丁香油在鳊模拟保活运输中的效果

文章研究了丁香油对鳊(Parabramis pekinensis)保活运输的影响。在单因素试验的基础上通过正交试验确定了最佳保活运输条件。并检测和分析了在模拟运输试验中水质指标和鱼体生化指标的影响。结果显示, 最佳保活运输条件为麻醉液浓度15 mg/L、水温9℃和鱼水质量比1﹕3时, 保活时间最长达50h, 且鱼体成活率为100%。在水体指标中, pH和溶氧量无显著变化, 麻醉组氨氮在48h内由0.049增加至4.034 mg/L, 水中微生物在24h内显著增加, 氨氮的增加和微生物的生长会影响鱼体的保活。在鱼体生化指标中, 麻醉组肌肉中糖元含量24h内显著下降, 乳酸含量先升后降, pH先降再升, 说明在保活运输中糖元消耗产生乳酸; 在鱼体血液指标中, 麻醉组谷草转氨酶(AST)活性, 乳酸脱氢酶(LDH)活性, 尿素和肌酐(CREA)在12h后有所上升, 血糖(GLU)在36h内显著增加(P<0.05), 然后降低; 说明随着保活时间的延长鱼体肝脏和肾脏组织代谢水平受到一定的影响。研究表明, 在鳊麻醉保活过程中, 适当使用丁香油麻醉剂, 有助于延长其保活时间和提高存活率。     

The ultrastructure of chloride cells in the gills of the teleostOreochromis mossambicus during exposure to acidified water

Summary Branchial chloride cells, which actively take up ions in the gills of freshwater fish, were studied in tilapia (Oreochromis mossambicus) exposed to sublethally acidified freshwater. Structural damage of cells, resulting in cell death by necrosis, only occurred transiently, when the reduction of water pH was acute rather than gradual. The most prominent effects of water acidification were the rapid increase in the number of chloride cells and the changes in frequency of the different stages of the chloride cell cycle. In the opercular inner epithelium, a twofold increase in cells occurred 48 h after gradual acidification. Cell density stabilized after 4 weeks at a level 5 times that of control fish. Four transitory stages were distinguished in the chloride cell cycle: accessory or replacement cells, immature, mature, and degenerating (apoptotic) cells. In control fish, mature chloride cells dominated (over 50%) with immature and apoptotic cells totalling about 40%. After 4 weeks in acid water, only 13% of the cells were mature. Immature and apoptotic cells dominated, each representing about 40% of the total number of chloride cells. Mature cells apparently age rapidly under these conditions. Thus, chloride cells turn over quickly in acid water, with a minor increase in ion transport capacity of the gills. This conclusion is supported by the observation that opercular and branchial Na⁺/K⁺ ATPase activities in treated fish are only 40%–50% higher than in controls.     

Spring cannibalism on 1 year walleye pollock in the Doto area,northern Japan: is it density dependent?

Cannibalism in walleye pollock off the eastern coast of the Hokkaido Island, Japan was important only during spring (April to June), and its importance increased from 0% in dry mass for <200 mm L _S fish to 48·9% for >400 mm L _S fish. Most of the prey was represented by age 1 year fish, showing a unimodal body size distribution with a mode at 121–130 mm. Although cannibal body size was larger in deeper (>150 m) water, there was no difference in prey size by depth, suggesting impingement of the predators inhabiting deeper water into the shallow areas to cannibalize 1 year fish. The minimum ratio cannibal: prey size was 1·74. There was a positive but non-significant correlation between the contribution of cannibalism to a potential predator's (>300 mm) diet and an estimate of the previous year's recruitment. This was due to an extremely high contribution of cannibalism during 1992, when a distinctly larger size of predators seemed to bias the contribution. When the 1992 data were removed from the analysis, a significant correlation was obtained ( r ²=0·77, P <0·01), showing that Pollock cannibalism is rather density dependent. Based on the results, it is hypothesized that the'overflow' of 1 year fish from the shelf waters due to their high abundance and the weak stratification in the spring water column results in increased co-occurrence with adult fish and consequent cannibalism.     

Contrasts in the hypo-osmoregulatory abilities of a freshwater and an anadromous population of inconnu

Juvenile freshwater and anadromous inconnu Stenodus leucichthys regulated plasma ions following a direct transfer from fresh to brackish water (10–15‰), but suffered osmoregulatory collapse with 100% mortality in 48 h when directly transferred to 25‰ salinity. Acclimation to brackish water for 2 weeks improved hypo-osmoregulatory capacity in both populations, with acclimated fish showing smaller increases in blood plasma ion concentrations, higher Na⁺-K⁺ ATPase activity, and lower mortality than non-acclimated fish following transfer to 25‰ sea water. Anadromous inconnu maintained pre-treatment plasma ion levels during acclimation, whereas these levels increased during acclimation in freshwater inconnu. Juvenile anadromous inconnu are therefore able to adapt physiologically to sea water of at least 25‰, if brackish-water acclimation is available, but freshwater inconnu have diminished saltwater tolerance, relative to the anadromous form.     

Near-bottom depletion of zooplankton over coral reefs: III: vertical gradient of predation pressure

Many diurnal planktivorous fish in coral reefs efficiently consume zooplankton drifting in the overlying water column. Our survey, carried out at two coral reefs in the Red Sea, showed that most of the diurnal planktivorous fish foraged near the bottom, close to the shelters from piscivores. The planktivorous fish were order of magnitude more abundant near (<1.5 m) the bottom than higher in the water column. The predation pressure exerted by these fish was assessed by measuring the consumption of brine shrimps tethered at different heights above the bottom on a vertical line which was pulled over the reef. Below 1.5 m above bottom, the shrimps survival probability sharply decreased toward the bottom. Higher in the water column, survivorship was nearly 100% with little vertical variation. Our results indicate that near-bottom depletion of zooplankton in coral reefs is likely due to intense predation at that boundary layer. Risk of predation by piscivorous fish apparently restricts planktivorous fish to forage near the bottom, with a distribution pattern greatly deviating from ideal-free distribution.     

Waterborne vs. dietary copper uptake in rainbow trout and the effects of previous waterborne copper exposure

Juvenile rainbow trout (Oncorhynchus mykiss) were exposed to waterborne Cu (22 microg/l) in moderately hard water for up to 28 days. Relative to control fish kept at background Cu levels (2 microg/l), Cu-preexposed fish displayed decreased uptake rates of waterborne Cu via the gills but not of dietary Cu via the gut during 48-h exposures to (64)Cu-radiolabeled water and diet, respectively. At normal dietary and waterborne Cu levels, the uptake rates of dietary Cu into the whole body without the gut were 0.40-0.90 ng. g(-1). h(-1), >10-fold higher than uptake rates of waterborne Cu into the whole body without the gills, which were 0.02-0.07 ng. g(-1). h(-1). Previously Cu-exposed fish showed decreased new Cu accumulation in the gills, liver, and carcass during waterborne (64)Cu exposures and in the liver during dietary (64)Cu exposures. A 3-h gill Cu-binding assay showed downregulation of the putative high-affinity, low-capacity Cu transporters and upregulation of the low-affinity, high-capacity Cu transporters at the gills in Cu-preexposed fish. Exchangeable Cu pools in all the tissues were higher during dietary than during waterborne (64)Cu exposures, and previous Cu exposure reduced waterborne exchangeable Cu pools in gill, liver, and carcass. Overall, these results suggest a quantitatively greater role for the dietary than for the waterborne route of Cu uptake, a key role for the gill in Cu homeostasis, and important roles for the liver and gut in the normal metabolism of Cu in fish.     

Degranulation of eosinophilic granule cells induced by capsaicin and substance P in the intestine of the rainbow trout (Oncorhynchus mykiss Walbaum)

Summary Adult rainbow trout (Oncorhynchus mykiss) were injected intraperitoneally with capsaicin, substance P, serotonin, or a control of saline vehicle or bovine serum albumin (0.5 g/g body weight). Fish were sacrificed 30 min and 1,2 and 4 h post-injection, the gut was dissected out, and a small section of the upper intestine was processed for electron microscopy. A significant proportion of eosinophilic granule cells (EGCs) of the intestine were in close association with non-myelinated neuronal bundles in all fish (4 fish per treatment and time period), but there was no significant difference between treatment or time, suggesting that the association was unaffected by these factors. Close examination of EGC ultrastructure showed that fish treated with capsaicin and substance P exhibited limited degranulation of the EGCs in the stratum compactum and extensive crinophagic-like degranulation in the lamina propria. Cells of the lamina propria contained characteristic multivesicular-like bodies. The degranulation was reminiscent of both mast cell degranulation and endocrine cell crinophagy. EGCs of fish treated with serotonin or a control were unaffected, suggesting that the serotoninergic neurons, believed to be involved in gut motility, were not responsible for degranulation. It is apparent that EGCs of the trout intestine may be under nervous control, as has been demonstrated previously for mammalian mast cells.     

Oxygen consumption and haematology of juvenile shortnose sturgeon Acipenser brevirostrum during an acute 24 h saltwater challenge

This study focused on the acute physiological responses to saltwater exposure in juvenile shortnose sturgeon Acipenser brevirostrum. In two separate laboratory experiments, 2 year‐old A. brevirostrum were exposed to either full (32) or half‐strength (16) seawater for up to 24 h. First, oxygen consumption rates were used to estimate the metabolic costs over 24 h. Secondly, blood and muscle samples were analysed at 6, 12 and 24 h for water loss, various measures of osmoregulatory status (plasma osmolality and ions) and other standard haematological variables. Juveniles exposed to full‐strength seawater showed significant decreases in oxygen consumption rates during the 24 h exposure. Furthermore, seawater‐exposed fish had significantly increased plasma osmolality, ions (Na⁺ and Cl^?) and a 17% decrease in total wet mass over the 24 h exposure period. To a lesser extent, increases in osmolality, ions and mass loss were observed in fish exposed to half‐strength seawater but no changes to oxygen consumption. Cortisol was also significantly increased in fish exposed to full‐strength seawater. While plasma protein was elevated following 24 h in full‐strength seawater, haemoglobin, haematocrit and plasma glucose levels did not change with increased salinity. These results imply an inability of juvenile A. brevirostrum to regulate water and ions in full‐strength seawater within 24 h. Nonetheless, no mortality occurred in any exposure, suggesting that juvenile A. brevirostrum can tolerate short periods in saline environments.     

The immune response of tilapia Oreochromis mossambicus and its susceptibility to Streptococcus iniae under stress in low and high temperatures

Mozambique tilapia Oreochromis mossambicus acclimated to 27 degrees C were then held at 19, 23, 27 (control), 31 and 35 degrees C, and were examined for non-specific cellular and humoral responses after 12-96 h. Total leucocyte count decreased significantly when fish were transferred to 19 and 23 degrees C after 48 and 96 h, and when transferred to 35 degrees C over 12-96 h, respectively. Respiratory burst decreased significantly when fish were transferred to 19, 31 and 35 degrees C over 24-96 h, whereas phagocytic activity and phagocytic index decreased significantly when fish were transferred to low temperatures (19 and 23 degrees C) and high temperatures (31 and 35 degrees C) over 12-96 h. Lysozyme activity decreased significantly when fish were transferred to 19 degrees C after 12-96 h, but increased significantly when transferred to 31 and 35 degrees C over 48-96 h. Alternative complement pathway (ACH(50)) also decreased significantly when transferred to 19 and 23 degrees C after 12h, but increased significantly when transferred to 31 and 35 degrees C after 24h. In another experiment, tilapia reared at 27 degrees C were injected intraperitoneally with Streptococcus iniae at a dose of 1 x 10(7)colony-forming units (cfu)fish(-1), and then reared onward at water temperatures of 19, 23, 27 (control), 31 and 35 degrees C. Over 48-168 h, the cumulative mortality of S. iniae-injected fish held in 19 and 35 degrees C was significantly higher than that of injected-fish held in 23, 27 and 31 degrees C. It is concluded that transfer of tilapia O. mossambicus from 27 degrees C to low temperatures (19 and 23 degrees C) after 12h, and transfer of fish from 27 degrees C to high temperatures (31 and 35 degrees C) reduced their immune capability. Moreover, tilapia under temperature stress at 19 and 35 degrees C from 27 degrees C decreased its resistance against S. iniae.     

The effects of calcitonin on plasma calcium levels and bone metabolism in the fresh water teleost Channa punctatus

Administration of salmon calcitonin (sCT) caused significant reduction in total and ultrafiltrable plasma calcium content in the plasma of a fresh water female teleost Channa punctatus. A time-bound analysis on the effect of sCT showed a highly significant short duration reduction in total and ultrafiltrable plasma calcium content in fish kept in normal tap water and low-calcium water and a moderate hypocalcemia in fish kept in high-calcium water. Sexually immature adult fish showed a greater response than the sexually mature ones. Using tartrate-resistant acid phosphatase (TRACP) and alkaline phosphatase (ALP) activities in plasma and hydroxyproline (HYP) excretion in urine, the effect of sCT on the inhibition of bone calcium resorption were examined. In both sexually mature and immature adult fish, kept in normal tap water, sCT significantly suppressed TRACP and ALP activities in plasma and excretion of HYP in urine within 2-6 h with a maximum at 4 h after injection. Salmon CT treatment to sexually immature adult fish caused significant increase in skeletal bone calcium concentration. Taken together, all this information indicates that CT in a fresh water female teleost is an effective regulator of plasma calcium levels, and its action, at least in part, operates through inhibition of bone calcium resorption.     

The Effect of Ration on Acclimation to Environmental Acidity in Rainbow Trout

Freshwater salmonids exposed to low environmental pH typically suffer a net loss of ions, primarily Na⁺ and Cl^–, across the gills, resulting in reduced plasma and tissue ion concentrations. However, in recent experiments in our laboratory, juvenile rainbow trout, Oncorhynchus mykiss, fed a ration of 1% body weight d^–1 or greater showed no ionoregulatory disturbance during chronic, sublethal acidification. This raised the possibility that these fish had acclimated to low pH in that they would be better able to withstand further, more severe acidification than fish that had no prior experience of acid conditions: previous studies had concluded that such acclimation does not occur. This hypothesis was tested by measuring unidirectional ion fluxes during a 24h acute acid challenge (pH 4.2) in juvenile rainbow trout that had previously been exposed to either ambient pH 6.2 (naive fish) or sublethal low pH 5.2 (acid pre-exposed fish) for 90 days, and fed a ration of either 1.0 or 0.25% d^–1 (wet basis). No mortalities were observed during the acute acid challenge in the fish fed the higher ration and no differences between the two groups in the response of Na⁺ fluxes were observed. Sodium influx in both groups was significantly inhibited throughout the challenge and Na⁺ net flux was significantly stimulated over the first 6h. Prior to the acute acid challenge, the fish fed the lower ration that had previously been exposed to pH 5.2 had significantly lower plasma ion concentrations than those fish previously exposed to pH 6.2. Both groups suffered mortalities; those of the naive fish (22% by 24h) being markedly lower than those of the acid pre-exposed fish (68% by 24h). However, there were no significant differences in either Na⁺ or Cl^– fluxes between the two groups of fish during the acid challenge: both showed significant inhibition of ion influxes and significantly greater net ion losses, resulting in reduced plasma ion concentrations. These results indicate that rainbow trout are unable to acclimate to environmental acidification irrespective of the availability of dietary salts.     

The relation between pituitary gland and thyroid growth during the lifespan of the annual fish Cynolebias whitei and Nothobranchius korthausae: gonadotropic and thyrotropic cells

Summary In the annual cyprinodont Cynolebias whitei the cell types responsible for the increase of pituitary growth at the onset of maturation and for pituitary hyperplasia in old specimens were identified as gonadotropic cells and thyrotropic cells, respectively. The gonadotropic cells showed a high affinity to anti-carp -GTH serum, both at light- and electron-microscopical levels. The allometric relation of total gonadotropic cell volume to body length, determined for fish from six weeks up to six months of age, showed no inflections. Therefore pituitary growth in maturing fish may be partly a result of proliferation of gonadotropes, although gonadotropic cells do not contribute to pituitary hyperplasia in old fish. Thyrotropic cells showed a weak affinity to anti-carp -GTH serum at light-microscopical level. Under the electron microscope thyrotropic cells displayed signs of activation in maturing fish and signs of proliferation in old fish. The allometric relation of thyroid gland volume to body length paralleled that of pituitary volume to body length. Histologically the thyroid gland showed signs of inactivity in adult fish and of hyperplasia in old fish. The possibility, that gonadal maturation, pituitary thyrotropic activity, and growth of the thyroid in maturing fish are related through the inhibitory action of gonadal steroids on thyroid hormone release, is discussed. Pituitary hyperplasia in old fish is the result of proliferation of thyrotropic cells. Similar hyperplasia of pituiary and thyroid glands was observed in old Nothobranchius korthausae.     

Effect of blood withdrawal and angiotensin II on prolactin release in the tilapia,Oreochromis mossambicus

Repeated blood withdrawal (5% of estimated blood volume at 0, 1, 4, 8, 24, 48 and 76 h) from tilapia acclimated to fresh water (FW) resulted in a marked increase in plasma levels of prolactin (PRL) during the first 8 h, reaching a peak above 300 ng/ml after 4 h. The increase in plasma PRL levels was significant except for the level after 72 h. A slight but significant decrease in plasma osmolality was observed at all time points after the blood withdrawal. Repeated blood withdrawal from fish acclimated to seawater (SW) resulted in a marked increase in plasma osmolality after 4 and 8 h. A significant increase was observed in plasma growth hormone (GH) in the fish in SW until the end of the experiment, but there was no change in plasma PRL. Plasma levels of cortisol were significantly higher in the fish in SW than in those in FW during the first 24 h. Blood withdrawal resulted in a significant reduction in hematocrit values in both FW- and SW-adapted fish, suggesting hemodilution. In a separate experiment, a single blood withdrawal (20% of total blood) stimulated drinking after 5 h, regardless of whether the fish were held in FW or SW. Plasma PRL level was also elevated following a single blood withdrawal in the fish acclimated to FW, but not in the fish in SW. Intraperitoneal injection of ANG II (1.0 microg/g) into the fish in FW significantly increased plasma PRL levels after 1 h. Activation of the renin-angiotensin system after blood withdrawal and the dipsogenic action of angiotensin II (ANG II) are well established in fish. The reduction in plasma osmolality after repeated blood withdrawal in FW and the increased osmolality in SW suggest that blood volume is restored, at least in part, by drinking environmental water. These results suggest that the marked increase in PRL concentration after blood withdrawal from the fish in FW is due, at least in part, to a facilitative effect between ANG II and reduced plasma osmolality.     

Osmoregulatory action of 17beta-estradiol in the gilthead sea bream Sparus auratus

The osmoregulatory action of 17beta-estradiol (E2) was examined in the euryhaline teleost Sparus auratas. In a first set of experiments, fish were injected once with vegetable oil containing E2 (1, 2 and 5 microg/g body weight), transferred 12h after injection from sea water (SW, 38 ppt salinity) to hypersaline water (HSW, 55 ppt) or to brackish water (BW, 5 ppt salinity) and sampled 12h later (i.e. 24 h post-injection). In a second experiment, fish were injected intraperitoneally with coconut oil alone or containing E2 (10 microg/g body weight) and sampled after 5 days. In the same experiment, after 5 days of treatment, fish of each group were transferred to HSW, BW and SW and sampled 4 days later (9 days post-implant). Gill Na+,K+ -ATPase activity, plasma E2 levels, plasma osmolality, and plasma levels of ions (sodium and calcium), glucose, lactate, protein, triglyceride, and hepatosomatic index were examined. Transfer from SW to HSW produced no significant effects on any parameters assessed. E2 treatment did not affect any parameter. Transfer from SW to BW resulted in a significant decrease in plasma osmolality and plasma sodium but did not affect gill Na+,K+ -ATPase activity. A single dose of E2 attenuated the decrease in these parameters after transfer from SW to BW, but was without effect on gill Na+,K+ -ATPase activity. An implant of E2 (10 microg/g body weight) for 5 days significantly increased plasma calcium, hepatosomatic index, plasma metabolic parameters, and gill Na+,K+ -ATPase activity. In coconut oil-implanted (sham) fish, transfer from SW to HSW or BW during 4 days significantly elevated gill Na+,K+ -ATPase. Gill Na+,K+ -ATPase activity remained unaltered after transfer of E2-treated fish to HSW or BW. However, in E2-treated fish transferred from SW to SW (9 days in SW after E2-implant), gill Na+,K+ -ATPase activity decreased with respect to HSW- or BW-transferred fish. Shams transferred to HSW showed increased levels of lactate, protein, and trygliceride in plasma, while those transferred to BW only displayed increased trygliceride levels. E2-treated fish transferred to HSW showed higher protein levels without any change in other plasmatic parameters, while those transferred to BW displayed elevated plasma glucose levels but decreased osmolality and protein levels. These results substantiate a chronic stimulatory action of E2 on gill Na+,K+ -ATPase activity in the euryhaline teleost Sparus auratas.     

家用洗涤剂对红剑鱼、孔雀鱼和食蚊鱼的急性毒性实验观察

目的 研究4种不同产地的家用洗涤剂对红剑鱼、孔雀鱼和食蚊鱼的急性毒性影响。方法 用水毒理学方法测定它们对3种鱼类的24hLC50,并将洗涤剂溶液存放15d和30d后测定其对鱼类的急性毒性。结果 在远低于日常使用量的浓度下,4种家用洗涤剂均对红剑鱼、孔雀鱼和食蚊鱼有急性毒性,24h LC50值在20mg／L～55mg／L;家用洗涤剂溶液存放一段时间后对鱼类的急性毒性作用无明显降低。结论 含有大量家用洗涤剂的生活污水排放到自然水体后将对鱼类产生持续的有害影响。     

Crystal Structure of Escherichia coli CusC,the Outer Membrane Component of a Heavy Metal Efflux Pump

Background

While copper has essential functions as an enzymatic co-factor, excess copper ions are toxic for cells, necessitating mechanisms for regulating its levels. The cusCBFA operon of E. coli encodes a four-component efflux pump dedicated to the extrusion of Cu(I) and Ag(I) ions.

Methodology/Principal Findings

We have solved the X-ray crystal structure of CusC, the outer membrane component of the Cus heavy metal efflux pump, to 2.3 Å resolution. The structure has the largest extracellular opening of any outer membrane factor (OMF) protein and suggests, for the first time, the presence of a tri-acylated N-terminal lipid anchor.

Conclusions/Significance

The CusC protein does not have any obvious features that would make it specific for metal ions, suggesting that the narrow substrate specificity of the pump is provided by other components of the pump, most likely by the inner membrane component CusA.     

Effects of food-deprivation on migratory restlessness and diurnal activity in the garden warbler Sylvia borin

Summary The effects of tadpole body size, tadpole sibship, and fish body size on predation of gray treefrog tadpoles, Hyla chrysoscelis, were studied in laboratory and artificial pond experiments. Tadpole body size had a significantly positive effect on the survival of tadpoles in all experiments. The relationship between tadpole biomass eaten and biomass available suggested that fish were not satiated when consuming the largest tadpoles. Large tadpoles were probably better able to evade predators. A difference in survival among full sib families of tadpoles was only present in one family, suggesting that genetic differences in predator avoidance behavior or palatability were probably secondarily important to body size per se. Fish body size had a significantly negative effect on the survival of tadpoles. Larger fish consumed a larger number and proportion of tadpoles as well as greater biomass. These results indicate that environmental factors affecting the growth rate of tadpoles cand dramatically alter their vulnerability to gape-limited predators.     

MNNG-induced mutations in the adult gill and hepatopancreas and in embryos of rpsL transgenic zebrafish

To evaluate the feasibility of a mutagenicity assay using adult rpsL transgenic zebrafish, 4- to 8-month-old females were exposed to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) (0, 15 or 30 mg/L in a water bath for 2 h). At 2 weeks after exposure, MNNG showed a concentration-dependent significant increase in mutant frequency (MF) of 8 x 10(-5), 18 x 10(-5), and 51 x 10(-5), respectively, in the gill. DNA sequencing revealed that 60-74% of the induced mutations were G:C to A:T transitions, consistent with the known mutagenic effects of MNNG. A marginal but significant increase in MF was observed in the hepatopancreas only in the group exposed to 30 mg/L, with the induction of some G:C to A:T transitions. A time-course of the appearance of mutations was determined in fish treated with 15 mg/L MNNG. In both, the gill and hepatopancreas, a higher MF was observed at 3 weeks than at 2 weeks, suggesting that an expression time of at least 3 weeks is preferable for the assay. When embryos (29 h post-fertilization) were exposed to MNNG (0, 50, and 150 mg/L) for 1 h, MFs increased significantly with an increase in the concentration of MNNG (5 x 10(-5), 40 x 10(-5), and 144 x 10(-5), respectively) at 3 days after exposure. G:C to A:T transitions were the predominant mutations, and these occurred at the same sites in the rpsL gene as in adult tissues. Thus, MNNG induces typical mutations in the gill and hepatopancreas of adult fish, and in embryos, suggesting that the rpsL zebrafish is a useful tool for monitoring genotoxicity caused by water-borne mutagens.     

Effect of sudden salinity change on Penaeus latisulcatus Kishinouye osmoregulation, ionoregulation and condition in inland saline water and potassium-fortified inland saline water

Two trials were conducted to determine the effect of sudden decrease in salinity of raw and potassium-fortified inland saline water on western king prawn Penaeus latisulcatus osmoregulation, ionoregulation and condition. Prawns were subjected to salinity decrease over 1 h from 32 to 25 ppt in the first trial and from 27 to 20 ppt in the second trial in three water types: inland saline water with potassium fortified to 100% and 80% of the marine water concentration (IS100, IS80), and raw inland saline water (ISW). In the first trial condition and ingestion rate were monitored over 19 days following salinity change. In the second trial condition, haemolymph osmo- and iono-regulation were recorded over 48 h following salinity change. In the first trial, 100% mortality was observed in ISW by day 13, with final survival 94% in IS80 and 100% in IS100. Tail muscle moisture content increased significantly (P < 0.05) over time in both trials and in all water types, suggesting loss of energy reserves. In the second trial, serum osmolality, sodium concentration and osmoregulatory capacity decreased following salinity change, stabilising by 24 h in IS100 and IS80 but continuing to decrease till 48 h in ISW, suggesting partial breakdown of osmoregulatory function in the potassium-deficient medium. Prawns were stronger regulators of divalent than monovalent cations. These trials demonstrate that potassium-deficient inland saline water requires fortification with potassium to allow prawn survival and efficient osmoregulation.     

Regulation of avilamycin biosynthesis in Streptomyces viridochromogenes: effects of glucose, ammonium ion, and inorganic phosphate

Effects of glucose, ammonium ions and phosphate on avilamycin biosynthesis in Streptomyces viridochromogenes AS4.126 were investigated. Twenty grams per liter of glucose, 10 mmol/L ammonium ions, and 10 mmol/L phosphate in the basal medium stimulated avilamycin biosynthesis. When the concentrations of glucose, ammonium ions, and phosphate in the basal medium exceeded 20 g/L, 10 mmol/L, and 10 mmol/L, respectively, avilamycin biosynthesis greatly decreased. When 20 g/L glucose was added at 32 h, avilamycin yield decreased by 70.2%. Avilamycin biosynthesis hardly continued when 2-deoxy-glucose was added into the basal medium at 32 h. There was little influence on avilamycin biosynthesis with the addition of the 3-methyl-glucose (20 g/L) at 32 h. In the presence of excess (NH₄)₂SO₄ (20 mmol/L), the activities of valine dehydrogenase and glucose-6-phosphate dehydrogenase were depressed 47.7 and 58.3%, respectively, of that of the control at 48 h. The activity of succinate dehydrogenase increased 49.5% compared to the control at 48 h. The intracellular adenosine triphosphate level and 6-phosphate glucose content of S. viridochromogenes were 128 and 129%, respectively, of that of the control at 48 h, with the addition of the 40 mmol/L of KH₂PO₄. As a result, high concentrations of glucose, ammonium ions, and inorganic phosphate all led to the absence of the precursors for avilamycin biosynthesis and affected antibiotic synthesis.