Prey extracts evoke swimming behavior in juvenile Atlantic halibut (Hippoglossus hippoglossus)

This study tested the efficacy of prey extracts to induce food search behavior in juvenile (15–25 cm total length, 0 year group) Atlantic halibut (Hippoglossus hippoglossus). In square culture tanks, halibut responded to shrimp and squid extract by tightly turning towards the source of the stimulus and by swimming in circles for 2–5 min following stimulus delivery. Cod extract, or a synthetic mixture consisting of glycine, proline, betaine, arginine, and alanine, failed to evoke this behavior.     

Application of DNA markers to the management of Atlantic halibut (Hippoglossus hippoglossus) broodstock

For many aquaculture finfish species, the current broodstock have been collected from the wild or have undergone only a few generations of domestication. The Atlantic halibut (Hippoglossus hippoglossus) aquaculture industry in Atlantic Canada has retained F₁ juveniles (n=145) from the 1996 spawning of wild adults for candidate broodstock. Through the development and use of a five-microsatellite DNA marker multiplex, we determined the parentage of these 1996 F1 individuals, which are being reared at one government and two industry hatcheries, and evaluated the change in genetic variation between the wild and the 1996 F₁ stock. In the three groups of F₁ fish, single parental pairs were assigned to 98%, 96% and 100% of individuals. Large full- and half-sibling groups were identified within and across F₁ groups and, overall, only 36% of attempted crosses were represented in the retained fish. Effective population size in the parental group decreased from 27 to 13 when variance in family size was accounted for and to 12.5 when changes in gene diversity (compared to the combined F₁ stocks) were considered. Statistically significant differences in measures of genetic variation were not widely observed between groups (original wild sample, parental group, three F₁ groups and combined F₁). However, the F₁ population shows a 26% decrease in total allele numbers compared to the wild sample. These observations demonstrate the utility of genetic tools in the evaluation of genetic diversity and determination of pedigree during the establishment of new broodstock. They also emphasize the necessity for closely monitoring future matings among these fish and suggest the need to introduce additional genetic variation into this group of Atlantic halibut broodstock.     

The impact of nutrition on metamorphosis in Atlantic halibut (Hippoglossus hippoglossus L.)

Fatty acids, vitamin A and thyroid hormone have all been shown to affect development of flatfish larvae and they are ligands to nuclear receptors that participate in the control of development. Our hypothesis was that one of these factors or an interaction between them may be the cause of abnormal development of flatfish larvae. Atlantic halibut larvae were fed either DHA-selco-enriched Artemia or copepods from first feeding. In fish that had been fed Artemia, only 7% had normal pigmentation and 10% normal eye migration. The numbers for fish fed copepods were 68% and 88%, respectively. Malpigmented fish fed Artemia were depigmented, while those fed copepods had ambicoloration. The differences in development were probably nutrient dependent, since all other conditions were similar for the two groups. Larvae fed copepods had markedly higher body levels of docosahexanoic acid (DHA, 22:6n−3) and eicosapentaenoic acid (EPA, 20:5n−3) and lower levels of arachidonic acid (ARA, 20:4 n−6) than larvae fed Artemia. The DHA/EPA ratio was similar in the two groups, but the EPA/ARA ratio was more than four times higher in larvae fed copepods than in larvae fed Artemia. Larvae fed copepods had higher body levels of total retinol than larvae fed Artemia, but the difference was due to higher levels of the storage forms, retinyl esters, whereas the levels of free retinol and retinal were similar in the two groups. The level of iodine was 700 times higher in copepods than in Artemia and 3–4 times higher in larvae fed copepods than in larvae fed Artemia. There was a significantly higher level of T₄ in larvae fed copepods during the “window of opportunity”, 15–30 days after first feeding. In an experiment where Atlantic halibut larvae were fed Artemia enriched in iodine up to the levels found in copepods, there was a significant effect on the body level of iodine and a non-significant tendency of higher levels of thyroid hormone, but no effect on pigmentation or eye migration. It is concluded that Artemia probably offers a sufficient access to vitamin A precursors to meet the larval requirement. More research should be done to elucidate possible effects of iodine on development of Atlantic halibut larvae. Fatty acid composition is still the most likely candidate for causing abnormal development in Atlantic halibut larvae.     

维生素A缺乏对建鲤生长性能及免疫功能的影响

为了探讨仿刺参幼参对配合饲料中维生素A(V_A)的适宜需求量,实验在基础饲料中分别添加维生素A乙酸酯,配制V_A含量分别为3 250 (D1)、5 187 (D2)、7 054 (D3)、8 970 (D4)、12 975 (D5)和16 400 (D6) IU/kg的6组等氮等能的实验饲料,饲喂初始体重为(15.48±0.01) g仿刺参幼参8周。结果显示,① V_A对仿刺参存活率(SR)无显著影响,显著提高了增重率(WG)和特定生长率(SGR);② V_A显著提高了体壁粗脂肪和V_A含量,降低了羟脯氨酸含量;③ 肠道脂肪酶(LPS)活性呈上升趋势,D1组显著低于其他组,淀粉酶(AMY)活性呈先下降后上升的趋势;④ 肠道谷草转氨酶(AST)、总抗氧化能力(T-SOD)及过氧化氢酶(CAT)活性均呈先升后降趋势,AST及CAT活性均在D4组出现最高值,D2～D5组T-SOD活性显著高于D1组,碱性磷酸酶(AKP)活性呈上升趋势,D1组显著低于其他组,丙二醛(MDA)含量逐渐降低。综上所述,饲料中适宜含量的V_A能促进仿刺参生长,提高机体脂肪代谢及抗氧化应激能力;以增重率为评价指标,经一元二次回归分析得出,初始体重为15.48 g的仿刺参对饲料中V_A的最适需求量为10 000 IU/kg。本实验结果可为仿刺参配合饲料中V_A的添加量提供参考,也可为仿刺参“微营养素平衡”配合饲料的开发提供依据。     

The effect of diet on ossification and eye migration in Atlantic halibut larvae (Hippoglossus hippoglossus L.)

Larval nutrition affects post-metamorphic phenotype in Atlantic halibut and many deformities are related to skeletal development. In a multidisciplinary study, 24,000 sibling halibut larvae were reared at an average temperature of 11.9 °C on either enriched Artemia or natural zooplankton in duplicate treatments and the development followed. One hundred and eighty sibling larvae up to about climax metamorphosis at 46 days post start feeding (psf) were cleared and stained for bone, and stereological measurements of bone and body area and degree of eye migration were registered. From day 21 psf, the zooplankton-fed fish had more calcified matrix relative to body size than did Artemia-fed halibut and from day 35 psf, this difference was significant (33.7%±1.9 SD vs. 28.6%±4.1, P<0.05). When related to ontogeny, the zooplankton-fed fish had a higher average percentage ossification than the Artemia-fed larvae at Stages 7, 8 and 9 (pro- and climax metamorphosis), but this difference was significant only at Stage 8 (34.1%±2.56 SD vs. 31.9%±2.32 SD, P<0.05). Asymmetry of the cranium and consequently eye migration began earlier (Stage 7 vs. Stage 9) and was significantly better in the zooplankton-fed fish. The results suggest that nutritional differences in content of vitamin A and thyroid hormones, which target osteoblasts and osteoclasts, may underlie differences in developmental trajectory. The results also support the hypothesis of a critical window of metamorphosis between 14 and 25 days post start feeding in halibut larvae.     

Appetite, gut transit, oxygen uptake and nitrogen excretion in captive Atlantic halibut, Hippoglossus hippoglossus L., and lemon sole, Microstomus kitt (Walbaum)

Atlantic halibut, Hippoglossus hippoglossus L., eat larger satiation meals (mean 11.7% body weight) than lemon sole, Microstomus kitt (Walbaum), (2.6% body weight). Total gut clearance time was about 120 h for halibut and 72 h for lemon sole. There are marked differences in feeding behaviour between the two species; halibut feed in midwater and require several body lengths of approach swimming before taking large items of food, while lemon sole eat only off the bottom. In shared tanks, no aggressive interaction was observed. A duoculture system holding small numbers of lemon sole with the more valuable halibut is recommended as a means of minimizing food waste and tank fouling. Oxygen uptakes of 0.07-0.11 ml O₂ g fish wt⁻¹ h⁻¹ (depending on nutritional state) were recorded for the two species. Ammonia nitrogen outputs were also similar. Starved halibut excreted 2.32 μg N g⁻¹ h⁻¹, fed animals 5.08 μg N g⁻¹ h⁻¹. The corresponding values for lemon sole were 3.26 μg N g⁻¹ h⁻¹ and 6.37 μg N g⁻¹ h⁻¹, respectively.     

Replacement of fish meal with wheat gluten in diets for Atlantic halibut (Hippoglossus hippoglossus): Effect on whole-body amino acid concentrations

The feasibility of replacing fish meal with wheat gluten (WG) in diets for Atlantic halibut (Hippoglossus hippoglossus) was studied. Four diets were produced containing 0, 10, 20 and 30% WG (60% crude protein and 27% lipid (dry matter (DM) basis)). The lysine concentration in these diets were 4.0, 3.6, 3.1 and 2.6% (dehydrated form), respectively. The diets were fed to triplicate groups of 60 g halibut in a 56-day comparative slaughter experiment. The data were analysed by ANOVA and regression. Fish growth (specific growth rate, overall mean 1.25 ± 0.03%/d) and feed efficiency (overall mean 1.63 ± 0.03 g gain/g DM intake) were good in this trial and were not influenced by dietary WG level. The whole-body protein concentration decreased significantly and the crude lipid concentration tended to increase with increasing dietary WG. These observations were taken as indications of problems with amino acid metabolism, and it was assumed that the diet containing 2.6% lysine was deficient in this amino acid. It was observed that the method of expression of the amino acid concentrations in the body was crucial for the detection of significant differences among treatments. Based on our results, we caution the use of crude protein as the denominator in the expression of amino acid concentrations. The finding in this dataset that dietary effects on the percentages of some amino acids in the fish are dependant on the use of hydrated or dehydrated amino acids encourages us to express the amino acids in the protein-bound (dehydrated) form, which also represents the form in which the overwhelming majority of amino acids are present in the body.The results from this trial indicate that WG is a suitable replacement protein source for fish meal, even at a high inclusion level of 20% of the diets. A further increase in the dietary WG level to 30% should be done with caution unless the diets are supplemented with lysine.     

Fertility and motility of sperm from Atlantic halibut (Hippoglossus hippoglossus) in relation to dose and timing of gonadotrophin-releasing hormone agonist implant

In broodstocks of Atlantic halibut, Hippoglossus hippoglossus, male and female gamete production often becomes unsynchronised towards the end of the spawning season—milt becomes very viscous and difficult to express while the females are still producing batches of good quality eggs. Gonadotrophin-releasing hormone agonist (GnRHa) has been shown to stimulate spermiation in a number of fish species. Therefore, we conducted two experiments where male halibut were implanted intramuscularly with pellets containing GnRHa. The effect of the pellets was tested at three periods: before, at the height of and at the end of spermiation. In the middle period, GnRHa was tested at two doses (5 and 25 μg/kg bodyweight). Measurements were made of milt hydration, sperm motility and fertilisation rate. Implanted males began spermiation at least 4 weeks before control males. Both doses of GnRHa increased the fluidity of the milt. This effect lasted for at least 20 days in the low dose group and for 40 days in the high dose group. When applied at the end of the season, GnRHa reversed the normal trend for the milt to become more viscous. GnRHa treatments did not affect fertilisation rates obtained with the sperm. However, towards the end of the spawning season, sperm motility was enhanced in males treated with the high dose of GnRHa (25 μg/kg) compared to controls. As described previously, plasma concentrations of the gonadal steroids, 5β-pregnane-3β,17,20β-triol 20-sulphate and 17,20-dihydroxy-4-pregnen-3-one, were significantly enhanced by GnRHa treatment. Concentrations of testosterone on the other hand decreased when spermiating males were treated with GnRHa. Our data suggest that 17,20β-dihydroxy-4-pregnen-3-one or its metabolites are involved in milt hydration, possibly through affecting ion transport.     

Artemia enriched with high n-3 HUFA may give a large improvement in performance of Atlantic halibut (Hippoglossus hippoglossus L.) larvae

Atlantic halibut larvae were fed Artemia enriched with two different oil emulsions (cod liver oil and 2050TG) from first feeding to 70 days after first-feeding (dpff). Larvae fed 2050TG enriched Artemia had better growth, survival and eye migration than larvae fed the cod liver oil enriched Artemia, while pigmentation rate was similar in the two groups. In addition to the difference in fatty acids, the two emulsions differed in lipid class composition, since 2050TG is a synthetic oil and a mixture of mono-, di- and tri-acylglycerol, while cod liver oil is a tri-acylglycerol. Total lipid level, estimated as fatty acid methyl esters (FAME) was similar in the two Artemia types, but sum of n-6 and n-3 fatty acids, arachidonic acid (20:4n-6, ARA), docosahexaenoic acid (22:6n-3, DHA) and eicosapentaenoic acid (20:5n-3, EPA) were higher in Artemia enriched with 2050TG than in the cod liver oil enriched Artemia. However, the main difference in fatty acid composition in the larvae, was a higher DHA (% of total fatty acids) in 2050TG larvae than in cod liver oil larvae. The lipid level measured as FAME was up to four times higher in the 2050TG larvae than in the cod liver oil larvae, and the reason for this may have been a better bioavailability of the partly digested lipid in the 2050TG emulsion. The correlation between a high level of lipid in the larval tissues (e.g. high energy status) and improved eye migration in larvae fed the 2050TG enriched Artemia supports the hypothesis that energy limitation on the larval stage may be a cause of the impaired eye migration commonly observed in farmed Atlantic halibut juveniles.     

Swimming behaviour as an indicator of low growth rate and impaired welfare in Atlantic halibut (Hippoglossus hippoglossus L.) reared at three stocking densities

The Atlantic halibut (Hippoglossus hippoglossus L.) is a new species in Norwegian aquaculture. However, in ongrowing trials, halibut shows variable and generally poor rates of growth. The halibut is a flatfish that spends most of its time resting on the bottom, and it was hypothesized that high stocking densities with frequent social interactions could lead to behaviour changes, reduced appetite and impaired welfare. Halibut were kept in six tanks at low, medium, and high densities (18%, 54% and 112% bottom coverage). All fish were individually tagged with Trovan™ passive implant transponder (PIT) tags, allowing an antenna to register fish swimming at the surface. Swimming and feeding behaviour was also recorded by underwater video cameras. Individual growth rates were highly variable, but food consumption and growth rates fell significantly with increasing stocking density, while individual swimming activity rose with increasing density. Frequent “surface swimmers” had a significantly lower growth rate than fish that were seldom recorded by the PIT antennae. Surface swimming may therefore be an indicator of suboptimal growth rates and impaired welfare in reared halibut.     

Stable isotope variations in otoliths of Pacific halibut (Hippoglossus stenolepis) and indications of the possible 1990 regime shift

Stable oxygen and carbon isotope ratios (δ¹⁸O and δ¹³C) from archived otoliths of Pacific halibut, Hippoglossus stenolepis, were measured to examine the most recent regime shifts in British Columbia and the Gulf of Alaska. δ¹⁸O values of these otoliths ranged from −1.5 to +2.8‰ VPDB, and were consistent with the life stages and migration behavior of halibut. δ¹³C varied from −3.3 to +0.9‰ VPDB, but did not show a transition from the juvenile to the adult stage as does δ¹⁸O. Evaluation of δ¹⁸O and δ¹³C values of mature halibut (ages 8–12) indicated that the 1977 regime shift might have a warming impact on the northeast Pacific fish stocks. In contrast, a possible regime shift around 1990 with a bottom seawater temperature decrease of about 2 °C might have occurred in both the areas. The connection between stable isotope variations in otoliths and the climate regime shifts is thus potentially useful in studying the population dynamics of Pacific halibut, and decadal scale (e.g., the last 20–30 years) ocean environmental changes.     

Absorption of glucose, amino acids, and dipeptides by the intestines of Atlantic salmon (Salmo salar L.)

Rates of glucose, amino acid and dipeptide absorption by the intestine of Atlantic salmon (Salmo salar L.) were measured in vitro at 10 °C as functions of concentration and region using intact tissues (everted sleeve method). Salmon (weight range 300–1300 g) fed a commercial, extruded salmon feed, were kept at 12–13 °C in freshwater. Maximum rates (V _max) of glucose and dipeptide transport were low compared to most amino acid V _max values. There was a declining proximal-to-distal gradient of absorption along the post-gastric intestinal tract. A saturable component of absorption was not evident for proline and glycyl-proline in the distal intestine, and glycyl-sarcosine in any region. `Apparent diffusion', which may include low affinity, high capacity carrier systems and carrier-independent influx, appears to account for the majority of total uptake at higher concentrations of amino acids and dipeptides. There was competition between the dipeptides for transporter sites in the pyloric ceca and mid intestine, suggesting a common carrier. There was also indication of hydrolysis of these dipeptides by brush border membrane enzymes.     

The influence of water temperature on spawning patterns and egg quality in the Atlantic halibut (Hippoglossus hippoglossus L.)

A three-year study was conducted to investigate the effects of water temperature on Atlantic halibut broodstock reproductive performance. Two groups of fish held under ambient photoperiod were established onto contrasting temperature regimes. The ‘chilled’ group were held at below 9 °C from late October and at approximately 6 °C from December until the end of the spawning period whilst the ‘ambient’ group received no temperature control. The temperature profiles for the ‘ambient’ group changed over the 3 years but were generally characterised by warmer conditions prior to spawning and an earlier temperature rise in the spring. Total egg production was higher in the ‘chilled’ group each year. Absolute fecundity was significantly reduced in the ‘ambient’ group compared to the ‘chilled’ group every year of the study (0.6 million eggs/female for ‘chilled’ group vs. 0.3 to 0.4 million eggs/female for ‘ambient’ group) and egg viability, in terms of fertilisation and hatch rate, was significantly impaired in the ‘ambient’ group in years 2 and 3 (mean fertilisation rate in the ‘ambient’ group was between 27.0% and 54.8%; vs. 63.4% to 77.4% in the ‘chilled’ group, mean hatch rate in the ‘ambient’ group was between 3.1% and 25.6% vs. 60.7% to 71.7% in the ‘chilled’ group). Eggs spawned at high temperatures, later in the season were generally of low viability. In the ‘ambient’ group the spawning season became progressively delayed during the study and average duration of spawning season over 3 years was shorter (between 23.5 to 26.3 days for the ‘ambient’ group vs. between 30.5 and 41.2 days for ‘chilled’ group). It is hypothesised that high temperature during the vitellogenesis period caused a delay in spawning and a reduction in quantity and quality of eggs and that this effect was exacerbated by high temperature during spawning.     

Lipid and amino acid metabolism during early development of Atlantic halibut (Hippoglossus hippoglossus)

Lipid classes, fatty acids, free amino acidsand protein content in captive Atlantic halibut(Hippoglossus hippoglossus) eggs weremeasured to investigate the changes in thebiochemical composition of eggs and larvae inboth the embryonic and early larval stages.Total free amino acids decreased continuously(p < 0.01) over the embryonic and larval stagesinvestigated. Triacylglycerol was significantlygreater at hatch than at all other stages(p < 0.05). When hatching occurred, there wasalso a significant increase in all phospholipidclasses. It is suggested that free amino acidsmay be the source of carbon skeletons for lipidsynthesis at hatching.     

Effects of moderately oxidized dietary lipid and the role of vitamin E on the development of skeletal abnormalities in juvenile Atlantic halibut (Hippoglossus hippoglossus)

A study was conducted to characterize the effects of oxidized marine fish oil (MFO) on skeletal development in juvenile Atlantic halibut (Hippoglossus hippoglossus) and to determine the role of vitamin E on their bone health and antioxidant defense mechanisms. Juvenile halibut (4.5 ± 0.1 g) were fed six experimental diets containing untreated (peroxide value (POV)  =0.6 meq kg^− 1), mod`rately oxidized (POV = 7.5 meq kg^− 1) and highly oxidized (POV = 15 meq kg^− 1) MFO either with or without α-tocopherol acetate (0 or 300 IU kg^− 1) supplementation for 14 weeks. No significant effects on growth, survival, hepatosomatic indices, or hematocrit were observed among the dietary treatments. Fish fed diets without vitamin E and highly oxidized dietary lipids showed increased hepatic malonaldehyde concentrations indicating a response to oxidative stress. Both muscle and liver α-tocopherol concentrations were significantly lower in fish fed diets without vitamin E supplementation. Alkaline phosphatase levels in serum and bone were increased when vitamin E was present within the diet indicating higher bone formation activity by osteoblasts. Oxidized lipids and lack of dietary vitamin E significantly increased saturated and decreased polyunsaturated hepatic fatty acids. Liver lipids of fish fed diets without vitamin E also exhibited a lower ratio of 22:6n-3 to 22:5n-3 and n-3 fatty acids. The most frequent skeletal deformity observed was scoliosis, spanning the cephalic/prehemal regions, as well as the anterior hemal region of the vertebral column, which increased the frequency according to elevated levels of oxidized dietary lipid. Lordosis was also observed, with no specific pattern along the vertebral column. The pattern and type of abnormalities observed were similar to those reported in an earlier study in halibut from a commercial hatchery.     

磷对生长期草鱼肌肉理化参数、游离氨基酸、呈味核苷酸和游离脂肪酸组成的影响

为探索磷对生长期草鱼肌肉常规营养组成和理化特性,肌肉中游离氨基酸、呈味核苷酸和游离脂肪酸组成的影响,实验选择初始体质量为[(256.22±0.60) g]的健康草鱼540尾,随机分为6组,每组3个重复,分别饲喂含有效磷0.95 (基础饲料组,未添加)、2.46、3.96、5.68、7.10和8.75 g/kg的饲料60 d。结果显示,饲料中适宜水平有效磷显著提高了生长期草鱼肌肉蛋白质、水分、羟脯氨酸、∑氨基酸、∑鲜味氨基酸(UAAs)、∑甜味氨基酸(SAAs)、肌苷酸(IMP)、∑不饱和脂肪酸、∑多不饱和脂肪酸(PUFA)含量以及pH0 h和pH12 h,而肌肉剪切力、组织蛋白酶B和L活性、乳酸、饱和脂肪酸(SFA)含量显著降低。此外,当饲料中有效磷水平分别增加到3.96和5.68 g/kg时,生长期草鱼肌肉IMP和∑呈味氨基酸(UAAs+SAAs)的滋味活性值(TAV)分别达到最大值。适宜水平有效磷还显著提高了生长期草鱼肌肉PUFA/UFA及n-3 PUFAs/n-6 PUFAs比值。研究表明,适宜水平有效磷提高了生长期草鱼肌肉蛋白质含量、肌肉嫩度、系水力和pH值,增加肌肉呈味氨基酸...     

江蓠中类菌孢素氨基酸(MAAs)分离纯化及其成分分析

存在于海洋生物中,尤其是藻类中的类菌孢素氨基酸(mycosporine-like amino acids,MAAs),是一种吸收紫外线的物质,可用于紫外线防护品的原料,具有商业开发的前景.对湛江沿海产江蓠中MAAs进行了分离和结构鉴定,确定江蓠MAAs的主要组成及比例.利用C-18 Sep-Pak固相萃取柱和半制备型HPLC对湛江产江蓠中MAAs成分进行分离纯化.根据化合物的特征、紫外吸收波长和波谱数据鉴定其主要成分的结构,并结合参考文献确定湛江产江蓠MAAs的4种主要成分是palythine、shinorine、palythinol和porphyra-334,其比例约为4.9∶1∶1.2∶9.9.同时,比较了UV法和HPLC法对湛江产江蓠MAAs主要成分porphyra-334含量检测的准确度,建立了两种检测方法的拟合曲线,并通过试验验证,最终确立了HPLC对MAAs主要组成成分的检测方法.     

Evaluation of feed protein quality by measuring plasma free amino acids in Atlantic salmon (Salmo salar L.) after dorsal aorta cannulation

Two successive experiments were conducted in order to assess plasma free amino acid (FAA) profiles as a method for evaluating protein quality of fish feeds for Atlantic salmon, Salmo salar (L.). In experiment 1, the importance of meal size and inter‐fish variation was assessed by using dorsal aorta cannulated fish and diets that contained different sources of fishmeal (menhaden versus herring) which in the case of herring, had been dried at either 70 or 100 °C. In experiment 2, an attempt was made to mimic a production situation by comparing the FAA profiles in salmon fed diets containing two commercially available fishmeals that had been produced in accordance with industrial standards (Norse‐LT94® and NorSeaMink®; Norsildmel AL, Fyllingsdalen, Norway). FAA profiles in plasma 6 h after feeding were compared with feed true protein digestibility as determined in mink. Cannulated fish, held in individual tanks, were hand‐fed twice daily to pellet rejection (satiety) and daily records of the actual rations consumed were maintained. A total of 24 different amino acids and other amino‐containing compounds were detected using high‐pressure liquid chromatography. Morning and evening meal size showed significant correlations. Meal size had a significant effect on blood levels of the majority of essential free amino acids (EAA) as well as the total sum of FAA (TFAA). In experiment 1, a marked inter‐individual effect was found, possibly because of incipient sexual maturation. FAA profiles were therefore corrected for meal size by linear regression while repeated sampling via the permanently implanted cannula allowed paired comparisons of the different test diets, minimizing inter‐individual variation. Significant differences in plasma FAA profile, EAA and TFAA were detected between fish fed all diets in both experiments. The preceding parameters for fish ingesting each feed were directly related to their respective mink protein digestibility in experiment 1, but not in experiment 2. Our results show that dietary protein quality can be differentiated by the aforementioned protocol, and by using fish with a low metabolic rate feed qualities could be ranked correctly as in experiment 1.     

Protease activities, plasma free amino acids and insulin at different ages of Atlantic salmon (Salmo salar L.) with genetically different trypsin isozymes

We show significant relationships between digestion rate of dietary protein, absorption/transport rate of amino acids, and plasma insulin concentration. Digestion rate of dietary protein was indicated by protease activity ratio of trypsin to chymotrypsin in the pyloric caeca. Plasma total free amino acids and/or the ratio of essential to non-essential free amino acids indicated absorption/transport rate of amino acids. These relationships are associated with and likely to be primarily affected by genetic variation in the expression of different isozymes of trypsin, a key enzyme for feed utilization and growth, affecting digestion, absorption/transport rate of amino acids and plasma insulin levels in Atlantic salmon (Salmo salar L.).     

圆斑星鲽仔稚鱼色素细胞发育和体色变化

为研究圆斑星鲽早期发育过程中色素细胞的形态和分布,实验对1~72日龄的圆斑星鲽鱼苗进行了连续的显微观察,并绘制了早期发育生长曲线。结果显示,圆斑星鲽从20日龄开始进入快速的增长期,在水温12~19.5°C时完成变态发育需要50 d,黑色素细胞最早出现,数量最多,黄色素细胞次之,虹彩细胞最后发育,数量最少。变态前黑色素细胞密度先升高后降低,在9日龄密度最大为1390个/mm~2,色素细胞逐渐密集鱼体两侧对称分布;变态开始后鱼体两侧色素不对称,有眼侧体表黑色素细胞逐渐溶解消退,由成体黑色素细胞代替,体色变深,黑色素细胞密度稳定在150个/mm~2;无眼侧黑色素细胞逐渐消溶退化,体色逐渐变白。白化个体在变态开始后出现,有眼侧不能形成成体黑色素细胞,形成白化。