THE EFFECT OF INITIAL STOCKING DENSITY ON GROWTH OF EUROPEAN CATFISH (Silurus glanis L.) LARVAE UNDER CONTROLLED CONDITIONS

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1 Arch. Ryb. Pol. Archives of Polish Fisheries Vol. 7 Fsc THE EFFECT OF INITIAL STOCKING DENSITY ON GROWTH OF EUROPEAN CATFISH (Silurus glnis L.) LARVAE UNDER CONTROLLED CONDITIONS Driusz Ulikowski, Izbel Borkowsk Inlnd Fisheries Institute in Olsztyn, Experimentl Fish Htchery Dg³ in Pieczrki ABSTRACT. Intensive initil rering of Europen ctfish (Silurus glnis) lrve ws crried out. Initil densities of the fish were: 10, 15, 20, nd 25 ind./dm 3. The fish grew fster t lower densities. Averge finl individul body weights of the fish were: 1.71, 1.55, 1.42, nd 1.27 g, nd verge body lengths (Lt): 5.60, 5.56, 5.51, nd 5.30 mm, respectively. Survivl ws high nd similr in ll experimentl groups ( %). The highest ctfish production of initil stock number 1000 ind. ws obtined t the lowest stocking density (10 ind./dm 3 ). It ws equl to 1.35 kg/m 3. In ll remining groups: of 15, 20, nd 25 ind./dm 3 production ws lower by: 17% (1.15 kg/m 3 ), 13.8% (1.19 kg/m 3 ), nd 28.6% (1.05 kg/m 3 ). All tested stocking densities (10-25 ind./dm 3 ), nd method of rering used in the experiment re pplicble to commercil conditions, but the period of rering t higher densities (20-25 ind./dm 3 ) should be limited to dys due to considerble decrese of fish condition. Key words: EUROPEAN CATFISH, FISH, REARING, LARVAE, Silurus glnis, DENSITY DISTRIBUTION INTRODUCTION Europen ctfish hs become populr in Polnd s n dditionl fish in crp ponds, nd rered in polyculture with cyprinid fish. Possibilities of such polyculture were described by Wiœniewolski (1989). Recently some successful ttempts of rering ctfish hve been done under controlled conditions, using rtificil feed (Heymnn 1990, Koz³owski et l. 1995, Wolnicki 1995, Kmiñski, Wolnicki 1996, Wolnicki, Strzonek 1996, Hmckov et l. 1997), or mixed food rtificil feed nd nturl food (Wiœniewolski 1989, Ziebrth 1991, Hmckov et l. 1992, Mejz et l. 1993, Koz³owski et l. 1995). Artificil feeds were lso useful in commercil-scle rering of Europen ctfish lrve (Wiœniewolski 1989, Ziebrth 1991, Mejz et l. 1993, Ko³drs et l. 1994, Kmiñski, Wolnicki 1996). Stocking density seems one of the most importnt fctors ffecting the results of ctfish rering. In numerous studies vrious stocking densities were pplied: from low ind./dm 3 (Szlmiñsk 1986, Kmiñski, Wolnicki 1996), to high 100 ind./dm 3 (Wiœniewolski 1989, Koz³owski et l. 1995), or

2 152 D. ULIKOWSKI, I. BORKOWSKA even ind./dm 3 when rered on live food (Mres, Kouril 1988). The results obtined by vrious uthors cnnot be, however, compred due to different conditions (wter temperture, wy of feeding nd type of food, durtion of rering etc.). Thus, n experiment ws performed in the Experimentl Fish Htchery Dg³ to study the effect of initil stocking density (from 10 to 25 ind./dm 3 ) on the results of intensive rering of Europen ctfish lrve under controlled conditions. MATERIAL AND METHODS Europen ctfish lrve were rered under controlled conditions, t semi-commercil scle, in 500 dm 3 tnks (2*1*0.5 m, t wter level 0.25 m), with wter recircultion nd purifiction system. Wter flow ws mintined so tht the oxygen level would not drop below 5 mg/dm 3. Wter temperture nd oxygen level t the wter outlet were mesured dily. Chemicl nlyses of wter: mmonium nitrogen (N-NH 4 ), nitrite nitrogen (N-NO 2 ), nd ph were performed every 2-3 dys. The fish were kept in drkness. Ech tnk ws stocked with Europen ctfish lrve ged 5 dys (L.t. = 10.8 mm, w 0 = 14.9 mg) with the yolk sc still present. The fish were divided into 4 groups of vrious stocking density: 10 (group A), 15 (group B), 20 (group C), nd 25 ind./dm 3 (group D), two replictes ech. The fish were rered t 26.3±1.8 o C, nd fed trout strter (Aller Molle Krystl 3600) contining 53% of crude protein, nd 12% of crude ft. The feed ws supplied 22 hours dy using conveyor feeders. Dily feeding rte ws equl to 30% of fish weight t the beginning of rering, nd from the third dy on this mount ws incresed every 2 dys by 50%. The fish were fed d libitum in ll groups. Additionlly, until 12-th dy of rering, the fish were supplied twice dy with frozen zooplnkton (stored t 18 o C for 1-3 months), t constnt rte of 3 g per every 1000 fish. The tnks were clened twice dy, nd ded fish were counted nd removed. Every 3 dys the fish were bthed in formldehyde solution (200 mg/dm 3 ) for 20 minutes, nd on 7 nd 14 dy in chlormine B solution (50 mg/dm 3 ) for 30 minutes. The experiment lsted 16 dys. Before the beginning of feeding, smple of 50 fish ws tken nd preserved in 4% formldehyde solution. The fish were lso smpled fter 7, 10, nd 13 dys of rering (35 individuls from ech tnk), nd preserved in the sme wy. After the end of the experiment, the fish were counted, nd 50 individuls from ech tnk were weighed nd mesured (nesthetised using 2-phenoxyethnol), with g nd 0.01 cm ccurcy.

3 THE EFFECT OF INITIAL STOCKING DENSITY ON GROWTH OF EUROPEAN CATFISH Food conversion rte (FCR), specific growth rte (SGR), nd condition (K) coefficients were clculted ccording to the formuls: FCR=P (B k B 0 ) -1, where: P - mount of consumed food [g], B k finl fish biomss [g], B 0 initil fish biomss [g]. SGR = (ln w k lnw 0 ) 100% t -1, where: w k finl individul body weight [g], w 0 initil individul body weight [g], t durtion of the experiment [dys]. K = 100 W L -3, where: W - individul body weight [g], L totl body length (L.t.) [cm]. The differences mong the groups were tested using nlysis of vrince (ANO- VA in STAGRAPHICS 4.2), t p<0.05. RESULTS During the experiment N-NH 4 concentrtion rnged from mg/dm 3, N-NO 2 from 0.01 to 0.05 mg/dm 3, nd wter ph from 7.3 to 8.1, not exceeding vlues ccepted for cyprinid fish rering (Kruger, Niewidomsk-Kruger 1990). On the 11-th dy of rering, the fish were invded by Ichthyobodo nectrix. The invded fish were immersed in 200 mg/dm 3 formldehyde solution nd in 1% solution of N Cl, for 20 minutes in ech of them. Dynmics of verge body weights in ll experimentl groups fter 7, 10, 13 nd 16 dys is shown in Fig. 1, dynmics of fish body lengths in Fig. 2, nd chnges of condition coefficient in Fig. 3. The finl results of rering of ctfish lrve re summrised in Tb. I. Mximum verge individul body weight, totl length, condition coefficients, nd specific growth rte were obtined by the fish of A group, nd the lowest vlues were obser-

4 154 D. ULIKOWSKI, I. BORKOWSKA 2 1,8 A B C D 1,6 b 1,4 bc c 1,2 W[g] 1 0,8 0,6 0,4 0, Dys of rering Fig. 1. Increse of verge body weight (W) of ctfish lrve fter 7, 10, 13, nd 16 dys of rering t vrious densities A 10 ind./dm 3,B 15ind./dm 3,C 20ind./dm 3,D 25ind./dm 3. The sme letter index indictes vlues tht do not differ significntly (p<0.05) 6 A B C D 5,5 b 5 4,5 L.t. [cm] 4 3,5 3 2, Dys of rering Fig. 2. Increse of verge totl body length (L.t.) of ctfish lrve fter 7, 10, 13, nd 16 dys of rering t vrious densitiesa 10ind./dm 3,B 15ind./dm 3,C 20ind./dm 3,D 25ind./dm 3. The sme letter index indictes vlues tht do not differ significntly (p<0.05)

5 THE EFFECT OF INITIAL STOCKING DENSITY ON GROWTH OF EUROPEAN CATFISH ved in group D (Tb. I). Sttisticlly significnt differences of body weight were observed between A nd B, C, D groups, nd between B nd D (Fig. 1). No differences were found between B nd C, nd between C nd D groups. Finl body length of fish differed significntly only between A, B, C nd D group (Fig. 2). TABLE I Finl results of 16- dy rering of Europen ctfish lrve t vrious initil stocking densities (stndrd devition in prentheses). Initil fish densities re given in brckets (ind./dm 3 ) under the group symbol Group W L.t. K SGR FCR [g] [cm] [g/cm 3 ] [%/dzieñ] [g/g] Survivl [%] A [10] ( 0.52) ( 0.51) ( 0.17) ( 1.9) B b [15] ( 0.37) ( 0.44) ( 0.14) ( 1.7) C b [20] ( 0.35) ( 0.46) ( 0.08) ( 1.6) D c [25] ( 0.34) ( 0.52) ( 0.07) ( 1.8) Dt in columns hving the sme superscipt do not differ in significnt wy (P < 0.05) W - verge body weight L.t. - men totl length K - condition fctor SGR - specific growth rte FCR - food conversion rte Condition coefficients were significntly different (p<0.05) lredy fter 13 dys of rering: group A differed from B, C, nd D, B nd C differed from D (Tb. I). The lowest vlue of food conversion coefficient (0.45) ws noted in group A, nd the highest (0.55) in group D (Tb. I). Survivl of fish ws high in ll experimentl groups (Tb. I), nd mortlity ws low during fish rering, except one tnk of group B (30%), where strong invsion of Ichthyobodo nectrix ws observed (Fig. 4). Mortlity incresed between 4 nd 7, nd 11 nd 15 dy of rering in ll groups (Fig. 4). In the first cse mortlities probbly took plce mongst the individuls unble to feed, or showing body mlformtions. The second mortlity pek ws cused by Ichthyobodo invsion.

6 156 D. ULIKOWSKI, I. BORKOWSKA 1,5 1,4 A B C D 1,3 K 1,2 1,1 1 b bc c 0,9 b c c 0,8 0,7 0,6 0, Dys of rering Fig. 3. Chnges of condition coefficient (K) of ctfish lrve fter 7, 10, 13, nd 16 dys of rering t vrious densities A 10 ind./dm 3,B 15ind./dm 3,C 20ind./dm 3,D 25ind./dm 3. The sme letter index indictes vlues tht do not differ significntly (p<0.05) 8 7 A B C D 6 Mortlity (%) Dys of rering Fig. 4. Mortlity of ctfish lrve during 16 dys of rering t vrious densities A 10ind./dm 3,B 15 ind./dm 3,C 20ind./dm 3,D 25ind./dm 3

7 THE EFFECT OF INITIAL STOCKING DENSITY ON GROWTH OF EUROPEAN CATFISH ,6 1,4 1,2 kg/m 3 /1000 szt. 1 0,8 0,6 A B C D 0,4 0, fish/dcm 3 Fig. 5. Production of ctfish fry (kg/m 3 ) obtined from 1000 individuls fter 16 dys of intensive rering t vrious initil stocking densities (ind./dm 3 ). Stndrd devition given t the top of the brs. Ctfish production t the initil number of 1000 lrve ws the highest in the group of the lowest stocking density 10 ind./dm kg/m 3 (Fig. 5). In ll other groups of stocking densities: 15, 20, nd 25 ind./dm 3, production ws lower by: 17% (1.15 kg/m 3 ), 13.8% (1.19 kg/m 3 ), nd 28.6% (1.05 kg/m 3 ), respectively. DISCUSSION The results of the experiment showed tht Europen ctfish grew better t lower initil stocking densities. Finl individul body weight of fish rered in density of 10 ind./dm 3 ws 10% higher compred to the fish from group of 15 ind./dm 3. It ws lso 19.5% higher thn in group of 20 ind./dm 3, nd 34.6% higher thn t 25 ind./dm 3. Despite considerble differences, the fish growth even t the highest density of 25 ind./dm 3 (verge body weight 1.27 g, verge totl body length 5.3 cm) ws similr or better compred to the results obtined by other uthors who fed ctfish in similr wy. For exmple, Ziebrth (1991) who rered ctfish lrve on mixed food contining trout strter, live nd frozen zooplnkton, t 24 o C nd initil stocking density of

8 158 D. ULIKOWSKI, I. BORKOWSKA 30 ind./dm 3 (from dy 6 10 ind./dm 3 ), obtined ctfish of g fter 15 dys of rering. Wiœniewolski (1989) fter 28 dys of rering t 21.3 o C, on trout strters nd zooplnkton, t initil stocking density ind./dm 3, obtined ctfish fry of g, nd cm. Koz³owski et l. (1995), fter 21 dys of rering (initil stocking density 100 ind./dm 3 ), t 24 o C, obtined fish of 0.34 g on mixed diet of decpsulted brine shrimp cysts nd trout strter. Survivl of ctfish lrve fter 16 dys of rering ( %) ws lso similr to the vlues obtined by other uthors on nturl food, rtificil feed, or mixed diet (Kouril et l. 1984, Toth, Ppp 1986, Mres, Kouril 1988, Wiœniewolski 1989, Heymnn 1990, Ziebrth 1991, Hmckov et l 1992, Mejz et l. 1993, Koz³owski et l. 1995, Kmiñski, Wolnicki 1996, Hmckov et l. 1997). Higher initil densities (over 25 ind./dm 3 ) in ctfish rering require further studies, s from the dy 13 of rering the differences of condition coefficients between the groups of higher nd lower densities incresed considerbly. This my indicte tht fish growth ws density-limited. CONCLUSIONS Europen ctfish lrve grew fster t lower stocking densities. Production of ctfish fry fter 16 dys of rering (for 1000 individuls of initil stock) ws the highest in the group of lowest initil density 10 ind./dm 3 (1.35 kg/m 3 ). In the remining groups of initil density 15, 20 nd 25 ind./dm 3, production ws lower: by 17% (1.15 kg/m 3 ), 13.8% (1.19 kg/m 3 ), nd 28.6% (1.05 kg/m 3 ), respectively. Stocking density did not significntly ffect the finl fish survivl which ws high in ll experimentl groups ( %). All stocking densities nd the method of rering used this study my be successfully used on commercil scle, but rering t higher densities (20-25 ind./dm 3 ) should be limited to dys due to the decrese of condition coefficient. REFERENCES Hmckov J., Kouril J., Admek Z., Vcht R., Vliv pridvku mikrobiotik Streptococcus fecium M-74 ke krmivu n rust pludku sumce velkeho (Silurus glnis L.) - Bul. VURH Vodnny, 28 (1):

9 THE EFFECT OF INITIAL STOCKING DENSITY ON GROWTH OF EUROPEAN CATFISH Hmckov J., Szlmiñsk M., Kouril J., Kozk P., ywienie lrw sum europejskiego psz¹ sztuczn¹ w trzech temperturch - Kom. Ryb., 3: Heymnn A., Intensivzucht des Welses (Silurus glnis) in Wrmwsser mit Trockenfutter - Z. Binnnfisch, 37 (12): Kminski R., Wolnicki J., Udny podchów wylêgu sum, Silurus glnis L., n pszy pstr¹gowej w skli pó³technicznej - Kom. Ryb., 6: 4-6. Ko³drs M., Mejz T., Mejz A., Wylêgnie ryb w wrunkch sztucznych i nturlnych w obiekcie doœwidczlnym RZD Lskow w Ztorze w 1994 roku - Kom. Ryb., 6: Kouril J., Mchcek J., Skcelov O., Odkrm rneho pludku sumce velkeho (Silurus glnis L.) tremi ruznymi dietmi - Bul. VURH Vodnny, 20 (2): Koz³owski J., Mmcrz A., Poczyczyñski P., Chybowski L., Jozs V., Rering of Europen shetfish (Silurus glnis L.) lrve on diffrent dry nd nturl food - Lrvi 95 - Fish & Shellfish Lrviculture Symposium, Gent, Belgium, , Europen Aquculture Society, Specil Publiction 24: Krüger A., Niewidomsk-Krüger D., Dopuszczlne stê eni minerlnych zwi¹zków zotowych w wodzie do chowu i hodowli ryb krpiowtych - Broszur IRS, nr 149. Mres J., Kouril J., Odchov rneho pludku sumce velkeho ve zlbch (Prehled) - Bul. VURH Vodnny, 2: Mejz T., Ko³drs M., Mejz A., Produkcj i podchów wylêgu sum w Rybckim Zk³dzie Doœwidczlnym w Ztorze - Kom. Ryb., 6: Szlmiñsk M., Podchów sum w wodzie o podwy szonej temperturze - Kom. Ryb., 6: 13. Toth O. E., Ppp G., Z., Microencpsulted egg diets for wels (Silurus glnis L.) - Aqucultur Hungric, 5: Wiœniewolski W., Zuchtmöglichkeiten des Welses in Teichen, in Polen - Roczniki Nuk Rolniczych H-102 (1): Wolnicki J., Ocen przydtnoœci psz komercyjnych i cyst rtemii w kontrolownym podchowie wylêgu sum, Silurus glnis L. - Kom. Ryb., 1: Wolnicki J., Strzonek I., Mo liwoœci wykorzystni strterów pstr¹gowych i cyst rtemii w kontrolownym podchowie wylêgu sum, Silurus glnis L. - Kom. Ryb., 1: Ziebrth G., Prktische Erfhrungen bei der Aufzucht von Welssetzlingen 1990 in der Kreislufnlge Eldenburg - Fischer & Teichwirt, 42 (10): 35. STRESZCZENIE WP YW RÓ NEGO ZAGÊSZCZENIA POCZ TKOWEGO OBSAD NA WZROST LARW SUMA EUROPEJSKIEGO (Silurus glnis L.) W CZASIE INTENSYWNEGO PODCHOWU W WARUNKACH KONTROLOWANYCH W skli pó³technicznej n obiegu z recyrkulcj¹ wody przeprowdzono 16-dniowy intensywny podchów lrw sum (Silurus glnis L.) przy zstosowniu ró nych zgêszczeñ pocz¹tkowych obsd wynosz¹cych: 10 szt./dcm 3, 15 szt./dcm 3, 20 szt./dcm 3 i 25 szt./dcm 3 wody. Lrwy sum ywiono przez 12 dni pokrmem miesznym (grnult pstr¹gowy plus zooplnkton mro ony), nstêpnie smym grnultem pstr¹gowym. Pszê zdwno przez 22 godz./dobê. Œredni tempertur wody w czsie podchowu wynosi³ C. Stwierdzono szybszy wzrost ryb podchowywnych w ni szych zgêszczenich obsd. Uzyskno nrybek sum o œredniej msie ci³ wynosz¹cej (odpowiednio do zgêszczeñ obsd): 1.71,

10 160 D. ULIKOWSKI, I. BORKOWSKA 1.55, 1.42 i 1.27 g i œredniej d³ugoœci c³kowitej: 5.60, 5.56, 5.51 i 5.30 cm. Obliczono wspó³czynniki: kondycji (0.96, 0.90, 0.84 i 0.84), dobowego przyrostu œredniej msy jednostkowej (29.4, 28.9, 28.3 i 27.6%/dzieñ) i pokrmowe (0.45, 0.50, 0.47 i 0.55). Testowne zgêszczeni pocz¹tkowe obsd nie wykz³y ich wp³ywu n prze ywlnoœæ koñcow¹ ryb, któr by³ wysok i wyrównn we wszystkich grupch ( %). Po 13 dnich podchowu nie stwierdzono sttystycznie istotnych (P<0.05) ró nic we wzroœcie ryb, le kondycj ich w grupie o zgêszczeniu pocz¹tkowym obsd 25 szt./dcm 3 by³ istotnie ni sz ni kondycj ryb z grup o zgêszczeniu pocz¹tkowym obsd szt./dcm 3. Produkcj nrybku sum po 16 dnich intensywnego podchowu w przeliczeniu n 1 m 3 wody i 1000 sztuk obsdzonych lrw by³ njwy sz w grupie o njmniejszym zgêszczeniu pocz¹tkowym obsd, tj. 10 szt./dcm 3 (1.35 kg). W pozost³ych grupch o zgêszczeniu pocz¹tkowym 15, 20 i 25 szt./dcm 3 by³ on ni sz odpowiednio o 17 % (1.15 kg), 13.8 % (1.19 kg) i o 28.6 % (1.05 kg). Wykorzystn metod podchowu lrw sum i testowne w przeprowdzonym doœwidczeniu zgêszczeni pocz¹tkowe obsd mog¹ byæ z powodzeniem stosowne w prktyce, le okres podchowu przy wy szych zgêszczenich pocz¹tkowych (20-25 szt./dcm 3 ) korzystnie jest skróciæ do dni. ADRES AUTORÓW: Mgr in. Driusz Ulikowski, Mgr in. Izbel Borkowsk Doœwidczlny Oœrodek Zrybieniowy Dg³ Pozezdrze Pieczrki