Showing papers in "Fish Physiology and Biochemistry in 1996"

Characterization of digestive enzyme activity during larval development of gilthead seabream (Sparus aurata).

Abstract: The evolution of the digestive enzyme equipment in seabream from hatching to 30 days old larvae was studied; there was a progressive increase in the activity of protease, amylase and acid and alkaline phosphatase from day 15 onwards. The use of specific inhibitors, and SDS-PAGE provided evidence to suggest that most of the proteases belonged to the serine group. A high α-amylase activity was also denoted. Zymograms of larval extracts indicated that exogenous food has more a qualitative than a quantitative role in the secretion of digestive enzymes in this species.

Motility of spermatozoa ofAlburnus alburnus (Cyprinidae) and its relationship to seminal plasma composition and sperm metabolism.

Abstract: The composition of seminal plasma and metabolism of sperm of the cyprinid fishAlburnus alburnus were investigated. Statistically significant correlations were found between motility parameters and seminal fluid osmolality, pH, Na(+), K(+) and protein levels (negative correlations: % immotile spermatozoa-Na(+), K(+); positive correlations: % motile spermatozoa-osmolality, pH, Na(+), K(+), protein; % linear motile spermatozoa-pH protein; swimming velocity of spermatozoa-pH, Na(+), protein). Spermatozoan motility and ATP metabolism and glycolysis were correlated as indicated by measurement of ATPase, pyruvate kinase, adenylate kinase and lactate dehydrogenase activity. The physiological meanings of these correlations and their possible significance for quality control of semen are discussed.

Cortisol-induced changes in oxygen consumption and ionic regulation in coastal cutthroat trout (Oncorhynchus clarki clarki) parr.

Abstract: The influence of cortisol on oxygen consumption and osmoregulatory variables was examined in coastal cutthroat trout (Oncorhynchus clarki clarki) parr kept in fresh water (FW) and transferred to seawater (SW). Intraperitoneal implants containing cortisol (50 μg g−1) in vegetable oil resulted in elevated plasma cortisol titres similar to those observed in fish following a 24h SW exposure. Cortisol treatment significantly increased the oxygen consumption and plasma glucose levels of trout in FW, consistent with the glucocorticoid role of cortisol. Cortisol treatment did not cause any changes in plasma ion concentrations or gill Na+,K+-ATPase activity in FW after 10 days. Cortisol-implanted fish exposed to SW for 24h showed slightly improved ion regulatory ability compare to non-implanted controls. The results of this study suggest that during SW transfer in juvenile salmonids, increases in cortisol may act as both a mineralocorticoid and a glucocorticoid, depending on the developmental state of the fish (e.g., smolt versus parr). Furthermore, the relative energetic costs of osmoregulation and that of the stress associated SW transfer cannot be discerned using whole-animal oxygen consumption rates.

Mitochondria-rich cells in the branchial epithelium of the teleost,Oreochromis mossambicus, acclimated to various hypotonic environments.

Abstract: Branchial mitochondria-rich (MR) cells were examined on the afferent side of gill filaments in tilapia (Oreochromis mossambicus) acclimated to different hypotonic environments, local fresh water (LFW), hard fresh water (HFW) and 5‰ salt water (SW) Scanning electron micrographs (SEM) identified three types of apical surfaces of the MR cells, wavy convex, shallow basin and deep hole In spite of the different types of apical surfaces, light microscopic (LM) and transmission electron microscopic (TEM) studies suggested that these cells were MR cells The relative abundance of these 3 types of branchial MR cells varied with external hypotonic milieus Wavy-convexed MR cells were dominant in the gills of fish adapted to HFW, whereas shallow-basined MR cells were evident in LFW-adapted fish In SW-adapted fish, most of the MR cells were deep holes Experiments on adaptation to various hypotonic milieus revealed that the changes of the branchial MR cells were reversible and occurred within 24 hours following transfer The morphological alterations of the MR cells correlated with ionic changes in different milieus, indicating that these distinct types of MR cells may play key roles for osmoregulation in hypotonic media

Food deprivation and refeeding in Atlantic salmon,Salmo salar: effects on brain and liver carbohydrate and ketone bodies metabolism.

Abstract: The capacity of carbohydrate and ketone bodies metabolism in brain and liver was evaluated in fed and food-deprived Atlantic salmon (Salmo salar) in a time period covering from 1 to 7 days (Experiment I), and in Atlantic salmon food deprived for 6 weeks, and food deprived for 4 weeks and refed for 2 weeks (Experiment II) The results obtained demonstrate for the first time in a teleost the existence of changes in brain metabolism due to food deprivation Thus, decreased glucose levels in plasma are reflected in the brain by an increased mobilization of glycogen reserves, and by a decreased glycolytic capacity Also, ketone bodies appear to increase their importance as a metabolic fuel from day 7 of food deprivation onwards A possible increase in the gluconeogenic potential in brain simultaneously is not discarded All these metabolic changes are reversed under refeeding conditions

Changes in the content of total lipid, lipid classes and their fatty acids of developing eggs and unfed larvae of the Senegal sole,Solea senegalensis Kaup.

Abstract: Total lipids, lipid classes and their associated fatty acids were quantified in developing eggs, yolk-sac larvae and starving larvae (from day 1 to day 5 after hatching) of the Senegal sole,Solea senegalensis Kaup. Larvae during early development and starvation consumed about 0.6% of its dry weight per day, mainly due to lipid catabolism. There was a net consumption of approximately 1.7% total lipid per day, and a net energy utilization of 1.3 kcal g−1 dry weight biomass day−1, mostly derived from lipid depletion. The overall decrease of total neutral lipids (mainly triacylglycerols and sterol esters) was 3.4 faster than that of total polar lipids (primarily phosphatidylcholine), with rates of 29.2 and 8.7 μg mg−1 dry weight biomass day−1, respectively. There was a concomitant increase in PE, PS and phosphatidic acid during the period under study. Total saturated and total monounsaturated fatty acids were catabolized (primarily 16∶0 and 16∶1 (n-7)) as energy substrates at rates of 7.4 and 10.9 μg mg−1 total lipid day−1, whereas total PUFAs were conserved. DHA was specifically retained in PE, whereas EPA and DHA were catabolized in PC and triacylglycerol. Total DMA and AA contents in total lipid increased during early development and starvation. The data denote a pattern of lipid metabolism during early development of Senegal sole similar to that of other marine larval fish, with eggs containing high amounts of total lipids (presence of oil globule/s), from temperate waters and with short developmental periods; the pattern contrasts with fish larvae from eggs of cold water fish species that contain low levels of total lipids (lack of oil globule/s) and have long developmental periods.

Endogenous antioxidant systems of two teleost fish, the rainbow trout and the black bullhead, and the effect of age.

Abstract: Antioxidant enzyme activities and glutathione status were determined in different tissues of two teleost species, the rainbow trout (Oncorhynchus mykiss) and the black bullhead (Ameiurus melas) to establish whether age-related changes exist between mature and immature individuals. Glutathione reductase and superoxide dismutase activities were significantly lower in hepatic and extrahepatic tissues of 3+ year than 1+ year trout and bullheads. Activities of glutathione peroxidase, catalase and glutathione S-transferase did not exhibit a clear pattern, with decreases in liver and kidney, but increases in gill and muscle tissues. Glutathione concentrations were significantly higher in most tissues of 3+ year than in 1+ year trout, but remained unchanged or decreased in tissues of older bullheads. The results imply an age- or maturation-dependent effect on key antioxidant enzymes in various tissues of these 2 teleost species. Thus, age and maturation may impact upon the use of oxidative stress parameters as indicators of contaminant exposure in environmental studies.

The nature of hematological response in fish : Studies on rainbow troutOncorhynchus mykiss exposed to simulated winter, spring and summer conditions.

Abstract: Hematological status was examined in rainbow trout,Oncorhynchus mykiss, held for 3–4 weeks under temperature, photoperiod and PO 2 conditions approximating those of their winter, spring and summer habitats. The most striking change observed was in red cell population composition. In ‘winter’ fish mature cells were predominant; juvenile and developing erythrocytes characterized ‘spring’ and ‘summer’ animals. Hemoglobin, hematocrit and both mean erythrocytic volume and hemoglobin were modestly lower in ‘spring’ and ‘summer’ than in ‘winter’ fish. Red cell numbers were not significantly affected. These observations suggest that avoidance of viscosity-based increases in circulatory work cost is more advantageous than elevation of blood O2-carrying capacity. Although hemoglobin isomorph profiles were significantly altered, there is little evidence that such changes are of critical adaptive importance. Given presumed age-based reduction in gas transport effectiveness, the replacement of mature and senescent cells by more metabolically-competent juvenile cells appears to be the pivotal event in hematological response. Leucocyte counts were significantly elevated in ‘spring’ and ‘summer’ as compared to ‘winter’ fish. Lymphocyte/heterophil ratios declined from 8.27 in ‘winter’ fish to 3.13 in ‘summer’ trout. Thrombocyte, monocyte, eosinophil and basophil abundances were little changed.

Amylase and trypsin responses to intake of dietary carbohydrate and protein depend on the developmental stage in sea bass (Dicentrarchus labrax) larvae.

Abstract: Sea bass (Dicentrarchus labrax) larvae were fed from day 15 to day 35 with 4 isoenergetic formulated diets that varied in protein (30, 40, 50, 60%) and carbohydrate (37, 27, 17, 7%) content. The diets were designated as P30, P40, P50 and P60, respectively. Best growth and survival were noted for P50 larvae. Poor growth and survival were observed for P30 larvae. The specific activity of amylase increased in direct relation to the dietary carbohydrate level from day 18 onwards. This increase was the result of extensive amylase synthesis. Trypsin activity was positively correlated with dietary protein level only at day 35. This study shows that the mechanisms involved in amylase regulation are efficient in very young sea bass larvae, while those related to trypsin appear later in ontogeny and thus suggests an age-dependent regulation of enzyme synthesis.

Immunochemical relationships of cytochrome P4503A-like proteins in teleost fish.

Abstract: Multiple P450 proteins have been purified from several teleost species, including rainbow trout (Oncorhynchus mykiss), scup (Stenotomus chrysops) and Atlantic cod (Gadus morhua) Identity, relationships and/or functions have been established in these fish species for the cytochrome P4501 As Information about the structure, function, regulation and relationships of other piscine cytochrome P450 (CYP) proteins is sparse In the present study we have focused on constitutively expressed CYP forms, P450con and LMC5 isolated from rainbow trout, P450A from scup, and P450b from Atlantic cod, and we consider evidence for the relationship of these proteins to mammalian members of the CYP3A subfamily Reciprocal western blot analysis shows that P450con and LMC5, isolated from rainbow trout in two different laboratories, are closely related and ostensibly identical proteins These trout proteins show specific reciprocal cross-reactivity with scup P450A, and polyclonal antibodies (PAb) to the trout and scup proteins both recognize cod P450b, indicating that rainbow trout P450con/LMC5, scup P450A and cod P450b are immunochemically-related proteins In analyses of liver microsomes of trout, scup and cod, PAb to trout P450con/LMC5 and scup P450A recognize only bands that are identical in migration to the CYP proteins purified from these species, and which were used as immunogens These CYP proteins purified from fish are each immunochemically-related to mammalian CYP3A proteins, showing recognition by PAb to human CYP3A4 and to rat CYP3A1 PAb to the mammalian CYP3As also recognize the same bands in liver microsomes from these fish species as seen by PAb to the fish proteins These results strongly suggest that these fish proteins are members of theCYP3 gene family and probably theCYP3A subfamily Although sequence analysis is required before their designation in the CYP3A subfamily can be confirmed and specified, we refer to these as CYP3A-like Immunoblot analyses of hepatic microsomes from other fish species with PAb to scup P450A and trout P450con show that multiple CYP3A-like proteins are expressed in liver of several species, including killifish (Fundulus heteroclitus) and winter flounder (Pleuronectes americanus) Important questions still remain to be addressed concerning CYP3A structure, multiplicity, physiological function, regulation and metabolism of endogenous as well as exogenous substrates in fish

Effect of environmental calcium levels on calcium uptake in tilapia larvae Oreochromis mossambicus

Abstract: Effects of environmental calcium concentrations on the survival, growth, body calcium content and calcium uptake kinetics in developing tilapia (Oreochromis mossambicus) larvae were studied. Fertilized eggs were incubated in high- and low-calcium artificial freshwater (0.88-0.96 mmol 1-1 vs. 0.02-0.03 mmol 1 -I CaCI 2 or CaSO4) until 3 days after hatching. Tilapia larvae showed similar hatching rates and wet weights in either high- or low-calcium medium, indicating neither the development nor the growth in tilapia larvae was affected by the environmental calcium levels. The body calcium content in low-calcium groups was about 9095% that of high-calcium groups, No matter what calcium source was used (CaCI.~ or CaSO4), acclimation to low calcium medium caused a stimulation of calcium uptake (measured in 0.2 mmol l -~ calcium), i.e., 1.21.3 fold higher than that of high calcium groups. This enhanced calcium uptake capacity was characterized by a 50% decrease in K m and a 25% increase in Jmax" Effect of different calcium salts on calcium influx was significant only in low calcium level, i.e., calcium influx in low-CaC12 group higher than that in low-CaSO 4 group. These results suggest that tilapia larvae are able to modulate their calcium uptake mechanism to maintain normal body calcium content and growth in environments with different levels of calcium.

Stress responses of Atlantic salmon (Salmo salar L.) elicited by water level reduction in rearing tanks.

Abstract: The Atlantic salmon (Salmo salar) stress response was examined by measuring plasma cortisol, glucose and chloride in fish after water level reduction within rearing tanks Maximum plasma cortisol levels (366±43 (SD) nM and 534±280 nM for Groups 1 and 2, respectively) were observed 20 min after application of the stressor Cortisol levels were down to control levels 24 h later The pattern for cortisol changes observed within these two groups were comparable Plasma glucose and chloride concentrations did not change significantly in either of the experimental groups The fish in group 2 were then repeatedly subjected to the same stressor every third day After the fifth exposure to the stressor, blood was obtained from fish at times corresponding to sampling after the first exposure Their maximum plasma cortisol level only reached 223 (±96) nM, and was down to prestress levels within 2 h Plasma glucose and chloride concentrations did not change significantly in this second experiment This challenge test revealed an acute primary response in Atlantic salmon without any apparent harmful secondary responses, that may thus serve as a standardized reference stressor using other fish groups under comparable conditions

Poor utilization of dietary free amino acids by white sturgeon.

Abstract: Three separate experiments were conducted to investigate the utilization of dietary free amino acids by white sturgeon,Acipenser transmontanus. In the first experiment, sturgeon were fed for 8 weeks with isoenergetic and isonitrogenous diets containing either intact protein, an amino acid mixture, or a neutralized amino acid mixture of similar composition. Sturgeon fed the two amino acid diets grew significantly (p<0.05) less, mainly because of reduced feed intake. In the second experiment, postprandial changes in plasma free amino acids of sturgeon force-fed the above diets were monitored at 2, 4, 6, 8, 12, and 24 h Total plasma amino acids in sturgeon force-fed the intact protein diet showed a gradual increase and reached peak levels at 8 h. In contrast, plasma amino acids of fish force-fed the amino acid diets showed a rapid increase and reached maximal levels at 2 h. In the third experiment, free amino acid diets showed a urine of sturgeon force-fed the three diets was monitored at 4, 8, 12, 16, 20, and 24 h. In all dietary groups, peak excretion of indispensable amino acids was detected at 8 h after feeding but with significantly higher levels from fish force-fed the amino acid diets. Sturgeon force-fed the neutralized amino acid diet excreted 35% less amino acids compared to fish force-fed the non-neutralized diet. Sturgeon force-fed the intact protein diet excreted significantly higher amounts of ammonia. Under amino acid feeding conditions, sturgeon excreted more amino acids in its urine, but the urinary excretion of amino acids was not a major route in dealing with the rapid absorption of dietary free amino acids.

Effects of season and dietary ascorbic acid on some biochemical characteristics of rainbow trout (Oncorhynchus mykiss) semen.

Abstract: During the reproductive season, rainbow trout spermatozoa are stored in the sperm ducts for several months. There is no sperm production at this time since spermatogenesis is completed before spawning. To leam more about characteristics of semen during such a long storage, we analyzed changes in protein concentrations, anti-proteinase activity in seminal plasma and sperm aspartate aminotransferase activity during an extended reproductive period during which fish were fed diets supplemented with various ascorbic acid concentrations. Seminal plasma protein concentration and anti-proteinase activity declined toward the end of the reproductive season. These phenomena may be related to oncoming proteolytic events leading to degradation of the sperm. Protein concentrations and anti-proteinase activities were strongly correlated within groups of different ascorbic acid supplementations and several sampling dates (r=0.6–0.9 in most cases, p<0.05). Ascorbic acid deficiency resulted in a decrease in both parameter levels as compared to levels in groups with vitamin C supplement (p<0.08). Deficiency also resulted in lower stimulation of aspartate aminotransferase by an exogenous pyridoxal 5′-phosphate in comparison to fish fed vitamin C-supplemented diets (p<0.05). These results support earlier studies suggesting a protective role of ascorbic acid toward maintaining sperm quality.

The effect of feeding on the secretion of pepsin, trypsin and chymotrypsin in the Atlantic salmon,Salmo salar L.

Abstract: Pepsin stored in the stomach mucosa of the Atlantic salmon (Salmo salar L.) increases within two days of the onset of starvation. Trypsin and chymotrypsin in the pyloric caeca/pancreas behave similarly, indicating that when no food is present in the gut, digestive enzymes accumulate in the secretory tissues. As a corollary, trypsin and chymotrypsin activities in the gut contents fell during starvation, indicating that secretion is greatly reduced when food is not present. At the onset of feeding, pepsin is rapidly synthesised in the mucosal tissues and then secreted. Twenty four hours after feeding, the pepsin levels of the mucosa are still low, suggesting that synthesis may be a rapid response to the presence of food in the stomach. Secretion of trypsin and chymotrypsin appears to take place as soon as digesta enters the intestine, between 4 and 14h after feeding, and resynthesis of enzyme precursors appears to be complete again within a further 11h. It is suggested that both synthesis and release may be under the control of cholecystokinin.

Gill morphometry of the facultative air-breathing loricariid fish,Hypostomus plecostomus (Walbaum) with, special emphasis on aquatic respiration.

Abstract: Gill respiratory surface area and oxygen consumption during aquatic respiration were measured in the facultative air-breathing loricariid fish,Hypostomus plecostomus. The fish did not surface to breathe atmospheric air in normoxic water; air-breathing was evoked by environmental hypoxia (water oxygen tension=35±2, mmHg) and did not show size-related threshold differences for air breathing.During gradual hypoxia, without access to atmospheric, air,H. plecostomus was found to be an oxyregulator and showed a reduced range of water oxygen tension in which the oxygen consumption remained constant in smaller fish. The critical oxygen tensions were 55 and 33 mmHg at 25°C for fish of 14-30 g and 31-80g body weight, respectively.The gill respiratory surface area (total lamellae area) is reduced, however, the lamellar frequency per mm of gill filament is high which facilitates the gas exchange. Moreover, the increase of gill respiratory surface area (b=0.666) is higher than the increase in routine VO2 (b=0.338) showing a positive relationship between the gill respiratory surface area /VO2 ratio and body mass (b=0.328); this indicates that the fish have greater gill respiratory surface area per unit of routine VO2 as they grow.

Hemoglobin level, metabolic rate, opercular abduction rate and swimming efficiency in female triploid brook trout (Salvelinus fontinalis).

Abstract: Metabolic (oxygen consumption) rate, opercular abduction rate and tail beat frequency were determined in two strains of diploid and triploid female brook trout (Salvelinus fontinalis) while these fish swam at 0.37±0.02 body lengths per sec in a Blazka respirometer. Total blood hemoglobin level was also measured and opercular condition examined. Total blood hemoglobin levels in diploids and triploids were equal. The opercular abduction rate was the same in diploids and triploids (regardless of whether triploid opercular condition was good or poor) yet triploids had a lower oxygen consumption rate than diploids, indicating that triploids take up less oxygen than diploids per opercular cycle. Tail beat frequency, an indicator of swimming effort, was the same in diploids and triploids, suggesting that triploids require less oxygen than diploids for a similar swimming effort.

Utilization of yolk fatty acids by goldfish embryos and larvae.

Abstract: In each of two separate experiments, eggs from a single female goldfish were fertilized, incubated at 22°C and sampled regularly up to day 6 when the larvae could be expected to commence feeding. Hatching normally occurred on Day 4. Lipids were extracted from the eggs and larvae and the neutral lipid and neutral phospholipids were isolated on aminopropyl columns. Fatty acid analysis of the eggs revealed the typical situation in fish where the phospholipids were rich in polyunsaturated fatty acids (PUFA) and the neutral lipids were rich in monounsaturated fatty acids (MUFA). Assay of lipid masses revealed that little depletion of lipid occurred until after hatch and that the neutral phospholipids were the principal fraction consumed. Although the neutral lipid mass did not change substantially during development, its fatty acid profile did. The proportions of several PUFA in the neutral lipids, especially 22∶6(n−3), 20∶5(n−3) and 20∶4(n−6), increased substantially during development while proportions of MUFA and 18∶2(n−6) declined. This appears to be a mechanism by which the larva can retain essential fatty acid released on hydrolysis of phospholipid while deriving the benefits of catabolism of phospholipid as fuel, namely the provision of phosphate and choline for intermediary metabolism and for the synthesis of macromolecules and neurotransmitter.

Hematological response in fish: pronephric and splenic involvements in the goldfish,Carassius auratus L.

Abstract: Pronephric and splenic involvements in erythropoiesis and in stress-induced hematological response by goldfish,Carassius auratus, were examined under conditions of minimal stress and following transient (3h) temperature-induced elevation of O2 demand and transient (3h) exposure to hypoxia. Although hemoglobin content and red cell numbers were little affected, the ontogenic composition of the circulating erythrocyte population was significantly altered by both types of respiratory challenge and also by the stresses associated with capture, air exposure during transfer and intraperitoneal administration of label. Juvenile cell numbers increased sharply while mature erythrocyte abundances declined. Consistent with this, [(3)H] methylthymidine-labeled cell numbers rose in both spleen and pronephros following imposition of stress. Splenic erythropoietic activity was modest relative to that of the pronephros. Our observations point to a readily triggered response involving: [1] release of cells reservoired in the spleen and pronephros, [2] increased erythropoiesis and [3] karyorrhexis. We suggest that while the magnitude of response may depend on the quality and magnitude of the imposed stress, its central features are essentially constant.

Effect of growth hormone on muscle protein synthesis in rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar).

Abstract: This paper reports on the effect of administration of mammalian growth hormone (GH) on muscle protein synthesis as measured in white muscle using the phenylalanine flooding technique. The effect of exogenous GH was compared with that of insulin and prolactin, and with endogenous GH.

Uptake, distribution and excretion of magnesium inOreochromis mossambicus: dependence on magnesium in diet and water.

Abstract: The euryhaline Mozambique tilapia (Oreochromis mossambicus) shows a more marked ability to adapt to low magnesium levels in food and water than many other fish species. Nonetheless, the internal distribution of magnesium is altered under low-magnesium conditions. The amount of magnesium in scales, and to a lesser extent the vertebral bone, is reduced and hence serve as magnesium reservoirs. The magnesium concentration of muscle is only marginally reduced by low external magnesium, suggesting that magnesium is partitioned to ensure normal muscle functioning. The water magnesium is of vital importance, as exposure to low-magnesium water markedly deminished the ability of tilapia to adapt to low-magnesium feeding. However, magnesium intake from the water, eithervia the integument or drinking, does not increase in lowmagnesium fed fish, despite an increased opercular chloride cell density. The growth related magnesium accumulation of tilapia under low-magnesium conditions approximates the total intake of the element (from the food and from the water), indicating that magnesium losses are minimized and that the magnesium absorption from the gastrointestinal tract may be highly efficient and very important.

Production of melatonin by the gilthead sea bream pineal: anin vivo andin vitro study

Abstract: This study deals with the variations of plasma melatonin content and ofin vitro pineal melatonin secretion, in one year-old male sea bream. Plasma melatonin levels varied from almost undetectable levels during the day to 150–200 pg ml−1 during the night, in animals maintained under a light/dark (12L/12D) cycle. The duration of the nocturnal surge corresponded to the duration of the night. A similar pattern of melatonin secretion was obtainedin vitro, with pineals cultured under a 24h L/D cycle. When the photoperiod cycle was advanced by 8h, the first nocturnal peak in melatonin secretion was more acute compared to the profile described above, but the rhythmic variations were immediately synchronized to the new L/D conditions. Under constant darkness (D/D), circadian variations in melatonin release were observed for no more than two 24h cycles. No melatonin was detected in the culture media from retinas cultured under L/D or under D/D. These results strongly suggest that the pineal is the major source of plasma melatonin in the gilthead sea bream, and that the 24h photoperiod cycle is a powerful synchronizer of the rhythmic production of melatonin by this organ.

Drinking rate in juvenile Atlantic salmon,Salmo salar L fry in response to a nitric oxide donor, sodium nitroprusside and an inhibitor of angiotensin converting enzyme, enalapril.

Abstract: Drinking in freshwater juvenile salmon was investigated in response to vasodilation by sodium nitroprusside (SNP), a nitric oxide donor, which significantly increased blood vessel diameter in Atlantic salmon alevins. Atlantic salmon fry (1–3 g), as previously shown, drank at a significant rate in fresh water which doubled to about 1.2 ml kg−1 h−1 following injection of SNP (100 μmol kg−1), through dilation of body vasculature and activation of a vasoconstrictive mechanism, the endogenous renin angiotensin system (RAS). This response was 50% inhibited by injection of about 100 mg kg−1 enalapril. Fry increased drinking in response to SNP administered in the water, though the concentration required for maximal response, 1.6 mmol l−1, was much greater than for injected SNP; this response was also inhibited by enalapril injection. Possible involvement of the gill vasculature and branchial osmoreceptors or baroreceptors in control of the drinking response is discussed.

Effects of cortisol on growth and development in tilapia larvae,Oreochromis mossambicus.

Abstract: Treatment of one-day-old yolksac larvae of tilapia (Oreochromis mossambicus), by immersion in cortisol solution for two weeks, significantly enhanced growth. The standard length, tail length, head width and wet weight showed dose-dependent increases at concentrations of cortisol (hydrocortisone) from 0.05 ppm to 0.5 ppm, with no further increase at 1.0 ppm. However, cortisol at 5.0 ppm retarded the growth of the larvae without causing any morphological abnormality. Yolk absorption and the onset of free-swimming activity in the larvae were also accelerated by cortisol treatment.

Testicular responsiveness to gonadotropic hormonein vitro and Leydig and Sertoli cell ultrastructure during pubertal development of male African catfish (Clarias gariepinus).

Abstract: The gonadotropin (GTH)-stimulated testicular androgen secretionin vitro and the ultrastructure of Leydig and Sertoli cells was studied during the pubertal development in male African catfish. Testicular weight increased from less than 1 mg in the ninth week of age to nearly 600 mg in the 28th week. Immature testes (stage I: spermatogonia) were highly sensitive to GTH and secreted very high amounts of androgens per mg of tissue. The secretion per mg tissue decreased gradually in stages II (spermatogonia and spermatocytes) and III (spermatogonia, spermatocytes, and spermatids), but precipitously in stage IV (all germ cell stages, including spermatozoa). However, due to the testicular weight gain, the total androgen output per pair of testes increased slightly in stage III and strongly in stage IV. The sensitivity to GTH decreased with the appearance of haploid germ cells in stage III. Leydig cells but not Sertoli cells showed the ultrastructural characteristics of steroid producing cells. Leydig cell morphology did not change in stages I–III, while in stage IV, more smooth endoplasmic reticulum was present. The ultrastructural characteristics of Sertoli cells did not change prominently. Thus, spermatogonial multiplication and spermatocyte formation takes place when the testicular steroidogenic system is highly active and responsive to GTH; whereas the differentiation of haploid germ cells is accompanied by a reduced responsiveness to GTH and by the secretion of several-fold lower androgen amounts per mg of tissue.

Dietary essential amino acids and heat increment in rainbow trout (Oncorhynchus mykiss).

Abstract: Oxygen consumption attributable to apparent heat increment (AHI) was measured in relation to varying essential amino acid proportions (EAA) infused into rainbow trout,Oncorhynchus mykiss (250–450 g), induced to swim at ≈1 BL s−1. Five diets, mimicking EAA concentrations in trout whole body protein, deficient in the branched chain amino acids (isoleucine, leucine and valine), containing unbalanced proportions of EAAs and supplying lysine in excessive and limiting proportions, were tested. Following infusion of the experimental diets, a significant increase in oxygen consumption was observed. Changes in plasma EAAs following infusion paralleled the time course of AHI (i.e., oxygen consumption). AHI represented the equivalent of 15–32% of the gross energy intake depending on dietary EAA composition. Diets supplying EAAs similar to trout whole body protein and limiting in lysine produced the lowest AHI values, indicating efficient utilization of dietary amino acids. Higher AHI values were associated with diets deficient in the branched chain amino acids and diets supplying lysine in excess. Duration of elevated metabolism was independent of both dietary composition and energy intake. Different proportions of EAAs in the diet can increase the energy expended as AHI. In an attempt to reduce the energy liberated as AHI, attention must be paid to the quality, quantity and balance of dietary EAAs.

Age-related changes in 2-[(125)I]-iodomelatonin binding sites in the brain of sea breams (Sparus aurata, L.).

Abstract: The pineal organ of fish, through its 24h rhythmic release of melatonin, acts as a transducer of the photoperiod, influencing different physiological functions (e.g., reproduction, growth). The target sites for melatonin are poorly known in fish, especially marine species. A radioligand study was undertaken using the gilthead sea bream (Sparus aurata) maintained under natural temperature and photoperiod (at 28°N latitude). This species exhibits the property of changing sex during growth. Brains of one year-old males were collected at 16:00h and brains of three year-old females at 03:00, 10:00, 16:00 and 23:00h. Membrane homogenate receptor assays were run using 2-[125I]iodomelatonin as a ligand. Binding sites were detected in brains of young and old fish. In the younger, the exhibited a Bmax between 3.52 and 4.29 fmol mg protein−1 and a KD between 358–380 pmol l−1. In the older fish, the KD varied according to a daily pattern: values were three times higher at 03:00 and 10:00h (500–600 pmol l−1) than at 16:00 and 23:00h (150–300 pmol l−1). The number of sites also were higher at 03:00 and 10:00h (180–200 fmol mg protein−1) than at 16:00 and 23:00h (95–110 fmol mg protein−1). Melatonin and iodomelatonin displaced 2-[125I]iodomelatonin binding in a dose dependent manner, the second being more potent than the first. Binding was also inhibited by GTP. The results provide the first evidence for the presence of membrane melatonin binding sites in the brain of an exclusively marine fish. They suggest that their number and affinity varies during growth and throughout a light/dark cycle. Future experiments will aim to precise the anatomical location and role of these binding sites.

Tyrosine hydroxylase activity and dopamine turnover of rainbow trout (Oncorhynchus mykiss) brain: the special status of the hypothalamus.

Abstract: The dynamics of catecholamine (CA)-synthesis enzymes have been poorly studied in fish Tyrosine hydroxylase (TH), the rate-limiting enzyme of CA synthesis has been only studied inin vitro conditions In the present report thein vivo CA synthesis and the CA metabolism were studied in different regions of the forebrain of the rainbow trout Levels of norepinephrine (NE), dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) and the rate of accumulation of 3,4-dihydroxyphenylalanine (DOPA) were determined by HPLC following a treatment with hydroxybenzylhydrazine (NSD), a potential inhibitor of DOPA decarboxylase Kinetics of the accumulation of DOPA and of the decline of DOPAC were in agreement with those found in rat, evidencing that the accumulation of DOPA following NSD can be used in trout to quantify thein vivo enzymatic activity of tyrosine hydroxylase Experiments using treatment with NSD or with methyl-p-tyrosine reached a same conclusion: the DA neuronal activity in trout is much higher than NE neuronal activity However, the hypothalamus had high DA levelsvs lowin vitro andin vivo TH activities and exhibited a low CA turnover

Ascorbic acid status as affected by dietary treatment in the Siberian sturgeon ( Acipenser baeri Brandt): tissue concentration, mobilisation and L-gulonolactone oxidase activity

Abstract: A study was conducted to evaluate tissue storage and mobilisation of L-ascorbic acid (AA) in the Siberian sturgeon (Acipenser baeri) fed three different experimental diets. The three treatments consisted of a diet devoid of vitamin C (diet A0) and two diets supplemented with equivalent of 300 mg AA kg−1 in the form of either silicone-coated ascorbic acid (diet SC) or of ascorbyl-2-polyphosphate (diet AP). During the first phase (4 months) of the trial, six batches of 130 Siberian sturgeon (initial body weight: 25.5±0.5 g) each were fed one of the three diets in duplicate. During the second phase (3 months), fish from groups SC and AP were switched to diet A0 and those fed diet A0 during the first phase were switched to diet SC. Irrespective of the dietary treatment, growth rates were not significantly different from each other. At the end of phase I, in all tissues studied, total ascorbic acid (TAA) concentrations were higher in Siberian sturgeon fed diet AP than in the other two groups. During phase II, tissue ascorbate depletion was also higher in the AP group than in the other two groups. Transfer of the AA-free diet fed group onto a diet supplemented with 300 mg AA kg−1 (diet SC) led to a slight increase in the TAA concentrations in all tissues. Blood plasma tyrosine concentrations were not significantly different between the three groups. Whole-body collagen levels were affected by dietary AA levels or forms at the end of phase I; the differences were not significant at the end of phase II. Muscle collagen levels were slightly affected. L-Gulonolactone oxidase activity was found in the kidney of Siberian sturgeon, but not in the liver. The ascorbyl-2-polyphosphate appears to be either better utilised by Siberian sturgeon, like in many other teleosts, or more stable than the silicone-coated AA during food processing and storage. Presence of L-gulonolactone oxidase activity in Siberian sturgeon kidney combined with the absence of gross scorbutic signs in AA-free diet fed groups expressing very good growth rates suggested no need of dietary AA byA. baeri.

Effect of triiodothyronine on the growth and survival of larval striped bass (Morone saxatilis).

Abstract: This study was carried out to test the effect of triiodothyronine (T3) on the growth and survival of larval striped bass (Morone saxatilis). Growth and survival of striped bass held in 5 ppt seawater and treated with various doses of T3 were measured beginning at 5 and 16 days after hatching. Body content of T3 was measured by radioimmunoassay. T3 dissolved in the 5 ppt seawater was taken up by larval striped bass in a dose-dependent manner, and affected the growth and survival of the fish. At 5 days after hatching, T3 at 100 ng ml−1 and 50 ng ml−1 retarded the growth of larval striped bass and caused a lower survival rate than T3 at 25 ng ml−1 or the control treatment. At 16 days after hatching, T3 at 100 ng ml−1 retarded the growth of larval fish and caused a higher mortality. T3 at 10 ng ml−1 and 1 ng ml−1 did not show any effect on either survival or growth. Body content of T3 returns to control levels within days following end of treatment. The results indicate that exogenous T3 can be detrimental to the growth and survival of larval striped bass.