Water balance in developing eggs of the codGadus morhua L.

Measurements of yolk osmolality from the embryo of codGadus morhua L. revealed significant variations in the hyposmolality during the embryonic development. The embryo proved to have an extremely low water permeability, protecting it from dehydration in the hyperosmotic seawater. The effect of temperature on the water permeability is high, expressed by an exceptionally high activation energy for water transfer. The agreement between embryonic volume decrease and diffusion permeability during the first 8–10 days after fertilization indicates that no water uptake mechanism is present at this time, thus leaving the embryo fully dependent on internal water stores. The cod egg is buoyant in seawater throughout development. The mechanism for providing hydrostatic lift is the large volume of diluted tissue water located in the yolk and subdermal spaces.     

马氏珠母贝精子的超低温保存

采用光镜和透射电镜方法，研究了不同盐度驯化下施氏鲟幼鱼鳃中泌氯细胞的分布和结构特征。结果显示，在淡水中，施氏鲟幼鱼鳃中的泌氯细胞数量较少，且主要分布在近鳃小片基部，胞体与核均较大而明显，胞内含大量线粒体；泌氯细胞中有网管和囊管，但网管欠发达，囊管分布面积小，细胞表面有顶隐窝。表现为典型的淡水型泌氯细胞（freshwater-type chloride cells）特征。与淡水组相比，盐度10组鳃泌氯细胞的分布和结构变化均不明显，仅数量略有增加，胞体变大。幼鱼在盐度25海水中驯化65d，鳃丝和鳃小片上泌氯细胞数量明显增加，泌氯细胞集中分布在鳃小片基部；超微结构显示，细胞内线粒体数量明显增加，胞质中网管颇为发达，囊管丰富，顶隐窝扩大，表面有微绒毛，表现为α-型（α-subtype）泌氯细胞特征。泌氯细胞具有分泌体内过多Na^＋、Cl-以及调节体液渗透平衡的功能，其数量和结构变化与幼鱼所处的高渗环境相适应。     

Immunolocalization of Na+, K+-ATPase-rich cells in the gill and urinary system of Persian sturgeon, Acipenser persicus, fry

Localization of Na⁺, K⁺-ATPase-rich cells in the gill and urinary system of Acipenser persicus fry was performed through immunofluorescence light microscopy using a mouse monoclonal antibody IgGα₅ raised against the α-subunit of chicken Na⁺, K⁺-ATPase. Different types of epithelia were clearly identified in the gill epithelium: epithelia of branchial arch, interbranchial septum, filament and lamellar epithelium. The Na⁺, K⁺-ATPase-rich cells were found in the epithelia of branchial arch, interbranchial septum, filament, interlamellar region and also in the lamellae. Histologically, the urinary system is divided into head kidney, trunk kidney and short caudal kidney. The head kidney is composed of the pronephric tubules and the haemopoietic tissues, while the trunk kidney is composed of a large number of glomeruli and convoluted nephrons. Each nephron consisted of a large glomerulus and tubules (neck, proximal, distal and collecting tubules) which connected to ureters. Posteriorly, ureters extended and joined together to form a small urinary bladder. In the urinary system, no specific fluorescence staining was observed in the glomerulus, neck segment and proximal tubules. The distal tubule cells and collecting tubule cells showed a strong immunostaining of Na⁺, K⁺-ATPase. Epithelia of ureters and urinary bladder also showed several isolated immunofluorescent cells. Immunofluorescent cells were rich in Na⁺, K⁺-ATPase enzyme which is very important for osmoregulation.     

Quality assessment of newly hatched mud crab,Scylla serrata,larvae

Starvation and exposure to formalin were investigated as possible stress tests for evaluating the quality of mud crab, Scylla serrata, larvae. For the starvation stress test, newly hatched zoeae stocked in 150‐ml containers were either starved or fed rotifers. Similarly, newly hatched zoeae were stocked in containers with seawater of 0 (control), 20, 30 and 40 mg/L formalin for the formalin stress test. The zoeae from the same batches were used for seed production to monitor their performance and validate the results of stress tests. Starvation was found to be unsuitable for larval quality evaluation. However, the impact of initial food deprivation on the newly hatched larvae indicates that feeding immediately after hatching is necessary for mud crab larvae. Exposure of larvae to 40 mg/L formalin for 3 hr appeared to be a reliable and practical method for larval quality assessment as the survival of larvae in the mass production tanks validated the classification of good and poor quality batches in the stress tests. On this basis, a hatchery operator can decide which batch should be cultured further. Finally, there appears to be a link between the quality of larvae and the performance at the megalopa and early juvenile crabs.     

Effects of different step‐wise temperature increment regimes during egg incubation of Atlantic cod (Gadus morhua L.) on egg viability and newly hatched larval quality

We carried out an experiment to determine how rapidly the early incubation temperature of Atlantic cod eggs can be increased without affecting normal embryonic development and hatching. Atlantic cod eggs were incubated at a constant low temperature (4.5 ± 0.5°C; T5 – control) and four temperature increment treatments where the temperatures were increased stepwise from 4.5°C at zygote stage to 9.5 ± 05°C (T1‐8 h, T2‐32 h, T3‐64 h and T4‐96 h). Embryonic cell symmetry, embryonic mortality, hatching success and larval skeletal abnormalities, length and yolk sac volume were recorded. Larval samples were also taken at hatch for histological analysis. Except for higher egg mortality and lower hatching success in the T1, the differences among experimental groups were minor. Cell asymmetries and embryo mortalities were not significantly different between the control and T2–T4 treatment groups. Control larvae were significantly longer and had smaller yolk reserves at hatch than T1–T4 larvae and larvae from T2 had the largest yolk reserves. Tissue and organ histology of hatched larvae were similar. Considering embryonic cleavage pattern, hatching success and larval morphology and histology, a gradual increment of temperature in 32 h seems to be the better choice for future developmental programming studies in Atlantic cod.     

温度、盐度对条石鲷胚胎发育影响及初孵仔鱼饥饿耐受力

研究了盐度、温度对条石鲷胚胎发育的影响和初孵仔鱼对饥饿的耐受力。结果表明,胚胎发育的适宜盐度范围为20～35,最适盐度范围为25～30,孵化率都在89%以上,盐度低于20或高于35,孵化率都降低。盐度对孵化时间有一定影响,盐度高于35或者低于15条件下孵化时间都延长。胚胎发育的适宜温度范围为21～27℃,孵化率都在77%以上,最适温度范围为23～25℃,孵化率达89%以上,低于19℃或者高于27℃时孵化率降低且初孵仔鱼畸形率升高。胚胎孵化时间与温度成负相关关系,胚胎发育速率与温度成正相关关系。条石鲷胚胎发育的生物学零度（阈温度）为10.06℃,有效积温值为405.3℃·h。对胚胎发育的Q10值进行了计算。饥饿条件下,条石鲷初孵仔鱼8日龄全部死亡,半数死亡时间出现在第6天,饥饿对初孵仔鱼生长具有明显的抑制作用。     

盐度和温度对褐菖鲉初孵仔鱼耐饥饿能力的影响

以褐菖鲉(Sebastiscus marmoratus)初孵仔鱼为研究对象,研究了3种水温(12、16、20℃)条件下,不同梯度盐度(5.0、7.5、10.0、15.0、20.0、25.0、30.0、35.0)对褐菖鲉初孵仔鱼不投饵存活指数(SAI)的影响.试验结果显示,在相同水温条件下,水体盐度对褐菖鲉初孵仔鱼的SA...     

Immunostimulation of larvae and juveniles of cod, Gadus morhua L

Cod larval culture is currently hampered by high mortalities in the first 2-3 weeks after hatching, often due to infectious diseases. The immune system of cod is not fully competent until 2-3 months after hatching. Conventional vaccination is, therefore, not of value before this time, and the larvae are wholly reliant on non-specific parameters for their defence against infection. A range of substances, generally derived from bacterial, fungal or plant origin, can activate these non-specific parameters. During three hatching seasons, 2001-2003, at the Marine Institute's Experimental Station, Stadur, Grindavik, Iceland, the effects of several immunostimulants on survival and disease resistance of cod larvae and juveniles were examined. Both bathing treatments and administration in the feed were used. One of these substances, lipopolysaccharide (LPS), isolated from the bacterium Aeromonas salmonicida (ssp. salmonicida or achromogenes), appeared in some instances to improve survival and have a beneficial effect on disease resistance. Other substances tested had limited effects. The results emphasize the need for further work in this field.     

不同盐度和驯养时间中华鲟子二代幼鱼鳃的显微结构变化

采用光学显微镜和组织切片方法,研究了不同盐度和驯养时间中华鲟幼鱼鳃及鳃中泌氯细胞的结构变化特征。试验用鱼为1+龄中华鲟子二代,平均全长50.7 cm,平均体重约441.9 g。试验前在养殖池中暂养1周。试验设2个盐度梯度(10、15)组和1个对照组(淡水)。盐度驯养为将中华鲟子二代从暂养池转入盐度10海水中驯养,分别取驯养1、3、6、9、12、24、48、72、96、120、144、168、192、216、240和264 h的幼鱼各1尾用于试验;将剩下的鱼再转入盐度15海水中驯养,分别取驯养24、48、72 h的幼鱼各1尾用于试验。结果显示,在淡水组中,中华鲟子二代幼鱼鳃丝发达,细胞饱满,鳃小片宽且长。鳃丝上皮的泌氯细胞数量较少,通常靠近鳃小片基部,呈近椭圆状。与淡水组相比,盐度10组的幼鱼鳃丝主干部明显变窄,鳃小片基部区域及鳃小片上泌氯细胞的数量略有增加,胞体变大,且随驯养时间的延长,出现了明显的细胞膜间隙。幼鱼在盐度15组中鳃丝主干明显变窄变短,鳃小片也显著缩短,鳃泌氯细胞数量显著增加,主要分布在鳃小片基部,有明显的分泌腔。中华鲟子二代幼鱼能够快速适应外界水体盐度的变化,这与鳃及鳃上皮中调节渗透压功能细胞的数量和结构变化相适应。     

Behavioural responses to visual environment in early stage Atlantic cod Gadus morhua L. larvae

Marine fish larvae exhibit species‐specific sensitivity to light, which changes during ontogeny. Our aim was to explore how visual environment, characterized by light intensity, microalgae addition and wall colour, affects spatial distribution of Atlantic cod larvae. We applied two different small‐scale factorial designs, each of them as a series of independent short‐term trials at fixed larval ages from 5 to 35 days post hatch (DPH). Positive phototaxis increased in larvae from 5 to ≈24 DPH, followed by reduced response at later ages. Effects from the experimental factors on larval behaviour changed with age, and significant interactions between factors were present. Algae significantly affected larvae only at 5 DPH, increasing phototactic response. White wall colour induced distribution of larvae close to the tank walls at all ages. The experimental approach demonstrated clear effects from visual environment on larval distribution, and revealed both relative importance of individual factors, interactive effects and temporal changes due to larval ontogeny. Our results suggest that by fine‐tuning the visual environment in tanks, the larval distribution may be managed to improve overall rearing conditions through a more even distribution with reduced closeness to tank walls.     

Effects of dietary fatty acids on the production and quality of eggs and larvae of Atlantic cod (Gadus morhua L.)

Cultivated Atlantic cod (Gadus morhua) entering their first year of gamete maturation were fed diets with different levels of arachidonic acid (ARA) and eicosapentaenoic acid (EPA) for 6.5 months prior to commencement of spawning. Gravid females were stripped three times: at the beginning, peak and end of spawning. Lipid composition and egg and larval quality of 34 family crosses were investigated. Results indicated that ARA uptake into eggs from broodstock diet was highly efficient achieving proportions of ARA up to 84% higher in eggs than in the diet. EPA was 42–76% higher, and DHA was 155–173% higher in eggs than in diets. Cod fed the diet with the lowest EPA/ARA ratio had the greatest egg production. Eggs from fish on a diet with high ARA level had significantly higher fertilization and hatching success than those fed low levels of ARA. This diet produced on average 71 viable eggs g^?1 female compared with 32.5 and 4 eggs in diet B and C, respectively. Furthermore, larval survival until 8 days posthatch was higher in diets with lower ARA levels. The combined results showed that ARA dietary supplementation and low EPA/ARA ratio yielded a greater number of viable larvae kg^?1 female.     

Expression of insulin-like growth factor-I in the gastrointestinal tract of Atlantic salmon (Salmo salar L.)

The expression of insulin-like growth factor (IGF-I) in the gut of Atlantic salmon (Salmo salar L.) smolt was investigated at the cellular level using in situ hybridization. A hybridization protocol was adapted for use on formalin fixed, paraffin embedded tissues and was based on a digoxigenin-labelled oligoprobe that recognised a conserved region of IGF-I mRNA. The specificity of the anti-sense IGF-I probe and the performance of the hybridization protocol were evaluated using a sense IGF-I probe, an Ep stein-Barr virus probe and an insulin probe cocktail on serial sections of fish gut, mouse thyroid and human lymph node tissue. In the gut of Atlantic salmon smolt, IGF-I was found to be expressed in single epithelial cells or small clusters of epithelial cells in the pyloric ampulla and in the pyloric caeca. Expression was not detected in the lamina propria of the gut or in epithelial cells of the stomach, midgut or hindgut. The restriction of IGF-I expression to the pyloric ampulla and pyloric caeca is consistent with the role of these gut segments in osmoregulation and the scattered epithelial expression supports the putative autocrine/paracrine mechanism of action of IGF-I in osmoregulation.     

Improved performance of Atlantic cod (Gadus morhua L.) larvae following enhancement of live feed using a fish protein hydrolysate

High larval mortalities and anatomical deformities are among the major obstacles restricting the development of Atlantic cod (Gadus morhua) aquaculture. The immune system of cod larvae is poorly developed at hatch, and innate immune parameters are therefore of importance for defence against environmental microorganisms. Two separate experiments were conducted with bioencapsulation of the live feed of cod larvae using a pollock (Pollachius virens) protein hydrolysate. Offering peptide enhanced live feed to larvae during the first weeks of exogenous feeding promoted larval development, with reduced incidence of severe deformities to 3.0% as compared with 9.6% deformities observed in the control group at 160 days posthatch. The production and distribution of IgM and lysozyme were furthermore increased in larvae fed peptide enhanced feed compared with control larvae. IgM was predominantly detected in the foregut and the epithelial lining of the digestive tract as well as in the epidermal mucus of the skin. Lysozyme was mainly detected in the epidermal mucus of the skin and in the foregut. Overall, the results indicate that live feed enhancement using a protein hydrolysate derived from pollock may reduce deformities and promote normal development during early production stages of cod larvae.     

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.     

A comparison of the fatty acid profiles of adult tissues,and newly hatched,fed and starved Lysmata amboinensis larvae

This study evaluated the lipid content and fatty acid (FA) profile of the hepatopancreas, ovaries and tail muscle of Lysmata amboinensis broodstock, as well as newly hatched larvae subjected to a period of starvation or feed from hatch to Zoea 2. The hepatopancreas had a high lipid content, confirming its role as a process and storage organ in L. amboinensis. Lipids were also a major component of ovarian dry weight, in agreement with reports on other crustaceans during maturation. The tail muscle, being a functional rather than a storage organ, contained low total lipids and was the tissue that closely resembled the FA profile of the newly hatched larvae. Saturated fatty acids (SFAs) and highly unsaturated fatty acids (HUFAs) were the most abundant components of the lipid profiles in broodstock and larvae. The HUFAs docosahexaenoic and eicosapentaenoic were preferentially retained during nutritional stress, confirming their importance for marine cleaner shrimp during early larval development. It appeared polyunsaturated fatty acid and HUFA requirements were met through the larval diet. The SFAs stearic and palmitic were abundant in adult tissues and larvae, whereas monounsaturated fatty acids may have been preferentially catabolized to meet energetic and metabolic larval requirements.     

Ammonia and urea excretion in the tidepool sculpin (Oligocottus maculosus): sites of excretion,effects of reduced salinity and mechanisms of urea transport

Tidepool sculpins live in a variable environment where water temperature, salinity, gas tensions, and pH can change considerably with the daily tide cycle. Tidepool sculpins are primarily ammoniotelic, with 8–17% of nitrogen wastes excreted as urea. The majority of net ammonia (J^net _amm; 85%) and urea (J^net _urea; 74%) excretion occurred across the gill, with the remainder excreted across the skin, the kidney, and/or gut. Acute (2h) exposure to 50% seawater significantly increased J^net _urea (2.8-fold), but reduced J^net _amm (3.5-fold). In fish exposed to 50% seawater for 1 week, J^net _urea returned to control values, but J^net _amm remained slightly depressed. Unidirectional urea influx (Jⁱⁿ _urea) and efflux (J^out _urea) were measured using¹⁴C-urea to determine if urea was excreted across the gills by simple diffusion or by a carrier-mediated mechanism. Jⁱⁿ _urea increased in a linear manner with increasing urea water levels (0–11 mmol N l^–1), while J^out _urea was independent of external urea concentrations. As well, J^net _urea and J^{out inurea} were not significantly different from one another, indicating the absence of back transport. Urea analogs and transport inhibitors added to the water did not have any consistent effect on unidirectional urea flux. These results demonstrate that ammonia and urea excretion rates and sites of excretion in tidepool sculpins are very similar to those found in other marine and freshwater teleosts. Urea and ammonia may play a role in osmoregulation as excretion rates and tissue levels were influenced by changes in water salinity. Finally, we found no evidence for a specific urea carrier; branchial urea excretion is likely dependent on simple diffusion.     

Ontogenic development of the digestive enzymes in common pandora, Pagellus erythrinus, L. larvae

Ontogenic development of some digestive enzymes (proteases, amylase and lipase) in common pandora Pagellus erythrinus larva was assayed during larval development. The green‐water technique was employed for larval rearing, and whole‐body homogenates were used for enzymatic assays in triplicate. Important alterations in specific activities of all digestive enzymes measured during the period of this study were mostly related to metamorphosis and weaning. Mouth opening was observed on day 3 at 2.23±0.01 mm total length synchronously with the first determination of trypsin and chymotrypsin activities. After this date, the specific activities of these slightly increased until 25 days after hatching (DAH), respectively, and then slightly decreased and changed. The pattern determined for pepsin was strongly related to stomach formation on day 25 at 9.72±2.3 mm total length and a sharp increase was found until 30 DAH and then a slight decrease was measured from this date until the end of the experiment. Both amylase and lipase were measured for the first time on days 2 and 4, respectively, and also the specific activities of these showed similar patterns during the first week of the study. Then, slight variations were observed until 30 DAH and while lipase‐specific activity had declined, an increase in the specific activity of amylase was found until the end of the experiment. Finally, it is thought that the variations observed in the specific activity in the profile of digestive enzymes were related to either metamorphosis such as formation of stomach (25 DAH) or to changes in characteristics of food (30 DAH). The pattern of development of the main digestive enzymes found in P. erythrinus is similar to that described in other Sparid species.