Salinity influence on the early stages of the African catfish

Experiments were conducted to determine the effect of various incubation salinities on the hatching and survival of eggs and hatched fry respectively of the African catfish (Clarias gariepinus). The optimal salinity for the hatching of the eggs ranged from 0–5. Above 5, hatching was significantly low and no hatching occurred at 8 incubation salinity. Median lethal times (LT50) for fry hatched in 0, 2 and 4 incubation salinities, when abruptly transferred to 10 were 59, 49.5 and 50 h respectively. Similarly, LT50 for fry hatched in 0, 2 and 4 incubation salinities, and abruptly transferred to 12 salinity were 17, 22 and 12.50 h respectively. Increase in incubation salinity of the eggs did not seem to enhance the salinity tolerance of the hatched fry.The gradual (stepwise) increase in salinity of 1 per day of the catfish fry hatched in various incubation salinities (0, 1, 2, 3, 4, 5 and 6) had median lethal salinity values of 8, 8, 8, 10, 10, 11 and 11 respectively. © Rapid Science Ltd. 1998     

Survival and Growth of Bighead Carp Fry Exposed to Low Salinities

Bighead carp (Aristichthys nobilis Oshima) fry of various ages (11, 18, and 35 days post-hatch) were exposed to the low salinities encountered during the annual intrusion of seawater in Laguna Lake, Philippines. Practical indices of salinity tolerance assessed the effect of a 96 h direct exposure to low salinities (0–16). Mean (MST) and median survival times (MST50) of fry decreased as salinity of rearing medium increased. Younger fry were less able to tolerate exposure to these salinities than their older cohorts. Median lethal salinity after 96 h (MLS) revealed higher tolerance among 35–day old fry (7.6) than 11 (2.3) and 18–day old fry (6.0), demonstrating that survival in saline water depends on their age at initial exposure to low salinities. Mean body weight of 18–day old fry reared in 0 and 2 for 3 and 4 weeks was higher than for those reared in 4 and 6 for the same period. Growth over these periods was inversely related with the range of salinities tested. These results demonstrate that, despite their known stenohalinity, bighead carp fry possess some degree of osmoregulatory capability, allowing them to survive and grow in lakes subjected periodically to saltwater inflow.     

Brackishwater carp culture in potentially waterlogged areas using animal wastes as pond fertilizers

In order to assess the possibilities of utilizing drainage effluents (salinity range 5.0–12.5), fish culture experiments were carried out. Experiments on polyculture using cow dung (24 000 kg ha^–1 y^–1) as pond fertilizer were conducted at five different salinity levels (0.3–8.5). Studies have revealed that carp perform well in salinities up to 7.5 and reasonably high fish production has been obtained. Even though the ponds had a high trophic status, higher salinities ( > 7.5) appear to repress fish growth probably due to low dissolved oxygen (DO), high BOD and high NH₄-N. Experiments on monoculture of common carp (Cyprinus carpio) conducted at two different salinity levels (0.3–0.9 and 6.0–7.0) using four different organic fertilizers (cow dung at 24 000 kg and 20 000 kg, poultry at 1500 kg, duck at 6000 kg and sheep/goat at 1500 kg ha^–1 y^–1) have revealed the highest fish growth to be in poultry-treated ponds, followed in decreasing order by duck and sheep/goat wastes. Similar trends in fish production were observed both in fresh- and salt-water ponds. However, fish production was lower in ponds having higher salinities ( > 7.5). Nevertheless, these studies indicated that inland saline waters can be utilized for fish culture. With minor modifications in the existing technology of fish culture in stagnant freshwater fish ponds, animal wastes could be used to fertilize brackishwater fish ponds.     

The effect of dietary sodium chloride on some osmoregulatory parameters of the teleost, Oreochromis niloticus, after transfer from freshwater to seawater

The aim of this work was to determine the effects of supplemental dietary sodium chloride on salt water acclimation of tilapia Oreochromis niloticus. Fish were fed a basal diet supplemented with NaCl (8%) during three weeks in fresh water (FW) and then transferred to salt water (SW) at 15 and 20. Changes in plasma osmolality, chloride ion concentration (Cl^–), plasma level of cortisol and gill Na⁺, K⁺-ATPase activity were measured at 6, 12, 24, 48, 72 and 168 h after transfer to 15SW, while the higher strength SW group (20) was only monitored up to 24 h. Morphological changes in the gill mitochondria-rich (MR) cells were examined in relation to environmental salinity. The changes associated with dietary NaCl were sporadic and of small magnitude. The plasma osmolality and Cl^– increased immediately after transfer up to 12–24 h, but fish fed dietary salt (S) showed lower values than the control group (C). The S group showed higher plasma levels of cortisol than the control, which maintained its initial levels during the experiment. Gill Na⁺, K⁺-ATPase activity of the S group began to increase in the first hours after transfer, reaching maximum at 12 h and returned to basal level at 24 h, while the control group maintained basal levels. The differences between gill Na⁺, K⁺-ATPase activity of S and C fish were significant (p < 0.05) at 12 h. Transmission electron microscopy (TEM) revealed that MR cells in SW show more mitochondria and a more developed tubular system arising from the basolateral membrane. The MR cells of both groups frequently formed a multicellular complex in SW, consisting of a main MR and one or more accessory cells. Such complexes are rarely observed in FW. Some MR cells of fish fed supplemented dietary salt displayed convex apical membrane in FW.     

Annual cycle of plasma insulin and glucose of sea bass.Dicentrarchus labrax,L.

Annual plasma insulin and glucose cycles were studied inDicentrarchus labrax maintained in either seawater (37.8) or brackish water (3.5). In both media, the highest insulin levels were found during the prespawning period (August–November) coincident to increases in weight and a decrease in plasma glucose. During spawning (December–April) and postspawning (May–July) periods, the decrease in insulin occurred at the same time as a reduction in growth and an increase of plasma glucose. Temperature and salinity conditions impeded spawning in the brackish water group, in which a minor weight loss was regained more quickly than in the sea water group; insulin levels were also higher.     

Studies on the use of hydrogen peroxide as a method for the control of sea lice on Atlantic salmon

Atlantic salmon (Salmo salar) post-smolts exposed to 1.23 hydrogen peroxide for 20 min at 13.5 C suffered an acute toxicity resulting in a 35% mortality within 2 h. Under similar conditions at 10 C no mortalities were observed with Atlantic salmon or goldsinny wrasse (Ctenolabrus rupestris). No histological changes were noted in tissues from exposed fish. Thirty-three per cent of adult and pre-adult sea lice (Lepeophtheirus salmonis) were immobilized or killed following exposure to 0.5 hydrogen peroxide at 10 C, rising to 98% at 2. Some lice were able to recover and regained normal swimming movements. Gas bubbles within the haemolymph caused affected lice to float on the water surface. A delay in the toxicity of hydrogen peroxide to copepodites occurred, with a 10% mortality following a 20 min exposure to 1.25 at 10 C rising to 100% mortality at 19 h post treatment.Dilute hydrogen peroxide was stable over the 20 min treatment period. Aeration and higher temperatures increased the long-term breakdown of a working concentration of hydrogen peroxide in seawater.     

Feed-growth relationships of Arctic charr transferred from freshwater to saltwater at different seasons

Groups of Arctic charr, Salvelinus alpinus (L.), originating from an anadromous stock, were transferred directly from freshwater to seawater (35 S), from freshwater to brackish water (20 S), or were gradually adapted to seawater over a period of 10 days. A control group was kept in freshwater. Feed intake and growth were then monitored during the following 59 days. Two experiments were carried out, one during winter (December–January) and the other during summer (June–July). Water temperature was maintained at 8 C. All fish had been held under natural photoperiod and temperature conditions from the end of the first feeding period (mid-April) until the experiments were carried out. Rates of growth did not differ between the groups of charr held in fresh- and brackish water, but growth of these groups was better than that of fish reared in seawater. Relationships between individual feed intake (FI) and individual specific growth rates (SGR), within groups were expressed as: ln (SGR+1) = a + ln (FI+1), and regression lines were compared using analysis of covariance. In winter, the regression line for fish transferred directly to seawater had a significantly steeper slope, and a lower elevation, than the lines for fish transferred to brackish water or held in freshwater. Fish transferred gradually to seawater had an intermediate position. In summer, the regressions for all groups were parallel with intercepts in the seawater groups being significantly lower than in the freshwater group. This indicates that the gross feed conversion efficiency (FCE) in Arctic charr was lower in seawater than in freshwater. The results are discussed in relation to digestion, gut function and osmoregulation. yc]Keywords xc]Arctic charr (Salvelinus alpinus (L.)) xc]Feed utilization xc]Salinity xc]Season     

Effects of acute temperature decreases on turbot fry and juveniles

Turbot fry (10–20 mm) and juveniles (85–110 mm) were transferred directly from 16.0–16.5 C to 1.0 C, 2.5 C, 5.5 C or 8.0 C seawater. The fry were more sensitive to cold water than juveniles. The fry survived for 1 week at 8.0 C but not at 5.5 C, whereas juveniles survived at 5.5 C but not at 2.5 C. Transfer of juveniles to 1.0 C and 2.5 C seawater caused a high mortality, a marked increase in plasma Cl^- concentration, decrease in muscle water content, and hyperglycaemia. Acclimation to 5.5 C (juveniles) or 8.0 C (fry and juveniles) markedly reduced the sensitivity to 1.0 C exposure.     

Influence of cortisol, growth hormone, insulin-like growth factor I and 3,3′,5-triiodo-l-thyronine on hypoosmoregulatory ability in the euryhaline teleost Fundulus heteroclitus

The capacity of cortisol, ovine growth hormone (oGH), recombinant bovine insulin-like growth factor I (rbIGF-I) and 3,3,5-triiodo-l-thyronine (T₃) to increase hypoosmoregulatory capacity in the euryhaline teleost Fundulus heteroclitus was examined. Fish acclimated to brackish water (BW, 10 ppt salinity) were injected with a single dose of hormone suspended in oil and transferred to seawater (SW, 35 ppt salinity) 10 days post-injection. Fish were sampled 24 h after transfer and plasma osmolality and gill Na⁺, K⁺-ATPase activity were examined. Transfer from BW to SW induced significantly increased plasma osmolality but not gill Na⁺, K⁺-ATPase activity. Cortisol (50 g g^–1 body weight) improved the ability to maintain plasma osmolality and to increase gill Na⁺, K⁺-ATPase activity. oGH (5 g g^–1 body weight) also increased hypoosmoregulatory ability and gill Na⁺, K⁺-ATPase activity. A cooperation between oGH and cortisol was observed in increasing hypoosmoregulatory ability but not in increasing gill Na⁺, K⁺-ATPase activity. rbIGF-I (0.5 g g^–1 body weight) alone was without effect in increasing salinity tolerance or gill Na⁺, K⁺-ATPase activity. rbIGF-I and oGH showed a positive interaction in increasing salinity tolerance, but not gill Na⁺, K⁺-ATPase activity. Treatment with T₃ (5 g g^–1 body weight) alone did not increase salinity tolerance or gill Na⁺, K⁺-ATPase activity, and there was no consistent significant interaction between cortisol and T₃ or between GH and T₃. The results confirm the classical role of cortisol as a seawater-adapting hormone and indicate an interaction between cortisol and the GH/IGF-I axis during seawater acclimation of Fundulus heteroclitus.     

The relationship between `deep-hole' mitochondria-rich cells and salinity adaptation in the euryhaline teleost, Oreochromis mossambicus

The present study elucidates the relationship between deep-hole MR cells (Lee et al. 1996) and salinity adaptation in tilapia (Oreochromis mossambicus). Freshwater tilapia were transferred to salt water of various salinities, i.e., 5 (hypotonic), 10 (isotonic), 20 (hypertonic), and 30 (hypertonic), for 2 weeks. The density of MR cells, protein content, activity, and localization of the sodium pump were examined. There was no significant difference in serum osmolarity and Na⁺, K⁺, Cl^– levels in fish of the various treatment groups. The amounts of protein and activity of Na,K-ATPase were elevated in fish from SW with the highest salinity. MR cells observed by scanning electron microscope revealed small pits (0.5–1.0 m in diameter) in groups from hypotonic and isotonic water and large crypts (2.4–3.8 m in diameter) in fish from hypertonic water. Moreover, the density of these deep-hole MR cells increased significantly in fish adapted to hypertonic SW. Larger and more numerous deep-hole MR cells of euryhaline tilapia may account for higher protein amounts and activities of Na,K-ATPase, probably to meet the physiological demand of euryhaline teleosts engaged in hyporegulation.     

Synthesis and regulation of 17α-hydroxy-20β-dihydroprogesterone in immature males of Oncorhynchus mykiss

Three experimental approaches were chosen to study the question if the progestin 17-hydroxy-20-dihydroprogesterone (1720OHP) is synthesised in testes of young Oncorhynchus mykiss, in which the absence of spermatozoa was verified histologically: first, in order to detect 20-hydroxysteroid dehydrogenase activity (20HSD), testes homogenates were incubated with ³H-labeled 17OHP.Metabolites were analysed by TLC, HPLC, and repeated crystallization to constant isotope ratios. One of the metabolites was identified as 1720OHP-³H, indicating that already immature testes contain 20HSD activity and are able to produce 20-reduced steroids. Second, 1720OHP was quantified by radioimmunoassay in incubates of testes fragments. The sensitivity of the gonads to gonadotropin II (GtH II) became evident when comparing incubations in the absence and presence of GtH II. Third, plasma levels of 1720OHP were significantly higher in animals injected with partially purified salmon gonadotropin, compared to controls. Thus, for the first time, it could be shown that 20HSD is present in testicular cells other than spermatozoa. Furthermore, 1720OHP is indeed secreted at a very early stage of testicular development; 1720OHP secretion is also responsive to GtH II. Future studies will have to show if the functions of this progestin include the stimulation of spermatogenesis.     

Biochemical and histochemical activities of tyrosinase in the skins of normal and albino turbot scophthalmus maximus

Albinism occurr frequently in hatchery-reared turbot, particularly in China. To elucidatethe mechanism of albinism, we comparedthe biochemical and histochemical activity of tyrosinase inthe skins of normal and albino turbot using substrate L-3,4-dihydroxyphenylalanine (L-dopa). It was foundthat: (1) tyrosinase activity existed in allthe skin extracts tested, including pigmented and non-pigmented skins from ocular or blind side of normal and albino turbot, andthe tyrosinase activity ofthe ocular skin extracts was significantly higherthanthat ofthe blind skin extracts from a single individual for both normal and albino turbot. Unexpectedly,the tyrosinase activity inthe extracts from albino skin ofthe ocular side of albino turbot (termed AOA skin) was about 56% higherthanthat from pigmented skin ofthe ocular side of normal turbot (termed PON skin); (2) histochemical staining showedthat tyrosinase activity was present only inthe PON skin but not inthe AOA skin, andthe white skin ofthe blind side of albino (termed WBA skin) and normal turbot (termed WBN skin). A large amount of positive black granules was formed inthe epidermal cells of PON skin but no black granules were formed inthe skins of AOA, WBA and WBN; (3) temperature and salinity have similar effects onthe tyrosinase activity of ocular pigmented and of albino skin extracts, andthe optimal temperature was 5560°C and optimal salinity 26; however, different pH values had different effects onthese tyrosinase activities, andthe optimal pH value of ocular pigmented skin extracts was 7.0 and ocular albino skin extracts 8.0; allthethree activators tested (SDS, trypsin and zymosan) can increasethe activity of tyrosinase in both ocular pigmented and albino skin extracts of turbot. Butthe level of activation onthe ocular albino skin extracts of albino turbot was significantly higherthanthat on ocular pigmented skin extracts of normal turbot.Onthe basis ofthese observations, it is suggestedthat a large amount of wild type tyrosinase is expressed in albino skin butthe tyrosinase activity is blocked by some unknown inhibitory factors andthe blocked activity of tyrosinase can be readily recovered bythe homogenization of skin tissues in vitro.the unknown inhibitory factors need further studying.     

Protein kinase C in the spleen of the turbot (Scophthalmus maximus L.)

PKC activity was detected in spleen extracts from the turbot, Scophthalmus maximus, a teleost flatfish that is farmed commercially in several countries, in assays with the substrate EGF- R651–658 as phosphate acceptor. The activity was purified about 700-fold by a three-step chromatographic procedure (DEAE-cellulose, phenyl-Sepharose and threonine-Sepharose). Maximal activity was obtained in the presence of the typical PKC cofactors Ca2+ (0.1 mM) PtdS (20 g ml–1) and either DAG (2 g ml–1) or PMA (2 g ml–1). Activity was dose-dependently inhibited by H7 and by the PKC-specific inhibitors PKC19–36 and N-myristoylated PKC19–31. The rate of phosphorylation was highest with the PKC-specific substrate MARCKS161–175. In immunoblotting, MC5 (a mouse monoclonal antibody raised against bovine PKC) recognized bands of 80 and 100 kDa. Immunoblotting with antibodies raised against mouse PKC isozymes (, , , , , , and ) indicated the presence of all these isozymes in turbot spleen.     

Physiological and biochemical parameters for egg quality determination in lake trout,Salmo trutta lacustris

The present study investigated the relationships between egg viability and ovarian fluid composition, egg physiology and egg metabolism in lake trout, Salmo trutta lacustris, to obtain biomarkers for egg quality determination. The ovarian fluid pH, protein levels and activities of aspartate aminotransferase and -d-glucuronidase were significantly correlated with egg viability expressed as the number of eyed stage embryos. Regression models demonstrated that an ovarian fluid pH between 8.44 and 8.57, protein levels below 235.56 mg 100 ml^–1ovarian fluid, aspartate aminotransferase activity below 31.65 m min^–1 l^–1ovarian fluid and -d-glucuronidase activity below 8.62 m min^–1 l^–1 ovarian fluid characterized egg batches with high viability (80%).The increase in the egg wet weight during water hardening was also significantly correlated with the number of eyed stage embryos, and egg batches with high egg viability (80%) increased in wet weight by 13% during water hardening.From the investigated metabolic parameters the number of eyed stage embryos was significantly correlated with activities of NADP-dependent isocitrate dehydrogenase (egg viability 80% at 2.07 nM min^–1 mg^–1 protein) and NAD-dependent malate dehydrogenase (egg viability 80% at 47.25 nM min^–1 mg^–1 protein), with the respiration rate (egg viability 80% at 8.71 nM min^–1 mg^–1 protein), with the ratio of NADH to NAD levels (egg viability 80% 0.872), with the levels of free, non-esterified fatty acids (egg viability 80% 72.34 g mg^–1 protein), and the ratio of non esterified to esterified fatty acids (egg viability 80% at 0.749). Also, subjective and visual control methods were described to distinguish between batches with viable and non viable eggs.     

Presence of maturation-promoting factor in 17α,20β-dihydroxy-4-pregnen-3-one-induced oocytes of catfish,Clarias batrachus

Full-grown immature Clarias batrachus oocytes respond in vitro to exogenous 17,20-dihydroxy-4-preg-nen-3-one ( 17,20-DP) by undergoing germinal vesicle breakdown (GVBD). Cytosolic extract (CE) prepared from 17,20-DP-induced oocytes has been shown to produce similar effect when microinjected into unstimulated immature oocytes of the same fish. A dose of 50 nl is enough to cause 100% GVBD after 4 h. Maturation-promoting factor was investigated from 17,20-DP-induced, immature and cycloheximide treated oocytes incubated in presence of [³⁵S] methionine. When the proteins were extracted and analyzed on SDS-PAGE, two prominent bands corresponding to molecular weight 34- and 46-kDa were detected in the CE of mature oocytes. However, labelling of [³⁵S] methionine was observed mainly in the region of 46 kDa protein band indicating de novo synthesis of this particular protein during l7,20-DP-induction. Further, immunoblotting study by using rabbit anti-cyclin B₁ antibody has clearly demonstrated that the protein which is newly synthesized is highly homologous to Xenopus cyclin B₁ and goldfish cyclin B.     

Oocyte maturation inClarias batrachus. III. Purification and characterization of maturation-inducing steroid

Maturation-inducing steroid (MIS) in the Indian female catfish,Clarias batrachus, was purified and characterized from the incubation medium in which fully grown but immature folliculated oocytes were incubated with salmon gonadotropin (SG-G100) for 36 h. Maturation-inducing (MI) activity of residues obtained at various steps of extraction and purification was assessed byin vitro germinal vesicle breakdown (GVBD) assay using folliculated oocytes ofC. batrachus. The post incubation medium was extracted with diethyl ether. The ether phase was partitioned using 50% methanol plus n-hexane. The methanol phase which had MI activity was fractionated into 7 fractions using reverse-phase high-performance liquid chromatography. Of these 7 fractions, fraction 3 was found to be active in having MI ability and identified as 17 ,20-dihydroxy-4-pregnen-3-one (17,20-diOHprog). The authenticity of 17,20-diOHprog as the major follicular mediator of gonadotropin-induced oocyte maturation was further confirmed by thin-layer chromatography (TLC) in which fraction 3 was run along with authentic 17,20-diOHprog standard. This investigation gives a direct evidence that 17,20-diOHprog is the major naturally occurring MIS in Indian female catfish,C. batrachus.     

盐度突降对拟穴青蟹大眼幼体生长发育和Na~+/-K~+-ATPase活性的影响

研究了盐度突降对拟穴青蟹(Scylla paramamosain)大眼幼体生长发育和Na+/-K+-ATPase活性的影响。实验用水由海水和淡水配制成20%、40%、60%、80%和100%SW,其盐度分别为6.4、12.8、19.2、25.6和32.0。在不同环境盐度突降条件下,盐度6.4处理组拟穴青蟹大眼幼体在24 h内全部死亡;盐度12.8、19.2、25.6和32.0处理组拟穴青蟹大眼幼体的存活率无显著差异(P≥0.05),各处理组幼体蜕皮持续时间分别为2、2、3和4 d;当发育至C1期第2天时,盐度12.8处理组体重平均增量低于盐度19.2、25.6和32.0处理组,且差异显著(P<0.05)。盐度6.4处理组酶活性从实验开始即急速增加,至6 h时与其它各组呈显著差异(P<0.05);盐度32.0处理组酶活性从实验开始就下降,至72 h后变化趋于平缓;盐度12.8、19.2和25.6处理组酶活性在6 h内逐渐上升,之后迅速下降,于72 h时降至最低,之后酶活性变化趋于平缓。在96~120 h内,盐度12.8处理组酶活性始终显著高于25.6和32.0处理组(P<0.05)。结果表明,拟穴青蟹大眼幼体生长的最适盐度为19.2,适宜生长盐度下限在12.8~19.2之间,生存盐度下限在6.4~12.8之间。     

大菱鲆(Scophthalmus maximus)PRL基因、Na+-K+-ATPase a1基因对盐度胁迫的响应

采用荧光定量PCR技术对不同盐度胁迫下各时间点大菱鲆(Scophthalmus maximus)幼鱼肠、鳃中催乳素(PRL)基因和Na+-K+-ATPase a1两种基因的表达量进行检测。以盐度30为对照组,盐度5、10、40和50为实验组进行数据分析。结果显示,两种基因在两种组织中均有表达,且基因的表达量具有组织和时间特异性。肠组织PRL、Na+-K+-ATPase a1基因的表达量,在盐度50和5条件下,随胁迫时间的延长呈先升高后降低的变化趋势;鳃组织PRL基因表达量,在盐度50和盐度5条件下,随胁迫时间延长先升高后降低,而Na+-K+-ATPase a1基因表达量在低盐条件下(盐度5)没有显著变化,在高盐条件下(盐度50)随时间延长呈现先降低后升高的变化趋势。在肠组织中,两种基因存在极显著的协同作用,随着盐度的升高,两种基因的表达量都呈现先升高后降低的趋势,且相关系数均接近于1;在鳃组织中,在10–40盐度范围内,两种基因的表达存在明显的拮抗作用,当PRL基因的表达量呈现升高(或下降)趋势时,Na+-K+-ATPase a1基因的表达量呈现下降(或升高)趋势,且两种基因的相关系数均为负值。研究表明,PRL具有抑制Na+/K+-ATP酶活性的作用,为今后盐度胁迫分子调控机理研究提供理论依据。     

Influence of growth hormone on the hepatic mixed function oxidase and transferase systems of rainbow trout

The effect of GH treatment on hepatic cytochrome P450 content, aryl hydrocarbon hydroxylase (AHH), aminopyrine-N-demethylase (AND), testosterone hydroxylase, testosterone 5- and 5-reductase, UDP-glucuronyl transferase (UDPGT) and glutathione S-transferase (GST) activities in immature rainbow trout were investigated. Hepatic cytochrome P450 content, AHH and GST activities were measured in both GH implanted and GH injected animals whereas other activities were assayed in GH implanted trout only.GH implants significantly decreased cytochrome P450 content at 15 days compared to the control but no significant effect was observed at 15 or 30 d when GH was injected biweekly. In both cases, AHH activity was significantly decreased by GH treatment compared to the control whereas GST remained unchanged. Compared to the control, GH implanted fish exhibited a pronounced inhibition of AND, a decreased 6 and 16-testosterone hydroxylation, an inhibition of UDPGT with testosterone as substrate and an enhanced 17-testosterone oxidation.     

Viability of the marine microalga Tetraselmis suecica grown free and immobilized in alginate beads

The growth responses of free and immobolized cultures of the marine alga Tetraselmis suecica (Chlorophyta, Prasinophyceae) were compared. Algal cells were immobilized in 2% calcium alginate solution; both entrapped and free cultures were maintained in synthetic sea water at 19 salinity and 14°C constant temperature. Algal growth was evaluated by cell abundance, growth constant (K) and generation time (gt), calculated from data obtained during the exponential phase. The biomass of T. suecica, in terms of chlorophyll a content, was also determined. Cell abundance of both immobilized and free cultures was quite similar. Analysis of the T. suecica life cycle showed the higher viability of the alga after immobilization in calcium aginate gel. In addition, the mean chlorophyll a content of the immobilized cells was higher in comparison to free cells. The growth rate of the entrapped cells, on the other hand, was lower. © Rapid Science Ltd. 1998