Seasonal changes in otolith and somatic growth in age-0 Pacific saury <Emphasis Type="Italic">Cololabis saira</Emphasis>

We evaluated the seasonal changes in otolith and somatic growth of age-0 Pacific saury Cololabis saira in 223 fish collected between June and November 2002. We calculated the age in days of each individual by measuring otolith growth increments under a scanning electron microscope. The age was correlated with body length and otolith radius. We also observed seasonal changes in the rate of increase in body length and otolith radius and in the pattern of otolith growth. Until August, both body length and otolith radius increased with age. Thereafter, the otolith radius continued to increase, whereas the rate of somatic growth decreased. As a result, the ratio of otolith radius to body length increased. After August, the percentage of otoliths with unreadable increments on their edge increased due to the formation of hyaline zones. Otoliths grew both radially and in thickness until July, but gradually stopped growing in thickness after August. Beginning in October, more than 80% of otoliths only grew radially. After August, the otolith not only continued growing but the morphological growth pattern also changed.     

Effects of replacing fish oil with canola oil on the growth performance,fatty acid composition and metabolic enzyme activity of juvenile yellowtail Seriola quinqueradiata (Temminck & Schlegel, 1845)

In this study, fish oil (FO) was replaced with canola oil (CO) in juvenile yellowtail diets to establish the optimal replacement levels that ensure adequate feed quality for aquaculture. Juvenile yellowtails (initial body weight: 104.7 g) were fed one of four diets for 10 weeks: 100% FO (FO group) or FO replacement with 25%, 50% or 100% CO (CO25, CO50 and CO100 groups respectively). Body weight, specific growth rate and feed efficiency were significantly affected by the replacement of FO with CO. The final body weight of the CO100 group was significantly lower than that of the FO (control) and CO50 groups. Furthermore, the CO50 group showed significantly higher feed efficiency than the FO group during the first 4 weeks (long photoperiod and high water temperature conditions). Increasing dietary CO increased serum glucose and triglyceride concentrations in a dose‐dependent manner. Regarding the proximate composition of fillet and liver, only crude protein in fillet was affected by the replacement of FO with CO. Fatty acid compositions of fillet and liver were correlated to the amount of CO in each diet. The activities of the metabolic enzymes phosphofructokinase and alanine aminotransferase were lowest in the CO25 and CO50 groups respectively. Thus, FO replacement with CO affected growth performance, serum components, fatty acid composition and the activity of metabolic enzymes. Overall, results obtained in the present study suggest that partial replacement (50%) of FO with CO is effective and might increase juvenile yellowtail growth under long photoperiod and/or high water temperature conditions.     

3个群体鳙鱼mtDNA D-loop区段的限制性片段长度多态性分析

鳙鱼（Aristichthys nobilis）采自江西瑞昌、湖南氐沙的天然群体以及天津宁河的人工繁殖群体共127尾，对其线粒体DNA的D-loop区段进行PCR扩增，使用12种核酸内切限制酶酶切。酶切结果显示，在12种内切酶中，8种有酶切位点，2种个体间有变异，为AfaⅠ和HinfⅠ，共得到7种单倍型。依据单倍型频率的组成情况，计算出瑞昌与长沙、宁河群体间的Rogers遗传距离分别为0．7283和0．5007，长沙和宁河群体间的Rogers遗传距离为0．8135。Afa Ⅰ的酶切类型C和HinfⅠ的酶切类型B组成的单倍型，在长沙群体中占87．5％，而在瑞昌和宁河群体中均为零。由此可以认为鳙鱼瑞昌群体和长沙群体可能是两个隔离的独立群体。     

在日本北海道Tokachi district, 马铃薯晚疫病菌占主导地位的基因型的变化及不同基因型在水平抗病品种‘Matilda''上产生不同病斑的研究

在Memuro城镇，位于日本北海道Tokachi地区中部，主要种植田间抗病品种Matida。1998年马铃薯晚疫病在此品种上发生较前几年早。为了了解Matilda品种抗性降低的原因，对1996－1999年Tokachi地区的晚疫病菌基因型的时间变化进行了研究及不同基因型间病菌产生病斑能力进行了比较。在1997年以前基因型JP－1在Tokachi地区占主导地位。在1997年基因型A首次在Tokachi地区被发现并且局限在Tokachi北部。在1998和1999年基因型A遍及整个Tokachi地区，1999年其比例上升至72％。用孢子囊悬浮液接种检测不同基因型病菌对Matilda品种的致病力结果发现，基因型A比基因型JP－1和基因型B产生更大的病斑。然而通过液滴接种所有3个基因型都可产生扩展的病斑。结果表明，Matilda减少的田间抗性是由于基因型A传播到Memuro城镇的Matilda品种上所致。