제브라피쉬（Danio rerio） 모델을 이용한 소형 열대성 어류의 저수온 스트레스 및 회복 반응에 관한 연구 = Cold stress and recovery responses in small tropical fish: a zebrafish （Danio rerio） model approach

다국어 초록 (Multilingual Abstract)

This study evaluated the effects of low-temperature exposure and subsequent recovery on growth characteristics, reproductive performance, and reproduction-related gene expression in zebrafish （Danio rerio）, as a model species for small tropical ornamental fish. The control group was maintained at 26 °C throughout the experiment, whereas the cold-exposed group was cooled from 26 °C to 10 °C at a rate of 1 °C every 12 h, maintained at 10 °C for 72 h, and then rewarmed to 26 °C at the same rate. Growth traits, reproductive traits, reciprocal crossing performance, gene expression in the ovary and testis, and reproductive traits at the onset of first spawning after juvenile-stage low-temperature exposure were assessed. Low-temperature exposure did not significantly affect total length or body weight during cooling, rewarming, or recovery. However, the cold-exposed group showed a higher condition factor at the lowest-temperature point and at some rewarming points. During recovery at 26 °C, the cold-exposed group showed temporarily higher weight gain and specific growth rate at two weeks after recovery, whereas no clear difference was observed thereafter. Feed conversion efficiency also did not differ significantly between groups. These results indicate that the low-temperature condition used in this study did not induce clear long-term growth impairment, although it temporarily affected growth and feeding responses during early recovery. Reproductive traits were more sensitive to low-temperature exposure than growth traits. Before low-temperature exposure, no clear differences were observed between groups in egg production, fertilization rate, hatching rate, malformation rate, or normal larvae production. After cooling began, egg production in the cold-exposed group decreased rapidly, and spawning ceased under sustained low-temperature conditions. After recovery to 26 °C, egg production and fertilization rate recovered relatively quickly, whereas hatching rate and normal larvae production remained low during early recovery and gradually recovered over time. In the reciprocal crossing experiment, hatching rate and normal larvae production were lower during early recovery in crossing groups that included cold-exposed males, whereas no clear difference was observed in the crossing group composed of cold-exposed females and control males. Gene expression analysis showed differential expression of star and hsd17b1 in the ovary and sod2, rec8b, tp53, and rad51 in the testis. In particular, testicular rec8b and rad51 were downregulated during low-temperature exposure and at the time of recovery to 26 °C, and the differences between groups decreased during later recovery. These results suggest that the reduction in early embryonic developmental success after low-temperature exposure may be more closely associated with paternal factors. In the preliminary assessment of first spawning after juvenile-stage low-temperature exposure, egg production and fertilization rate did not differ significantly between groups. However, the cold-exposed group showed a lower hatching rate and a partially increased malformation rate, suggesting that low-temperature exposure during the immature stage may affect embryonic developmental success and offspring quality after sexual maturation. In conclusion, the low-temperature exposure condition used in this study had a more pronounced effect on reproductive performance, particularly post-fertilization early embryonic developmental success, than on growth in zebrafish. These findings provide basic information for evaluating reproductive recovery and potential environmental establishment of small tropical ornamental fish after low-temperature stress.

목차 (Table of Contents)

• I. 서론 1
• II. 재료 및 방법 4
• 2.1. 실험어 및 사육 조건 4
• 2.2. 저수온 노출 및 회복 조건 4
• 2.3. 성장특성 평가 실험 6
• 2.3.1 실험어 및 수조 배치 6
• 2.3.2 성장특성 평가 8
• 2.4. 1차 생식특성 평가 실험 10
• 2.4.1 실험어 및 수조 배치 10
• 2.4.2 생식특성 평가 11
• 2.5. 2차 생식특성 평가 실험 13
• 2.5.1 실험어 및 수조 배치 14
• 2.5.2 상반교배를 통한 생식특성 평가 15
• 2.5.3 유전자 발현 분석을 위한 샘플링 17
• 2.6. 3차 생식특성 평가 실험 17
• 2.6.1 실험어 및 수조 배치 17
• 2.6.2 생애 최초 산란 관련 특성의 예비적 평가 18
• 2.7. 유전자 발현 분석 19
• 2.7.1 Total RNA 추출 및 cDNA 합성 19
• 2.7.2 Real-time 정량 PCR (RT-qPCR) 20
• 2.8. 통계분석 21
• III. 결과 23
• 3.1. 저수온 스트레스 및 회복 과정에서의 성장특성 변화 23
• 3.1.1 전장, 체중 및 비만도 변화 23
• 3.1.2 증체량 및 일간 성장률 변화 23
• 3.1.3 사료 섭취량 및 사료 전환 효율 변화 25
• 3.2. 저수온 스트레스 및 회복 과정에서의 생식특성 변화 27
• 3.2.1 저수온 노출 및 재가온 기간의 생식특성 변화 27
• 3.2.2 정상 수온 도달 후 회복 기간의 생식특성 변화 32
• 3.3. 상반교배 조합에 따른 생식특성 변화 32
• 3.3.1 상반교배 조합별 산란량 및 수정률 변화 34
• 3.3.2 상반교배 조합별 부화율 및 기형률 변화 34
• 3.3.3 상반교배 조합별 정상 부화자어 생산량 변화 36
• 3.4. 저수온 스트레스 및 회복 과정에서의 유전자 발현 변화 36
• 3.4.1 난소 내 생식 관련 유전자 발현 변화 36
• 3.4.2 정소 내 생식 관련 유전자 발현 변화 39
• 3.5. 미성숙기 저수온 노출 후 생애 최초 산란 관련 특성의 예비적 평가 41
• 3.5.1 생애 최초 산란기의 산란량 및 수정률 변화 41
• 3.5.2 생애 최초 산란기의 부화율 및 기형률 변화 43
• 3.5.3 생애 최초 산란기의 정상 부화자어 생산량 변화 43
• IV. 고찰 44
• 국문 요약 55
• 감사의 글 57
• 참고 문헌 59