Optimising recreational harvests of blue cod: The effects of catch-and-release mortality and size selectivity

A yield-per-recruit model is developed for the recreational fishery on blue cod (Parapercis colias: Pinguipedidae) in the Marlborough Sounds, New Zealand. The model incorporates sex differences in growth rates, protogyny, minimum size limits, catch-and-release mortality and size-selective fishing. Mortality of released fish due to hooking damage and post-release predation is a potentially significant factor for blue cod management. High levels of catch-and-release mortality favour small minimum size limits and reduced fishing intensity. Even in the absence of size limits, hook and line fishing for blue cod is highly selective on larger fish and this greatly reduces the potential impact of catch-and-release mortality on yields and management choices. Catch-and-release mortality will also lower the spawning stock biomass-per-recruit and therefore has the potential to impact on stock sustainability as well as yields. In protogynous species the effects of fishing on spawning stock biomass will be different for males and females and it is important to model these separately, as well as understanding the cues for, or timing and extent of, sex change. Catch-and-release mortality can also slow the recovery of stocks when no-take rules still allow fishing for other species and therefore by-catch of the species targeted for protection. It is suggested that a small reduction in size limit and a small increase in daily bag limit relative to present regulations, would result in optimal yields from this fishery. Predation on fish released by recreational anglers is less widely reported than mortality due to hooking damage but both have the potential to negate the benefits of minimum size limits.     

饲料中添加浒苔对凡纳滨对虾生长性能和肌肉品质的影响

为了探究在不同鱼粉含量的饲料中添加浒苔对凡纳滨对虾的生长性能和肌肉品质的影响,实验采用2×3双因子实验设计,在鱼粉含量分别为18％(A)和15％ (B)的基础饲料中添加0、3％和6％浒苔(分别记为A0、A3、A6、B0、B3和B6),制成6组等氮等能饲料(粗蛋白含量为38.5％).饲喂初始体质量为(3.0±0.1)g的...     

蚕豆水提取物及维生素C和E对草鱼肌肉质构、营养成分以及氧化应激的影响

为探究高浓度蚕豆水提取物、维生素C和E (V_C/V_E)提升草鱼肌肉品质(质构特性等)的效果,实验以普通配合饲料为对照,30%蚕豆水提取物、30%蚕豆水提取物+V_C/V_E(400 mg/kg V_C+200 mg/kg V_E)、蚕豆配合饲料为处理组,分别饲喂(250±20) g草鱼120 d。在40、80和120 d 3个时间点测定草鱼的肌肉和肠道中活性氧(ROS)含量及ROS消除和生成相关酶活性、肌肉细胞中线粒体膜通透性转换孔和线粒体膜电位水平的变化。在120 d时分析草鱼的生长特性和肌肉及肠道的显微结构。结果显示,与蚕豆组相比,30%蚕豆水提取物和30%蚕豆水提取物+V_C/V_E两组草鱼的生长增加、饲料系数和腹腔脂肪水平显著下降,但蚕豆水提取物+V_C/V_E组草鱼肌肉质构特性高于30%蚕豆水提取物组。30%蚕豆水提取物和30%蚕豆水提取物+V_C/V     

The effects of salinity on the survival, growth and haemolymph osmolality of early juvenile blue swimmer crabs, Portunus pelagicus

The blue swimmer crab, Portunus pelagicus, is an emerging aquaculture species in the Indo-Pacific. Two experiments were performed to determine the effects of salinity on survival, growth and haemolymph osmolality of early juvenile P. pelagicus crabs. The salinities tested for the first experiment were 10, 15, 25 and 40 ppt, and for the second experiment 5, 20, 30, 35 and 45 ppt. Each salinity experiment was triplicated, with each replicate consisting of 10 stage 4 juveniles. Each experiment lasted 45 days. Mortalities and incidence of “molt death syndrome” were recorded daily, while the intermolt period, carapace length, carapace width and wet weight were measured at each molt. At the end of the experiments the haemolymph osmolality and dry weights were measured.

Results demonstrate that salinity significantly affects both the survival and growth of early P. pelagicus juveniles. Mortality was significantly higher (p < 0.01) for juveniles cultured at salinities ≤ 15 ppt and at 45 ppt. At a salinity of 5 ppt a complete mortality occurred on day 20. In all salinity treatments, the majority of mortalities were due to “molt death syndrome”. In experiment 1, immediate effects of salinity on growth and development were seen at 10 ppt as the intermolt period was significantly longer (p < 0.01) and the mean carapace size increase was significantly less (p < 0.01) at the first molt compared to the other treatments. Meanwhile, the specific growth rates (carapace length, width and wet weight) were significantly lower (p < 0.05) at high salinities (≥ 40 ppt) due to longer intermolt periods and significantly lower (p < 0.05) carapace size or wet weight increases.

The haemolymph osmolality exhibited a positive linear relationship with the culture medium with an isosmotic point of 1106 mOsm/kg, equal to a salinity of approximately 38 ppt. Based on the osmolality graph, high metabolic cost for osmoregulation due to increased hyper- and hypo-osmotic stress appeared to cause lower survival and specific growth rates of the crabs. The results demonstrate that a salinity range of 20–35 ppt is suitable for the culture of early juvenile P. pelagicus.     

栅栏技术在淡腌半干鲈鱼加工工艺中的应用

为探讨活鱼宰前预冷对后期鱼片冷藏保鲜品质的影响,将鲜活大口黑鲈 (Micropterus salmoides) 置于不同温度 (15 ℃、10 ℃、5 ℃) 的水槽中暂养0.5 h后,宰杀并取鱼片冰藏,分析第0、第3、第6、第9、第12、第15、第18和第21天时的鱼肉感官、理化指标 [ pH、挥发性盐基氮 (TVB-N)、鲜度指标 (K值)、硫代巴比妥酸 (TBA值) ] 及微生物 [菌落总数 (TVC) ] 变化情况,综合评价宰前预冷处理对大口黑鲈冰藏品质的影响。结果表明,15 ℃预冷处理可较好地保持大口黑鲈冰藏期间的品质,维持鱼肉感官品质,降低细菌的生长繁殖速度,延缓pH、TVB-N、K值、TBA值及菌落总数的上升,货架期较对照组延长约3 d。

     

Mortality of yellowtail flounder, Limanda ferruginea (Storer), eggs: effects of temperature and hormone-induced ovulation

Yellowtail flounder, Limanda ferruginea (Storer, 1839), is a highly marketable fish species that used to be a significant groundfish in the northwest Atlantic region. The potential of yellowtail flounder for mass rearing has recently been investigated, but studies into aspects of mortality during early ontogeny are lacking. We investigated the impact of spawning inducement on mortality of eggs from fertilisation until hatch, and the effects of rearing temperature on mortality and hatching time in this multiple batch spawning flounder. An ash-free dry mass (AFDM) technique for determining mortality was employed. This technique reduced rearing tank disturbances and provided quantitative mortality estimates. We found (1) that spontaneously ovulated (SO) mean egg mass (AFDM 24.84±0.73 μg) was significantly higher than mean egg mass from induced ovulation (IO) (AFDM 20.09±0.54 μg); (2) that mortality of SO eggs was lower than IO eggs (p=0.028), (3) that SO eggs reached a relatively constant (maximum) mortality by about day 3 and IO eggs by about day 5; (4) that there was no significant difference in mortality between eggs incubated at 10 °C and those incubated at 4 °C (p=0.320); and (5) that time to 100% hatch took significantly longer for eggs incubated at 4 °C (256.0±73.5 h) than those incubated at 10 °C (77.9±11.6 h) (p=0.003). There was considerable variation in egg mortality among batches and females; nevertheless, general trends indicate that GnRHa-induction of ovulation tends to decrease egg quality. In addition, the AFDM technique was an easily employed and accurate method of determining mortality. We recommend that unless coordination of spawning is important to a particular rearing protocol, induced ovulation should not be employed.     

我国克氏原螯虾产业调查分析与发展对策建议

为探究克氏原螯虾配合饲料经发酵处理后的饲喂效果,分别用未发酵和发酵饲料在室内循环水系统中饲养体重为(4.91±0.18) g的克氏原螯虾幼虾8周,采样分析发酵饲料对克氏原螯虾生长、肌肉品质、消化力、抗氧化能力及肠道菌群结构的影响。结果显示,①发酵饲料水中溶失率显著低于未发酵饲料;②发酵饲料显著提高克氏原螯虾增重率和特定生长率,降低饲料系数,但对存活率、肝体比、含肉率和体成分无显著影响;③发酵饲料显著提高克氏原螯虾肌肉硬度、弹性、咀嚼性和胶黏性,降低了黏附性;④发酵饲料显著提高克氏原螯虾肝胰腺及肠道中胰蛋白酶和脂肪酶活性,血清和肝胰腺中超氧化物歧化酶、酸性磷酸酶和碱性磷酸酶活性,以及肝胰腺总抗氧化能力;⑤发酵饲料显著提高了肠道绒毛长度和宽度;⑥发酵饲料改善了克氏原螯虾肠道微生物结构,显著升高了厚壁菌门和放线菌门相对丰度,同时提高了肠道菌群多样性。研究表明,饲料经发酵处理后可以有效提高克氏原螯虾生长性能、肌肉品质、消化力和抗氧化能力,改善了肠道组织结构,改变了肠道微生物结构,为克氏原螯虾新型环保饲料的生产提供理论依据。

     

Inhibition of embryo development of the commercial bivalves Ruditapes decussatus and Mytilus galloprovincialis by trace metals; implications for the implementation of seawater quality criteria

This study evaluates the risk posed by trace metals on the culture of bivalves in the Galician coast (NW Iberian Peninsula), which depends on collection of natural seed and larval rearing with natural seawater in hatcheries. With this aim, toxicity tests were carried out with embryos of the commercial bivalves Ruditapes decussatus and Mytilus galloprovincialis, and the toxicity of Hg, Cu, Zn, Cd and Pb was quantified in terms of median effective concentration (EC₅₀) and toxicity threshold, using embryogenesis success as endpoint. The EC₅₀ values ranged from 4 to 10 μg/l for Hg and Cu, from 100 to 300 μg/l for Zn and Pb, and from 400 to 2000 μg/l for Cd. The toxicity of copper and zinc combinations could be predicted using a strictly additive model. Effective concentrations found were compared to measured metal concentrations in the Galician Rias, and to local and international seawater quality criteria, in an attempt to evaluate the risk posed by metals to these commercial species. Zinc and especially copper pollution were found to represent a serious threat in certain areas. Furthermore, local seawater quality criteria recently implemented are, in the case of copper and zinc, two orders of magnitude too high to offer any protection for these sensitive early life stages of bivalves.     

Diet of blue cod,Parapercis colias,living on undisturbed biogenic reefs and on seabed modified by oyster dredging in Foveaux Strait,New Zealand

• 1. Little has been done to assess the potential impact of habitat modification by bottom fishing gear on the feeding habits of demersal fishes. An analysis is presented of the diet of blue cod in Foveaux Strait, southern New Zealand, based on the gut content of fish taken in winter 1999 from two sites where each site consisted of both undisturbed biogenic reefs and reefs modified by oyster dredging.
• 2. Of the 420 guts collected, 13% were empty. The overall mean wet weight of gut content was <4 g. No significant habitat or site effects were detected for the proportion of empty guts or the amount of food consumed.
• 3. A pattern was detected that blue cod on dredged habitats generally fed on more crustaceans than those on undistributed habitats. Blue cod from undisturbed habitat also displayed a more diverse diet than those taken from dredged habitat. These results suggest that long‐term disturbance of seabed habitat by the oyster fishery in Foveaux Strait has caused changes to the diet of blue cod. The findings also suggest that actions should be taken to protect the biogenic reefs from further damage if the blue cod fishery and related resources are to be effectively managed.
• 4. Changes in prey diversity with increasing fish size were also found, with prey diversity (Shannon–Wiener index) increasing from 0.83 to 1.35 over a range of fish size from <25 cm to larger than 34 cm. A total of 52 prey taxa were identified in the diet of blue cod. Crustaceans were the main component, followed by mollusca and polychaeta. Fish, echinodermata and ‘other’ were less important in the diet.

Copyright © 2002 John Wiley & Sons, Ltd.     

Electrical stunning followed by decapitation or chilling of African catfish (Clarias gariepinus): assessment of behavioural and neural parameters and product quality

The objective of this study was to assess neural and behavioural responses in farmed African catfish (Clarias gariepinus) upon electrical stunning in combination with decapitation or chilling. To assess the possibility of scaling up one or both experimental methods, two trials were performed in an experimental setting. The product quality of the collected samples was compared with the currently applied industrial method: live chilling. After electrical stunning in combination with decapitation, the fish showed spikes alternated with theta and delta waves on the EEG, followed by minimal brain activity after 20±10 s. The same traces on the EEGs were observed after electrical stunning in combination with chilling. Here, minimal brain activity occurred after 22±11 s. Within a confidence level of 95%, the percentage of African catfish that was effectively stunned after administration of an electrical current of 1.5 A dm⁻², 300 V (50 Hz a.c.), followed by decapitation or chilling was above 91%. The analysis yield and evolution of liquid loss showed significant (P<0.05) differences among the batches, which could be explained by the stunning method used. The course values of the pH in the different batches were significantly (P<0.05) dependent on the stunning method, sex and location (visceral or skin side). It is concluded that African catfish can be stunned effectively using electrical stunning in a water tank, followed by decapitation or chilling in ice. Dutch commercial processors prefer to combine electrical stunning with chilling in flake ice in a rotating tumbler, as the outer slime layer is then removed, which facilitates further processing.     

抗生素处理对坛紫菜叶状体生长和藻际微生物的影响

设计了氨苄青霉素、硫酸庆大霉素和卡那霉素3种抗生素的不同组合处理坛紫菜叶状体,旨在筛选出坛紫菜叶状体藻际微生物的最优去除方法;同时,探究紫菜叶状体生长与微生物群落变化之间的关系。结果显示,低浓度(10μg/mL)的硫酸庆大霉素或高浓度(800μg/mL)的卡那霉素处理,对坛紫菜叶状体生长均具一定的抑制作用,而不同浓度的氨苄青霉素处理均促进了叶状体生长。500μg/mL的氨苄青霉素、500μg/mL的硫酸庆大霉素与300μg/mL的卡那霉素3种抗生素混合处理叶状体24 h,不会抑制叶状体的生长;同时,对藻际微生物有较强的抑制性。不同的坛紫菜品系,不同的叶状体日龄和培养密度,以及在不同的海水盐度和不同浓度的营养盐中培养,抗生素处理组圆盘体的生长均比对照组快。通过比较抗生素处理组与对照组分离的菌株后发现,抗生素处理组有两株菌落形态和菌株形态与对照组显著不同的特有菌株。研究表明,在坛紫菜叶状体的生长过程中,某些对叶状体生长起阻碍作用的细菌如果大量繁殖,会抑制对叶状体生长有益的细菌繁殖,当用抗生素抑制了阻碍生长的细菌,就会使益生菌成为优势菌,促进叶状体的生长,益生菌对上述抗生素的处理不太敏感,但由于培养条件的改变,抗生素对阻碍生长的细菌的抑制作用会减弱,使得它们大量繁殖,从而抑制叶状体的生长。     

盐度对中华绒螯蟹繁殖特性及胚胎质量的影响

为探究盐度对中华绒螯蟹亲体繁殖特性及所产胚胎质量的影响,开展了不同盐度(3、6、9、12、15、18、21)下亲体的生殖产卵实验,分析了各盐度下亲体的产卵量、生殖指数和生殖力等繁殖特性及所产胚胎的卵径、重量、生化成分和脂肪酸组成。结果显示：(1)中华绒螯蟹产卵的最低盐度为6,在盐度6～21的范围内,中华绒螯蟹亲本的产卵量、生殖指数和生殖力均表现为先升高后下降的趋势,其中盐度18时,亲本的产卵量、生殖指数和生殖力均最高,且与其他各组都有显著差异。(2)盐度6时胚胎直径最大,平均为(391.13±12.27)μm,显著高于其他各组。盐度12时单个胚胎湿重和干重均最高,分别为(50.64±2.80)μg和(14.85±0.31)μg,且与其他各组均有显著差异。(3)随盐度的增加,中华绒螯蟹胚胎的粗蛋白、总脂肪和水分含量都呈现先升高后降低的变化趋势。其中盐度15时,胚胎中粗蛋白、总脂肪和灰分含量均达到最高,平均分别为(20.64%±3.42%)、(8.65%±1.44%)和(1.30%±0.22%)。各盐度下胚胎水分含量无显著差异。胚胎中胆固醇和磷脂含量均随盐度的增加呈现出先上升后下降的变化趋...     

牛磺酸对急性氨中毒的鲫和草鱼抗氧化及炎症相关基因表达影响的比较

为了比较牛磺酸对急性氨中毒的鲫和草鱼缓释作用的差异,实验分别构建了4个处理组,组1实验鱼通过腹腔注射生理盐水,组2注射醋酸铵(鲫7 mmol/g,草鱼9 mmol/g),组3注射醋酸铵和牛磺酸(100μg/g),组4注射牛磺酸。毒性实验持续96 h。结果显示,组2鲫肝脏中SOD、CuZnSOD和CAT基因mRNA表达量显著低于组1和组3;组2和组3鲫肝脏中GPx基因mRNA表达量显著低于组1;组1鲫大脑中SOD、CuZnSOD、CAT和GPx基因mRNA表达量最高;组2草鱼肝脏中SOD、CuZnSOD、CAT和GPx基因mRNA表达量显著高于其他组;组2和组4草鱼大脑中SOD和CuZnSOD基因mRNA表达量显著低于组1和组3;组3草鱼大脑中CAT和GPx基因mRNA表达量最高;此外,组2鲫和草鱼肝脏及大脑中TNF和IL基因mRNA表达量均显著高于其他组。研究表明,鱼类氨中毒会扰乱机体的抗氧化酶系统和免疫应答,引起氧化损伤和炎症反应;草鱼通过提高抗氧化相关基因表达以应对氨中毒;牛磺酸能够有效缓解氨中毒对鲫和草鱼造成的氧化伤害,但牛磺酸并不能降低氨中毒对鲫和草鱼造成的炎症反应。     

Pre-stocking acclimatisation of brown trout Salmo trutta: effects on growth and capture in a fast-flowing river

Abstract  A field experiment was carried out over two consecutive years in a fast-flowing river to evaluate the effects of a 5-day acclimation period on the subsequent growth and capture of stocked juvenile brown trout, Salmo trutta L. Post-stocking growth of both acclimated and non-acclimated fish remained very poor for at least 44 to 50 days. After this slow start, all fish grew significantly but acclimated trout performed 40.1% better than non-acclimated individuals. However, the better growth did not lead to higher capture rates. Capture success post-stocking was low, regardless of acclimation. Flooding, combined with low fitness of the stocked fish in the first weeks was considered the main reason for the unsatisfactory stocking success. It was concluded that in-stream acclimation aids rapid adaptation of stocked trout and thus imparts some growth advantages, although this does not necessarily result in higher yields.     

池塘养殖和大湖养殖对“华海1号”团头鲂鱼肉品质的影响

为探究不同养殖模式下新品种“华海1号”团头鲂的品质差异，实验以不同养殖模式(池塘组及大湖组)的“华海1号”团头鲂为对象，采用色差仪、质构仪对其表观及质地进行测定，采用超高效液相色谱仪或气相色谱-质谱联用仪等对营养特性和风味物质进行测定。结果显示，大湖养殖团头鲂肉质的亮度、白度、弹性、咀嚼性、回复性均显著高于池塘组，且大湖组肌肉水分含量更高，粗脂肪含量更低。池塘组和大湖组鱼肉EAA/TAA及EAA/NEAA比值分别为0.41、0.82以及0.38、0.72，均符合FAO/WHO推荐的理想必需氨基酸构成。池塘组必需氨基酸指数虽高于大湖组，但其必需氨基酸中仅赖氨酸含量显著高于大湖组，而大湖组鱼肉中非必需氨基酸及半必需氨基酸含量分别为池塘组的1.05倍及1.01倍，且大湖组总脂肪酸含量下降21.09%，多不饱和脂肪酸占比提升4.00%,EPA和DHA含量分别为池塘组的14.20倍和7.51倍，故大湖组鱼肉营养更为均衡。池塘组鱼肉谷氨酸及丙氨酸TAV值均大于1，大湖组赖氨酸TAV值大于1，但大湖组鱼肉中鲜味及甜味氨基酸总占比更高，苦味氨基酸总占比更低，且大湖组呈鲜味的AMP及IMP含量为池塘组的...     

南极磷虾粉替代鱼粉对黄颡鱼生长、免疫及肌肉品质的影响

为研究南极磷虾粉替代鱼粉对黄颡鱼生长性能、血清免疫指标及肌肉品质的影响,实验以初始体质量为(10.51±0.13)g的黄颡鱼为研究对象,南极磷虾粉替代基础饲料(30％鱼粉)中0％(KM0,对照组)、2.5％(KM2.5)、5.0％(KM5)、7.5％(KM7.5)和10％(KM10)的鱼粉,共配制5组等氮等脂的饲料,每...     

大菱鲆对饲料精氨酸的需求量及饲料精氨酸水平对大菱鲆生长和代谢的影响

为研究大菱鲆最适饲料精氨酸需求量及饲料精氨酸水平对大菱鲆生长和代谢的影响,选取初始体质量为(43.07±0.10) g的大菱鲆为对象,使用酪蛋白和明胶作为蛋白质来源,鱼油和大豆卵磷脂作为脂质来源,配制5组等氮等脂(51%粗蛋白和12.5%粗脂肪)的精制饲料,通过添加晶体氨基酸混合物,使得饲料中精氨酸含量分别为干物质的1.92%、2.65%、3.40%、4.17%和4.88%(对应饲料号为1、2、3、4、5),以喂食1.92%精氨酸水平饲料的处理组作为对照组,每个处理3个重复,每个重复12尾鱼,养殖周期为10周。结果显示,与对照组相比,3.40%～4.88%饲料精氨酸水平(占饲料蛋白质6.66%～9.52%)显著改善了大菱鲆的生长性能和饲料利用率。基于特定生长率(SGR)的折线回归分析,大菱鲆的最适饲料精氨酸需求量为饲料干物质的3.17%,饲料蛋白质的6.21%。适宜的饲料精氨酸水平显著提高了鱼体蛋白含量和血浆总蛋白水平,同时显著降低了血浆葡萄糖水平。此外,适宜的饲料精氨酸水平显著提高了肝脏脂肪酸合成、脂肪酸β-氧化、糖酵解、三羧酸循环和氧化磷酸化相关基因的表达,而显著降低了肝脏氨基酸降解相关基因的表达。研究表明,3.40%～4.88%饲料精氨酸水平(占饲料蛋白质6.66%～9.52%)可以调节大菱鲆的营养代谢,并促进大菱鲆的生长。     

高温应激下无乳链球菌感染对尼罗罗非鱼血清生化指标和组织病理的影响

为探究高水温对尼罗罗非鱼无乳链球菌病暴发的影响,以体质量为(62.0±3.33)g的尼罗罗非鱼为研究对象,设置生长最适宜组(29°C)和高温应激组(33°C)2个处理水平,暂养7 d后分别进行人工感染实验统计累计死亡率,并于攻毒后0、12、24、48、96和120 h采集血液和组织样本,开展高温应激下无乳链球菌感染对尼罗罗非鱼血清生化指标和组织病理影响的研究。结果显示,水温33°C高温应激组尼罗罗非鱼累计死亡率显著高于29°C组;谷丙转氨酶(ALT)活性在感染96 h之后33°C组的值显著高于29°C组;谷草转氨酶(AST)活性在感染48 h之后33°C组的值显著高于29°C组;钾(K+)和钠(Na+)含量感染120 h时29°C组的值和攻毒前都没有显著性差异,而33°C组分别显著高于和低于攻毒前;肌酐(CREA)含量在感染12 h以后33°C组的值都显著高于29°C组;白蛋白/球蛋白(A/G)的值在120 h时33°C组的值显著低于29°C组;血清碱性磷酸酶(AKP)活性29°C组随时间延长而升高,33°C组则先升高后降低,但33°C组的达峰时间更短;超氧化物歧化酶(SOD)活性的变化趋势都是先升高后降低再升高;组织病理学观察显示高温应激使肝细胞排列紊乱,索状结构不清,脾脏和肾脏轻微充血;感染12 h后脾脏均严重充血,感染24 h后脾脏结构均被破坏,呈淀粉样变性,坏死;感染48 h后肾小球均发生萎缩,肾小管上皮细胞变性、坏死;33°C组鱼的肝脏感染96 h后严重脂肪变性和细胞内玻璃样变性,而29°C组鱼的肝脏在感染120 h后才发生相似的病理变化。研究表明高温应激抑制了鱼体免疫系统,降低了尼罗罗非鱼对无乳链球菌的抵抗力,脾脏对无乳链球菌感染响应最快,高温应激使病原菌感染对肝脏损伤更为迅速,感染后期受损更严重。     

盐度对大菱鲆幼鱼生长和肌肉营养成分的影响

将平均体质量为(7.16±0.07)g的大菱鲆幼鱼分别饲养在不同盐度(12、18、24、30和36)的水体中60 d,以探讨盐度对幼鱼特定生长率、生长激素、成活率、摄食率、饲料效率和肌肉营养成分的影响。结果表明:大菱鲆幼鱼在盐度分别为18、24、30和36的水体中均生长良好,成活率为100%,特定生长率分别为1.97、1.87、1.87和2.00 %/d;在盐度为12的水体中,幼鱼的成活率和特定生长率均显著低于盐度30组(对照组)(P<0.05),分别为80.77%和1.45 %/d。生长激素为0.41～1.66 ng/mL时,盐度18和36组均显著高于盐度30组(P<0.05),而盐度12组显著低于盐度30组(P<0.05)。饲料效率为1.12%～1.38%时,盐度18、24和36组均显著高于盐度30组(P<0.05),而盐度12组显著低于盐度30组(P<0.05)。摄食率为1.19～1.28 %/d时,盐度12和24组均显著低于盐度30组(P<0.05),其它盐度组之间均无显著差异(P>0.05)。幼鱼特定生长率随血清生长激素和饲料效率的升高而增大,与盐度的相关性不显著。幼鱼肌肉中的粗蛋白质含量随水体盐度的升高而降低,除盐度12和18组之间无显著性差异外(P>0.05),其余各盐度组之间均存在显著性差异(P<0.05);盐度12组幼鱼肌肉中的粗脂肪低于其它盐度组,灰分显著高于其它盐度组(P<0.05),其余各盐度组之间粗脂肪和灰分均无显著性差异(P>0.05);各盐度组之间幼鱼肌肉中的水分均无显著性差异(P>0.05)。综上所述,适当降低盐度可改善大菱鲆幼鱼生长和肌肉品质,其适宜盐度为18。     

The effects of the decomposition of mangrove leaf litter on water quality, growth and survival of black tiger shrimp (Penaeus monodon Fabricius, 1798)

An experiment was conducted for 8 weeks at the Cantho University, Vietnam, to determine the acceptable level of mangrove leaf litter load and its effect on water quality, growth and survival rate of tiger shrimp (Penaeus monodon). Shrimps were cultured in plastic tanks containing 50 L of brackish water (salinity of 15‰). Leaf litter of Rhizophora apiculata, Avicennia officinalis, Excoecaria agallocha and Acacia auriculiformis were loaded to tanks at rates of 0.0 (control), 0.125, 0.25, 0.5, 1.0 and 2.0 g L^− 1 with and without aeration. Tiger shrimp post-larvae (PL; 0.05 ± 0.01 g) obtained from the shrimp hatchery of Cantho University were stocked at a density of 20 PL per tank and fed with pelleted feed containing 38% protein at a rate of 10% body weight (BW) day^− 1.

The high leaf-loading rates significantly reduced dissolved oxygen (DO) and survival rates of shrimp in the non-aerated treatments, and all shrimps died after 2 days in the treatments with loading rates above 0.5 g L^− 1. Leaf litter loads significantly increased tannin content, chemical oxygen demand (COD), H₂S and pH in the aerated treatments. Stepwise regression analysis showed COD, tannin and H₂S concentrations had negative effects on shrimp growth in the aerated treatments. Tannin concentration was found to be highest in the treatments with Excoecaria (32 mg L^− 1) and Avicennia (24 mg L^− 1) leaves. However, there were no significant differences in growth and survival rates of shrimp among the aerobic treatments loaded with different leaf types. The results of this study showed that moderate load of mangrove leaves could play an important role in promoting shrimp growth and survival in aerobic condition. Mangrove leaves at a loading rate of 1 g L^− 1 positively influenced both the survival and growth rate of shrimps.