Electrophoretic evidence for extensive hybrid gene introgression into commercial Oreochromis niloticus (L.) stocks in the Philippines*

Abstract. The usefulness of isozyme and protein markers in identifying tilapia species and their hybrids is demonstrated Genetic characterization of Oreochromis niloticus populations from commercial farms, experimental stations, and government hatcheries in Luzon, Visayas and Mindanao in the Philippines indicates well-established introgression with O mossambicus Genetic differentiation of the O niloticus stocks, measured by Nei's genetic distance, was highly correlated with O mossambicus gene content The implications of these results for tilapia genetic improvement are discussed.     

Soybean meal alters autochthonous microbial populations, microvilli morphology and compromises intestinal enterocyte integrity of rainbow trout, Oncorhynchus mykiss (Walbaum)

Rainbow trout were fed either a diet containing fishmeal (FM) as the crude protein source or a diet containing 50% replacement with soybean meal (SBM) for 16 weeks. An enteritis-like effect was observed in the SBM group; villi, enterocytes and microvilli were noticeably damaged compared with the FM group. The posterior intestine microvilli of SBM-fed fish were significantly shorter and the anterior intestine microvilli significantly less dense than the FM-fed fish. Electron microscopy confirmed the presence of autochthonous bacterial populations associated with microvilli of both fish groups. Reduced density of microvilli consequently led to increased exposure of enterocyte tight junctions, which combined with necrotic enterocytes is likely to diminish the protective barrier of the intestinal epithelium. No significant differences in total viable counts of culturable microbial populations were found between the groups in any of the intestinal regions. A total of 1500 isolates were tentatively placed into groups or genera, according to standard methods. Subsequent partial 16S rRNA sequencing revealed species that have not been identified from the rainbow trout intestine previously. Compared with the FM group levels of Psychrobacter spp. and yeast were considerably higher in the SBM group; a reduction of Aeromonas spp. was also observed.     

对虾病毒病的研究现状

主要依据９０年代关于对虾病毒病的资料,就对虾病毒的病原、诊断技术、预防进行综合述评,总结概括了对虾病毒病的研究现状。     

n‐3 and n‐6 fatty acid bioconversion abilities in Eurasian perch (Perca fluviatilis) at two developmental stages

The aim of this work was to study the fatty acid (FA) bioconversion ability in Eurasian perch fed with diets differing in their polyunsaturated fatty acids (PUFA) from n‐3 and n‐6 series content at two development stages: adults in exogenous vitellogenesis, and juveniles during the on‐growing phase. Duplicate groups of adults and juveniles were fed for 12 weeks with four diets: D1 and D2, two diets prepared with fish oil partially or totally as the lipid source, and so containing long‐chain PUFA (LC‐PUFA). Those two diets differed by their n‐3/n‐6 FA dietary ratio (0.2 and 7.0, respectively), D1 being characterized by a high n‐6 LC‐PUFA level, while D2 had a high level of n‐3 LC‐PUFA. D3 and D4 were constituted only with vegetable oils, and were therefore devoid of LC‐PUFA. D3 was characterized by a high level of 18:2 n‐6 (n‐6/n‐3 ratio of 0.3), while D4 was characterized by a high level of 18:3 n‐3 (n‐3/n‐6 ratio of 1.9). Both groups of fish were able to elongate and desaturate the 18:3 n‐3 precursor into eicosapentaenoic acid and docosahexaenoic acid, regarding the FA profile of livers. Furthermore, total elongation/desaturation from [1‐¹⁴C]18:3 n‐3 of LC‐PUFA was higher in fish fed with the high dietary 18:3 n‐3 level compared to the diet rich in n‐3 LC‐PUFA. By opposition, the bioconversion of 18:2 n‐6 into LC‐PUFA was limited, regarding the elongation/desaturation activity of LC‐PUFA from [1‐¹⁴C]18:2 n‐6. In view of the great ability for bioconversion of n‐3 FA, linseed oil is a promising alternative to fish oil in formulating feed for juveniles perch as there were no differences in terms of specific growth rate between the treatments, but adults undergoing maturation should have at least partially LC‐PUFA in their diet, particularly arachidonic acid (ARA) which is important during maturation, as breeders are not able to bioconvert 18:2 n‐6 into ARA.     

Evaluation of Streptocephalus dichotomus nauplii as a larval diet for freshwater prawn Macrobrachium rosenbergii

This study was performed to assess the nutritional value of Streptocephalus dichotomus nauplii and compared with standard larval diet and parthenogenetic strain of Artemia nauplii. The effectiveness of live feed was determined by feeding freshwater prawn Macrobrachium rosenbergii postlarvae. Results on the growth rate, weight gain, survival, fatty acid and amino acid composition show a significant variation between the dietary treatments. Mean larval growth was significantly different ( P  < 0.001) between control diet (13.5 ± 0.5 mm) and live feeds ( Streptocephalus nauplii; 18.4 ± 0.5 mm and Artemia nauplii 18.7 ± 0.2 mm). The weight of larvae-fed Streptocephalus (41.1 ± 1.44 mg) and Artemia nauplii (41.7 ± 0.2 mg) was not significantly different; however, treatment with live feeds was significantly higher than the control (16.3 ± 0.5 mg) ( P  < 0.001). Proximate composition on the fairy shrimp reveals that they are rich in protein, lipid, essential amino acids (EAA) and essential fatty acids (EFA). The polyenoic unsaturated fatty acid (18 : 2 n-6 and 18 : 3 n-3) and highly unsaturated fatty acid (20 : 4 n-3 and 20 : 5 n-3) show a dramatic increase in larval tissue relative to its proportional composition in the live diets. Amino acid composition in the live feeds, Streptocephalus and Artemia nauplii, perfectly reflects on the amino acid proportions in the larvae-fed diets which confirm its utilization.     

Angling for endangered fish: conservation problem or conservation action?

Recreational angling has been implicated in population declines of some marine and freshwater fish, but this activity is rarely considered as a threat or even halted when endangered species are targeted. Indeed, in some cases, anglers are drawn to fish for rare or endangered species. Conservation‐oriented behaviours such as catch‐and‐release are often practiced voluntarily due to the ethics of anglers, yet even in these cases, some fishing mortality occurs. Nonetheless, there are many indirect conservation benefits associated with recreational angling. Here, we present a series of case‐studies and consider whether catch‐and‐release angling for endangered fish is a conservation problem or a conservation action. If recreational angling activities contribute to population‐level consequences that are contrary to recovery strategies, then angling for endangered species would seem to be a poor option. However, as revealed by several case‐studies, there is much evidence that anglers are vocal and effective proponents of fish and habitat conservation, and for endangered species, they are often the only voice when other stakeholders are not engaged. Anglers may contribute directly to conservation actions via user fees (e.g. licences), philanthropic donations or by volunteering in research, education and restoration activities. However, it is important to quantify post‐release mortality as well as understand the full suite of factors influencing a given population or species to know the potential risks. A risk assessment approach outlined in the paper may be used by managers to determine when the benefits of angling for endangered species outweigh the risks.     

两种盐度下凡纳滨对虾饲料中的最适动植物蛋白比

试验研究了不同盐度下（3和22）,以鱼粉和大豆浓缩蛋白为蛋白源,配制6种不同动植物蛋白比的饲料对凡纳滨对虾生长、成活和肝胰腺可溶性蛋白质含量的影响,饲养试验为期40 d。结果显示：（1）饲料动植物蛋白比可显著影响凡纳滨对虾增重率、成活率、肝体指数、肥满度和肝胰腺中可溶性蛋白质含量。增重率随饲料动植物蛋白比升高而升高,但当饲料中动植物蛋白比升至29∶8时,增重率不再明显升高,其它指标均先随饲料动植物蛋白比升高至一定程度,而后则稍有下降;（2）盐度22组对虾的增重率、成活率和肥满度显著高于盐度3组对虾,肝体指数却显著低于盐度3组,不同的盐度对凡纳滨对虾肝胰腺可溶性蛋白含量的影响不显著;（3）双因素方差分析结果显示,盐度和饲料动植物蛋白比对凡纳滨对虾增重率、成活率和肝体指数存在显著交互作用,最大值分别出现在盐度22下全动物蛋白饲料组、盐度22下全动物蛋白和动植物蛋白为29∶8的饲料组、盐度3下饲料动植物蛋白比为14∶23的饲料组中;（4）Broken-Line分析表明,3‰盐度下凡纳滨对虾最适饲料蛋白比为29.12∶7.79~30.29∶6.71,盐度22时为26.05∶10.95~29.03∶7.44。结果提示,饲料中氨基酸的组成和含量会随配方中动植物蛋白配比而改变,且不同盐度下凡纳滨对虾对饲料中动植物蛋白比的要求有所不同,但配饵中适当的动植物蛋白比可以满足虾对各种氨基酸的适宜需求。因此,在养殖过程中,需结合实际的养殖环境和饲料蛋白源种类,来设计适宜的实用饲料配方,这样才能达到降低生产成本,提高经济效益的目的。     

二氯异氰尿酸钠、溴氯海因、敌杀死对鲶鱼的急性毒性试验

用生物毒性试验方法进行二氯异氰尿酸钠、溴氯海因、敌杀死对鲶鱼 (9～ 1 1cm )的急性毒性试验 ,结果表明三种药物的安全浓度分别为 0 1 8mg/L、 0 56mg/L、 0 0 0 4mg/L。     

皱纹盘鲍幼鲍溃烂病病原菌的研究

从患有溃烂病的皱纹盘鲍幼鲍体上，分离到一种致病性细菌。经人工感染试验，证实该菌为皱纹盘鲍幼鲍溃烂病的病原菌。显微镜观察该细菌为革兰氏阴性，极生１～３根鞭毛，能运动的杆菌，大小为０．７～０．８×２．３～２．８ｕｍ。经细菌分类试验鉴定，该菌生长最适温度为２０～３０℃，最适ｐＨ值５．５～８．５。该菌在培养基Ｂ上产生蓝色的荧光素。能利用葡萄糖产酸不产气，果糖、Ｄ－半乳糖、甘露糖、木糖、阿拉伯糖、海藻糖发酵反应阳性，不能发酵乳糖、麦芽糖、鼠李糖、蔗糖，可分解山梨醇、肌醇、肌苷。过氧化氢酶、脲酶、氧化酶、及明胶液化反应阳性；能利用柠檬酸，不还原亚硝酸盐，不产生吲哚和硫化氢，ＭＲ和Ｖ．Ｐ．试验阴性。初步鉴定该病原菌为荧光假单胞杆菌。还进行了病原菌药敏试验，该菌对卡那霉素、呋喃唑酮、恶喹酸敏感，这些药物可作为防治该病的首选药。