Biochemical indices (RNA/DNA ratio and protein content) in studying the nutritional status of Ruditapes decussatus (Linnaeus 1758) juveniles

In this work, we investigated the nutritional status of Ruditapes decussatus juveniles under different rearing conditions, using biochemical indices (RNA/DNA ratio and protein content) and the linear instantaneous growth rate (IGR). Two experiments were conducted to study the effect of starvation, addition of substrate (sand) as rearing support and diet composition on somatic growth and biochemical indices. Results show that biochemical indices of fed juveniles were significantly (P<0.05) higher. Highest RNA/DNA values and protein content were recorded in fed juveniles reared with substrate (P<0.05); conversely, lowest values were recorded in starved ones reared without substrate. In the second experiment, the highest RNA/DNA ratio was recorded in juveniles fed with control algal mixture composed of species commonly used in bivalve nurseries [Isochrysis galbana (clone T-Iso), Chaetoceros calcitrans and Tetraselmis suecica] and lowest in those fed with algal species isolated from Tunisian coasts. This confirms the usefulness of the RNA/DNA ratio and protein content in the clam's nutritional status evaluation. This assay is useful to provide information about the nutritional status and health of the clam in field conditions.     

Effects of starvation and recovery on the survival, growth and RNA/DNA ratio in loliginid squid paralarvae

The ability of Loligo opalescens paralarvae to resist and recover from starvation was examined by measuring their survival, growth rate and RNA/DNA ratios during starvation and refeeding. Paralarvae were fed Artemia sp. nauplii, zooplankton and mysid shrimp. Fourteen days after hatching they were separated into five feeding treatments: a control treatment (food was always available) and treatments starved for 2, 3, 4 and 5 days, and then refed. Each day, 5–7 paralarvae from each treatment were anesthetized to measure mantle length and wet weight (WW), and then RNA and DNA were extracted using an ethidium bromide fluorometric technique. Paralarvae did not survive 4 and 5 days of starvation, showing that at 15 days of age and at 16 °C the limit to recovery was 3 days of starvation. Paralarvae starved for 2 and 3 days showed compensatory growth that mitigated the effects of starvation, in that at the end of the experiment (10 days), they attained mean final body weights similar to the control treatment. Differences in the RNA/DNA ratios between control and starved paralarvae were detected within 2 days of food deprivation. For paralarvae starved 2 and 3 days, it took 1 day after refeeding to attain RNA/DNA ratios not significantly different from the control treatment. Additionally, RNA/DNA ratios were highest during the day (0800, 1200, 1600 h) and lowest at night (0000, 0400 h), suggesting daytime feeding activity. Growth rates ranged from − 14% to 21% WW day^− 1 and the resulting equation between RNA/DNA ratio and growth rate (GR) of paralarvae was GR = 1.74 RNA/DNA − 11.79 (R² = 0.70). After starvation, there was a reduction in growth variability in all starved treatments, while growth variability remained high in the control treatment. Findings from the present study indicate that nucleic acids are a valid indicator of nutritional condition and growth in squid paralarvae.     

饥饿与再投喂对方斑东风螺生长、基本营养成分及RNA/DNA比值的影响

在(25.8±1.7)℃条件下,测定了方斑东风螺(5.25±0.53)g在不同时间(7、15、25和40d)饥饿处理后再投饵30d过程中的生长参数、基本营养成分及组织RNA/DNA比值的变化。饥饿状态下,螺体水分含量逐渐上升,第15天时显著高于对照组;脂肪与糖原含量均下降,并分别于饥饿15d、25d时显著低于对照组(P<0.05);而蛋白质含量在不同处理组间无显著性差异(P>0.05);足肌与肝胰脏中RNA/DNA比值均随饥饿时间延长而逐渐降低。恢复生长后,除饥饿40d组含水量显著高于对照组外(P<0.05),该组其余营养成分及其它各组相应指标均恢复至或接近对照组;RNA/DNA比值除在饥饿40d组肝胰脏中仍较低外均接近或显著高于对照组。各组幼螺摄食率(FR)均高于或显著高于对照组(P<0.05),体重增量、食物转化率(FCE)在前3处理组及特殊生长率(SGR)在饥饿7d与25d组均与对照组间无显著差异(P>0.05),而饥饿15d组的SGR显著高于对照组(P<0.05);饥饿40d组尽管FR显著提高,但体重增量、FCE及SGR均显著低于对照组(P<0.05)。结果表明,方斑东风螺幼螺饥饿时主要消耗脂肪与糖原...     

饥饿和补偿生长对史氏鲟幼鱼摄食、生长和体成分的影响

报道了饥饿和再投喂对史氏鲟幼鱼摄食、生长以及生化组成的影响.22±2℃条件下,随着饥饿时间延长,幼鱼白肌的RNA/DNA比值不断减小,体重逐渐下降,后者与同期对照组之间存在极显著性差异(P<0.01).饥饿7d,鱼的肝糖原和肌糖原含量显著降低(P<0.05),但随着饥饿时间的延长,肝糖原和肌糖原含量则出现不同程度的回升;脂肪含量和蛋白质含量分别在饥饿14d和21d时下降幅度最大,提示史氏鲟幼鱼动用储存物质的顺序依次是糖原、脂肪和蛋白质.而饥饿过程中鱼体水分和灰分含量则有所上升.恢复投食后,饥饿幼鱼的摄食强度增大,生长加快,其中7d、14d饥饿组幼鱼的RNA/DNA比值达到或接近正常投喂组水平,但21d饥饿组的比值仍明显低于正常投喂组(P<0.05).恢复投食30d后,7d和14d饥饿组幼鱼体重接近对照组(P>0.05),21d饥饿组的终体重未能赶上对照组(P<0.05),这表明史氏鲟幼鱼的补偿生长随饥饿时间不同而异.试验结束时,各处理组鱼体生化组成与正常投喂组没有显著差异(P>0.05).     

Hepatic RNA:DNA ratio as a reliable indicator of the growth performance of juvenile <Emphasis Type="Italic">Pelodiscus sinensis</Emphasis> under nutritional stress

We investigated the reliability of the ratio of RNA to DNA in juvenile Pelodiscus sinensis under moderate nutritional stress from lack of sufficient protein. The control diet contained 45% protein. Two experimental diets containing 40 and 35% protein were used to trigger nutritional stress. One hundred fifty-six turtles were randomly divided into the three diet groups and fed for 90 days. Four turtles were randomly sampled from each group on days 2, 4, 7, 15, 30, 45, 60, 75 and 90 of the trial and their hepatic RNA:DNA was measured. Each turtle was weighed on days 15, 30, 45, 60, 75 and 90. Obvious positive correlations between RNA:DNA and specific growth rate (SGR) were found, which were affected by dietary protein levels. The exponential regression model of the relationship between RNA:DNA (x) and SGR (y) in turtles fed 45% protein diet was y = 0.8001e^0.3072x , in the 40% protein diet it was y = 0.5374e^0.4297x , and in the 35% protein diet it was y = 0.7867e^0.369x . From day 7 until the end of the trial, RNA:DNA accurately distinguished differences among the three groups. We suggest that hepatic RNA:DNA is a sensitive and quick indicator of growth performance in juvenile turtles, especially in studies related to nutritional stress.     

饥饿和再投喂对白斑狗鱼体内RNA/DNA比值影响的研究

研究了饥饿和再投喂过程中自斑狗鱼肝脏和肌肉RNA/DNA比值的变化.随着饥饿时间的延长,白斑狗鱼体内RNA/DNA比值不断下降,体重逐渐减小,饥饿561时RNA/DNA比值下降幅度达到最大.恢复投喂后,白斑狗鱼摄食强度明显增大,生长加快,各组试验中肝脏和肌肉RNA/DNA比值均超过正常投喂水平.试验结果表明RNA/DNA比值与体重变化呈正相关,进一步证明RNA/DNA比值可作为衡量鱼类生长的重要指标之一.     

Growth performance and RNA/DNA ratio of noble crayfish (Astacus astacus) and narrow‐clawed crayfish (Pontastacus leptodactylus) fed fish waste diets

New and viable species for aquaponics and integrated multi‐trophic aquaculture (IMTA) in freshwater systems can improve yields and sustainability of aquaculture. Freshwater crayfish species such as Astacus astacus and Pontastacus leptodactylus are omnivorous feeders and considered candidates for feeding on faecal matters in existing aquaculture systems. Feeding trials were conducted to determine growth response and RNA/DNA ratio in freshwater crayfish fed fish waste. Carapace length and wet weight were measured to determine the growth response. Juvenile A. astacus was fed faeces of hybrid striped bass (Morone chrysops × Morone saxatilis) and rainbow trout (Oncorhynchus mykiss), while adult P. leptodactylus was fed with two commercial pellet diets and pikeperch (Sander lucioperca) faeces. The nutritional composition of hybrid striped bass faeces was close to optimal diet composition of A. astacus, and crayfish showed significantly higher carapace growth, weight gain and weight gain per moult as the group fed rainbow trout faeces. The growth of P. leptodactylus was significantly lower in terms of weight gain and weight gain percentage per moult for crayfish fed on pikeperch faeces. Thus, this study can recommend a co‐cultivation of hybrid striped bass and A. astacus within one system, but cannot recommend co‐cultivation of P. leptodactylus with pikeperch. Additionally, this study showed controversial results of RNA/DNA ratio and weight gain of both crayfish species. Thus, RNA/DNA ratio cannot be approved for investigations on crayfish physiological status in controlled feeding experiments if animals are fed with an inadequate diet.     

饲料中糖/脂肪比对暗纹东方鲀幼鱼生长、血液指标、肝代谢酶活性及PEPCK基因表达的影响

配制6种不同糖/脂肪比例（CHO∶L分别为4.29、2.79、1.86、1.19、0.73和0.41）的等氮等能饲料,饲养暗纹东方鲀幼鱼[初始体重为(11.2 ± 0.5) g] 60 d,探讨饲料中糖与脂肪比例对其生长、饲料利用、生理生化指标和PEPCK基因表达的影响。试验结果表明：随饲料中CHO∶L降低,暗纹东方鲀特定生长率（SGR）、蛋白质效率（PER）和饲料效率（FE）先升高后降低,且均在CHO∶L为1.86时达最大,显著高于CHO∶L为0.41、0.73和4.29时的值(P<0.05)。血浆甘油三酯和肝脏脂肪含量随CHO∶L降低而显著增加(P<0.05),而血糖和肝糖原含量随CHO∶L降低而显著降低(P<0.05)。随饲料中CHO∶L降低,肝脏脂肪酶和脂肪合成酶活性先增加后降低,分别在CHO∶L为1.19和1.86时活性最高。CHO∶L为1.86-4.29时PK活性显著高于其他饲料组(P<0.05)。CHO：L为0.41和0.73时,AMS活性显著低于其他饲料组(P<0.05),而PEPCK活性和mRNA相对表达量显著高于其他饲料组(P<0.05)。饲料中CHO∶L对暗纹东方鲀存活率和血浆总胆固醇含量无显著影响(P>0.05)。分别用二次多项回归模型拟合SGR、PER、FE和CHO∶L的关系,得到暗纹东方鲀幼鱼饲料中CHO∶L的适宜范围为2.01~2.16,且其对碳水化合物的利用能力要高于脂肪。     

Effect of dietary protein:energy ratio on intake, growth and metabolism of juvenile green abalone Haliotis fulgens

Juvenile green abalone Haliotis rufescens were grown under laboratory conditions at 21±1 °C and fed formulated diets consisting of different protein:energy ratios (mg protein/kcal), 62, 74, 85, 100, 108, for 60 days. The level of crude protein ranged from approximately 26% to 44% while the energy content remained constant at about 4.1 kcal g⁻¹. Growth ranged from 3.63 to 12.33 mg day⁻¹. The growth of abalone fed the 100 and 108 diets was significantly greater than that of each of the other diets. Protein efficiency ratio increased as the dietary protein content increased except for the T108 diet (44% crude protein). Abalone apparently consume food to satisfy an energy requirement. Caloric expenditure due to metabolism was estimated for abalone fed diets with protein ratios of 62, 85, 100. Energy loss due to respiration did not vary appreciably among abalone fed the different diets. The proportional distribution of dietary energy into fecal, digestible, growth, and metabolic energy was estimated for abalone fed these diets. Apparent dry matter digestibility was among the lowest for abalone fed the 100 P:E diet, but growth of abalone fed this diet was significantly higher than that of each of the other treatments except the 108 diet. Unexplained energy loss to achieve balance ranged from 7% to 28.5%, some of which is probably due to differential mucus and ammonia production. Results suggest a potential for the reduction of both dietary protein and lipid without causing any adverse effects on the growth response.     

Effects of starvation on kidney melano-macrophage centre in olive flounder, Paralichthys olivaceus (Temminck and Schlegel)

We investigated the influence of nutritional conditions on histological changes in melano‐macrophage (MM) accumulation in the kidney caused by long‐term starvation. These data were used to determine nutritional indices for olive flounder, Paralichthys olivaceus (Temminck and Schlegel). Experimental groups were established: control, fed and starved. All fish were fed daily with commercial feed at 1–3% of their total body weight for 2 weeks before the start of the experiment (initial control). The control group received feed at 1–3% of their total body weight and the fed group received feed ad libitum, while the starved group fasted throughout the experiment. Ten fish were removed from the initial control at the start of the experiment and each of the three groups every 4 weeks during the 12 weeks of the experiment to examine to investigate kidney MM accumulation. Kidney MMs with dark brown pigment were randomly distributed in the kidneys of starved fish, increasing rapidly after week 4, while deposition levels remained low throughout the experiment in the control and fed groups. These results suggest that catabolic tissue breakdown is a major factor contributing to the formation of pigments within MMs. These results suggest that the degree of MMs deposition in the kidney can be used as alternative indicators to identify starvation in wild and cultured olive flounder.     

Effect of starvation on biochemical composition and gametogenesis in the Pacific oyster <Emphasis Type="Italic">Crassostrea gigas</Emphasis>

The effects of starvation on biochemical composition and gametogenesis were investigated in the Pacific oyster Crassostrea gigas. Histological analysis, combined with oocyte examination and measurements of protein, glycogen and lipid levels and RNA/DNA ratio from gonad, adductor muscle and mantle tissue of each sex were performed. In the starved groups, C. gigas showed gonad development, but the progress was delayed during the experiment. Glycogen was the first substrate used by C. gigas for dealing with lack of food. While glycogen was rapidly consumed, protein and lipid contents decreased gradually. A decrease in the RNA/DNA ratio in the starved groups in all the body components was found during starvation, illustrating that RNA/DNA ratio was a valid indicator of nutritional condition in C. gigas. A significant increase in water and ash contents and a corresponding decrease in condition index were observed in the starved groups, showing that the water and ash content and condition index were related to the usage of glycogen, lipid and protein reserves in body composition. During starvation, energy reserves were mobilized for survival and gonad development, but spawning was arrested. The information obtained in this study is useful for broodstock management in the Pacific oyster industry.     

温度胁迫及恢复过程中褐牙鲆幼鱼GH、IGF-I、RNA／DNA比值和糖原的变化

褐牙鲆（Paralichthysolivaceus）幼鱼分别在温度8．5℃（T8.5）、13．0℃（T13.0）、17．5℃（T17.5）、22．0℃（T22.0）、26．5℃（T26.5）下养殖10d后,调整至生长最快的温度22．0℃养殖30d,研究了生长激素（GH）、类胰岛素生长因子I（IGF-I）、RNA／DNA比值和糖原质量分数的变化。除在胁迫阶段T17.5处理血浆IGF-I质量浓度显著低于T22.0处理外,不同处理的血浆GH和IGF-I质量浓度在胁迫和恢复阶段均无显著差异。不同处理的肝脏RNA／DNA比值仅在20-40d阶段有显著差异,不同处理的肌肉RNA／DNA比值在所有时间均无显著差异。胁迫结束时T8.5、T13.0、T26．5处理的肝脏糖原质量分数显著低于T17.5,处理,试验结束时T22.0处理肝糖原质量分数略低于其余处理。胁迫结束时T25.5处理肌肉糖原质量分数最高,而在恢复的第一个10d时T13.0处理肌肉糖原质量分数最高。不同温度下养殖10d导致的生长减缓能够在恢复至22．0℃后的30d内获得完全补偿生长,但此试验中GH、IGF-I和RNA／DNA比值与生长率不存在明显的相关性。     

Optimal dietary carbohydrate to lipid ratio for juvenile yellowfin seabream (Sparus latus)

A growth experiment was conducted to determine the optimal carbohydrate‐to‐lipid (CHO: L) ratio for juvenile yellowfin seabream cultured in 340‐L indoor recirculating tanks. Seven isonitrogenous (450 g kg⁻¹ dietary protein) and isoenergetic (14.1 MJ kg⁻¹) diets with increasing CHO: L ratios (0.03–5.09 g: g) were fed to triplicate groups of 30 fish with an initial weight of 4.91 g for 56 days. Fish were fed to satiation twice a day and the water temperature ranged between 28 and 31.7 °C during the experimental period. Survival was high in all the groups and was not affected by dietary treatments. Best weight gain (WG) and specific growth rate (SGR) were observed in fish fed diets with CHO: L ratios of 0.29 and 0.72, which were not significantly different from that of 0.03, 1.26 and 1.92, but apparently higher than that of 3.22 and 5.09. Feed efficiency (FE), protein efficiency ratio (PER) and protein production value (PPV) followed the same general pattern as WG and SGR. Highest level of energy production value (EPV) was found in fish fed diets with CHO: L ratio of 0.72. Proximate compositions of fish whole body and tissues were markedly affected by dietary CHO: L ratios. Whole body, muscle and liver lipid increased as CHO: L ratios decreased, whereas moisture contents were reduced. Dietary CHO: L ratios had no significant effect on protein content in whole body and muscle. Plasma total cholesterol levels of fish fed diets with CHO: L ratios less than 0.72 were significantly higher than those of the other groups. Triacylglyceride levels decreased linearly as dietary CHO: L ratios increased. Viscerosomatic index (VSI) significantly increased as dietary CHO: L ratios decreased. Intraperitoneal fat ratio (IPF) of fish fed diets with CHO: L ratios less than 1.92 were significantly higher than those fed CHO: L ratios of 3.22 and 5.09. Hepatosomatic index (HSI) did not vary between the test diets. Based on second‐order polynomial regression analysis of WG against dietary carbohydrate and lipid levels, 84.1 g kg⁻¹ of carbohydrate and 136.3 g kg⁻¹ of lipid, corresponding to a CHO: L ratio of 0.62, in a diet holding 450 g kg⁻¹ of crude protein and 14 KJ g⁻¹ of metabolizable energy, proved to be optimal for juvenile yellowfin seabream.     

饥饿和再投喂对黑尾近红鲌幼鱼体成分、消化酶活性和RNA/DNA比值的影响

在室内水温23～26℃的条件下,分别对黑尾近红鲌(Ancherythroculter nigrocauda)幼鱼进行不同时间(0、5、10、15、20和25 d)的饥饿处理和饥饿后恢复投喂(25 d)试验。结果显示:在饥饿过程中,幼鱼随着饥饿时间的延长,体重和RNA/DNA比值不断减小。脂肪含量在饥饿前期下降明显,后期下降缓慢;蛋白质含量在饥饿前期下降缓慢,后期下降明显,表明幼鱼是优先利用脂肪作为能量来源,其次再利用蛋白质。饥饿5、10 d组幼鱼的消化酶活性下降显著(P<0.05)。肝脏的蛋白酶、淀粉酶活性饥饿至15 d下降显著,之后随着饥饿时间延长,下降趋于平缓;消化道的脂肪酶、淀粉酶活性饥饿至15 d显著下降,之后下降趋于平缓。恢复投喂后,饥饿5、10、15、20 d组幼鱼的消化酶、生化组成及RNA/DNA比值均恢复到对照组水平,而饥饿25 d组幼鱼的水分含量、蛋白质含量、RNA/DNA比值、消化酶均未恢复到对照组水平(P<0.05)。饥饿5、10 d组幼鱼体重均恢复到对照组水平(P>0.05),饥饿15、20、25 d组幼鱼体重与对照组差异显著(P<0.05),这表明黑尾近红鲌幼鱼的补偿生长随饥饿时间的不同而异。     

<Superscript>1</Superscript>H-NMR metabolite profiling of abalone digestive gland in response to short-term starvation

The effect of a short-term feeding and starvation experiment on juvenile abalone (Haliotis rubra × H. laevigata) was investigated (average length = 67 mm; average weight = 48 g). All aquaculture experiments were conducted at The University of Melbourne, Australia. Artificial feed was supplied ad libitum to the fed group, and no feed was supplied to the starved group. A modified metabolite extraction protocol using deuterated solvents was developed for ¹H-NMR-based metabolite profiling of digestive gland in response to the short-term feeding/starvation experiment, to avoid lyophilisation prior to biochemical analysis. PLS-DA revealed that fed and starved abalone are metabolically distinct from each other after 28 and 56 days. After 28 days, the fed group was defined by an increase in arginine, glucose, glutamate, glycine, inosine and uracil (P < 0.05), and the starved group was defined by an increase in N,N-dimethylglycine. After 56 days, the fed group still displayed increased glucose (P < 0.05), while N,N-dimethylglycine remained elevated in the starved group (P < 0.05). Arginine and glycogen were all higher at 28 days compared to 56 days, suggesting decreased anaerobic energy production at the later time point. Only glucose and N,N-dimethylglycine were significantly different between the fed and starved groups after 56 days, suggesting that abalone had not acclimatised to the starvation treatment after 28 days. These results infer N,N-dimethylglycine is a robust marker for short-term starvation in abalone. ¹H-NMR was also conducted on the artificial feed and starved abalone faecal matter, revealing the biochemical differences between them and digestive gland tissue. These methodology and results will facilitate a deeper understanding of the nutritional and physiological requirements of abalone in an aquaculture setting.     

Effects of dietary microbial levan on growth performance,RNA/DNA ratio and some physio‐biochemical responses of Labeo rohita (Hamilton) juveniles

Six isonitrogenous and isocaloric semi‐purified diets were prepared with different levels of microbial levan: control (Basal), T1 (Basal + 2.5 g kg^?1 diet), T2 (Basal + 5 g kg^?1 diet), T3 (Basal + 7.5 g kg^?1 diet), T4 (Basal + 10 g kg^?1 diet) and T5 (Basal + 12.5 g kg^?1 diet), fed to six groups of fish in triplicate tanks. The results of the 60 days feeding trail showed that supplementation of dietary levan significantly affected the weight gain percentage and specific growth rate of the treatment groups fed at 10 g kg^?1 or more levan. Lowest feed conversion ratio (FCR) value and highest survival percentage among levan fed groups were observed with 12.5 g kg^?1 incorporation (T5) and was comparable with (T4) group. Significant increase in muscle RNA level and RNA/DNA ratio was observed with the increasing dietary levan. Fish fed 12.5 g kg^?1 levan had significantly higher protease, amylase and lipase activities compare with the control group. Lowest Aspartate aminotransferase (AST) activity in the liver and muscle was observed in the T5 group fed with highest level of dietary levan. Overall results conclude that dietary microbial levan incorporation at 12.5 g kg^?1 could be used as potent dietary prebiotic for the culture of L. rohita juveniles.     

Effects of starvation and feeding on the fatty acid profiles of Stage I phyllosoma of the spiny lobster, Jasus edwardsii

Fatty acid analyses were conducted on newly hatched and 8‐day‐old‐starved and fed Stage I phyllosoma larvae of the spiny lobster, Jasus edwardsii. Fed animals were offered excess 1.5 mm juvenile Artemia (enriched using the alga Isochrysis galbana, Tahitian isolate, T. iso.). After 8 days, there were significant increases in larval dry weight and the proportion of lipid in fed phyllosoma, whereas these parameters decreased in starved phyllosoma. The abundance of the saturated fatty acids 16 : 0 and 18 : 0 increased in both starved and fed phyllosoma, whereas the main monounsaturated fatty acids 16 : 1n‐7, 18 : 1n‐9 and 18 : 1n‐7 increased with feeding but decreased with starvation. There were no significant differences in the relative proportions of the highly unsaturated fatty acids (HUFAs) arachidonic (AA, 20 : 4n‐6), eicosapentaenoic (EPA, 20 : 5n‐3) and docosahexanoic (DHA, 22 : 6n‐3) acids between newly hatched and starved animals, whereas quantitatively DHA decreased with starvation and feeding. The DHA/EPA ratio was significantly lower in the starved and fed phyllosoma (0.5) compared with that found in the newly hatched phyllosoma (0.9). The lipid profiles of the newly hatched, starved and fed phyllosoma contained large amounts of n‐6 fatty acids resulting in low n‐3 : n‐6 ratios (2.8, 2.7 and 1.6 respectively). The importance of these results and the ability of enriched Artemia to provide a suitable fatty acid profile for this species are discussed.     

不同循环饥饿投喂模式对尼罗罗非鱼补偿生长的影响

为了探讨尼罗罗非鱼对不同循环饥饿投喂模式的补偿生长效应,本实验分别采用每天投喂(S0)及饥饿1 d+投喂3 d(S1F3)、饥饿1 d+投喂5 d(S1F5)、饥饿1 d+投喂7 d(S1F7)、饥饿2 d+投喂3 d(S2F3)、饥饿2 d+投喂5 d(S2F5)和饥饿2 d+投喂7 d(S2F7)6种不同的循环投喂模式,用含33%蛋白质和8%脂肪的饲料饲养尼罗罗非鱼(均重13.50 g),饲喂期为43 d。结果显示,S0组的增重率(806.74%)最高,与S1F3、S1F5和S1F7组差异不显著,但分别比S2F3、S2F5和S2F7组显著提高40.3%、33.6%和10.4%;S0组的特定生长率最低(5.36%),显著低于其他各组;与对照组相比,采用循环投喂模式没有改善饲料转化率和蛋白质效率,但却能明显提高日摄食率;各实验处理组肝体比、脏体比、肥满度、鱼体灰分含量、肌肉RNA/DNA比值及血清总胆固醇、高密度脂蛋白胆固醇、低密度脂蛋白胆固醇和尿素氮含量与对照组差异不显著;S1F3、S1F5和S1F7组鱼体蛋白质和脂肪含量、血清甘油三酯含量及血清谷丙转氨酶和谷草转氨酶活性与S0组差异不显著,但S2F3、S2F5和S2F7组鱼体蛋白质和脂肪含量及血清甘油三酯含量显著低于S0组,血清谷丙转氨酶和谷草转氨酶活性显著高于S0组。研究表明,尼罗罗非鱼在S1F3、S1F5和S1F7模式下获得了完全补偿生长,而在S2F3、S2F5和S2F7模式下仅获得了部分补偿生长,且均是通过提高恢复投喂期间的摄食量来实现补偿生长。在获得完全补偿生长的3组中,S1F3组的实际投喂天数最短,仅为33 d,比每天投喂模式缩短了23.3%,因此在本实验条件下,饥饿1 d+投喂3 d是最佳的循环饥饿投喂模式。     

Effects of delayed first feeding on larval growth,survival and development of the sea cucumber Apostichopus japonicus (Holothuroidea)

The time of first feeding is an important factor for establishing successful exogenous feeding in aquaculture hatcheries as it is crucial for larval survival and growth. The effects of delayed first feeding by the sea cucumber Apostichopus japonicus larvae were investigated. Groups of larvae were fed immediately after completion of the digestive tract (fed control) or starved for 24, 48, 72, 108 and 120 h post fertilization. The growth rates of A. japonicus larvae were the same as those of the control group when first feeding was delayed for less than 72 h. When the period of starvation was beyond 72 h, growth rates were reduced. The fed control group had the highest percentage of late auricularia larvae (70.0%) on day 11, followed by the groups starved for 24, 48, and 72 h, respectively, which had 35.00%, 43.48% and 41.67% of late auricularia larvae. When larvae were starved for more than 72 h, the percentage of late auricularia larvae never exceeded 12.0%. Most larvae halted in development and were deformed before reaching metamorphosis when starved for 108 and 120 h. Prolonged exposure to starvation (more than 48 h) resulted in a significant decrease in percentage of larvae reaching settlement. The point‐of‐no‐return (PNR) of A. japonicus larvae was calculated 110.4 h. Ratios of stomach length to total length, stomach width to total width were more sensitive to starvation than other larval morphometrics. To avoid mortality and obtain adequate growth and development, A. japonicus larvae in commercial culture should be fed within 48 h of the completion of the digestive tract.     

Response of rainbow trout (Oncorhynchus mykiss) to varying dietary astaxanthin/canthaxanthin ratio: colour and carotenoid retention of the muscle

Rainbow trout with an average initial weight of 160 g were fed during 42 days diets containing varied keto‐carotenoids astaxanthin (Ax)/canthaxanthin (Cx) ratio, as follows: Ax 100% : Cx 0%; Ax 75% : Cx 25%; Ax 50% : Cx 50%; Ax 25% : Cx 75% and Ax 0% : Cx 100%. Muscle colour and carotenoid muscle retention were studied. Colour parameter values for mixed astaxanthin–canthaxanthin‐fed fish were intermediate between those obtained for Ax 0% : Cx 100% fed fish group and for Ax 100% : Cx 0% fed fish group. Concerning muscle carotenoid retention, it has been observed that as the level of canthaxanthin in diet increased, the muscle total carotenoid retention decreased. In the mean time, as the level of canthaxanthin in diet increased, the muscle astaxanthin retention decreased while that of canthaxanthin increased. The results reported here provide further evidence of non‐beneficial effects in terms of muscle colour and muscle carotenoid retention of the use of varying dietary astaxanthin/canthaxanthin ratio for feeding rainbow trout compared to values obtained for astaxanthin‐only feed.