首页 >  水产学报 >  LED光色及注射褪黑素对虹鳟抗氧化酶活性及相关激素含量的影响

2021, 45(1): 44-54. doi: 10.11964/jfc.20200812379

LED光色及注射褪黑素对虹鳟抗氧化酶活性及相关激素含量的影响

1. 中国海洋大学,海水养殖教育部重点实验室,山东 青岛    266100

2. 青岛海洋科学与技术国家实验室,海洋渔业科学与食物产出过程功能实验室,山东 青岛    266235

3. 海南热带海洋学院水产与生命学院,海南 三亚    572022

通讯作者: 李丽, l_li@ouc.edu.cn

收稿日期:2020-08-20
修回日期:2020-09-17

基金项目:   国家重点研发计划(2017YFE0122100) 

关键词: 虹鳟 , 光色 , 抗氧化酶 , 皮质醇 , 褪黑素

Effects of LED colors and melatonin treatment on antioxidant enzyme activities and relevant hormone concentrations of rainbow trout (Oncorhynchus mykiss)

1. Key Laboratory of Mariculture, Ocean University of China, Ministry of Education, Qingdao    266100, China

2. Function Laboratory for Marine Fisheries Science and Food Production Processes, Qingdao National Laboratory for Marine Science and Technology, Qingdao    266235, China

3. School of Aquaculture and Life, Hainan Tropical Ocean University, Sanya    572022, China

Corresponding author: Li LI, l_li@ouc.edu.cn

Received Date:2020-08-20
Accepted Date:2020-09-17

Keywords: Oncorhynchus mykiss , light color , antioxidant enzyme , cortisol , melatonin

为探究光色对虹鳟抗氧化酶活性及相关激素含量的影响,对体质量(42.0±1.5) g的虹鳟进行了28 h的持续光照及注射褪黑素处理。实验设置白、红、绿、蓝4种光色,注射和不注射褪黑素两种处理方法,共8个处理组,分别在实验开始后的4、8、12、16、20、24和28 h取样,检测血清SOD和头肾CAT的活性以及血清皮质醇和褪黑素的含量。结果显示:①SOD和CAT活性以及皮质醇含量均呈现先下降后升高再下降后趋于平稳的趋势,在实验16 h处于较高水平,实验24~28 h趋于稳定。②SOD和CAT平均活性以及皮质醇平均含量均为红光下显著高于其他光色下,除CAT平均活性绿光与白光下差异不显著外,SOD活性和皮质醇含量均为绿光下显著低于其他光色下。③注射褪黑素使SOD和CAT活性以及皮质醇含量在28 h持续光照过程中呈下降趋势;相比较未注射处理组,注射褪黑素在各光色下均可显著降低SOD和CAT活性及皮质醇含量,提高褪黑素含量。研究表明,在28 h急性光照射下,虹鳟在16 h受到的胁迫最强烈,实验后期机体逐渐适应光环境;红光对虹鳟氧化胁迫最强烈,绿光对虹鳟基本不产生胁迫;注射褪黑素可缓解光照对虹鳟的胁迫作用。

At present, marine aquaculture in China and other countries around the world is mainly carried out in shallow coastal waters, which has caused a series of environmental problems and affected the sustainable development of aquaculture. Chinese researchers have been working on salmon mariculture far offshore in the Yellow Sea, and rainbow trout (Oncorhynchus mykiss) is one of the popular salmonid. Light color, which can affect the entire life cycle of aquatic species, is an important factor in the management of far offshore cultures. The sunlight irradiated on the water surface enters the water body after refraction, and the incident light will be absorbed and scattered strongly by the water and will attenuate rapidly. Blue light has strong penetrating power in clean sea water. Red light and ultraviolet light attenuate rapidly when passing through clean water. It is important to explore the effects of light color on the antioxidant enzyme activities and related hormone concentrations of O. mykiss, which will provide important information for the practical management of far offshore cultures. O. mykiss were injected with different concentrations of melatonin (0 and 3 mg/mL) and were exposed under four light colors (white, red, green, and blue) for 28 hours. Totally eight treatments were set up i. e. white light group of control, red light group of control, green light group of control, blue light group of control, white light group treated with melatonin, red light group treated with melatonin, green light group treated with melatonin, and blue light group treated with melatonin. O. mykiss (42.0±1.5) g were cultured in twenty-four tanks (PVC, length× height× width: 80 cm× 60 cm× 50 cm) and all tank sides were covered with opaque covers, light sources were placed above the surface of water. Serum and head kidney tissues of O. mykiss were collected at 4, 8, 12, 16, 20, 24, and 28 hours of the experiment to detect superoxide dismutase (SOD), cortisol, and melatonin in serum and catalase (CAT) in head kidney. The results showed that the activities of SOD and CAT, and the concentrations of cortisol were higher at 16 hours and were stable from 24 to 28 hours during the study. The average activities of SOD, CAT, and the average concentrations of cortisol in red light groups were significantly higher than the other light groups (P < 0.05). And the average activities of SOD and the average concentrations of cortisol in green light groups were significantly lower than the other light groups. The average activities of CAT in green light groups were significantly lower than the red and blue light groups. The SOD and CAT activities and cortisol concentrations in O. mykiss injected with melatonin showed a down trend during the experiment. Compared with the non-injection melatonin groups, melatonin injection made the activities of SOD and CAT and the concentrations of cortisol decrease significantly and the concentrations of melatonin increase significantly in O. mykiss. This study indicated that in a 28-hour experiment, O. mykiss were strongly stressed by light at 16 hours, and then the fish adapted to the light environment; red light stressed O. mykiss and green light did not produce stress; injection melatonin could release red light pressure for fish. In sum, green light and intraperitoneal melatonin injection could be used in O. mykiss production to relieve the fish oxidative stress response. Red light stresses fish and is unsuitable for fish cultivation. Long-term experiments should be carried out to study the effects of different light colors on the growth, physiological, and biochemical responses of O. mykiss.

目前,包括中国在内的世界各国海水养殖主要在近岸浅水海域开展,产生了一系列环境问题,影响了水产养殖业可持续发展,而发展深远海养殖是解决这些问题的重要方法[1]。我国已建成养殖工船和全潜式深水网箱“深蓝1号”,开始在黄海冷水团海域进行鲑鳟鱼类试养工作[2]。虹鳟(Oncorhynchus mykiss),属鲑形目(Salmoniformes),鲑科(Salmonidae),大麻哈鱼属(Oncorhynchus),具有很高的经济价值,是发展黄海冷水团绿色养殖的重要备选鱼类之一。

不同波长的光因穿透力不同,在不同深度的海水中分布不同[3],例如在干净的海水中,长波光红光会被迅速吸收,较深处海水中短波光蓝光因穿透力强而占主导地位。硬骨鱼具有感光细胞,可帮助其辨别特定波长(277~737 nm)的光[4]。光色作为重要的环境因子,对养殖鱼类的影响不容忽视。前期研究表明,适宜光色对鱼类免疫、抗氧化应激等方面起到促进作用,不适宜光色会对鱼类产生环境胁迫[5-10]。深水网箱中光照不足且以短波光为主,因此急需开发深水网箱中的智能补光技术。

现有研究关于光色对虹鳟的胁迫、抗氧化应激等方面的影响结论不一:Heydarnejad等[11]发现红光使虹鳟产生强烈的应激反应,生长受到抑制;但Karakatsouli等[7]研究发现,虹鳟生长的最佳光色是红光。光色对虹鳟的影响较为复杂且影响机制尚未完全明确,仍需更多的基础研究提供理论支撑[12]

当鱼类受到胁迫发生应激反应时,机体的抗氧化酶防御系统在清除氧自由基方面发挥着重要作用,其中超氧化物歧化酶(SOD)和过氧化氢酶(CAT)是重要的抗氧化物酶[13];皮质醇是硬骨鱼重要的应激激素,研究证明环境胁迫可促进血清皮质醇含量激增。硬骨鱼类的褪黑素是由松果体产生的一种抗氧化剂[14-15],可消除机体内自由基[16-17];现有研究表明,将褪黑素注射到硬骨鱼体内可以有效缓解机体因缺氧、捕捞、低水位和高密度养殖等产生的胁迫[18-19],但对其能否改善不适宜光色带来的应激尚不清楚。此外,为鱼体注射褪黑素能否影响抗氧化酶活性、皮质醇及内源褪黑素含量还需研究。

在鱼类养殖中应用广泛的发光二极管(LED)具有功效低、寿命长、效率高、光色可调节等优点,同样适用于光实验的研究中[20-21]。本研究在实验室养殖条件下,探讨不同LED光色及注射褪黑素对虹鳟抗氧化酶活性及相关激素含量的影响,以期为开发深水网箱中虹鳟的智能补光技术提供理论支持。

1    材料与方法

1.1    实验条件

本实验于2019年6月在中国海洋大学鱼山校区水产馆实验室进行。实验用虹鳟购自山东潍坊鸢柳淡水鱼养殖场,种质来源相同,体表无损伤、活力正常。

实验用虹鳟先在7个PVC水族箱(长×宽×高:80 cm×60 cm×50 cm,水体约240 L)中暂养2周,以白光(全光谱)LED灯(发光二极管)作为光源,光照周期为12 h光照∶12 h黑暗(早08:00开灯,晚20:00关灯),随机选取水面6个点进行光强检测,测得光照强度平均值为260 lx。暂养期间每天于08:00和16:00各投喂1次商品配合饲料(水分8.0%、粗蛋白50.5%、粗脂肪12.6%、灰分15.0%),日投喂量为鱼体总体质量的2%。投喂2 h后换水,每次换水量为水体总体积的100%。养殖用水为经过24 h曝气处理的自来水。每天使用便携式溶解氧仪(YSI 550A, Fisher Scientific, Hanover Park, Illinois, USA)、盐度计(YSI EC300A, Fisher Scientific, Hanover Park, Illinois, USA)、pH计(YSI pH100A, Fisher Scientific, Hanover Park, Illinois, USA)测定水温[(16.5±0.5)°C]、盐度(0.6)、pH (8.0±0.8)等指标。养殖水族箱采用充氧泵不间断曝气,以提供充足溶解氧[(6.8~7.7) mg/L]。暂养期间维持各水质指标稳定:总氨氮(TAN)不高于1.0 mg/L、硝态氮(−N)不高于2.0 mg/L、亚硝态氮(−N)不高于0.5 mg/L。

1.2    实验设计

暂养结束时禁食24 h以确保酶活性和激素含量的基本水平,选取规格均一的虹鳟[体质量(42.0±1.5) g,体长(14.5±0.5) cm]放入玻璃纤维水族箱(长×宽×高:60 cm×40 cm×30 cm)中开始实验。实验采用双因子完全正交组合设计,设置白光(全光谱,对照组)、红光(620 nm)、绿光(540 nm)和蓝光(450 nm)4种光色,注射和不注射褪黑素2种处理方式,共8个处理组,即不注射褪黑素白光组(white light group of control, CW)、不注射褪黑素红光组(red light group of control, CR)、不注射褪黑素绿光组(green light group of control, CG)、不注射褪黑素蓝光组(blue light group of control, CB)、注射褪黑素白光组(white light group treated with melatonin, TW)、注射褪黑素红光组(red light group treated with melatonin, TR)、注射褪黑素绿光组(green light group treated with melatonin, TG)、注射褪黑素蓝光组(blue light group treated with melatonin, TB),每个处理分别设3个独立的养殖水族箱作为3个重复,每个水族箱中饲养虹鳟7尾,实验过程中不投饵。

实验光源为LED灯(发光二极管)。为避免环境光源干扰,水族箱所有面均用不透光油纸覆盖,水族箱顶部设置一不透光PVC板以固定光源,光照强度与暂养期间相同。实验开始前配制褪黑素溶液,按照每克实验用鱼30 μg褪黑素粉末(Sigma)称取110 mg褪黑素溶解在0.9%生理盐水中。鱼经麻醉剂MS-222(Sigma, USA)麻醉后,腹腔注射褪黑素溶液(每克体质量10 μL),于早07:00完成褪黑素注射后,立即将鱼放回水族箱观察,开始实验计时。

1.3    样品的收集、保存与处理

实验共进行28 h,实验过程中每隔4 h取样1次,采样时间为11:00、15:00、19:00、23:00、03:00、07:00、11:00 (分别标记为T4、T8、T12、T16、T20、T24、T28)。

每次每个水族箱取虹鳟1尾进行取样,每个处理采集3尾,用MS-222 (Sigma, USA)麻醉后立即采集血液和头肾。采集的血液在4 °C条件下静置过夜,之后置于低温离心机中离心10 min(4 °C,3000 r/min),随后取上清液置于−80 °C超低温冰箱保存用于后续检测。头肾组织离体后立即放入液氮中快速冷冻,后置于−80 °C超低温冰箱保存用于后续检测。为降低环境光色干扰,采样在昏暗环境中进行。

血清中褪黑素、皮质醇和SOD活性使用酶联免疫吸附(ELISA)测定试剂盒(上海艾莱萨生物科技有限公司)检测。头肾(g)与生理盐水(mL)按照1∶9混合,组织匀浆(4 °C,3000 r/min,离心20 min)后取上清液,用可见光法试剂盒(南京建成生物工程研究所)测定CAT活性。

1.4    数据分析

实验数据均采用平均值±标准差(mean±SD)表示。使用SPSS 24软件进行数据分析。采用Kolmogorov-Smirnov检验和Levene检验方法分别进行数据的正态分布检验和方差齐性检验。对符合正态分布且方差齐的样本进行单因素方差分析(One-Way ANOVA),分析不同处理虹鳟的血清SOD和头肾CAT活性及血清皮质醇和褪黑素含量的差异显著性,若差异显著(P<0.05),使用Turkey检验进行组间多重比较分析。抗氧化酶活性及激素含量在注射与未注射褪黑素组的差异使用t检验进行比较,显著水平P<0.05。对符合正态分布且方差齐的样本进行三因素方差分析(Three-Way ANOVA),分析取样时间、光色及褪黑素处理对不同测试指标的影响。

2    结果

2.1    光色及注射褪黑素对虹鳟血清SOD活性的影响

实验过程中,除TB组外,其余处理组的SOD活性在不同取样时间差异显著(P<0.05)。未注射褪黑素的虹鳟,SOD活性随时间呈先下降后升高再下降后平稳的趋势。除CW组外,其余处理组均为T4时活性显著高于T8时(P<0.05),T4和T16时无显著差异(P>0.05),且高于T20~T28时。腹腔注射褪黑素的虹鳟,血清SOD活性随时间呈下降趋势。TR组SOD活性在T4时显著高于T24和T28时(P<0.05);TW组T8时显著高于T16时(P<0.05);TG组T4和T8时显著高于T28时(P<0.05)(图1-a)。

图1 不同处理组虹鳟血清SOD(a)和头肾CAT(b)活性及血清皮质醇(c)和褪黑素(d)含量变化趋势 Figure1. Fluctuations of O. mykiss serum SOD (a) and head kidney CAT (b) activities, serum cortisol (c) and melatonin (d) concentrations at different treatments during the period of the experiment

各处理组SOD活性在各取样时间点均存在显著差异(P<0.05)(表1),且注射褪黑素组(TW、TR、TG和TB)的虹鳟血清SOD活性显著低于未注射褪黑素组(CW、CR、CG和CB) (P<0.05)。未注射褪黑素组,CR组活性显著高于CG组(P<0.05);除T20外,CR组均显著高于CW组(P<0.05);除T16外。CR组均与CB组无显著差异(P>0.05)。CR组平均活性显著高于其他光色下(P<0.05),CG组平均活性显著低于其他光色下(P<0.05)。注射褪黑素组,除T16外,TR组均显著高于TG和TW组(P<0.05);除T12、T16和T24时外,TR组均显著高于TB组(P<0.05)。

表1 同一时间不同处理虹鳟血清SOD和头肾CAT活性及血清皮质醇和褪黑素含量差异的单因素方差分析 Table1. O. mykiss serum SOD and head kidney CAT activities, serum cortisol and melatonin concentrations among different treatments at the same sampling time based on One-Way ANOVA
指标
parameters
显著性(P值) significance (P value)
T4T8T12T16T20T24T28
SOD/(U/mL) *** *** ** *** ** ** **
CAT/(U/mg prot) *** *** *** *** *** *** ***
皮质醇/(pg/mL) cortisol NS * * ** *** ** **
褪黑素/(pg/mL) melatonin *** *** * *** ** *** ***
注:P为显著性水平。NS为无显著性差异,*为存在显著性差异且P<0.05,**为存在显著性差异且P<0.01,***为存在显著性差异且P<0.001,下同
Notes: NS is no significant difference, * is significant difference at P<0.05, ** is significant difference at P<0.01, *** is significant difference at P<0.001, the same below
表1 同一时间不同处理虹鳟血清SOD和头肾CAT活性及血清皮质醇和褪黑素含量差异的单因素方差分析
Table1. O. mykiss serum SOD and head kidney CAT activities, serum cortisol and melatonin concentrations among different treatments at the same sampling time based on One-Way ANOVA

三因素方差分析结果显示,取样时间、光色和褪黑素处理均显著影响SOD活性(P<0.001),取样时间与褪黑素处理、光色与褪黑素处理均对SOD活性的影响存在交互作用,且取样时间、光色及褪黑素处理三因素间存在交互作用(表2)。

表2 时间、光色和褪黑素处理及其交互作用在虹鳟血清SOD和头肾CAT活性及血清皮质醇和褪黑素含量差异的三因素方差分析 Table2. Effects of sampling time, light colors, melatonin treatments and their interactions on O. mykiss serum SOD and head kidney CAT activities, serum cortisol and melatonin concentrations based on Three-Way ANOVA
指标
parameters
显著性(P值) significance (P value)
时间
time
光色
color
褪黑素
melatonin
时间×光色
time×color
时间×褪黑素
time×melatonin
光色×褪黑素
color×melatonin
时间×光色×褪黑素
time×color×melatonin
SOD/(U/mL) *** *** *** NS *** ** *
CAT/(U/mg prot) *** *** *** ** *** ** NS
皮质醇/(pg/mL) cortisol *** *** *** * *** *** *
褪黑素/(pg/mL) melatonin NS *** *** NS *** NS NS
表2 时间、光色和褪黑素处理及其交互作用在虹鳟血清SOD和头肾CAT活性及血清皮质醇和褪黑素含量差异的三因素方差分析
Table2. Effects of sampling time, light colors, melatonin treatments and their interactions on O. mykiss serum SOD and head kidney CAT activities, serum cortisol and melatonin concentrations based on Three-Way ANOVA

2.2    光色及注射褪黑素对虹鳟头肾CAT活性的影响

实验过程中,所有处理组的CAT活性在不同取样时间差异显著(P<0.05)。未注射褪黑素的虹鳟,CAT活性随时间呈先下降后升高再下降后平稳的趋势。CW、CR、CG和CB组均为T4和T16时活性显著高于T24和T28时(P<0.05),T8和T12时显著低于T4时(P<0.05),T24和T28时无显著差异(P>0.05)。注射褪黑素的虹鳟,血清CAT活性随时间呈下降趋势。TW、TR、TG和TB组的活性均为T4和T16时显著高于T24和T28时(P<0.05),除TW组外,T12~T20时其余处理组间差异均不显著(P>0.05),但活性随时间变化呈下降趋势(图1-b)。

各处理组CAT活性在每个取样时间点均存在显著差异(P<0.001)(表1),且注射褪黑素组(TW、TR、TG和TB)活性显著低于未注射褪黑素组(CW、CR、CG和CB)(P<0.05)。未注射褪黑素组,CR组活性最高。除T4~T12时外,CR组均显著高于CG组(P<0.05),除T4和T12~T16时外,CR组均显著高于CW组(P<0.05),T24和T28时CR组显著高于CB组(P<0.05)。CR组平均活性显著高于其他光色下(P<0.05),除CW组外,CG组平均活性显著低于其他光色下(P<0.05)。注射褪黑素组,TR组活性均高于TG组,T8和T20~T24时,TR组显著高于TW组(P<0.05),T4~T28时,TR和TB组均无显著差异(P>0.05)。

三因素方差分析结果显示,时间、光色和褪黑素处理(P<0.001)对CAT活性的单独影响显著,且时间与光色、时间与褪黑素处理以及光色与褪黑素处理间均存在交互影响(表2)。

2.3    光色及注射褪黑素对虹鳟血清皮质醇含量的影响

实验过程中,除CR组外,其余处理组皮质醇含量在不同取样时间差异显著(P<0.05)。未注射褪黑素的虹鳟,T4、T16和T20时皮质醇含量较高,且随时间呈先下降后升高再下降后平稳的趋势。CW和CG组,T16时含量均显著高于T24~T28时(P<0.05),且与T4时无显著差异(P>0.05);CB组T20时显著高于其他时间(P<0.05),但与T16时差异不显著(P>0.05)。注射褪黑素的虹鳟血清皮质醇含量随时间呈下降趋势。各处理组T4时含量最高,且T8~T16时均无显著差异(P>0.05);除TW组外,其余处理组T4时均显著高于T16~T28时(P<0.05)(图1-c)。

除T4时外,8个处理组的皮质醇含量在各取样时间点均存在显著差异(P<0.05)(表1)。注射组(TW、TR、TG和TB)皮质醇含量低于未注射组(CW、CR、CG和CB)。未注射褪黑素组,T4和T8时CW、CR、CG和CB组差异不显著(P>0.05),但CR含量较高。除T16外,CR组均显著高于CG组(P<0.05);除T12和T28外,CR组均显著高于CW组(P<0.05);除T12外,CR与CB组均无显著差异(P>0.05)。CR组平均含量显著高于其他光色下(P<0.05),CG组平均含量显著低于其他光色下(P<0.05)。注射褪黑素组中,TR组含量均显著高于其他光色组(P<0.05),且TW、TG和TB组间无显著差异(P>0.05)。

三因素方差分析结果显示,时间、光色及褪黑素处理对虹鳟血清皮质醇含量影响的单独效应显著(P<0.001),且三因素间存在显著的交互作用(P<0.05)。

2.4    光色及注射褪黑素对虹鳟血清褪黑素含量的影响

实验过程中,除CB和TB组外,其余处理组褪黑素含量在不同取样时间均无显著差异(P>0.05)。CB组T28时含量显著低于T4时(P<0.05),TB组T4时含量显著高于T24时(P<0.05) (图1-d)。

各处理组褪黑素含量在各取样时间点均存在显著差异(P<0.001)(表1),且注射褪黑素组(TW、TR、TG和TB)的血清褪黑素含量显著高于未注射褪黑素组(CW、CR、CG和CB)(P<0.05)。未注射褪黑素组,除T4外,CR组均显著高于CW、CG和CB组(P<0.05)。注射褪黑素组,除T28时TR与TB组差异不显著外(P>0.05),TR组均显著高于其他处理组(P<0.05)。

对取样时间、光色及褪黑素处理三因素进行方差分析,结果表明,光色和褪黑素处理对血清褪黑素含量存在单独效应(P<0.001),仅时间与褪黑素处理存在交互作用(P<0.001),其他的影响均不显著(表2)。

3    讨论

光色在水中分布不均匀,水深1 m处的干净海水中长波光红光会被迅速吸收,10 m深处短波光蓝光因穿透力强而占主导地位;因蓝光更容易被水中溶解的有机物和颗粒物吸收,在透明度低的水体中,短波光蓝光逐渐被中波长的绿光或黄光取代,水体颜色发生改变[3]。视网膜和松果体是虹鳟的感光器官,视杆细胞和视锥细胞组成虹鳟的感光细胞,其中视锥细胞包括短、中和长波长视蛋白[22-23],帮助虹鳟感知外界光信号、识别特定波长(277~737 nm)的光[4]。本研究选择光学三原色红光(620 nm)、绿光(540 nm)和蓝光(450 nm)作为实验光色,可以被虹鳟识别,因全光谱的白光是自然光的最佳替代光源,故选取白光作为对照光色。

3.1    光色对抗氧化酶的影响

当外界环境或机体内环境发生剧烈变化时,鱼类会发生应激反应,产生大量的氧自由基(ROS)危害机体健康[24-25]。鱼类作为低等脊椎动物,其特异性免疫系统发育较不完善,非特异性免疫系统特别是抗氧化系统在抵抗外界环境胁迫方面发挥着重要的作用[26]。抗氧化酶系统主要由SOD和CAT等酶组成,用于抵抗外界对机体的氧化应激。SOD能够清除机体内部的活性氧自由基,将其转化为H2O2,随后在CAT等酶的作用下继续分解成水和氧气,减少机体的氧化应激损伤[27]。本研究结果显示,28 h急性光色照射使虹鳟血清SOD和头肾CAT的活性变化呈现先降低后升高再降低后平稳的趋势。表明实验进行至16 h,光色对鱼体产生胁迫,机体通过抗氧化防御系统产生大量抗氧化酶以应对光色胁迫[28],24 h后鱼体逐步适应环境光色。Shin等[21]和Jung等[29]分别研究了28和24 h不同光色照射(不同光色处理组光照强度相同)对克氏双锯鱼(Amphiprion clarkii)和金鱼(Carassius auratus)的影响,表明抗氧化酶SOD和CAT活性在16 h下降,分别在28和24 h再次升高,没有表现出光色适应性。由此可知,鱼体对光色的适应存在种类差异性。SOD和CAT等抗氧化酶活性受相关基因调控,外界胁迫会作用于鱼体Keap1-Nrf2-ARE信号通路,激活下游基因转录,进而翻译出SOD和CAT等蛋白酶以发挥抗氧化等生理功能[30]。Shin等[21]的研究得出红光可诱导克氏双锯鱼氧化应激,引起SOD和CAT等酶活性升高。相似的是,在本研究中红光组虹鳟血清SOD和头肾CAT平均活性最高,受到的氧化应激最强烈。Heydarnejad等[11]也得出结论,红光会对虹鳟造成胁迫,影响虹鳟福利。Choi等[31]研究表明,因黑双锯鱼(A. melanopus)的感光细胞无法感知长波光,红光成为一种应激源诱导了黑双锯鱼的氧化应激反应,而虹鳟的光感受细胞对红光的感知能力有待进一步探究。综上所述,虹鳟在24 h后可逐步适应光环境,且红光对虹鳟的氧化应激最强烈。

3.2    光色对皮质醇的影响

皮质醇是肾上腺皮质释放的一种应激激素,当环境光色对鱼体产生胁迫时会激活下丘脑—垂体—肾间组织轴(HPI),诱导皮质醇的合成与释放[32]。有研究表明,鱼体受到急性应激后的5~10 min皮质醇迅速升高,24 h后恢复至正常值[33],因此皮质醇常被用作表征机体急性应激反应的指标。抵抗胁迫是一个能量消耗的过程,需要鱼体消耗大量的储能物质以补充机体所需的能量消耗[34]。皮质醇可促进糖原分解增加葡萄糖含量,并通过糖异生作用促进脂质的利用,进而为机体供能[35]。本研究中,虹鳟血清皮质醇含量在16 h出现峰值,随后有下降趋势。表明光色胁迫在16 h时最强,鱼体需要消耗大量能量以抵抗氧化胁迫,后逐渐适应环境光色和胁迫缓解。Song等[36]研究表明,红光下饲养金鱼使其皮质醇含量升高,绿光下皮质醇含量降低。Volpato等[37]研究表明,绿光下养殖的尼罗罗非鱼(Oreochromis niloticus)皮质醇含量显著低于红光下。Luchiari等[38]研究指出,中波长的绿光是虹鳟生长的最佳光色;也有研究表明,绿光照射可有效缓解高温对鱼体造成的胁迫反应[29]。本研究也得出类似结论,红光组虹鳟血清皮质醇含量最高,受到的胁迫最强;绿光组含量最低,胁迫程度最弱或未受到胁迫。

3.3    光色对褪黑素的影响

López-Patiño等[18]研究发现,虹鳟受到高密度养殖和水位降低的胁迫时,其血清褪黑素含量显著低于对照组含量。这可能是因为当机体处于应激状态时,非特异性免疫系统产生的褪黑素用于清除机体内的氧自由基,使在血清中被检测到的褪黑素含量显著降低。胁迫条件下,与褪黑素产生有关的5-羟色胺含量增加、芳基烷基胺N-乙酰基转移酶表达量下调也会抑制褪黑素的合成[18]。此外,褪黑素的分泌受光色调节,且不同光色的调节作用存在差异,如红光等长波光穿透鱼类脑部的能力较强,对调节松果体中褪黑素的分泌更显著[39]。有研究表明,红光会抑制欧鳎(Solea senegalensis)体内褪黑素的分泌,使欧鳎产生氧化应激[19]。本研究也发现,红光组褪黑素含量显著低于其他光色组,红光对虹鳟的氧化胁迫最强烈。此外,有报道称红光作为胁迫光色会诱导鱼类视网膜细胞凋亡[36],进而对多种鱼类的生长、免疫产生抑制作用;Villamizar等[20]研究表明,舌齿鲈(Dicentrarchus labrax)仔稚鱼因受到红光胁迫而生长缓慢。由此得出,红光对虹鳟产生了一系列胁迫反应,可能不适于虹鳟的养殖。

3.4    注射褪黑素对抗氧化酶、皮质醇和褪黑素的影响

硬骨鱼类的褪黑素是一种能高效清除羟基和过氧自由基的抗氧化剂[10,19,40-41]。目前,很多研究通过注射褪黑素来缓解鱼类的应激反应[21,29,42-44],如López-Patiño等[19]曾报道注射褪黑素可以减轻环境胁迫对欧鳎造成的应激反应。外源褪黑素的注射使血清褪黑素含量显著升高,为机体抵抗氧化应激提供更多活性氧清除剂,减轻氧化损伤[21,36,45-46]。在本研究中,注射褪黑素的虹鳟血清褪黑素含量在4 h时处于高水平,随后下降并稳定。前期研究也表明,外源褪黑素注射到鱼体内,会使其血清中的褪黑素含量激增,随着实验的进行,褪黑素含量有所下降,这是因为鱼体通过内环境调节将褪黑素含量控制在一定水平以维持内环境稳态[47]。Jung等[29]研究表明,注射褪黑素可使SOD和CAT的mRNA表达量显著下调,进而影响鱼体SOD和CAT活性。本研究中,注射组虹鳟SOD和CAT活性较未注射褪黑素组有所降低,氧化应激状态得到缓解,在Shin等[21]褪黑素注射实验中也得出同样结论。在缺氧和高密度养殖等环境条件对鱼体产生胁迫时,褪黑素能抑制皮质醇的合成与释放,显著降低皮质醇含量[18-19,42-43,45]。在本研究中,注射褪黑素使虹鳟皮质醇含量随时间下降显著。有研究表明,褪黑素可抑制促肾上腺皮质激素的合成进而抑制皮质醇的合成[48-49]。还有报道称,褪黑素可直接作用于下丘脑,进而调控皮质醇的合成与分泌[39]。褪黑素抑制皮质醇合成与释放的作用机制复杂且尚未研究清楚。综上,外源褪黑素注射可有效缓解光色对虹鳟造成的氧化应激胁迫。

4    结论

28 h的急性光照射实验中,虹鳟在16 h时受到的光色胁迫最强烈,血清SOD和头肾CAT活性以及血清皮质醇含量上调,机体处于应激状态,24 h后机体逐渐适应光环境。红光条件下,虹鳟受到胁迫,抗氧化酶SOD和CAT活性升高,皮质醇含量上调,血清褪黑素合成受到抑制;而绿光可能对虹鳟不产生胁迫。注射褪黑素能有效缓解光色对虹鳟的胁迫反应,使虹鳟快速适应光环境。基于本研究的结果,虹鳟养殖生产上可以选择绿光,并给予腹腔注射褪黑素处理,以降低机体的氧化应激反应,而红光不适于虹鳟的养殖。后期可通过长期的养殖实验,多方面深入探究不同光色对虹鳟的生长和生理生化指标的影响,为虹鳟养殖生产提供理论参考。

图1 不同处理组虹鳟血清SOD(a)和头肾CAT(b)活性及血清皮质醇(c)和褪黑素(d)含量变化趋势 Figure1. Fluctuations of O. mykiss serum SOD (a) and head kidney CAT (b) activities, serum cortisol (c) and melatonin (d) concentrations at different treatments during the period of the experiment
表1 同一时间不同处理虹鳟血清SOD和头肾CAT活性及血清皮质醇和褪黑素含量差异的单因素方差分析 Table1 O. mykiss serum SOD and head kidney CAT activities, serum cortisol and melatonin concentrations among different treatments at the same sampling time based on One-Way ANOVA
指标
parameters
显著性(P值) significance (P value)
T4T8T12T16T20T24T28
SOD/(U/mL) *** *** ** *** ** ** **
CAT/(U/mg prot) *** *** *** *** *** *** ***
皮质醇/(pg/mL) cortisol NS * * ** *** ** **
褪黑素/(pg/mL) melatonin *** *** * *** ** *** ***
注:P为显著性水平。NS为无显著性差异,*为存在显著性差异且P<0.05,**为存在显著性差异且P<0.01,***为存在显著性差异且P<0.001,下同
Notes: NS is no significant difference, * is significant difference at P<0.05, ** is significant difference at P<0.01, *** is significant difference at P<0.001, the same below
表2 时间、光色和褪黑素处理及其交互作用在虹鳟血清SOD和头肾CAT活性及血清皮质醇和褪黑素含量差异的三因素方差分析 Table2 Effects of sampling time, light colors, melatonin treatments and their interactions on O. mykiss serum SOD and head kidney CAT activities, serum cortisol and melatonin concentrations based on Three-Way ANOVA
指标
parameters
显著性(P值) significance (P value)
时间
time
光色
color
褪黑素
melatonin
时间×光色
time×color
时间×褪黑素
time×melatonin
光色×褪黑素
color×melatonin
时间×光色×褪黑素
time×color×melatonin
SOD/(U/mL) *** *** *** NS *** ** *
CAT/(U/mg prot) *** *** *** ** *** ** NS
皮质醇/(pg/mL) cortisol *** *** *** * *** *** *
褪黑素/(pg/mL) melatonin NS *** *** NS *** NS NS

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LED光色及注射褪黑素对虹鳟抗氧化酶活性及相关激素含量的影响