Kor J Fish Aquat Sci 44(3), 225-231 한수지, 44(3), 225-231, 2011 DOI:10.5657/KFAS.2011.0225 해수순치에따른무지개송어 (Oncorhynchus mykiss) 의프로락틴및성장호르몬유전자의발현변화 Corresponding author: ycsohn@gwnu.ac.kr 신지혜 1 이철호 2 조미희 1 홍관의 2 김동수 3,4 손영창 1,4 1 강릉원주대학교해양분자생명공학과, 2 수산자원사업단양양연어사업소, 3 부경대학교해양바이오신소재학과, 4 부경대학교해양수산형질전환생물연구소 Changes in Prolactin and Growth Hormone Gene Expression of Rainbow Trout Oncorhynchus mykiss Adapted to Seawater Jihye Shin 1, Cheul Ho Lee 2, Mihee Jo 1, Kwan Eui Hong 2, Dong Soo Kim 3,4 and Young Chang Sohn 1,4 * 1 Department of Marine Molecular Biotechnology, Gangneung-Wonju National University, Gangneung 210-702, Korea 2 Yangyang Salmon Station, Korea Fisheries Resources Agency, Yang-yang, Gangwon 215-821, Korea 3 Department of Marine Bio-Materials and Aquaculture, Pukyung National University, Busan 608-737, Korea 4 Center for Risk Assessment of Marine Living Modified Organisms, Pukyung National University, Busan 608-737, Korea Prolactin (PRL) plays an important role in freshwater (FW) osmoregulation by preventing the loss of ions and the uptake of water in fish. Growth hormone (GH) promotes acclimation to seawater (SW) in several teleosts. We acclimated rainbow trout Oncorhynchus mykiss weighting 68.2±16.6, 138.3±24, and 287.5±42.1 g in separate experiments to SW under slow-acclimation (SSW) or acute-acclimation (ASW) conditions, and then examined the PRL and GH mrna levels using the real-time quantitative polymerase chain reaction. The PRL mrna levels in all three experimental groups decreased significantly with both the SSW and ASW treatments, as compared to a control group kept in FW for 30 days. The GH mrna levels increased with ASW in the largest fish, whereas the levels in the other groups did not change significantly. The mortality rate of the largest fish was lower than for the other groups, whereas the growth rate among the three experimental groups did not differ significantly. The growth rate of the ASW group was highest for the smallest fish. These results suggest that SW acclimation is associated with the gene expression levels of PRL and GH in relatively large rainbow trout. In addition, the fish mortality and growth rate on FW-SW transfer seem to be related to body weight, and the SW acclimation method may be applied to the hatcheries industry. Key words: Rainbow trout, Prolactin, Growth hormone, Seawater acclimation, Real-time PCR 서론경골어류인무지개송어 (Oncorhynchus mykiss) 는우리나라의내수면양식어중냉수성어류의대표적어종으로서양식이도입된 1965년부터년간약 4,000톤내외로생산되는산업으로정착되었다. 현재, 시대의변화에따른소비성향이바뀌면서기존의횟감위주에서가공품에의한소비로전환되는추세에있다 (Baik et al., 2007). 이에따라무지개송어는대형어 (2 kg 이상 ) 로의사육이대두되고있으나, 육상양어장에대한제한된환경여건으로인해대형어생산이어려워지면서해면에서의사육으로확대할필요성이요구되어지고있다. 최근, 우리나라에서는무지개송어의해면사육을통한대형어생산을시도하고있으나, 염분변화에의한어류의생리학적 이온과수분불균형, 성장지연및폐사가초래됨으로서높은생산성을유지하지는못하고있는실정이다 (Tsuzuki et al., 2001; Partridge and Jenkins, 2002). 어류는환경수의염분변화에적응하기위하여항상성 (homeostasis) 유지를위한삼투압조절 (osmoregulation) 기구를가지고있으며 (Morgan and Iwama, 1991; Jarvis and Ballantyne, 2003), 경골어류의삼투압조절은주로아가미, 소화관및신장에서이뤄진다 (Maina 1990). 삼투압조절에관여하는대표적인호르몬은뇌하수체에서분비되는프로락틴 (prolactin, PRL) 과성장호르몬 (growth hormone, GH) 으로서두호르몬은서로유사한펩타이드의이황화결합구조를포함하고있다 (Kawauchi and Sower, 2006). 경골어류의 PRL 은환경수의담수조건에서, GH 는해수조건에서높게발현되어이질적인발현패턴으로삼투조절에관여한다. 두호르몬은 225
226 신지혜 이철호 조미희 홍관의 김동수 손영창 2 유사한펩타이드구조를근거로공통의선조유전자로부터분화되었지만 (Kawauchi and Sower, 2006), 기능적인측면에서는독자적인진화의과정을거쳐왔다고추정되고있다 (Madsen and Bern, 1992; Manzon, 2002). 도미 (Sparus auratus), 감성돔 (Acanthopagrus schlegeli) 과같은광염성경골어류의뇌하수체 PRL mrna 는담수환경조건에서높게발현되어지며, GH mrna 는이와대조적으로낮은발현양상을나타낸다 (Laiz-Carrion et al., 2009; Tomy et al., 2009). 해수로부터담수로순치할경우, 틸라피아 (Oreochromis mossambicus) 의혈장내 PRL 농도는높아지고, 삼투압은저하되며, 역으로담수에서해수로순치시, 혈장내 GH 와삼투압은높아진다고보고된바있다 (Seale et al., 2002). In vitro 실험에서도저삼투압배지에서배양된뇌하수체세포에서증가된 PRL 의분비와고삼투압배지조건에서 GH 의분비가증가되는경향이 radioimmunoassay (RIA) 방법으로증명되었다 (Seale et al., 2002). GH 뿐만아니라그것의조절인자인인슐린양성장인자 (insulin-like growth factor 1, IGF-1) 또한광염성어류틸라피아 (O. mossambicus) (Fruchtman et al., 2000) 와송사리 (Fundulus heteroclitus) (Mancera and McCormick, 1998) 그리고무지개송어 (McCormick et al., 1991) 의해수적응을조절하는데관여한다는보고가있다. 본연구의목적은무지개송어의점진적혹은급진적해수순치에따른생존율의비교와삼투압조절호르몬 PRL 과 GH mrna 발현변화를분자수준에서밝히고자하였으며, GH 유전자발현변화와개체의성장에따른연관성을조사하였다. 또한, 무지개송어의염분변화에따른항상성유지에필요한생리적조절기구를이해하고, 향후산업현장에서필요한해수사육에관한기초자료로활용될것으로사료된다. 재료및방법실험어와실험조건실험에사용된무지개송어는선명수산 ( 강원도, 정선 ) 에서제공받았으며, 실험은국립수산과학원냉수성어류연구센터 ( 강원도, 양양 ) 에서실시하였다. 해수순치사육이적용되기에적합한무지개송어를선택하기위하여, 각각 1차실험군 ( 평균전장 18.1±1.7 cm, 평균체중 68.2±16.6 g, n=282, 부화후약 5개월 ), 2차실험군 ( 평균전장 22.3±1.5 cm, 평균체중 138.3± 24 g, n=207, 부화후약 7개월 ), 3차실험군 ( 평균전장 26.9±1.3 cm, 평균체중 287.5±42.1 g, n=102, 부화후약 9개월 ) 으로나누어진행하였다. 실험전 1-2일동안제공된실험어를담수에서안정화시킨후해수순치를시작하였다. 어류는냉각기가부착된 3개의사각형수조 (140 80 60 cm) 에서자연일장및 15 내외로유지된수온으로사육하였으며, 3-5회 / 일로동일한양의사료를공급하였다. 각실험은담수 (FW, freshwater), 점진적해수순치 (SSW, slow-acclimation in seawater), 그리고급진적해수순치 (ASW, acute-acclimation in seawater) 그룹으로나누어진행하였다. SSW는 5일동안점진적 (20% 40% 60% 80% 100%) 으로해수를첨가하였으며, ASW는 2일동안급진적 (50% 100%) 으로해수를첨가하였다. FW 는대조군으로서 SSW 와동일한양의담수를 5 일동안첨가하였다. 시료채취해수순치 7 일과 30 일후, 각그룹의무지개송어를 0.1% 2-phenoloxyethanol 로마취시켜전장과체중을측정하였다. 참수하여채취한뇌하수체는즉시액체질소에급속동결하였으며, total RNA 를추출하기전까지 -80 에서보관하였다 (n=6-8). 뇌하수체 total RNA( 각 0.5μg) 는 RNeasy Mini Kit (QIAGEN, Valencia, CA, USA) 로추출하였으며, cdna 는 QuantiTect Reverse Transcription Kit (QIAGEN) 로합성하였다. Real-time Polymerase Chain Reaction (real-time PCR) 해수순치에따른 PRL 과 GH 유전자발현분석은 Real-time PCR 방법으로조사하였다. 사용된 oligo primers 는 GenBank 에등록된염기서열을바탕으로 Primer Express v3.0 software (Applied Biosystems, Boston, MA, USA) 를이용하여제작하였다 (Table 1). 뇌하수체 cdna (0.5μg) 를주형으로 oligo primers (10μM) 2x SYBR primix Ex-Taq, 50x ROX Referance Dye II, oligo primer (10μM) 와함께총량 20μL 로 real-time PCR (Applied Biosystems 7500) 을수행하였다. PCR 조건은 50 에서 2 분, 95 에서 10 분반응후, two-step PCR 방법으로 95 에서 15 초, 60 에서 1 분으로총 40 cycles 을수행하였다. Table 1. Oligo primers used in the Real-Time PCR primer direction sequence rtprl-f rtprl-r rtgh-f rtgh-r rtβ-actin-f rtβ-actin-r Forward Reverse Forward Reverse Forward Reverse 5'- CCA ATG GGA CGA GTG ATG ATG -3' 5'- TGA CAA GAC CTC CCG CCT C -3' 5'- CAT CAA CCT GCT CAT CAC GG -3' 5'- CCT GAC CGT CGC CAA GTG -3' 5'- CTT CCT CGG TAT GGA GTC TTG C -3' 5'- CTG GGG GGG CGA TGA T -3' 통계처리각각의실험결과로부터얻어진자료값사이의유의성검정은 SPSS 통계패키지 (V.17) 를이용하여분산분석후, Neuman-Keuls test와 t-test, χ 2 test로분석하였다 (P<0.05). 결과폐사율실험기간동안실험어의폐사율은실험어의무게와해수순치의방법에따라차이를보였다. 1차, 2차실험군에서 FW ( 대조군 ; 0-5.8%) 와비교하여 SSW (20.2-39.7%) 와 ASW (47.1-58.5%) 은높은폐사율을보였다. 특히, 급진적해수순치를시도한 ASW그룹의폐사율이상대적으로높았다 (P<0.05, χ 2 test). 한편, 3차실험군의 SSW그룹 (11.8%) 및 ASW그룹 (17.6%) 의폐사율은 1차, 2차실험군과비교하여감소된경향을보였다 (P<0.05, χ 2 test) (Table 2). 뇌하수체 PRL mrna 발현변화 1 차실험군에서 30 일동안지속된담수사육의결과, 뇌하수
3 해수순치무지개송어의프로락틴및성장호르몬유전자발현변화 227 Table 2. The mortalities of three experimental groups during 30 days (%) FW SSW ASW p 1 st experiment 2 nd experiment 3 rd experiment p 0 5.8 0 0.023* 20.2 39.7 11.8 0.003* 58.5 47.1 17.6 <0.001* <0.001* <0.001* 0.045* Note. FW, control group in freshwater; SSW, slowacclimation in seawater; ASW, acute-acclimation in seawater (P<0.05). *, χ 2 test. 체 PRL mrna의발현이높은수준으로증가되는경향을보였으며, 이와대조적으로 SSW, ASW 처리는상대적으로낮은발현수준을보였으며, 해수순치 7일후와 30일후간의유의적인차이를나타내지않았다 (P<0.05) (Fig. 1A). 2차실험군의경우, 해수순치 7일후 SSW, ASW 그룹의 PRL mrna 발현수준은 FW 그룹과비교하여유의적으로낮은발현수준을보였으며, 이와같은경향은해수순치 30일까지지속되었다 (P<0.05) (Fig. 1B). 3차실험군의경우각그룹간의 PRL mrna 발현은유의적인차이가관찰되지않았으나, 해수순치 7일및 30일째 SSW 처리된어체의 PRL 발현은대조군에비해유의적으로낮은수준을나타내었다 (P<0.05, t-test) (Fig. 1C). 뇌하수체 GH mrna 발현변화 1차실험군에서해수순치 7일후 ASW 처리군의 GH mrna 발현이증가하였으나 (P<0.05), 30일후해수순치에의한유의적인발현차이는관찰되지않았다 (Fig. 2A). 2차실험군은 FW, SSW, ASW 그룹사이에 GH mrna의유의적인차이는관찰되지않았다 (Fig. 2B). 한편, 3차실험군의경우, 해수순치 7일및 30일째의 ASW에서 GH mrna의발현이유의적으로증가하는경향을보였다 (P<0.05) (Fig. 2C). 성장율해수순치 7 일후 FW, SSW, ASW 그룹의실험어평균체중 과비교하여해수순치 30일후의평균체중변화를조사하였다. 1차실험군의 ASW 그룹은해수순치 30일째약 2.5배증가된성장률을보였으며, 이는 FW 그룹 ( 약 1.5배 ) 와비교하여유의적으로증가된성장률을나타내었다 (P<0.05) (Fig. 3A). 2차및 3차실험군의경우, 해수순치로인하여성장이증가하는경향을보였으나, FW와비교하여 SSW, ASW 처리그룹사이에유의적인차이는관찰되지않았다 (Fig. 3B, 3C). 고찰송어류의체내염분농도는해수의약 1/3 미만으로유지되는데, 이는담수에서는아가미나체표를통해유입된환경수를신장에서뇨로배설시키고, 해수에서는체내에과잉축적된염분을아가미의염류세포를통하여체외로방출시킴으로서체내항상성이유지될수있기때문이다. 이와같은생리적인조절이가능한무지개송어는연어 송어류의급증하는수요 Fig. 1. Expression levels of prolactin (PRL) mrna in the pituitary of rainbow trout that were exposed to SSW and ASW at 7 or 30 days after transfer. The relative PRL mrna levels were nomalized by β-actin values. Data were represented by the mean±s.e.m of six independent samples (P<0.05). *, t-test; (A) 1 st experiment; (B) 2 nd experiment; (C) 3 rd experiment. 량을충족시키기위한적절한방법으로제시되는해수사육이가능한어종이다 (Chen and Lin, 1994). 무지개송어의해수사육에대한연구가일부실행되고있으나, 사육어의폐사문제로인하여실용화되지못하는상황에당면하고있다. 이러한문제는어류의염분내성과밀접한관련이있으며, 특히연어과어류는어체의크기가큰개체일수록염분내성이높은것으로알려져있다 (Parry, 1958; Houston, 1961; Heifetz et al., 1989; Dempson, 1993). 본연구에서도개체무게별 (1 차, 2 차, 3 차실험군 ) 로해수순치에따른무지개송어의폐사율을조사한결과, 해수순치시전반적으로어체중이낮은어류가높은폐사율을나타내었으며, 특히급진적해수순치에따른
228 신지혜 이철호 조미희 홍관의 김동수 손영창 2 Fig. 2. Expression levels of growth hormone (GH) mrna in the pituitary of rainbow trout that were exposed to SSW and ASW at 7 or 30 days after transfer. The relative GH mrna levels were nomalized by β-actin values. Data were represented by the mean±s.e.m of six independent samples (P<0.05). (A) 1 st experiment; (B) 2 nd experiment; (C) 3 rd experiment. 폐사율이현저히높은것을확인할수있었다 (Table 2). 이는해수사육에대한염분내성이어체의중량과밀접한상관관계를가지며, 더불어점진적인염분변화의환경조건이어류폐사율의감소에효과가있음을확인할수있었다. 하지만모든어종의크기및무게가염분내성과절대적인연관성을갖는것은아니다. 홍연어 (O. nerka) 의염분내성은어체의크기에의한영향이없는것으로보고된바있다 (Kaeriyama et al., 1987). 또한, 무지개송어치어의염분내성은성장외에도집단간의유전적요인이관여하고, 이에따른염분내성이강한우량형질의확보가능성을제안한바있다 (Choe and Yeo, 2002). 어류는환경수의염분변화에적응하기위하여체내항상성유지측면에서삼투압조절기구 ( 아가미, 장및신장 ) (Jarvis Fig. 3. Rates of increased body weight of rainbow trout that were exposed to SSW or ASW during 30 days after transfer. Data were represented by the mean±s.e.m. of six independent samples (P<0.05). (A) 1 st experiment; (B) 2 nd experiment; (C) 3 rd experiment. and Ballantyne, 2003; Morgan and Iwama, 1991; Maina, 1990; Shin and Sohn, 2008) 를가지고있으며, 이는삼투압조절호르몬인 PRL 과 GH 의작용에의해이루어진다고알려져있다. 경골어류의 PRL 은뇌하수체로부터생산 분비되며, 낮은삼투압환경에적응시분비가촉진된다. 광염성어류틸라피아 (O. mossambicus) 는아미노기의아미노산수가다른두가지의 PRL (PRL177 과 PRL188) 을생산하며, 담수순치에의한혈중및뇌하수체내두 PRL 의발현은유사한패턴으로증가한다 (Yamaguchi et al., 1988). 상대적으로낮은광염성을지닌틸라피아 (O. niloticus) 의두 PRL 은발현수준의차이는있으나, 공통적으로담수순치에의해높은발현패턴을나타내며, 특히 PRL177 의발현이현저하게증가하는경향을나타낸다 (Ayson et al., 1993). 이와반대로고염분의환경수사육에따른틸라피아의혈장 PRL 농도는감소된다는보고가있다 (Auperin et al., 1994). PRL 은어류의담수적응에관여하는
3 해수순치무지개송어의프로락틴및성장호르몬유전자발현변화 229 중요한삼투조절호르몬으로작용하지만모든어종이그러한것은아니다. 회유성어류뱀장어 (Anguilla japonica), 연어과어류산천어 (O. masou) 와담수어붕어 (Carassius auratus) 의 PRL 발현은다른경향을보인다. 뱀장어, 산천어의뇌하수체내 PRL mrna 발현은해수순치에의해감소되는패턴을보이나, 붕어의그것은 50% 염도의기수조건에서유의적인차이를나타내지않으며해수사육을유도할경우, 전개체가모두폐사한다는보고가있다 (Park et al., 2008). 본연구에서는무지개송어를통하여해수순치에의한담수적응호르몬 PRL 발현이유의적으로변화되는것을관찰하였다. 삼투조절을위한 PRL 발현은개체의중량의차이그리고해수순치방법에따라상이한발현경향을나타냈다. 상대적으로높은어체중의실험군 (2차, 3차실험군 ) 에서 PRL은담수적응에따라신속한유전자발현증가반응을보였으나, 낮은어체중의실험군 (1차실험군 ) 은담수사육 30일후에비로소증가된 PRL의발현을나타내었다. 또한급진적해수순치에따른 PRL의발현은고체중의개체군 (3차실험군 ) 에서담수에비해유의적인발현차이를나타내지않았다 (Fig. 1). 이러한세실험군간의 PRL 발현차이는개체의중량에따른삼투조절의차이라사료된다. 실제로 150 g 전후의연어과어류는은화 (smoltification) 가진행됨으로서환경수의염분에대한높은감수성이보이며, 어류의중량및연령에따라삼투조절반응은변화될수있다 (Boeuf, 1993). 경골어류의 GH는어류의삼투조절과더불어성장, 대사, 생식그리고발생등의다양한생리작용에관여한다 (Bern and Madsen, 1992; Donaldson et al., 1979; McLean and Donaldson, 1993; Shepherd et al., 1997). GH의조절인자인 IGF-I 또한어류의해수적응을돕는작용을하며이는무지개송어 (McCormick et al., 1991) 와틸라피아 (O. mossambicus) (Fruchtman et al., 2000) 그리고바다송사리 (F. heteroclitus) (Mancera and McCormick, 1998) 에서보고된바있다. 광염성틸라피아중에서상대적으로낮은광염성을지닌어종 (O. niloticus) 의경우고염도의환경수에대한 GH의삼투압조절영향이나타나지않고, 높은광염성을지닌틸라피아 (O. mossambicus) 는뇌하수체내 GH의수준과세포활성이현저히높아지게되는데, 이를근거로 Auperin et al. (1995) 은 GH의해수적응효과는광염성을지닌어류에서제한적으로나타난다고제안하였다. 본연구에서는상대적으로고체중의 3차실험군에서해수순치로인한뇌하수체 GH mrna 발현이증가되는경향을확인하였다. 특히급진적으로해수에적응시킨그룹은담수대조군과비교하여유의적으로증가된 GH mrna 발현패턴이관찰되었다. 한편, 1차및 2차실험군은해수순치에의한 GH mrna의발현변화에유의적인차이를보이지않았다 (Fig. 2). 그러므로어종과개체의중량에따라해수적응에대한 GH의분비반응은다른경향을보이는것으로사료된다. 광염성해산어인도미 (S. auratus) 와넙치 (Paralichthys olivaceus) 의경우해수순치에대한 GH 발현패턴이이질적인경향을보이기도한다. 도미는해수 (38 ppt) 에서 PRL mrna의발현이감소하고, GH mrna의발현은증가 하는패턴을보인다 (Laiz-Carrion et al., 2009). 하지만넙치의경우, 해수에대한 PRL는낮은수준으로발현되어지나 GH의발현변화는유의적인차이를보이지않으므로서종에따라 GH의삼투조절반응에대한차이가있다고할수있다 (Cho et al., 2006). 본연구에서전반적으로급진적해수순치로인한 GH mrna의발현이증가하는경향을나타내는데, 이는체내항상성유지를위한삼투조절반응이기도하지만, 높은환경수의염분에대한스트레스와도상관관계가있을수있다. 높은 GH의발현은환경변화유래의스트레스로인한에너지대사와간접적으로연관성이있다 (Pickering et al., 1991; Wendelaar Bonga, 1997). 또한, 은화과정에따른세실험군간의삼투반응에대한감수성의차이와도관계될수있다. 특히연어는은화과정중코르티졸과 GH의분비가급격히증가하며, 이는아가미염류세포의수와활성을증대시켜체내흡수된과잉의염분을능동적으로배출시키는효과를나타낸다 (Bjornsson et al., 2010). 이러한삼투반응에따른 GH의감수성은상대적으로고체중의무지개송어에서민감하게나타난다고사료된다. 현재까지다양한어종의해면사육이시도된바있다. 담수어잉어 (C. carpio), 초어 (Ctenopharyngodon idella), 러시아철갑상어 (Acipenser gueldenstaedtii) 를기수 (2 ppt) 에서사육할시, 개체의섭이율과성장률이현저히증가되는경향을보였으며 (Konstantinow and Martynova, 1993), 광염성차노스 (Chanos chanos) 의경우에도고염분 (55 ppt) 에서사육하면성장률이급격히증가하는경향을나타낸다는보고가있다 (Swanson, 1998). 한편, 본연구에서는 1차실험군에서해수순치에의해무지개송어의성장이증가되는것을확인할수있었지만, 상대적으로고체중의 2차, 3차실험군성장률은유의적인차이가없었다. (Fig. 3A). 따라서, 고염분또는 GH의발현이어류의성장률을증가시키는데전적으로관여되지는않는다고사료된다. 광염성숭어 (Mugil cephalus) (1.3 g 혹은 20 g 개체 ) 의경우, 기수사육 (25% SW) 을유도할시담수혹은해수에비해빠른성장을보였으며 (Chang and Hur, 1999), 감성돔 (A. schlegeli) 은해수혹은담수조건에서모두성장이유의적으로증가한다는보고가있다 (Min et al., 2005). 또한, 틸라피아 (O. niloticus) 의해수사육을통하여환경수의염분이높아질수록개체의산소소비가급증하고, 이는삼투조절에필요한에너지생성에산소가다량사용되기때문으로알려져있다 (Farmer and Beamish, 1969). 따라서, 해수사육으로인한세실험군간의성장률의차이는개체중량에따른삼투조절과에너지대사간의차이점에유래할것으로추정되지만, 추가적인연구가필요할것으로사료된다. 이상의결과를정리하면본연구는무지개송어의해수순치시, 뇌하수체내 PRL은감소하고 GH은증가하는경향을확인하였으며, 두호르몬의이질적인발현패턴이무지개송어의해수적응을위한효과적인삼투조절에기여된다는것을시사하고있다. PRL은모든그룹에서해수에대한낮은발현패턴을보이나, GH는상대적으로높은중량의개체에서해수에의해유의적으로높게발현되는것을확인하였다. 하지만이
230 신지혜 이철호 조미희 홍관의 김동수 손영창 2 러한삼투조절호르몬의발현양상이실험어의최종성장률과는밀접한연관성을나타내지않았으나, 개체중량이높을수록혹은점진적으로해수를첨가하여순치시킬수록폐사율이감소되는효과를얻었다. 이러한연구결과는무지개송어의해면사육시요구되는개체의선택과순치조건을결정하는데중요한연구자료가될것이며, 향후산업화에적용할수있고생산성향상에기여될것이라사료된다. 사 본연구는국토해양부의재원으로한국해양과학기술진흥원의지원을받아수행된해양환경기술개발사업 (20088033-1) 과국립수산과학원내수면양식기술개발사업 (RP-2010-AQ- 070) 의지원에의하여수행되었으며, 실험어관리에도움을준냉수성어류연구센터김경식님에게사의를표합니다. 참고문헌 Auperin B, Rentier-Delrue F, Martial JA and Prunet P. 1994. Evidence that two tilapia (Oreochromis niloticus) prolactins have different osmoregulatory functions during adaptation to a hyperosmotic environment. J Mol Endocrinol 12, 13-24. Auperin B, Leguen I, Rentier-Delrue F, Smal J and Prunet P. 1995. Absence of a tigh effect on adaptability to brackish water in tilapia (Oreochromis niloticus). Gen Comp Endocrinol 97, 145-159. Ayson FG, Kaneko T, Tagawa M, Hasegawa S, Grau EG, Nishioka RS, David SK, Bern HA and Hirano T. 1993. Effects of acclimation to hypertonic environment on plasma and pituitary levels of two prolactins and growth hormone in two species of tilapia, Oreochromis mossambicus and Oreochromis niloticus. Gen Comp Endocrinol 89, 138-148. Baik KK, Choi YH, Lee JC, Park IS, Kim YK, Kim DY, Lee CS. 2007. Studies on seed production of rainbow trout, Oncorhynchus mykiss-hatching rate and early stage performance of USA strain rainbow trout, Oncorhynchus mykiss. J Aquaculture 20, 85-89. Bern HA and Madsen SS. 1992. A selective survey of the endocrine systerm of the rainbow trout (Oncorhynchus mykiss) with emphasis on the hormonal regulation of ion balance. Aquaculture 100, 237-262. Bjornsson BT, Stefansson SO and McCormick SD. 2010. Environmental endocrinology of salmon smoltification. Gen Comp Endocrinol in press. Boeuf G, Marc AM, Le Bail PY, Prunet P and Smal J. 1994. Stimulation of parr-smolt transformation by hormonal treatment in Atlantic salmon (Salmo salar 사 L.). Aquaculture 121, 195-208. Chang YJ, Lee YC and Lee BK. 1996. Comparison of growth and survival rates of juvenile grey mullets (Mugil cephalus) in different salinities. J Aquaculture 9, 311-320. Chen JC, Lin JL. 1994. Osmolality and chloride concentration in the hemolymph of subadult Penaeus chinensis subjected to different salinity levels. Aquaculture 125, 167-174. Cho YM, Shin J and Sohn YC. 2006. Gene expression levels of growth hormone, prolactin and their receptors of olive flounder Paralichthys olivaceus by salinity changes. J Kor Fish Soc 39, 326-332. Choe MK and Yeo IK. 2002. Studies on the salinity tolerance of juvenile rainbow trout, Oncorhynchus mykiss. Korean J Ichthyol 14, 205-211. Dempson JB. 1993. Salinity tolerance of freshwater acclimated, small-sized arctic charr, Salvelinus alpinus from northern labrador. J Fish Biol 43, 451-462. Donaldson EM, Fagerlund UHM, Higgs DA and McBride JR. 1979. Hormonal enhancement of growth in fish. In: Hoar, W.S., Randall, D.J., Brett, J.R. (Eds.), Fish Physiology: Bioenergetics and Growth, vol. 8. Academic Press, New York, U.S.A., 456-597. Farmer GJ and Beamish FWH. 1969. Oxygen consumption of Tilapia nilotica in relation to swimming speed and salinity. J Fish Res Bd Canada 26, 2807-2821. Fruchtman S, Jackson L and Borski R. 2000. Insulin-like growth factor I disparately regulates prolactin and growth hormone synthesis and secretion: studies using the teleost pituitary model. Endocrinology 141, 2886-2894. Heifetz J, Johnson SW, Koski KV and Murphy ML. 1989. Migration timing, size, and salinity tolerance of sea-type sockeye salmon (Oncorhynchus nerka) in an Alaska estuary. Can J Fish Aqua Sci 46, 633-637. Houston AH. 1961. Influence of size upon the adaptation of steelhead trout (Salmo gairdneri) and chum salmon (Oncorhynchus keta) to sea water. J Fish Res Board Can 18, 401-415. Jarvis PL and Ballantyne JS. 2003. Metabolic responses to salinity acclimation in juvenile shortnose sturgeon Acipenser brevirostrum. Aquaculture 219, 891-909. Kaeriyama M, Shimizu I and Kakizaki H. 1987. Seasonal changes in seawater adaptation of sockeye salmon reared in the freshwater. Sci Rep Hokkaido Salm Hatch 41, 129-135. Kawauchi H and Sower SA. 2006. The dawn and evolution
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