. 16.04. 23.03. 30.03. 8.04. 16.04. Lake P o outlet st. 1 Wyp yw z jeziora P o st. 1 Copepoda 48.3 48.6 72.6 26.7 0.5257 0.3465 0.2998 0.1336 112.19 73.95 59.48 34.91 Cladocera 1.8 8.1 0.3 10.5 0.0605 0.2921 0.0007 0.1297 12.91 62.34 0.15 27.68 Rotatoria 100.2 49.5 57.6 115.5 0.093 0.3312 0.3431 0.1647 21.47 71.00 75.16 52.22 Nematoda 0.3 0.009 1.92 Total Razem 188.7 121.8 192.3 153 0.6867 0.9713 0.6621 0.467 146.57 207.29 134.78 116.73 24.03. 1.04. 9.04. 17.04. 24.03. 1.04. 9.04. 17.04. 24.03. 1.04. 9.04. 17.04. Holding pond outlet ZbR 2 Wyp yw ze stawu retencyjnego ZbR 2 Copepoda 88.5 26.4 24 32.5 0.3148 0.2975 0.2095 0.3502 7.32 11.57 5.50 9.01 Cladocera 1.8 0.6 0.0578 0.0106 2.25 0.28 Rotatoria 54 50.7 28.8 25.2 0.3611 0.1954 0.0365 0.0719 12.81 7.60 0.96 1.85 Total Razem 174.9 95.7 60.9 80.5 0.6759 0.5507 0.2566 0.4221 20.14 21.43 6.74 10.86 Piscaria 6 (1) 2007

20 R. Czerniawski, P. Czerniejewski Table 2. Survival rate of sea trout fry during the rearing cycle, % Tabela 2. Prze ywalno larw troci w czasie podchowu, % A1 A2 A3 A4 A5 B1 B2 B3 B4 B5 C1 C2 D After 7 days Po 7 dniach After 14 days Po 14 dniach After 21 days Po 21 dniach After 28 days Po 28 dniach 98 100 100 98 96 99 98 100 100 100 100 100 100 100 98 100 100 100 98 100 100 100 98 100 100 100 100 98 100 100 100 98 100 100 100 100 100 100 100 100 97 100 98 97 100 98 100 100 100 100 100 100 A 1 A 5 number of replications in the tanks with the fry fed on zooplankton carried from lake P o ; B 1 B 5 number of replications in the tanks with the fry fed on zooplankton carried from the second holding pond of the Police Chemical Plant wastewater treatment facility; C 1 and C 2 number of replications in tanks with the fry fed on the feed; D rearing of the fry in one tank with the fry fed on both feed and zooplankton. A 1 A 5 liczba powtórze w akwariach z wyl giem karmionym zooplanktonem wynoszonym jeziora P o ; B 1 B 5 liczba powtórze w akwariach z wyl giem karmionym zooplanktonem wynoszonym z drugiego zbiornika retencyjnego oczyszczalni cieków Zak adów Chemicznych Police ; C 1 i C 2 liczba powtórze w akwariach z wyl giem karmionym pasz ; D podchów wyl gu w jednym akwarium z wyl giem karmionym pasz i zooplanktonem. The SGR, which was calculated for the entire period of the sea trout fry raising, allows concluding that the fish fed on the zooplankton of the river P onia gained 0.79% per day, those fed on the zooplankton from the treated wastewater holding pond gained 1.02% per day, those fed on feeds 2.21% per day, and those fed on both feeds and zooplankton 2.39% per day. Weight gains of the fry The gains in weight of the fry are presented in Fig. 1. On the day of the first feeding, the larvae weighed 0.0971 g on average. The mean body weight observed after one week was similar in all the experiment variants, A 0.1123 g, B 0.1156 g, C 0.1176 g, and D 0.1172 g. After two weeks, the mean weights did not differ significantly between the variants and were as follows: A 0.1161 g, B 0.1170 g, C 0.1248 g, and D 0.1314 g. After the third week, a considerably deviating value of the mean body weight was observed in the sea trout fry fed on feeds and zooplankton, which reached 0.1417 g and differed significantly (p < 0.05) from the mean body weight of the fry fed on the zooplankton from the river P onia. After 28 days from the date when raising started, the fry reached the following mean bosy weights: A 0.1213 g, B 0.1291 g, C 0.1803 g, and D 0.1896 g. The weights of the fry fed on zooplankton differed significantly from those fed on the feed or on the feed plus zooplankton. Cluster analysis of the fry body weight on the last week of raising has demonstrated that the fish fed on zooplankton differed considerably from those fed on the feed and the feed plus zooplankton (Fig. 2). Acta Sci. Pol.

Rearing sea trout... 21 g 0.20 0,2 0,18 0.18 0,16 0.16 0,14 0.14 A B C D 0,12 0.12 0.10 0,1 00.08,08 25.03. 1.04. 8.04. 15.04. 22.04. Date of research Data badania Fig. 1. Growth of weight (g) of sea trout fry fed on zooplankton carried from lake P o (A) zooplankton carried from the secondary holding pond of Police Chemical Plant (B) feed (C) and feed plus zooplankton (D) Rys. 1. Wzrost masy (g) larw troci karmionych zooplanktonem wynoszonym z jeziora P o (A). zooplanktonem z drugiego zbiornika retencyjnego ZCH Police (B) pasz (C) oraz pasz i zooplanktonem (D) 1.002 Euclid s distances Odleg o ci euklidesowe 1.002 1.001 1.001 1.001 1.001 1.000 1.000 1.000 1.000 D C B A Fig. 2. Rys. 2. Body weight cluster analysis of sea trout fry fed on zooplankton carried from lake P o (A), zooplankton carried from the secondary holding pond of Police Chemical Plant (B), feed (C), and feed plus zooplankton (D) after the last week of rearing Analiza aglomeracyjna masy cia a wyl gu troci karmionych zooplanktonem wynoszonym z jeziora P o (A), zooplanktonem z drugiego zbiornika retencyjnego ZCH Police (B), pasz (C) oraz pasz i zooplanktonem (D) po ostatnim tygodniu podchowu Piscaria 6 (1) 2007

22 R. Czerniawski, P. Czerniejewski Length gains of the fry The length increments of the fry are presented in Fig. 3. On the first feeding day, the length of the sea trout larvae was 22.6 mm on average. Observed mean length after the first week was similar in nearly all the variants, A 25.29, B 25.71, and C 25.87, except for that of the fry fed on both the feed and zooplankton (24.52 mm), which differed significantly (p < 0.05) from the mean lengths of those fed on the zooplankton from the holding pond and those fed on the feed. After the second week of the rearing cycle, the mean lengths of the fry in all the variants did not differ substantially, whereas after three weeks the value of the analysed parameter was the highest in variant D, 27.55 mm, differing significantly from the other variants. After 28 days from the beginning of feeding, the fry attained the following mean lengths: A 26.89 mm, B 27.25 mm, C 27.98 mm, D 27.71 mm. Cluster analysis of the sea trout fry body lengths carried out in the last week of rearing has demonstrated the highest similarity between the fish fed on the feed and those fed on the feed plus zooplankton (Euclidean distance between the values of body length was 1.04, Fig. 4). Body lengths of this group of fish considerably differed from those of the fry fed on zooplankton alone. 29 28 27 26 A B C D mm 25 24 23 22 21 25.03. 1.04. 8.04. 15.04. 22.04. Date of research Data badania Fig. 3. Growth of length (mm) of sea trout fry fed on zooplankton carried from lake P o (A), zooplankton carried from the secondary holding pond of Police Chemical Plant (B), feed (C), and feed plus zooplankton (D) Rys. 3. Wzrost d ugo ci (mm) larw troci karmionych zooplanktonem wynoszonym z jeziora P o (A), zooplanktonem z drugiego zbiornika retencyjnego ZCH Police (B), pasz (C) oraz pasz i zooplanktonem (D) Acta Sci. Pol.

Rearing sea trout... 23 1.5 Euclid s distances Odleg o c i eukli desowe 1.4 1.3 1.2 1.1 1.0 0.9 D C B A Fig. 4. Rys. 4. Body length cluster analysis of sea trout fry fed on zooplankton carried from lake P o (A), zooplankton carried from the secondary holding pond of Police Chemical Plant (B), feed (C), and feed plus zooplankton (D) after the last week of rearing Analiza aglomeracyjna d ugo ci cia a wyl gu troci karmionych zooplanktonem wynoszonym z jeziora P o (A), zooplanktonem z drugiego zbiornika retencyjnego ZCH Police (B), pasz (C) oraz pasz i zooplanktonem (D) po ostatnim tygodniu podchowu Euclid s distances Odleg o ci eukli desow e 1.016 1.014 1.012 1.010 1.008 1.006 1.004 1.002 1.000 0.998 D C B A Fig. 5. Fulton's condition factor cluster analysis of sea trout fry fed on zooplankton carried from lake P o (A), zooplankton carried from the secondary holding pond of Police Chemical Plant (B), feed (C), and feed plus zooplankton (D) after the last week of rearing Rys. 5. Analiza aglomer acyjna wspó czynn ika kondycji Fultona wyl gu troci karmionych zooplanktonem wynoszonym z jeziora P o (A), zooplanktonem z drugiego zbiornika retencyjnego ZCH Police (B), pasz (C) oraz pasz i zooplanktonem (D) po ostatnim tygodniu podchowu Piscaria 6 (1) 2007

24 R. Czerniawski, P. Czerniejewski Fulton's condition factor Analysis of the mean Fulton's condition factor for each group of the sea trout fry has revealed that the condition of the fish differed significantly after the first and the last week of the rearing cycle. In the previous case, such difference was found between variants B and D, where Fulton's condition factors were, respectively, 0.68 and 0.79. In the latter, on the other hand, a difference was found between the following variants: A (0.64) and C (0.81), B (0.64) and C, A and D (0.87), as wall as B and D. Cluster analysis of the condition factor in the sea trout fry carried out in the last week has demonstrated the highest similarity between the fish fed on the zooplankton from lake P o and the holding pond in Police (Euclidean distance between the values of the condition factor was 1, Fig. 5). The condition factor of this group of fry considerably differed from the factor of the sea trout fry fed with both the feed and zooplankton. DISCUSSION Presently, we are witnessing a constantly growing interest in completely ecological feeding [Wedekind 2003], a category which certainly includes zooplankton. Large biomass of this food that can be taken from most lake outlets and its relatively low food conversion factor, about 5 [Karzinkin 1955], are indeed satisfactory elements. Many authors who search for methods to increase the efficacy of stocking nonfry also seek the appropriate food, which would comprise a complete reared and reared source of nutrients. Artificial dry feeds, excellent for commercial fish feeding, fully meet the needs of fish farms, since they allow the farmers to raise the fish to the desired size and weight in a relatively short cycle of controlled rearing. It seems, however, that artificial feeds are not a fully sufficient diet for the fry reared with the perspective of release to streams and lakes. Namely, dry feed does not allow the fish to develop their hunting instinct, which in their natural habitats may represent the most important factor of survival. Although some authors who reared sea trout fry on the feed prior to stocking achieved satisfactory results in terms of survival, e.g. 45% [Trzebiatowski and Domaga a 1991, 1992], early fry feeding with their natural food would presumably improve the stocking success considerably. The analyses of alimentary tract contents in lake trout fry in the brook Trzebiocha by Ró a ska [1961] allow concluding that the trout fry basically do not feed on plankton and, as soon as they start independent feeding, the fry forage for benthic organisms, with insect larvae and small crustaceans as the main food components. Many authors, however, report that both juvenile and adult salmonid fish feed on zooplankton. Jorgensen et al. [2000] state that juvenile stages of Atlantic salmon and sea trout that inhabit cold Norwegian lakes fed in the littoral zone on invertebrates, which included zooplankton, mainly Daphnia longispina and Bosmina longirostris. Björnsson [2001] also reported that juvenile forms of salmonids living in lakes fed on zooplankton, mainly on cladocerans. Langeland and Nost [1995] maintain that the salmonid fishes Acta Sci. Pol.

Rearing sea trout... 25 found commonly in Scandinavian lakes are indeed opportunistic planktivores. Moreover, Nilssen and Waervagen [2002] report that it is important that a number of Scandinavian lakes stocked with sea trout fry should provide available food in the form of zooplankton and other invertebrates. The studies by these authors confirm that the sea trout preferably select some zooplankton to their diet. The cited reports seem to confirm the rationale and importance of raising the sea trout fry on natural food prior to their release to streams or lakes. As it was mentioned before, the natural food source for the sea trout fry comprised the zooplankton carried thought the outlets from lake P o and the second holding pond of the wastewater treatment facilities of the Police Chemical Plant during the early spring. It should be kept in mind that the zooplankton flowing out of the water bodies during such period of the year is pure, without algae, contrary to the summer season, when algae blooming affect the quality of planktonic animals treated later as a food for the fish. For salmonids, fishes considered difficult to rear, such pure, early-spring food supply in the form of zooplankton is most recommended. In both zooplankton feeding variants, the water supplied to the tanks contained adult forms of the crustaceans. Bearing in mind food selectivity of the fish, we can presume that the sea trout fry discriminated the zooplankton by size choosing larger organisms, as water sampled on the day following each feeding contained basically no large planktonic animals. Szlauer [1976] found nearly exclusively mature and grown-up animal specimens in the guts of sea trout fry fed on zooplankton. Reiriz et al. [1998] stated that salmonid fishes exhibit food selectivity in relation to the energetic requirements of their growth. Juvenile forms of Atlantic salmon studied by these authors, which were fed on insect larvae and gammarids (Gammarus sp.), chose primarily the crustaceans. Langeland and Nost [1995] found mainly large zooplankton components in the stomachs of salmonids living in Scandinavian lakes, though organisms were also found that were smaller than the gaps between the fish's filtrating gill rakers. Also the studies by Nilssen and Waervagen [2002] prove that sea trout prefer large cladocerans in their diet. The authors of this paper have found the survival rate of the fry either fed on zooplankton or on the feeds as very good. In any of the three feeding variants, the value did not drop below 96%, with the fry fed on zooplankton plus the feed showing zero mortality throughout the experiment. Szczepkowska et al. [1998], who fed sea trout fry on an artificial feed also achieved low mortality of 2.4%. Such a high survival rate probably resulted from fully controlled environment of rearing, most optimum for sea trout fry survival. The small percentage of dead fish were those that starved to death because they did not take food at all. Goryczko [2001] stated that emaciation and darkening of the body are visible symptoms of irreversible starvation changes of rainbow trout fry [which may also refer to sea trout]. Considering the remarks of this author and the appearance of the dead fry, we presume that the fish in our experiment died because they had not eaten any food. Piscaria 6 (1) 2007

26 R. Czerniawski, P. Czerniejewski The stocked densities in all the replications ranged between 2.9 and 2 fish per 1 dm 3. Szlauer and Winnicki [1980], who fed sea trout fry on zooplankton, applied a density of 2 fish per dm 3. From the very beginning of the experiment, the fry fed on the feed was characterised by the highest mean growth rate in length or weight. Similar values of the analysed parameters were observed for the fry fed on both zooplankton and the feed, which may imply that the fry preferred the feed in their diet. Szlauer and Winnicki [1980], who reared sea trout fry, did not observe such large differences in weight gains and found that the fry fed on live food attained nearly identical size as those fed on dry feed. The cause underlying these discrepancies between our results and those reported by Szlauer and Winnicki [1980] may be the fact that different kinds of feeds were applied some 20 years ago. kawski [1973] stated that 40% of protein and 8% of fat were sufficient values for the feeds for the salmonid fishes. The feeds that are used today contain higher levels of these nutrients [Bontemps 2004]. Szczepkowska et al. [1998] reared sea trout fry to 3.1 cm and about 0.42 g in 28 days of rearing with the Ekostart 17 feed. The differences we have observed in the growth in length and weight between the variants of feeding may have resulted from the nutritional values of the feed. Poczyczy ski [1996 a] and Marmulla and Rösch [1990] state that nutritional values of feeds are definitely higher than those of zooplankton fed to the fish. Artificial feeds contain compounds that promote rapid growth [Brett 1971, Poczyczy ski 1996 b]. Wolska-Neja [2000] concludes that comparing both types of food in terms of nutritional values only, one must favour artificial feeds which considerably improve the raising results; however, natural food, although poorer in energy, has its specific advantages. The activity of digestive enzymes of the fry is weaker than that of adult forms of the same species, and the shortage of own proteolytic enzymes is partly made up for through the enzymes of the consumed zooplankton [Poczyczy ski 1996 a]. After all, natural food, which forms hunting instincts in the fry reared for stocking purposes, is certainly a better solution than artificial diet. During the described sea trout rearing, we have come up with conclusions that may affect the process and improve the experiment, namely that the raising process must be carried out under controlled environment with aerating equipment, in circulating water, and that, in order to avoid zooplankton deficit in the tanks, the fry should be fed ad libitum. It has also been observed that food supplies in the form of zooplankton were sufficient to achieve optimum growth of the sea trout fry reared for stocking purposes and that the zooplankton was the kind of food developing the behaviour in the juvenile sea trout that is characteristic for predators from as early as the first days of independent feeding. REFERENCES Björnsson B., 2001. Diel changes in the feeding behaviour of Arctic charr (Salvelinus alpinus L.) and brown trout (Salmo trutta L.) in Ellidavatn, a small lake in Southwest Iceland. Limnol. 31, 281 288. Acta Sci. Pol.

Rearing sea trout... 27 Bontemps S., 2004. Analiza produkcji i sprzeda y pstr gów t czowych w 2003 roku [Analysis of production and sale rainbow trout in 2003 year]. Kom. Ryb. 4, 1 15 [in Polish]. Brett J.R., 1971. Satiation time, appetite and maximum food intake of sockeye salmon (Oncorhynchus nerka). J. Fish. Res. Bd. Can. 28, 409 415. Czerniawski R., 2004. Zooplankton exported from Lake Adamowo. Zool. Pol. 49 (1 4), 129 147. Czerniawski R., Czerniejewski P., 2003. Perspektywy wykorzystania zooplanktonu wynoszonego z jeziora Adamowo do podchowu wyl gu ryb i narybku [Zooplankton exported from Lake Adamowo and chances its utilization as feeding for clutch of fish and young fish]. Kom. Ryb. 3, 9 14 [in Polish]. Czerniawski R., Wolska M., 2004. Zooplankton wynoszony z jeziora Gra yna przez rzek Draw [Zooplankton exported from Lake Gra yna by the River Drawa]. Streszczenia Jubileuszowej Sesji Naukowej pt. Nauki Rolnicze w S u bie Cz owieka i Przyrody, AR Szczecin, 206 [in Polish]. Filipiak J., Raczy ski M., 2000. Jeziora zachodniopomorskie [West Pomeranian Lakes]. Wydaw. AR, Szczecin [in Polish]. Füllner G., 2001 a. Zur Situation der Binnenfischerei in der Tschechischen Republik. Bericht einer Reise nach Vodnany [Situation of freshwater fishery in Czech Republik]. Fischer und Teichwirt 7, 252 253 [in German]. Füllner G., 2001 b. Die situation der Fischerei in Bulgarien [Situation of fishery in Bulgary]. Fischer und Teichwirt 6, 214 215 [in German]. Fulton T.W., 1904. The rate of growth of fishes. Fisheries Board of Scotland Annual Report 22, 141 241. Goryczko K., 2001. Pstr gi. Chów i hodowla [Trouts. Breeding and Rearing]. IR, Olsztyn [in Polish]. Jorgensen L., Halvorsen M., Amundsen P.A., 2000. Resource partitioning between lake dwelling Atlantic salmon (Salmo salar L.) parr, brown trout (Salmo trutta L.) and Arctic charr (Salvelinus alpinus L.). Ecol. Freshw. Fish. 9, 202 209. Karzinkin G., 1955. Podstawy biologicznej wydajno ci zbiorników wodnych [Fundamentals of biological effectiveness of water bodies]. PWRiL, Warszawa [in Polish]. Kibria G., Nugegoda D., Fairclough R., Lam P., Bradley A., 1999. Utilization of wastewatergrown zooplankton: Nutritional quality of zooplankton and performance of silver perch Bidyanus bidyanus (Mitchell 1838) (Teraponidae) fed on wastewater-grown zooplankton. Aquaculture Nutr. 5 (4) 1, 221 227. La ngeland A., Nost T., 1995. Gill raker structure and selective predation on zooplankton by particulate feeding fish. J. Fish Biol. 47, 719 732. Leonard J.W., Leonard F.A., 1946. An analisis of the feeding habits of rainbow trout and lake trout in Birch Lake, Cass County, Michigan. Trans. Am. Fish. Soc. kawski G.K., 1973. Pasze dla ryb ososiowatych [Dry food for salmonids]. Broszura IR 63, Olsztyn [in Polish]. Marmulla G., Rösch R., 1990. Maximum daily ratio of juvenile fish fed on living natural zooplankton. J. Fish Biol. 36, 789 801. Millamena O.M., Penaflorida V.D., Subosa P.F., 1990. The macronutrient composition of natural food organisms mass cultured as larval feed for fish and prawns. Isr. J. Aquaculture Bamidgeh. 42 (3), 77 83. Munilla-Moran R., Stark J.R., Barbout A., 1990. The role of exogenous enzymes in digestion in cultured turbot larvae (Scophthalamus maximus L.). Aquaculture 88, 337 350. Nilssen J.P., Waervagen S.B., 2002. Intensive fish predation: an obstacle to biological recovery following liming of acidified lakes? J. Aquat. Ecosystem Stress and Recovery 9, 73 84. Nilsson N.A., 1955. Studies on the feeding habits of trout and char in North Swedish Lakes. Annu. Rep. of the Year 1954, 36. Ogino C., 1963. Studies on the chemical composition of some natural foods of aquatic animals. Bull. Jpn. Soc. Sci. Fish. 29, 459 462 [in Japanese]. Piscaria 6 (1) 2007

28 R. Czerniawski, P. Czerniejewski Piasecki W., 1998. Wyst powanie, biologia i wp yw na ichtiofaun Acanthocyclops robustus (Sars) (Crustacea, Copepoda) [The occurrence, biology and influence on fish Acanthocyclops robustus (Sars) (Crustacea, Copepoda)]. Rozprawa doktorska, AR, Szczecin [in Polish]. Pillay T.V.R., 1990. Aquaculture Principles and Practices. Fishing News Books, London. Poczyczy ski P., 1996 a. ywienie larw ryb podstawy teoretyczne I. Pasze sztuczne w ywieniu larwy [Feeding of fish larvae theoretical fundamentals I. Dry feed]. Kom. Ryb. 4, 19 20 [in Polish]. Poczyczy ski P., 1996 b. ywienie larw ryb podstawy teoretyczne II. Procesy trawienne larw ryb [Feeding of fish larvae theoretical fundamentals II. Digestion course]. Kom. Ryb. 3, 7 8 [in Polish]. Raczy ski M., Czerniejewski P., Czerniawski R., 2005. Mo liwo ci wykorzystania cieków zlewni jeziora Adamowo do podchowu ryb ososiowatych przeznaczonych do zarybie wód Drawie skiego Parku Narodowego [Capabilities of utilization of rivers of Adamowo Lake for breeding of salmonids for stocking of Drawienski National Park]. Kom. Ryb. 6, 15 21 [in Polish]. Reiriz L., Nicieza A.G., Brana F., 1998. Prey selection by experienced and naive juvenile Atlantic salmon. J. Fish Biol. 53, 100 114. Ró a ska Z., 1961. Pokarm wyl gu troci jeziorowej (Salmo trutta m. lacustris L.) i innych gatunków ryb w potoku Trzebiocha [Feed of clutch a brown trout (Salmo trutta m. lacustris L.) and other species of fish in stream Trzebiocha]. Rocz. Nauk. Rol. 93 D, 387 422 [in Polish]. Stanisz A., 1998. Przyst pny kurs statystyki [Accessible course of statistics]. StatSoft Polska, Kraków [in Polish]. Steffens W., 2001. Forellenproduktion und Forellenverarbeitung in Frankreich [Production of trout in France]. Fischer und Teichwirt 7, 258 259 [in German]. Szczerbowski J.A., 1993. Rybactwo ródl dowe [Freshwater Fishery]. IR, Olsztyn [in Polish]. Szczepkowska B., Szczepkowski H., Chybowski., 1998. Podchów wyl gu troci jeziorowej na paszy Ekostart 17 [Breeding clutch of brown trout on commercial dry feed Ekostart 17]. Kom. Ryb. 1, 4 6 [in Polish]. Szlauer B., 1976. Próba karmienia narybku troci i pstr ga t czowego zimowym zooplanktonem jeziornym [An attempt to feeding young fish of brown trout and rainbow trout a winter zooplankton from lake]. Gospod. Ryb. 9, 21 [in Polish]. Szlauer B., 1977. The zooplankton removal from lakes by the River P onia. Acta Ichtyol. Piscat. 6 (2), 39 53. Szlauer L., 1974. Wykorzystanie do karmienia narybku siei Coregonus lavaretus (Linnaeus, 1758) zooplanktonu, wynoszonego z jezior przez odp ywy [The use of zooplankton outflowing from lakes as food for young Coregonus lavaretus (Linnaeus, 1758)]. Rocz. Nauk. Rol. 96 H 2, 89 107 [in Polish]. Szlauer L., Winnicki A., 1980. Propozycja wykorzystania zimowego zooplanktonu do podchowu narybku troci [Proposal of using winter zooplankton as food for young brown trout]. Gospod. Ryb. 12, 9 10 [in Polish]. Trojanowska A., Mc Carthy T.K., Zalewski M., 2003. Zespo y zooplanktonu i fitoplanktonu pó nocnego i po udniowego basenu Jeziora Lough Corrid (Irlandia) w odniesieniu do stanu troficznego i zmian jako ci wody na przestrzeni ostatnich 21 lat [Communities of zooplankton and phytoplankton in Lake Lough (Ireland) in view trophic status and changes of quality water in last 21 years]. Streszczenia Zjazdu Hydrobiologów Polskich, Warszawa, 196 [in Polish]. Trzebiatowski R., Domaga a J., 1991. Zarybianie ma ych cieków wyl giem podchowanym troci (Salmo trutta L.) sposobem na zwi kszenie efektywno ci zarybiania [Stocking fry trouts of small rivers manner of boost of efficiency of stocking]. Materia y sesji naukowej pt. XL lat Wydzia u Rybactwa Morskiego i Technologii ywno ci, Szczecin, 20 22 wrze nia 1991, AR, Szczecin, 67 68. Acta Sci. Pol.

Rearing sea trout... 29 Trzebiatowski R., Domaga a J., 1992. Mo liwo ci zwi kszenia efektywno ci zarybiania cieków wyl giem troci (Salmo trutta L.) [Capabilities of boosts of efficiency of stocking of trout fry]. Zesz. Nauk AR Wroc. 37 (218), 41 44. Wedekind H., 2003. Vergleich eines konventionellen mit einem ökologischen Forellenfuttermittel [Compare dry feed with ecological feed for trouts]. Fischer und Teichwirt 12, 443 444. Wojno T., 1961. Od ywianie si troci (Salmo trutta m. lacustris L.) w jeziorze Wdzydze [Feed of brown trout (Salmo trutta m. lacustris L.) in Lake Wdzydze]. Rocz. Nauk Rol. 93 D [in Polish]. Wolska M., Czerniawski R., 2004. Porównanie letniego i zimowego zooplanktonu jeziora Adamowo i zasilaj cego je cieku [Comparison of summer and winter zooplankton of Adamowo Lake and river]. Streszczenia Jubileuszowej Sesji Naukowej pt. Nauki Rolnicze w S u bie Cz owieka i Przyrody, Szczecin 29 wrze nia 2004, AR, Szczecin, 205. Wolska-Neja B., 2000. Mo liwo ci rybackiego wykorzystania cieków z zak adów przetwórstwa rybnego [Possibilities of fishery using sevage waters from fish manufacture]. Praca doktorska, AR Szczecin [in Polish]. Yurkowski M., Tabachek J.L., 1979. Proximate and amino acid composition of some natural fish foods (in: Proceedings of the World Symposium on Finfish Nutrition and Fish Feed Technology). Hamburg 20 23 June 1978. J.E. Halver, K. Tiews (Eds.). Vol. II, Heenemann, Hamburg, 435 448. PODCHÓW LARW TROCI W DROWNEJ (Salmo trutta m. trutta L., 1758) POTENCJALNEGO MATERIA U ZARYBIENIOWEGO NA ZOOPLANKT ONIE POZYSKIWANYM W ODP YWACH Z NATURALNYCH I SZTUCZNYCH ZBIORNIKÓW Streszczenie. Ryby ososiowate stanowi wa ny element gospodarki rybackiej w Polsce i na wiecie. Liczebno tej rodziny ryb w wodach naturalnych, w g ównej mierze, uzale niona jest od warunków pokarmowych w ciekach, do których zosta y wprowadzone jako wyl g lub narybek. Ich wcze niejszy podchów na pokarmie sztucznym, w warunkach kontrolowanych pozwala na osi gni cie cz sto zadowalaj cych wyników zarybie, przede wszystkim ze wzgl du na wy szy stopie prze ycia w porównaniu z wyl giem p ywaj cym. Istnieje jednak przypuszczenie, e podchów wyl gu troci na pokarmie naturalnym w postaci zooplanktonu móg by znacznie wp yn na popraw warunków prze ycia w cieku. Pokarm naturalny w przeciwie stwie do sztucznego rozwija u wyl gu ryb instynkt owiecki, b d cy cz sto jedynym czynnikiem decyduj cym o prze yciu. W niniejszej pracy przedstawiono wyniki podchowu wyl gu troci na pokarmie naturalnym, które porównano z wynikami podchowu na pokarmie sztucznym. Baz pokarmow w postaci zooplanktonu stanowi zooplankton pozyskiwany z odp ywu z naturalnego i sztucznego zbiornika. S owa kluczowe: chów, pokarm, tro, wyl g ryb, zarybianie, zooplankton Accepted for print Zaakceptowano do druku: 19.12.2006 Piscaria 6 (1) 2007