Changes in serum thyroxine and triiodothyronine concentrations during metamorphosis of the Southern Hemisphere Lamprey Geotria australis,and the effect of propylthiouracil,triiodothyronine and environmental temperature on serum thyroid hormone concentrations of ammocoetes

Serum thyroid hormone concentrations were measured during the seven stages of metamorphosis (1–7) of the southern hemisphere lamprey, Geotria australis. The respective mean concentrations ± SEM of serum thyroxine (T₄) and triiodothyronine (T₃) fell from 31.73 ± 4.09 and 5.06 ± 0.70 nM in large ammocoetes sampled in February, at the time when metamorphosis was initiated, to 4.54 ± 0.36 and 1.03 ± 0.12 nM at stage 5. Although there was a small, but significant, recovery of serum T₄ concentrations during stages 6 and 7, no such corresponding statistically significant rise occurred in serum T₃ concentrations. Serum thyroid hormone concentrations in ammocoetes sampled during the period when metamorphosis was taking place, exhibited a marked seasonal increase between February and May–June (late autumn/early winter); serum T₃ and T₄ concentrations peaked in May–June and were, respectively, > 2 fold and > 8 fold higher than those recorded for samples in late February (mid summer). By mid-July the serum T₄ and T₃ levels had declined from the peak values. Ammocoetes taken from streams at 16°C in June and acclimated to aquaria water at 25°C or 6°C had significantly lower serum T₃ and T₄ concentrations at the higher temperature, and also a lower serum T₄, but not T₃ concentration, at the lower temperature. Treatment of separate groups of ammocoetes with either propylthiouracil or T₃ for 70 days significantly depressed and raised respectively, the serum thyroid hormone and hepatic T₃ concentrations and caused significant changes in the body weight, but did not induce the onset of metamorphosis.     

Seasonal and estradiol-17β-stimulated changes in thyroid function of adult Geotria australis,a southern hemisphere lamprey

Measurable in vitro hepatic monodeiodinase activity of the southern hemisphere lamprey, Geotria australis, was present only during the first 5 of the 16 month upstream spawning migration of this species. The production of T3 from T4 in vitro was pH-sensitive, and exhibited typical Michaelis-Menton kinetics. No consistent differences in the serum T4 concentrations were found in animals sampled at different times during the period of their residence in fresh water. However, serum T3 concentrations underwent a progressive decline during this period. Estradiol-17β (E2), administered as a suspension in hydrogenated coconut oil, induced a lowering of serum T4 concentrations and a rise in serum T3:T4 ratios, but had no measureable effect on liver size and serum concentrations of total calcium and protein. In the males, E2 induced the production of a small amount of a serum protein assumed to be vitellogenin, but there was no conspicuous increase in the amount of the same protein in females. This response to E2-challenge parallels more closely that of cyprinids than that of salmonids.     

Oxygen consumption and responses to hypoxia of ammocoetes of the southern hemisphere lampreyGeotria australis

The standard rate of oxygen consumption of ammocoetes (larvae) ofGeotria australis with a mean weight of c. 0.5 g was 9.6, 31.4 and 59.4l g^–1 h^–1 at 4.5, 15.5 and 25.0°C respectively, which gives an overall Q₁₀ of 2.4. The regression coefficient for the logarithmic relationship between oxygen consumption and body weight at 15.5°C was 0.704. The ammocoetes ofG. australis have a much lower rate of oxygen consumption at 15.5 and 25.0°C than those of holarctic lampreys. This presumably reflects the lower oxygen delivery pressure to their tissues and helps account for their slow growth rate. At 15.5°C, ammocoetes ofG. australis emerged from the substrate at 21–25 mm Hg and, unlike those of the Northern HemisphereIchthyomyzon greeleyi, died at 14–17 mm Hg. Thus, despite having a thinner water/blood barrier in the gills and blood with a higher oxygen affinity and capacity than holarctic ammocoetes, the larvae ofG. australis cannot survive very low dissolved oxygen tensions. This is apparently related to an inability of larvalG. australis to meet the high oxygen requirements of the respiratory pump at these oxygen tensions. During metamorphosis, oxygen consumption at 15.5°C rose from approximately 27l g^–1 h^–1 at the beginning of transformation to 33.2l g^–1 h^–1 by Stage 3 and then rapidly to 66l g^–1 h^–1 at Stage 6. It remained near this level in Stage 7 and the downstream migrant.     

Growth patterns of reed (Phragmites australis): the development of reed stands in carp ponds

Reed stands exhibit apparent differences of stem diameter, shoot length, density, and invasiveness. In carp ponds, five characteristic growth patterns can be distinguished. These growth patterns are ontogenetic states of a time-dependent stand development. Invasive reeds with short shoots are found in newly occupied habitats. With continuing establishment of the stand, the shoots in the inner regions become taller and fewer, a growth pattern described as central reed. Later, only a few shoots with thick stems remain. Two alternative pathways of stand development exist: steep shore reed and reed tussocks. By mowing, the directional development of reed stands can be turned into a circulation of growth patterns. The growth patterns have implications for the selection of reed stand areas for conservation purposes.     

氮饥饿与磷饥饿促使缺刻缘绿藻花生四烯酸含量增加的比较

以富含花生四烯酸(AA)的缺刻缘绿藻H4301为研究对象,探讨了不同光照强度条件下氮饥饿与磷饥饿对藻生物量、AA及脂肪酸含量变化的影响。发现氮饥饿与磷饥饿均降低了藻类的生长速率与生物量,当在60 μmol photons/(m²·s)的低光照强度下,磷饥饿时的藻类平均生长速率最低［0.025 g/(d·L)］,不足BG-11完全培养基中该藻生长速率的一半;氮饥饿与磷饥饿均能提高藻细胞总脂肪酸及AA的含量,但在低光照强度下磷饥饿的促进效果比较差;无论是完全培养基中还是饥饿处理时,200 μmol photons/(m²·s)的高光照强度都不利于藻细胞AA及多不饱和脂肪酸的合成与积累;随着饥饿时间的不断持续,AA占总脂肪酸的百分含量逐渐增加,而亚油酸的百分含量逐渐降低,但在磷饥饿时,油酸的百分含量也增加,特别在高光照强度下,以油酸为主的单不饱和脂肪酸含量在第27天时占细胞干重的5.28%,以致AA含量的增加没有氮饥饿时的显著。从脂肪酸成分的变化来分析,该藻在氮或磷饥饿过程中主要是从亚油酸到γ-亚麻酸再到20∶3ω6这个途径来合成并积累AA,其中Δ6去饱和酶是限速酶,而ω3去饱和酶催化步骤受饥饿处理的负调控对确保AA的合成与积累有较大的积极作用。氮饥饿使藻细胞蛋白质合成受阻以及磷饥饿使核酸合成、糖类与能量代谢产生障碍,从而阻止藻类的生长并迫使细胞代谢流转向不含氮和磷的脂肪酸合成代谢,以提高藻细胞总脂肪酸及AA含量。     

臭氧对条石鲷幼鱼鳃组织结构和抗氧化系统的影响

臭氧(O₃)在工厂化养殖水处理中有较高的应用价值,为了解臭氧对条石鲷幼鱼的影响,采用自制的臭氧毒性试验装置(授权利号:ZL 200920122441.3),对条石鲷幼鱼进行了不同质量浓度(0、0.08、0.13、0.17、0.22、0.28和0.32 mg/L)和不同时间(0.5、1、6、12、18和24 h)的急性胁迫试验,并分析了臭氧对条石鲷幼鱼的行为响应、半致死浓度、幼鱼鳃的组织形态学、酶活性等的影响。结果表明,随着臭氧胁迫浓度的升高,条石鲷幼鱼在水层中的分布位置逐渐上移,呼吸频率逐渐加快,受惊反应逐渐迟缓;条石鲷幼鱼的开始死亡时间与臭氧浓度负相关,12 h的半致死方程为Y=16.815 8+20.340 5X(r=0.998 7),半致死浓度为0.262 5 mg/L。24 h的半致死方程为Y=17.614 1+17.898 3X(r=0.950 0),半致死浓度为0.197 4 mg/L;条石鲷幼鱼鳃SOD和GPX活性与臭氧胁迫时间和胁迫浓度负相关,并都在胁迫24 h、质量浓度0.32 mg/L时降至谷值;MDA含量与臭氧胁迫时间和胁迫浓度正相关,并在胁迫24 h、质量浓度0.32 mg/L时达到峰值;在臭氧胁迫下,条石鲷幼鱼的鳃小片细胞排列不规则并萎缩,鳃小片上皮细胞脱落或粘滞于鳃小片间,鳃小片末端膨大,鳃丝血管固缩无腔或变空腔,管壁粗糙、干缩,血细胞固缩、坏死,零散分布或紧贴血管壁。     

Intraperitoneal injection of sulfur amino acids enhance the hepatic cysteine dioxygenase activity in rainbow trout (Oncorhynchus mykiss)

As part of the investigation into cysteine metabolism in fish, sulfur amino acids and their derivatives were injected intraperitoneally to fingerling rainbow trout (Oncorhynchus mykiss) to examine how the doses of these compounds affect the hepatic cysteine dioxygenase [EC 1.12.11.20] in this species. A dose of 0.25 mmol L-cysteine per 100 g body weight induced the enzyme activity as much as 2.5 times that of the control fish within 4h after the injection. The activity increased proportionally to the increasing dose of cysteine up to the dose of 0.15 mmol per 100 g body weight. The induction was observed to be rather specific to L-cysteine. These findings suggested that the cysteine sulfinate pathway might play an important role in the metabolism of excess cysteine in rainbow trout. The dosage of L-cysteine larger than 0.50 mmol per 100g body weight led to mortality of the fish. The pathway of cysteine catabolism was considered to function to prevent toxic accumulation of cysteine in rainbow trout, as in the case of mammals.     

Stress-induced changes in the affinity and abundance of cytosolic cortisol-binding sites in the liver of rainbow trout,Oncorhynchus mykiss (Walbaum), are not accompanied by changes in measurable nuclear binding

Plasma cortisol levels and the number (N_max) and affinity (K_d) of specific hepatic cortisol-binding sites were determined in rainbow trout subjected to chronic confinement stress for 14 days. Confinement significantly elevated plasma cortisol levels to 47.3 ± 13.5 ng ml^–1 within 24h and although levels declined to 8.0 ± 3.0 ng ml^–1 after 14 days, they were significantly higher throughout than levels in unstressed control fish (< 2.0 ng ml^–1). There was a 60% reduction in cytosolic N_max in stressed fish during the first 24h of confinement (35.8 ± 7.9 cf. 129.0 ± 15.2 fmol mg^–1 protein), a decline which was sustained at 7 days after the onset of stress but, although numbers of binding sites in the liver of stressed fish were still lower than in unstressed fish, the difference was no longer significant after 14 days of confinement. There was an accompanying significant rise in the K_d of cortisol binding in stressed fish during confinement, from 4.0 ± 0.6 nM at time 0 to 8.4 ± 0.8 nM after 24 h confinement. This increment in K_d was sustained at a level significantly higher than in control fish throughout the 14 day confinement period, despite marked reductions in cortisol levels and increases in N_max in stressed fish. Throughout the study, specific binding of cortisol could not be consistently detected in high-salt nuclear extracts from stressed or unstressed fish, suggesting either that high-affinity binding sites for cortisol were absent from these preparations, that receptors were present but unable to interact with ligand because they were occupied, or that receptors were present but not being extracted. These possibilities were investigated using a range of extraction procedures, by varying the temperature of incubation, by employing dexamethasone as ligand and by examining binding in purified, intact, nuclei. Estradiol was employed as a methodological control throughout and substantial amounts of specific estradiol binding were detected in all compartments and preparations. Specific cortisol-binding sites were detected in intact nuclei of both stressed and unstressed fish, at levels an order of magnitude lower than estradiol binding in the same preparations. These data demonstrate that activation of the pituitary-interrenal axis leads to significant changes in the nature of target-tissue binding of cortisol in rainbow trout, and reveal a clear difference in the subcellular distribution of binding-sites for estradiol and cortisol, which reflects the situation in mammalian tissues.     

Substrate concentration affects the in vitro metabolism of 17-hydroxyprogesterone by ovaries of the carp,Cyprinus carpio

Carp ovarian tissue was incubated with ³H-17-hydroxyprogesterone in the presence of 0, 0.1, 1, 10, and 100 μg ml⁻¹ unlabeled 17-hydroxyprogesterone. The pattern of metabolites formed showed a marked variation with substrate concentration. Formation of glucuronide and sulphate conjugates was important only at low substrate concentration. At high substrate concentration (10 and 100 μg ml⁻¹) 17,20α-dihydroxy-4-pregnen-3-one was the major metabolite, but at intermediate concentrations polar 7α-hydroxypregnanetetrols predominated. The results support the hypothesis that at low substrate concentrations conjugating, 5α-reducing and 7α-hydroxylating enzymes, of high activity but low capacity, act as scavengers to deactivate any steroids formed during the relatively low pituitary gonadotrophin secretions which are necessary for oocyte development, but that during the prespawning gonadotrophin surge when high levels of substrate are present these enzymes are saturated and 17,20α-dihydroxy-4-pregnen-3-one (17,20αP) becomes the major ovarian steroid. The possible role of 17,20αP during oocyte final maturation requires further examination.     

花鲈等渗点分析及海水淡化对Na+/K+/Cl-浓度、Na+-K+-ATP酶活性及基因表达的影响

广盐性鱼类有着较为复杂的渗透调节机制,能够在较大盐度范围内存活并生长。通常认为鱼类在等渗环境下用于渗透调节的代谢能量最少,有利于鱼类生长。本实验首先根据不同盐度下花鲈血清渗透压对应水体渗透压的变化,计算得到花鲈的等渗点为11.4。而后进行海水淡化和淡水适应两个阶段的盐度实验,通过对花鲈两个阶段中血清渗透压、Na~+/K~+/Cl-浓度、Na~+-K~+-ATP酶(Na~+-K~+-ATPase,NKA)活性及其基因表达的测定,探讨了海水淡化对花鲈的生理影响与分子响应机制。在盐度实验中,Na~+和Cl-浓度变化和血清渗透压变化趋势一致,在淡化阶段显著下降,在淡水适应阶段逐渐恢复稳定,但仍低于起始水平。鳃组织中NKA基因表达结果显示,NKAα1a和NKAα1b的变化趋势与Na~+-K~+-ATP酶活性变化趋势基本一致,在淡化阶段显著下降,随后回升至稳定,不同的是,淡水适应后花鲈NKAα1a表达量与盐度30组无显著性差异,而NKAα1b表达量显著低于盐度30;NKAα3在淡化第1天,表达量显著降低,且在淡水(盐度0)环境下一直处于较低水平;NKAβ在淡水适应过程中的表达量总体高于淡化过程。相关性分析中,海水淡化阶段,Na~+-K~+-ATP酶和NKAα1a呈极显著相关。本研究通过对花鲈等渗点以及海水淡化和淡水适应阶段相关离子、酶、基因表达的测定,弥补有关花鲈等渗点研究的空白,同时为花鲈的淡化养殖提供一定的理论指导。     

Stimulation of acetylcholinesterase activity by triiodothyronine in the brain of Singi fish,Heteropneustes fossilis (Bloch)

Three consecutive days of injections of triiodothyronine (T₃)(0.038, 0.075, 0.15 and 1.54 nmoles/g) significantly elevated the acetylcholinesterase (AchE) activity in the brain of Singi fish, Heteropneustes fossilis (Bloch). The higher doses of 0.075, 0.15 and 1.54 nmoles of T₃/g induced a greater increase in enzyme activity than 0.038 nmoles/g. A T₃ dose of 0.019 nmoles/g was found to be ineffective. The T₃ action on AchE activity was blocked by cycloheximide. Thiourea treatment for 30 days decreased the AchE activity below the control level. This reduced level of the enzyme activity was brought back even above the control level by T₃ injections. It is, therefore, suggested that thyroid hormone is involved in the sustenance of AchE activity in fish brain.