본 연구는 온배수가 유입되는 대구시 달서천을 대상으로 나일틸라피아의 개체군 특성을 파악하기 위해 2019년 1월부터 11월까지 조사를 실시하였다. 물리적 서식환경 분석 결과 낮은 수심과 자갈, 모래/진흙의 비율이 높은 하상구조를 유지하고 있는 것으로 나타났다. 이화학적 서식 환경 분석 결과 달서천의 전기전도도 (EC)는 매우 높은 것으로 확인되었다. 기온 및 수온 분석 결과 달서천은 연중 10°C 이상의 수온을 지속적으로 유지하는 것으로 나타났으며, 금호강은 3월부터 10°C 이상의 수온을 유지하는 것으로 확인되었다. 어류상 조사결과 총 8과 20종 4,247개체가 출현하였다. 상대풍부도 분석 결과 나일틸라피아가 1,306개체 (30.75%)로 우점하고 있는 것으로 나타났다. 조사 시기별 나일틸라피아 개체수 분석 결과 6월 30일 조사시 급격한 개체수 증가를 보였다. 나일틸라피아 개체군의 길이-무게 분석 결과 회귀계수 b값은 3.1496으로 나타났으며, 비만도지수 (k) 기울기는 0.0025로 양의 기울기로 분석되었다. 조사시기별 달서천의 수온과 나일틸라피아 전장을 비교·분석한 결과 22°C 이상의 수온을 유지하는 5월 29일 조사시 당년생 개체가 출현하였다. 전장빈도 분포 분석 결과 당년생은 0~110 mm, 1년생~2년생은 120~210mm, 2년생 이상의 개체는 >210 mm의 범위로 추정되었다. 나일틸라피아 개체군 생식소중량지수 (GSI) 분석 결과 수컷과 암컷 모두 3월 11일 조사시 중앙값이 가장 높았으며, 3월 이후 중앙값은 감소하는 것으로 나타났다. 나일틸라피아의 개체 무게 (BW), 생식소중량 (GS), 생식소중량지수 (GSI) 간의 상관 분석 결과 개체 무게가 유사더라도 암컷 개체의 생식소중량과 생식소중량지수가 더 높은 것으로 분석되었다. 결과적으로 달서천에 서식하고 있는 나일틸라피아 개체군은 온배수로 인해 겨울철에도 생존이 가능하며, 안정적인 생활사를 유지하고 있는 것으로 판단된다. 또한 수온이 10°C 이상으로 상승하는 3월 이후부터는 달서천에서 금호강으로 서식처 이동이 가능할 것으로 예상된다. 따라서 금호강을 중심으로 나일틸라피아 개체군의 서식 분포 파악을 통해 나일틸라피아 개체군 관리 및 담수어류 종다양성 보존을 위한 하천관리 방안 마련이 필요할 것으로 판단된다.

전기자극에 대한 역돔, Oreochromis niloticus［Linnaeus］의 심전도를 구명하기 위하여, 어체내에 전극을 삽입하여 3 가지 전기자극원(20, 30, 40 Vp ; 10 msec)으로 실험어에 자극을 가하였을 때의 심전도를 서간과 야간으로 구분하여 60분간 조사한 심박수와 생체전위를 자극 전(마취상태, 안정상태)과 자극 후(자극-회복상태, 회복상태)로 구분하여 비교 분석한 결과는 다음과 같다. 1. 역돔은 마취 후 3 분 뒤에 안정상태에 도달하였고, 안정상태에서의 평균상심박수는 서간에 45.8 beat/min, 야간에 45.0 beat/min였고, 평균생체전위는 서간에 1.76 μ V, 야간에 1.75 μ V였다. 2. 자극별 평균심박수는 ① 자극-회복상태에서 전기자극이 20 Vp인 경우, 서간에 34.9 beat/min, 야간에 33.4 beat/min였고, 30 Vp인 경우, 서간에 36.8 beat/min, 야간에 36.0 beat/min였으며, 40Vp인 경우 서간에 38.0 beat/min, 야간에 36.4 beat/min로 나타났다. ② 회복상태에서 전기자극이 20 Vp인 경우, 서간에 45.5 beat/min, 야간에 45.1 beat/min였고, 30 Vp인 경우, 서간에 47.9 beat/min, 야간에 49.0 beat/min 였으며, 40 Vp인 경우, 서간에 51.4 beat/min, 야간에 50.7 beat/min로 나타났다. 3. 자극별 평균생체전위는 ① 자극-회복상태에서 전기자극이 20Vp인 경우, 서간에 2.54μ V 야간에 2.39μ V였고,30Vp인 경우, 서간에 3.30μ V, 야간에 2.30 μ V였으며, 40Vp 인 경우 서간에 6.05 μ V, 야간에 3.23 μ V로 나타났다. ② 회복상태에서 전기자극이 20 Vp인 경우, 서간에 1.92 μ V, 야간에 1.95 μ V 였고, 30 Vp인 경우, 서간에 2.78 μ V, 야간에 2.21 μ V 였으며, 40 Vp인 경우 서간에 3.60μ V 야간에 2.98μ V로 나타났다.

광자극에 대한 역돔, Oreochromis niloticus[Linnaeus]의 심전도를 구명하기 위하여 16~18℃ 수온에서 어체내에 전극을 삽입하여 3가지 광자극 (10, 100, 400 luχ)에 대한 심전도를 서간과 야간으로 구분하여 60분간 연속적으로 조사한 심전도를 상태별로 분석한 심박수와 생체전위는 다음과 같다. 1. 역돔은 마취 후 3분 뒤에 안정상태에 도달하였고, 안정상태에서 평균심박수는 서간에 47.6 beat/min, 야간에 45.1 beat/min였고, 평균생체 전위는 서간에 1.04 μ V, 야간에 1.24 μ V로 나타났다. 2 자극별 평균심박수는 ① 자극상태에서, 10 luχ인 경우 서간에 39.7 beat/min, 야간에 38.2 beat/min였고, 100 luχ인 경우 서간에 38.7 beat/min, 야간에 36.9 beat/min였으며, 400 luχ인 경우 서간에 36.8 beat/min, 야간에 35.8 beat/min로 나타났고, ② 회복상태에서, 10 luχ인 경우 서간에 47.1 beat/min, 야간에 46.0 beat/min였고, 100 luχ인 경우 서간에 47.2 beat/min, 야간에 45.6 beat/min였으며, 400 luχ인 경우 서간에 48.1 beat/min, 야간에 46.6 beat/min로 나타났다. 3. 자극별 평균생체전위는 ① 자극상태에서, 10 luχ인 경우 서간에 1.22 μ V, 야간에 0.71μ V였고, 100 luχ인 경우 서간에 0.63 μ V, 야간에 0.90 μ V였으며, 400 luχ 인 경우 서간에 1.39 μ V, 야간에 1.63 μ V로 나타났고, ② 회복상태에서, 10 luχ인 경우 서간에 1.26 μ V, 야간에 1.59 μ V였고, 100 luχ인 경우 서간에 2.63 μ V 야간에 3.65 μ V였으며, 400 luχ인 경우 서간에 2.52 μ V, 야간에 3.67 μ V로 나타났다.

Neurokinin B (NKB) and neurokinin B related peptide (NKBRP) belong to tachykinin peptide family. They act as a neurotransmitter and/or neuromodulator. Mutation of NKB and/or its cognate receptor, NK3R resulted in hypogonadotropic hypogonadism in mammals, implying a strong involvement of NKB/NK3R system in controlling mammalian reproduction. Teleosts possess NKBRP as well as NKB, but their roles in fish reproduction need to be clarified. In this study, NKB and NKBRP coding gene (tac3) was cloned from Nile tilapia and sequenced. Based on the sequence, Nile tilapia NKB and NKBRP peptide were synthesized and their biological potencies were tested in vitro pituitary culture. The synthetic NKBRP showed direct inhibitory effect on the expression of GTH subunits at the pituitary level. This inhibitory effect was confirmed in vivo by means of intraperitoneal (ip) injection of synthetic NKB and NKBRP to mature female tilapia (20 pmol/g body weight [BW]). Both NKB and NKBRP had no effect on the plasma level of sex steroids, E2 and 11-KT. However, NKBRP caused declines of expression level of GnRH I, Kiss2 and tac3 mRNAs in the brain while NKB seemed to have no distinct effect. These results indicate some inhibitory roles of NKBRP in reproduction of mature female Nile tilapia, although their exact functions are not clear at the moment.

Gonadotropin-inhibitory hormone (GnIH) has been found to inhibit the synthesis and release of gonadotropin (GTH) in avian and mammalian species. It was originally identified in the brain of a quail as a novel hypothalamic neuropeptide with a C-terminal Arg-Phe-NH2 motif (RFamide peptide). Homologs of this peptide have been identified in a couple of model fish species such as goldfish (Carassius auratus) and zebrafish (Danio rerio). Understanding GnIH system could be particularly useful in some aquaculture species with problems of frequent reproduction and/or precautious sexual maturation. However, GnIH system in such species has not been studied yet. In this study, we have identified a pupative GnIH gene in the Nile tilapia (Oreochromis niloticus). We also investigated the role of GnIH in the reproduction of this species. The full length sequence of putative tilapia GnIH gene coded for a protein (197 amino acids) containing two modified RFamides (MPLRF and LSQRF) and a LPQRF cDNA sequence of 594 bp. This putative GnIH gene showed high homology with the GnIH genes of Takifugu rubripes (72%) and Tetraodon nigroviridis (74%). PCR analysis showed that expression of this gene was ubiquitously distributed in the whole brain, ovary and testis as well as in the peripheral tissues examined in this study (liver, kidney, intestine, spleen, muscle and gill) except heart and eye. Expression level of this gene in sexually inactive group was significantly higher than the expression level in first gonadal development and sexually active groups (P<0.05). On the contrary, the expression level of LH-β gene was low in sexually inactive group but significantly higher in first gonadal development and sexually active groups (P<0.05). However, no significant difference was observed in the level of FSH-β gene expression between different reproductive phases in this species. In vitro studies revealed an inhibitory effect of GnIH on LH-β mRNA and FSH-β mRNA levels. No significant difference between GnIH and GnIH with LHRH-a treatments on LH-β and FSH-β mRNA expression in female tilapia pituitary cells.

Kiss/GPR 54 system은 포유류에서 성 성숙 및 번식과 연관되어 있는 것으로 밝혀지고 있으며, 어류의 성 성숙 및 번식 과정에서도 Kiss/GPR 54 system이 중요한 역할을 할 가능성이 높다. 어류에서는 포유류와 달리 Kiss1 뿐만 아니라 Kiss2 유전자도 존재한다는 것이 밝혀졌다. 어류에서 Kiss2는 대부분 아미노산 서열 FNFNPFGLRF를 갖는 decapeptide를 생성하는 유전자이다. Kiss2 유전자는 시상하부에서 GnRH neuron을 자극하여 GTH 분비를 촉진시킨다고 알려져 있다. 그러나 뇌하수체에서 kisspeptin의 직접적인 영향은 아직 불명확하거나 결과가 상이하다. 본 연구에서는 나일 틸라피아(O. niloticus)를 대상으로 나일 틸라피아 Kiss2 유전자의 kisspeptin-10(Kp-10, FNYNPLSLRF) 투여가 뇌하수체에서 직접적으로 번식관련 유전자를 조절할 수 있는지 in vitro 실험을 통해 조사하였다. 사용된 실험어는 나일 틸라피아로 체장과 체중은 각각 13.06±0.76 cm, 39.88±9.48 g이였다(n=16). 멸균조건에서 뇌하수체를 적출하여 96-multiwell plate에 80%(v/v) Leibovitz L15 medium(Gibco), pH 7.4, 10% fetal bovine serum, 100 IU/ml penicillin, 그리고 100 μg/ml streptomycin이 첨가된 배양액에 각각 수용하였다. 뇌하수체를 안정화시키기 위해서 암조건에서 27℃로 3시간 배양한 후 나일 틸라피아 Kiss2 유전자의 Kp-10을 첨가한 배양액(0, 0.01, 1, 100 μM)으로 교환해 주었다(n=4 per treatment). 새로운 배양액에서 16시간 배양 후 각각의 뇌하수체로부터 TRI Reagent (MRC, Inc.)를 이용해 total RNA를 추출하였다. 추출한 total RNA(1 μg)을 이용해 cDNA를 합성 한 후 Kp-10 투여 농도 별로 GTH subunits(LHβ와 FSHβ)의 발현량을 qRT-PCR로 비교하였고, 참조유전자는 β-actin을 이용하였다. 뇌하수체에서 LHβ, FSHβ mRNA 발현은 Kp-10 투여농도에 의존하여 영향을 받았다. LHβ, FSHβ 모두 Kp-10 1 μM 투여구에서 가장 높은 발현량을 나타냈으며, Kp-10 100 μM 투여구에서 다시 낮아지는 경향을 나타냈다. 이러한 결과는 100 μM의 농도가 mRNA 발현을 촉진시키는데 적정한 농도 수준을 벗어난 과도한 농도였기 때문으로 판단된다. 본 연구는 뇌하수체에서 Kisspeptin이 직접적으로 GTH subunits을 조절할 수 있다는 가능성을 확인하였다. 그러나 Kisspeptin을 이용한 최적의 투여효과를 조사하기 위해서는 Kp-10 농도범위와 배양시간을 좀 더 세분화하여 실험을 진행할 필요가 있다.

Kisspeptin has been implicated in the process of puberty onset in various animal groups. This peptide is encoded by a gene, Kiss1 in avian and mammalian species. Contrary to these higher vertebrates, however, fish appeared to have another gene, Kiss2 that also codes for the precursor peptide of kisspeptin. To figure out biological significance of this gene during the puberty onset in fish, the expression profile of Kiss2 gene was investigated in the brain of Nile tilapia together with genes of GPR54, GnRH receptorI (rGnRHI) and GTH subunits ( and ). Expression of Kiss2 mRNA significantly increased at 2 weeks post hatch (wph) and 13 wph (<0.05). This increase coincided with the increases of GPR54 and rGnRH I gene expression. Detection of and subunit gene expression was possible later than 13 wph, indicating the activation of gonadotrophs in the pituitary. Data obtained from this study strongly suggest that, in addition to Kiss1 gene, Kiss2 gene is deeply associated with the onset of puberty by the activation of hypothalamus pituitary gonadal axis in Nile tilapia.

Fish reproduction is influenced by various external environmental factors. Among these factors, changes of photic conditions are thought be most closely related to the reproduction of many fish species. In recent studies, melatonin that mediates the changes of photic condition outside has been used in an attempt to get a similar effect to photoperiod manipulation without changing photoperiod. However, the effects of exogenous melatonin vary depending on life stages. We have previously investigated the effect of melatonin on reproductive activity in mature Nile tilapia (Oreochromis niloticus). In this study, effects of exogenous melatonin on the spawning activity, the rate of mouth brooding success rate and early survival rate of lavae produced from melatonin treated Nile tilapia were investigated. Nile tilapia at the time of puberty were randomly divided into three groups and fed on control (0 ㎍/g), low-dose melatonin (2.5 ㎍/g BW) or high-dose melatonin (25 ㎍/g BW) diet. Fish were reared indoor tanks at 27～28℃ under natural-photoperiod and fed twice a day at 10:00 and16:00 during the experiment (120 days). Fish were sampled to examine growth and gonadal development on Day 30, 60, 90 and 120. There were no significant differences of somatic growth between control (no melatonin) and melatonin-treated groups, indicating that melatonin administration did not cause any negative effects on the growth of experimental fish. The patterns of gonadal development were almost the same between control and melatonin-treated groups. In juvenile tilapia, treatment with low-dose melatonin resulted in the increase of spawning rate, the rate of mouth brooding success and early survival rate of laval tilapia. However, high-dose melatonin resulted in the decrease of spawning rate, the rate of mouth brooding success and early survival rate of laval tilapia, although the earliest spawning occurred in one of the high-dose group fish. Fish in high-dose melatonin group failed to recover from reproductively suppressed state even after the cease of melatonin treatment, indicating that too much melatonin might act negatively on spawning activities and gonadal maturation in Nile tilapia. In conclusion, the results from this study suggest the possibility that a pertinent dose of melatonin treatment can effectively accelerate the spawning rate and the rate of mouth brooding success, and bring positive effects on early survival rate of tilapia lavae.

Water temperature influences on various key biological events in fish, but the internal pathway of the temperature effects are not well understood. Heat shock proteins (HSPs), known to respond in the level of cells to many environmental factors including temperature, could improve our understanding on the pathway. Some biological processes such as gonadal development and sex differentiation in the Nile tilapia Oreochromis niloticus is particularly sensitive to water temperature. In this study, we have investigated the expressions of HSP70 and HSP90 genes in young tilapia at an ordinary temperature () and elevated water temperature (). The distribution of the expressions of HSP70 and HSP90 mRNA in this species were found to be almost ubiquitous, being detected in all tissues studied here (brain, gonad, liver and muscle), suggesting the house keeping functions of these genes. Heat shock by elevating temperature from to significantly increased the expression of HSP70 mRNA in the gonad, liver and muscle for several hours (P<0.05) (brain tissue was not examined for this). The increased level of HSP70 gene expression recovered to the level at control temperature () when fish were kept continuously at high temperature () for 24 hours. Contrary to this, expression of HSP90 mRNA did not show significant increase in the gonad and muscle by the same heat shock (P>0.05), except in the liver where the expression of HSP90 mRNA increased continuously for 24 hours at . The results obtained in this study suggest that response to temperature change in different tissue or organ may utilize different heat shock proteins, and that HSP70 may have some importance in temperature-sensitive gonadal event in the Nile tilapia.

Photoperiod is known to be the most potent environmental stimulus for reproduction in many lower vertebrates, and it exerts an endogenous effect by causing a rhythmic change in melatonin level, which increases during the dark phase and decreases during the light phase. In recent studies, melatonin administration was capable of changing seasonal reproductive activities in several fish species, and also resulted in modulating the timing of smoltification in a salmonid fish (Amano et al., 2004; Ligo et al., 2005). In this study, we have investigated the changes of spawning activities (number of eggs, frequency of spawning) by oral administration of melatonin in the Nile tilapia, Oreochromis niloticus. Fish were obtained from a local fish farm (Chungju, Chung Buk) and acclimatized in fish rearing facilities in Sunmoon University (Asan, Chung Nam). Randomly selected 24 fishes (12 males, 12 females; 200～400 g in body weight, BW) were divided into three groups and each fish was accommodated into glass aquarium individually. Fish were fed either with control diet (0 ㎎ melatonin) or low-dose melatonin diet (0.3 ㎎ melatonin/㎏, BW) or high-dose melatonin diet (3 ㎎/㎏, BW). Fish were individually checked everyday for the presence of eggs in their mouths, and the eggs were removed and counted when found. Fish were fed twice a day, but melatonin treated diet was given only once a day at 10:00a.m.. The daily feeding ration was set at 2% of the body weight so that the fish ate all the pellets provided. Fish were sampled for blood parameters (Hb, Glu, GOT, GPT) on March 2 (Day 30), April 2 (Day 60), May 3 (Day 90), June 3 (Day 120) and July 14 (Day 160). The sampling was done between 14:00 and 16:00 p.m.. For the sampling, fish were anesthetized in 50 ppm benzocaine, and body length (BL) and BW were measured. Blood sample was collected using a heparinized syringe from the caudal blood vessel. Melatonin affects several photoperiodic signals including reproductive activities in fish. Low-dose melatonin administration appeared to disturb spawning and sexual maturation in Nile tilapia in this study. Fish treated with low-dose melatonin spawned less numbers of egg than the fish treated with high-dose. In contrast, high-dose melatonin administration caused more frequent spawning than low-dose melatonin. On the other hand, somatic growth and blood parameter were not affected by melatonin treatments. These results suggest that pertinent melatonin could be involved in providing photoperiodic information as short day photoperiod. Fish treated with over dose melatonin seemed to have no melatonin-free interval. In that circumstance the melatonin message might have not been conveyed as a proper signal.

Nile tilapia (Oreochromis niloticus) are mouth-brooders so that the females holding eggs in their mouth sacrifice their somatic growth for reproduction. For this reason, artificial control of reproduction for the culture of this species has been of interest. Manipulation of photoperiod is an emerging technique for such purpose, but little information is available to establish appropriate photoperiod regime. To obtain necessary basic information, sexually mature females were individually accommodated to glass aquarium, and the spawning activity of these females were monitored for two years under natural photoperiod regime. Female tilapia spawned most frequently on March, April and May when the day length gradually increased from 11 hours to 14 hours and least frequently on September, October, November and December when the day length gradually decreased from 13 hours to less than 10 hours in the first year. The decrease of spawning frequency as day length decreased was also observed in the second year, although the increase of spawning frequency as day length increased was less clear. Spawning of female tilapia was less active when the night was dark due to the disappearance of moonlight (Dark Phase), compared to the Phase of Getting Lighter, Light Phase and Phase of Getting Darker. Results from this study suggest that long day length, particularly increasing phase, is favoured for active spawning of Nile tilapia, and that this species, as a tropical fish species, may utilize changing lunar phases as a secondary environmental cue for reproduction.

어류의 체내에서 성분화를 유도하는 물질이 성스테로이드호르몬(sex steroid hormone)이라는 사실이 잘 밝혀져 있으며, 성스테로이드 생합성 효소의 하나인 aromatase도 성분화에 직접적인 역할을 하는 것으로 알려져 있다. 본 연구에서는 유전적으로 암컷인 틸라피아 자어(larvae) 집단을 aromatase 저해제(aromatase inhibitor, AI)인 Fadrozole로 침지 처리하여 초기 발생단계 중 어느 시기에 aromatase가