光照周期对美洲鲥生长及耗氧率的影响

为探究光照周期对美洲鲥生长及耗氧率的影响,在工厂化循环水养殖系统中,设置9L∶15D、12L∶12D、15L∶9D、24L∶0D(光L∶暗D)共4个光照周期处理组,开展为期60 d的试验,通过测算各组美洲鲥的摄食率、体质量增加率及成活率,研究光照周期对美洲鲥生长的影响,并采用封闭流水式呼吸装置,测定了上述4个光照周期条件下美洲鲥的24 h耗氧率。试验结果显示:随着光照时间的延长,摄食率和耗氧率均呈上升趋势,体质量增加率呈下降趋势,其中24L∶0D处理组摄食率和耗氧率显著高于9L∶15D处理组,体质量增加率显著低于9L∶15D处理组(P0.05)。试验期间各处理组美洲鲥的成活率没有显著差异。     

不同钙、镁浓度对褐牙鲆幼鱼生长及SOD和CAT酶活力的影响

在盐度30和水温20℃条件下,配制钙、镁(1∶3)总浓度A(700mg/L)、B(1100mg/L)、C(1600mg/L,对照)、D(2200mg/L)、E(2800mg/L)的人工海水,研究了5种人工海水对褐牙鲆Paralichthys olivaceus幼鱼生长、肝脏超氧化物歧化酶(SOD)和过氧化氢酶(CAT)活力的影响。观察发现,褐牙鲆幼鱼初次接触高钙、镁浓度人工海水(D组和E组)时产生应激反应,鱼体呈弓形,呼吸频率降低,摄食不积极,适应7d左右恢复正常。经60d养殖实验,各处理组实验鱼食物转化效率(FCE)无显著差异(P0.05),成活率均在90%以上。0~20d时实验鱼特定生长率(SGR)和摄食率(FI)差异显著(P0.05),低浓度组大于高浓度组,20d后,FI无显著差异(P0.05),40~60d时低浓度组SGR小于高浓度组。各处理组SGR和FI随钙、镁总浓度上升呈下降趋势,实验进行到60d时,低浓度组A的SGR和FI分别为高浓度组E的1.13倍和1.04倍。不同钙、镁浓度对实验鱼的免疫酶活性亦有显著影响。D组实验鱼SOD酶活力和肝比重显著高于其他各处理组;E组SOD酶活力显著低于其他实验组(P0.05),CAT酶活力也低于其他处理组,但各组间差异不显著(P0.05)。研究结果表明,实验初期钙、镁浓度通过影响褐牙鲆的摄食而影响其生长,低钙、镁浓度组实验鱼生长较快,高浓度组生长较慢。经60d养殖驯化,除E组外的各处理组特定生长率差异不显著,过高浓度钙、镁对褐牙鲆的免疫酶活性产生一定抑制作用。建议养殖褐牙鲆时应注意避免水体钙、镁含量过高。     

褐牙鲆幼鱼能量分配对限制溶解氧供应及恢复的响应

实验采用循环水养殖系统,通过水流量控制溶解氧供给,设计不同溶解氧供应和限制溶解氧供应及恢复两个实验来研究褐牙鲆(Paralichthys olivaceus)幼鱼生长及能量分配等指标的响应。在不同溶解氧供应实验中,溶解氧含量梯度设置为2.24 mg/L,3.14 mg/L,4.27 mg/L,5.38 mg/L,6.94 mg/L,实验结束时褐牙鲆幼鱼体重、日生长系数、摄食率、以湿重表示的饲料转化效率与溶解氧含量呈正相关(P0.05)。单尾鱼的摄食能随着溶解氧含量的下降而减少,生长能的比例在溶氧为5.38 mg/L时最高。排粪能的比例则随着溶解氧含量的下降而上升,排泄能比例随溶解氧含量下降也略有增加,代谢能的比例随着溶解氧含量的下降呈先下降后上升的趋势,在溶解氧含量为5.38 mg/L时最低(37.66%)。单位体重能量收支中,所有指标与溶解氧含量都有明显的正相关关系(P0.05),随着溶解氧含量的提高而显著提高。实验表明,低溶解氧含量下,褐牙鲆幼鱼通过减少能量供应降低摄食率和饲料转化效率,其生长受到抑制。在限制溶解氧供应及恢复实验中,经历10 d低溶解氧含量2 mg/L(S_2)和4 mg/L(S_4)胁迫的褐牙鲆幼鱼生长受到抑制,但在恢复正常溶解氧后10 d内体重即与对照组无显著差异(P0.05)。恢复期间褐牙鲆幼鱼的摄食率明显高于对照组(P0.05),饲料转化效率略高于对照组。恢复阶段不同处理在摄食能、生长能比例和呼吸能比例上没有显著差异(P0.05),但经历低溶解氧胁迫的处理摄食能和生长能比例略高于对照处理,而代谢耗能比例略低于对照处理。S2处理的排泄能比例显著低于其余2个处理(P0.05)。实验表明褐牙鲆幼鱼对短期低溶解氧含量有较强的适应能力,能够通过提高摄食率在较短的恢复期获得完全补偿生长。本研究揭示了褐牙鲆在低溶氧胁迫下的能量分配规律,为深入研究鱼类适应溶解氧波动环境的策略积累资料。     

低盐度胁迫不同时间对褐牙鲆幼鱼生长的影响

将驯养于海水盐度为19的褐牙鲆（Paralichthys olivaceus）幼鱼放入盐度为5的海水中胁迫0周（对照）、1周、2周、3周和4周后,立即将海水盐度调节至19,养殖到第10周,观察幼鱼的生长情况。研究发现,低盐度海水养殖的褐牙鲆幼鱼体质量仅在低盐胁迫的第1周内显著小于对照组,不同处理的日生长系数在第3周与第5周呈现显著性差异,其余时间阶段内不同处理的体质量和日生长系数未见显著差异。胁迫阶段褐牙鲆幼鱼摄食率整体上略低于对照处理,但恢复阶段摄食率未出现大于对照处理的一致趋势。整个试验期间经低盐度处理的褐牙鲆幼鱼饲料转化效率略大于对照处理。试验结果显示,低盐度5对褐牙鲆幼鱼的生长没有产生长期影响,也不能通过较长时间的低盐度养殖引起褐牙鲆幼鱼的补偿生长效应。     

盐度对褐牙鲆幼鱼生长的影响及其在盐度胁迫后的补偿生长

褐牙鲆（Paralichthys olivaceus）幼鱼取自山东省胶南市养殖场,盐度设置范围分别为12-40和5-47。实验表明,盐度12-40对平均初始体质量约2.6g的褐牙鲆幼鱼的湿重生长、湿重摄食率和湿重饲料转化效率均没有显著影响（P〉0.05）,但对蛋白质和能量表示的特定生长率、摄食率、饲料转化效率都有显著影响（实验周期为30d）。盐度5（IS5）和47（IS47）处理能够使初始体质量为6.93g的褐牙鲆幼鱼在10d内的生长显著比盐度19（IS19）处理慢（P〈0.05）,并且由于低盐度（盐度为5）引起的生长阻滞能够在30d内得到完全补偿,而高盐度（47）引起的生长阻滞未能得到补偿。在整个恢复期间（11-40d）,IS5处理的摄食率显著高于IS47处理（P〈0.05）,IS19处理处于中间水平。在盐度恢复至19后,不同处理在所有阶段的饲料转化效率和整个实验期间的平均饲料转化效率相互之间不存在显著差异。以上结果表明,低盐度（盐度为5）导致的生长阻滞的补偿主要依靠提高摄食率获得。结论认为,褐牙鲆幼鱼对盐度尤其对低盐度的适应能力较强。     

高温—最佳温度循环对褐牙鲆生长、能量分配和身体成分的影响

环境温度短周期波动对鱼类的生长和能量代谢有重要影响,实验在室内可控条件下,对褐牙鲆幼鱼在经历高温—最佳温度循环的生长与能量分配进行了研究。在为期40 d的实验中,驯养于20 ℃的褐牙鲆幼鱼在每个为期10 d的循环中分别经历0 d(H₀)、2 d(H₂)、4 d(H₄)、6 d(H₆)和8 d(H₈)的26.5 ℃高温胁迫后,剩余的天数恢复到最佳温度(20 ℃)下养殖。实验结束时,经历不同天数高温胁迫的各处理组的褐牙鲆幼鱼以干重、湿重、蛋白质和能量表示的鱼体重均显著小于对照组(H₀)。实验期间摄食量少和分配于生长的能量减少是导致经历高温胁迫的处理生长减慢的主要原因。经历高温胁迫的处理组的摄食量都显著低于对照组,但摄食率、消化率以及饲料转化效率都与对照组无明显差异。经受高温处理的H₂、H₄和H₆组分配于生长的能量与对照组没有显著差异,但H₄组的能量损失于粪便最多,H₆组的能量损失于排泄的比例最高。H₈组褐牙鲆幼鱼个体分配于生长的能量比例显著低于其他处理,代谢消耗的能量比例显著高于其他处理。经历不同温度循环处理的褐牙鲆幼鱼单位体重日摄食能与对照组相比没有显著差异,但分配于生长的能量却显著低于对照组。结果表明,褐牙鲆幼鱼对高温—最佳温度循环的适应能力较差,生长受到温度周期波动的抑制。     

不同光周期下欧洲舌齿鲈幼鱼生长、摄食和肌肉营养成分的比较

选取450尾欧洲舌齿鲈（）幼鱼，体长（13.50±0.52）cm，体重（46.04±0.61）g，监测其在5种光周期（0L：24D、8L：16D、12L：12D、16L：8D、24L：0D，L表示光照时间，D表示黑暗时间）下的生长、摄食及肌肉营养成分等相关指标。实验周期为60 d。结果表明，8L：16D处理组的欧洲舌齿鲈的日增重系数显著高于其他各组（<0.05）；0L：24D和8L：16D处理组粗脂肪含量分别较16L：8D处理组分别提高了19.70%和21.67%（<0.05）。5种光周期下的欧洲舌齿鲈幼鱼肌肉中均检测到17种氨基酸，其中8L：16D和12L：12D处理组的肌肉中氨基酸总含量较0L：24D组分别提高11.60%和9.16%（>0.05）；肌肉中二十碳五烯酸（EPA）与二十二碳六烯酸（DHA）总含量在8L：16D处理组中最高，为14.21%，在0L：24D处理组中最低，为12.30%。不同光照周期对欧洲舌齿鲈幼鱼生长、摄食和肌肉营养品质均产生了不同程度的影响，综上所述，8L：16D和12L：12D光照环境更适宜欧洲舌齿鲈的生长。     

盐度胁迫及恢复对牙鲆幼鱼生长、能量分配和身体成分的影响

采用生物能量学方法对不同盐度对褐牙鲆幼鱼生长和补偿生长的影响进行了研究.研究结果表明,盐度12～40的范围对平均体重为2.6g的褐牙鲆幼鱼的湿重生长没有显著影响,而盐度5(IS5)和47(IS47)会明显阻碍平均体重为6.9g幼鱼的生长,但IS5的生长延缓在30d的恢复生长(盐度19,IS19)后获得完全补偿,而IS47处理最终未能赶上IS19处理.盐度操作对幼鱼摄食能、摄入的能量分配于呼吸消耗、排粪的比例均有显著影响,而对排泄损失的能量比例没有明显影响.对于单位体重日能量分配而言,盐度操作对摄食能、呼吸消耗、生长、排粪损失的能量有明显的影响,但对排泄能量损失没有显著影响.研究还发现,盐度操作对褐牙鲆幼鱼身体水分和蛋白质含量没有显著影响,但对脂肪和能量含量有一定影响.结果表明,盐度19左右为褐牙鲆幼鱼生长最适合的盐度,其对盐度的适应范围较广,特别是对低盐度表现出极强的耐受和适应能力.     

光照对纤细裸藻生长及光合色素含量影响的研究

为探讨光照对纤细裸藻的生长以及光合色素含量的影响,将纤细裸藻分别置于不同光照度(0、1500、3000、4500、6000 lx)、光照周期(16L∶8D、14L∶10D、12L∶12D、10L∶14D、8L∶16D)、光质(绿光495~530 nm、蓝光450~480 nm、红光615~650 nm、白光450~465 nm、黄光580~595 nm)条件下于恒温光照培养箱中静置培养,进行细胞密度以及色素含量的测定。试验结果显示,光照度、光照周期和光质对纤细裸藻生长及光合色素质量浓度有显著影响( P <0.05)。光照度1500、3000、4500 lx对纤细裸藻的生长均有积极作用,其中3000 lx光照度作用最为显著,细胞生长状态良好,光合色素质量浓度也高于1500、4500 lx;光照周期16L∶8D、14L∶10D和12L∶12D对纤细裸藻的生长有促进作用,其中14L∶10D组生长状况和光合色素质量浓度均优于其他处理组,8L∶16D组使纤细裸藻的生长受到抑制,其色素质量浓度也显著低于其他处理组( P <0.05);蓝光与白光组对纤细裸藻生长有显著促进作用( P <0.05),蓝光条件下色素质量浓度达到最高,更利于光合色素的积累。试验结果表明,适宜纤细裸藻生长及光合色素积累的光照条件为:光照度3000 lx,光照周期14L∶10D,蓝光培养。     

LED光谱对舌齿鲈幼鱼摄食、生长和能量分配的影响

在海水循环水养殖系统中,分别设置白光(λ_(400～780 nm))、红光(λ_(630 nm))、黄光(λ_(595 nm))、绿光(λ_(530 nm))、蓝光(λ_(455 nm))5组不同LED光谱处理组,研究5种不同LED光谱对舌齿鲈幼鱼[(29.91±0.39) g、(13.78±0.35) cm)]摄食、生长和能量分配的影响。结果显示,不同LED光谱对舌齿鲈幼鱼摄食、生长和能量分配具有显著性影响。红光谱下舌齿鲈幼鱼生长较好(41.09±5.70) g,蓝光谱下舌齿鲈幼鱼生长较差(36.02±4.18) g;蓝光谱下舌齿鲈幼鱼DGC(daily growth coefficient)显著低于其他各组,其他各组之间差异不显著;5组LED光谱处理组舌齿鲈幼鱼摄食率存在显著性差异,其中红光谱摄食率最高。类胰岛素生长因子IGF-1和IGF-2测定结果表明,白光谱下IGF-1的mRNA表达量最高;黄光谱下IGF-2的mRNA表达量最高。能量分配方面,红光谱下舌齿鲈幼鱼排粪能和代谢能较低,摄食能和生长能较高;蓝光谱下舌齿鲈幼鱼排粪能较高,摄食能和代谢能较低,生长能最低。对舌齿鲈幼鱼肌肉和肝脏RNA/DNA比值测定结果表明,蓝光谱下,舌齿鲈幼鱼肝脏RNA/DNA比值显著高于其他各组;蓝光谱和白光谱下舌齿鲈幼鱼肌肉中RNA/DNA比值存在显著性差异,其他各组之间不具有显著性差异。研究表明,红光谱下舌齿鲈幼鱼摄食、生长均表现较好,且红光谱下舌齿鲈幼鱼具有较高的摄食能和生长能;蓝光谱下舌齿鲈幼鱼摄食、生长表现较差,排粪能较高,生长能较低。因此,红光谱对舌齿鲈幼鱼摄食、生长具有积极影响;蓝光谱对舌齿鲈幼鱼摄食、生长具有不利影响。     

Reproduction,growth and stress response in adult red sea bream,Pagrus major (Temminck & Schlegel) exposed to different photoperiods at spawning season

Adult red sea bream, Pagrus major (body weight, 1.0–2.0 kg) was exposed to three photoperiods [12 h light:12 h dark (12L:12D), 16 h light:8 h dark (16L:8D) and 24 h light:0 h dark (24L:0D)] from 2 months before spawning till the end of the spawning season to investigate growth, spawning and stress response. During the spawning season, tanks were checked every morning for spawned eggs. The growth performance in fish under 24L:0D was stimulated with significantly higher feed intake than those under other photoperiods (P<0.05). The number of eggs and gonadal histology confirmed that three and five females out of six in each of duplicate tanks of the 16L:8D treatment spawned. In contrast, only two out of six females in one tank of the 24L:0D treatment spawned, and no spawns were observed in the 12L:12D treatment. At the end of the spawning period, both 17β‐estradiol and testosterone levels were significantly higher in fish exposed to 16L:8D followed by 12L:12D and 24L:0D photoperiods (P<0.05). Photoperiod manipulation did not cause significant stress response in fish (P>0.05). The results suggest that stimulating the growth performance of red sea bream at reproductive stage with a 24L:0D photoperiod is possible if the fish are subjected to this photoperiod long before the onset of the spawning season.     

Effects of different photoperiods on growth, stress and haematological parameters in juvenile great sturgeon Huso huso

The effects of constant light (24L:00D), no light (00L:24D) and two light–dark periods (18L:06D;12L:12D) on the growth, stress and haematological variables were assessed in juvenile great sturgeon, Huso huso . During the 8-week experimental period, juveniles (22.5 ± 0.6 g) were kept under a 150 lx light intensity in fibreglass tanks (0.8 m², 500 L). Differences in growth were insignificant during the experiment, but lactate levels were higher in the 00L:24D and 24L:00D photoperiods compared with 12L:12D and 18L:06D photoperiods. Cortisol levels did not show differences among the various photoperiods. At the end of the experimental period, fish reared under a 12L:12D photoperiod had higher haemoglobin values and erythrocyte numbers than in the other photoperiods, while no differences were found between groups with regard to haematocrit values or leucocyte numbers. The highest survival rate (89%) was observed in the 12L:12D period in which the levels of lactate and cortisol as stress indicators were minimal. The results indicate that various photoperiods cause different stress levels in juvenile great sturgeon and have no significant effects on growth, at least in short time periods.     

Feeding interval and photoperiod influence the growth performance of striped knifejaw,Oplegnathus fasciatus

A two‐factor experiment incorporating two photoperiods (16 L:8 D and 24 L:0 D) and four feeding intervals (6, 9, 12 and 24 h) was carried out to determine the most efficient feeding interval and photoperiod for striped knifejaw, Oplegnathus fasciatus. Fish were fed a commercial diet to apparent satiation for 10 weeks. Blood was collected to measure the stress indicators. Both the photoperiod and the feeding intervals had a significant effect on the growth performance of striped knifejaw; however, their interaction did not produce any significant effect. The final body weight, weight gain (%) and feed intake at 6‐, 9‐ and 12‐h feeding intervals under 16 L:8 D were significantly higher than those at the 24‐h interval irrespective of the photoperiod (P<0.05). The specific growth rate at 6, 9 and 12 h intervals of the 16 L:8 D photoperiod was significantly higher than that of the other feeding intervals, except at 12 h of the 24 L:0 D photoperiod (P<0.05). At the end of the experiment, there were no significant differences in the plasma levels of cortisol, glucose and total protein observed in fish exposed to different photoperiods compared with the initial levels. The results suggested that a combination of a 16 L:8 D photoperiod and either of 6‐, 9‐ or 12‐h intervals can be used to stimulate the growth performance in striped knifejaw.     

Enhanced growth and retarded gonadal development of farmed rainbow trout,Oncorhynchus mykiss (Walbaum) following a long‐day photoperiod

Long‐day photoperiods are considered as an effective managerial tool in manipulating of reproduction and somatic growth in a number of fish species. In this study, the effects of three different artificial photoperiods on the gonadal development and somatic growth of rainbow trout (Oncorhynchus mykiss L.) were investigated. Two years‐old immature female rainbow trout (279.94 ±2.25 g) were exposed to three artificial photoperiod regimes of 24L:0D, 18L:6D and 6L:18D and natural light (NL) regime for 5 months. The highest gonadosomatic indices were recorded in NL and 6L:18D groups while the rates were significantly lower in fish maintained under 18L:6D and 24L:0D photoperiods (P < 0.05). Mean oocyte diameters in fish exposed to 24L:0D and also to 18L:6D were significantly lower than the 6L:18D and NL groups. Photoperiods with 24L:0D and 18L:6D regimes resulted in significantly higher mean final weights and specific growth rates (SGR) than NL regime. The highest mean final weight (635.45 ± 16.19 g) and SGR (1.03 ± 0.04% day^?1) were obtained under 24L:0D photoperiod. Fish exposed to 24L:0D and 18L:6D showed the highest condition factor as 1.44 ± 0.01 and 1.44 ± 0.02 respectively, when compared with the NL (1.27 ± 0.01) and 6L:18D (1.34 ± 0.02) groups. Basically, the results suggested that continuous artificial lightning can be used as an influential factor in delaying gonadal development and enhancing somatic growth in rainbow trout during gonadal growth phase.     

The effect of photoperiod on growth, survival, colour and activity of juvenile southern rock lobster, Jasus edwardsii

Juvenile (1–10 g) southern rock lobsters, Jasus edwardsii, were subjected to five photoperiods [0L(light):24D(dark); 6L:18D; 12L:12D; 18L:6D; 24L:0D] during a 112‐day trial, and growth, survival, colour, food consumption and activity were examined. Lobsters grown under the 6L:18D and 24L:0D photoperiods had significantly lower (P < 0.05) final mean weight and specific growth rate than any other treatments. Photoperiod had no effect on survival or colour of lobsters. Food consumption differed significantly during the first week of the trial; after 5 weeks, food consumption was similar in all treatments. Major peaks in activity occurred during dark periods for lobsters exposed to photoperiods that had a light:dark regime. Activity of lobsters exposed to continuous light or dark regimes remained constant and at low levels during the 24‐h period. Food consumption or activity does not appear to determine the rate of growth of lobsters in the different photoregimes. One over‐riding outcome of this and other studies on photoperiod is that the growth and survival response of juvenile J. edwardsii was not significantly better than those of the standard 12L:12D cycle.     

Stimulation of growth performance without causing stress response in young red sea bream, Pagrus major (Temminck & Schlegel), by photoperiod manipulation

Three photoperiods (12L:12D, 16L:8D and 24L:0D) were used to investigate the growth performance and stress response in red sea bream, Pagrus major (body weight 200–400 g). Fish were fed a commercial diet to apparent satiation, two times a day for 8 weeks. Fish exposed to a 24L:0D photoperiod showed a significantly higher weight gain (%) than those exposed to other photoperiods (P<0.05). The best specific growth rate and feed conversion efficiency were achieved at 24L:0D and 16L:8D, without significant differences among them. Although fish exposed to 16L:8D showed a significantly higher plasma level of cortisol than those exposed to other photoperiods in the third week, there was no major variation in the cortisol level among the treatments either at the sixth week or at the end of this study. There were no significant differences either in the haematocrit level or the plasma levels of glucose, total cholesterol and total protein among the treatments during this study. The results revealed that the growth performance of red sea bream reared from 200 to 400 g can be stimulated significantly using a continuous (24L:0D) photoperiod without any measurable significant stress response in fish.     

Growth performance and physiological responses in striped knifejaw, Oplegnathus fasciatus, held under different photoperiods

The growth performance and stress response in striped knifejaw, Oplegnathus fasciatus (body weight 100–300 g) reared under four photoperiods (6L:6D, 12L:12D, 16L:8D and 24L:0D) were investigated. Fish were fed a commercial diet to apparent satiation, two times a day for 8 weeks. A trial of acute handling and confinement stress was also carried out to investigate the stress-induced levels of different stress indicators in O. fasciatus. Blood was also collected from undisturbed fish which was considered as control. Although there were no significant differences in weight gain, specific growth rate (SGR) and feed conversion efficiency (FCE) in fish exposed to 6L:6D, 16L:8D and 24L:0D photoperiods, all parameters in these photoperiods were significantly higher than those of 12L:12D photoperiod (P < 0.05). There was no significant difference in protein retention efficiency (PRE) between fish exposed to 16L:8D and 24L:0D photoperiods, but PRE in both photoperiods was significantly higher than that of 12L:12D photoperiod.Acute stress significantly increased the plasma levels of cortisol (110.3 ng ml^− 1) and glucose (195.4 mg dl^− 1), and decreased plasma levels of total protein (0.8 g dl^− 1); however, all parameters were returned back to the levels indistinguishable from those of control, undisturbed fish within 24 h. The levels of cortisol, glucose and total protein in fish exposed to different photoperiods during the study were far from the stress-induced levels (P < 0.05). The results demonstrated that the growth performance of O. fasciatus reared from 100 to 300 g can be stimulated significantly by using the manipulated photoperiods where feeding time may be playing an important role to increase food intake and feed conversion efficiency. It also revealed that the artificial photoperiods did not cause significant stress response in fish.     

Physiological changes in male and female pikeperch Sander lucioperca (Linnaeus, 1758) subjected to different photoperiods and handling stress during the reproductive season

Pikeperch broodstocks were exposed to different photoperiods: constant light (24L:0D), constant darkness (0L:24D), and 12 h light, 12 h darkness (12L:12D), for 40 days. Half of the broodstocks of each photoperiod were exposed to handling stress at a specific time of the day. Results showed that cortisol and lactate did not reveal any significant difference. However, glucose levels in females increased in the stress-free darkness period in comparison with stressful darkness photoperiods (0L:24D-s). Red blood cells in males and white blood cells in females showed a significant difference under different photoperiod regimes. Both sexes showed no significant difference in the differential count of leukocytes under different photoperiods and handling stress. Constant photoperiods and handling stress affected the hematological parameters, particularly, the number of lymphocytes and neutrophils in females. Our findings revealed that due to a long-term exposure to stressors, pikeperch brooders become adapted to stressful conditions.     

Effect of Photoperiod Manipulation on Growth Performance,Physiological and Hematological Indices in Juvenile Persian Sturgeon,Acipenser persicus

The effect of five different light regimes on growth, stress and hematological indices was studied in Persian sturgeon, Acipenser persicus. Fish with average weight of 645.3 ± 11.2 g were subjected to different photoperiods (24 L, 12 L:12 D, 16 L:8 D, 8 L:16 D and 24 D) for 8 wk. Blood samples were collected at the end of the experiment for measuring cortisol, glucose and hematological features. The whole growth parameters showed no significant difference. Plasma cortisol concentration was significantly higher in 12 L:12 D, while the lowest level was observed in fish exposed to 24 D. No significant changes were observed among the treatments for glucose concentration. Lactate concentration varied significantly among the treatments. Some hematological indices including hematocrit and number of white blood cells were affected by different light regimes, but the others (hemoglobin and number of red blood cells) were not affected significantly. The results showed that photoperiod manipulation can alters some stress‐related metabolites and may enhance growth rate in fish exposing to continuous darkness.     

Effect of photoperiod and tank colour on growth and survival of pelagic‐phase seahorse Hippocampus reidi

The effect of photoperiod and tank colour on the survival and growth of juvenile seahorse Hippocampus reidi was investigated in the first 15 days after release (DAR). In the first experiment, newly released seahorses were exposed to six photoperiods – 6 h of light (L):18 h of darkness (D), 10L:14D, 12L:12D, 14L:10D, 18L:6D and 24L:0D. In the second experiment, juveniles were kept in tanks of different background colours – blue, white, black, clear and red. No significant differences were observed in the growth and survival among seahorse subjected to 10–24 h of light (P > 0.05). At the end of 15 DAR, fish exposed to 6L:18D showed lower growth in height and weight compared to other treatments (13.8 mm vs. 20.0–22.2 mm and 13.4 mg vs. 37.2–43.2 mg respectively) and lower survival (80% vs. 88–95% respectively). Tank colour did not affect growth and survival of juveniles up to 15 DAR.