Essential fatty acid requirements of cultured marine fish larvae

Feeding of marine fish larvae is, in most cases, limited to the administration of two species of live prey. This reduction in the range of food available for the cultured larvae may occasionally lead to nutritional imbalances or deficiencies. A large amount of research has been recently devoted to the study of the essential fatty acid requirements of marine fish larvae. Studies on the biochemical composition of developing eggs and larvae, as well as the comparison of the patterns of loss and conservation during starvation, pointed out the importance of n-3 HUFA and arachidonic acid as essential fatty acids for larvae of marine fish. The biochemical composition of marine fish larvae, in terms of lipid content and fatty acid composition of total and polar lipids, is modified by dietary levels of essential fatty acids. Larval growth, survival and activity have also been reported to be affected by dietary levels of essential fatty acids. In addition, some pathological signs, such as hydrops or abnormal pigmentation, have been related to essential fatty acid deficiency in these fish. Based on these effects, the essential fatty acid requirements of marine larval fish have been reported to range between 0.3 and 55 g kg^?1 n-3 HUFA on a dry weight basis, suggesting that quantitative requirements of fish larvae may differ from those of juveniles or adults. But quantitative requirements for larvae of the same species reported by various authors are often contradictory. These differences are discussed in relation to the dietary lipid content, ratio 20:5n-3/22:6n-3 and culture conditions used.     

Characterization and distribution of undersulfated chondroitin sulfate and chondroitin in leptocephalous larvae of elopomorph fishes

Undersulfated chondroitin sulfate (i.e., chondroitin sulfate with sulfate: hexosamine molar ratios ranging from 0.06–0.17) has been identified as a principal glycosaminoglycan (GAG) in whole-body extracts of leptocephalous larvae of four species of marine teleost fishes, representing two orders and three families. These include the eels (Anguilliformes)Ariosoma balearicum (Congridae),Rhechias dubia (Congridae) and Ophichthus sp. (Ophichthidae) and the ladyfish (Elopiformes: Elopidae: Elops saurus). A second GAG found in relatively large amounts in A. balearicum has been identified as chondroitin. Chondroitin and undersulfated chondroitin sulfate formed distinctive precipitates during extraction and were easily separated. Undersulfated chondroitin sulfate also was extracted and purified from early metamorphosing bonefish (Albuliformes: Albulidae: Albula sp.) leptocephali, where it is a minor GAG component, and was shown to be similar in composition to the compounds obtained from eels and ladyfish.     

危害莼菜的几种摇蚊幼虫

莼菜为长江中下游地区民众喜爱的菜肴,具有较高的营养价值。本文重点叙述主要危害莼菜的三带环足摇蚊Cricotopus trifasciatur(Panzer)幼虫,记述了这种幼虫的特征和生长环境以及这类幼虫危害莼菜的过程和结果。同时亦简要介绍了另外两种对莼菜危害较轻的摇蚊幼虫,描述了它们的形态和分布。最后作者对防治方法提出了探讨性意见。     

Variation in the distribution of yellowfin sole Limanda aspera larvae in warm and cold years in the eastern Bering Sea

Multiyear periods of relatively cold temperatures (2007–2013) and warm temperatures (2001–2005 and 2014–2018) altered the eastern Bering Sea ecosystem, affecting ocean currents and wind patterns, plankton community, and spatial distribution of fishes. Yellowfin sole Limanda aspera larvae were collected from the inner domain (≤50 m depth) of the eastern Bering Sea among four warm years (2002, 2004, 2005, 2016), an average year (2006), and three cold years (2007, 2010, 2012). Spatial distribution and density of larvae among those years was analyzed using generalized additive models that included timing of sea-ice retreat, areal coverage of water ≤0°C, and water temperature as covariates. Analyses indicated a combination of temperature effects on the location and timing of spawning, and on egg and larval survival, may explain the variation in larval density and distribution among years. During warm years, higher density and wider spatial distribution of larvae may be due to earlier spawning, an expansion of the spawning area, and higher egg and larvae survival due to favorable temperatures. Larval distribution contracted shoreward, and density was lower during cold conditions and was likely due to fish spawning closer to shore to remain in preferred temperatures, later spawning, and increased mortality. Predicted drift trajectories from spawning areas showed that larvae would reach nursery grounds in most years. Years when the drift period was longer than the pelagic phase of the larvae occurred during both warm and cold conditions indicating that settlement outside of nursery areas could happen during either temperature condition.     

两种斑皮蠹幼虫头部化学感觉器的形态比较

用扫描电镜观察谷斑皮蠢 Trogoderma granarium 和花斑皮蠢 T.variabile 幼虫头部化学感觉器。在触角端部,谷斑皮蠢幼虫有2个栓状感觉器,花斑皮蠢幼虫有一个栓状感觉器;在下颚须端部,两种幼虫均有10个栓状感觉器;在下唇须端部,谷斑皮蠢幼虫有10个栓状感觉器,花斑皮幼虫有6个栓锥状感觉器和4个栓状感觉器。作者认为昆虫幼虫头部化学感觉器的形态特征可用于幼虫的分类和鉴定。     

家蝇幼虫溶菌酶II基因的克隆、表达及抑菌活性研究

以本实验室构建的鸡致病性大肠杆菌诱导家蝇幼虫抑制性消减杂交文库(SSH)为基础,对家蝇幼虫溶菌酶II基因(MdL-II)进行克隆,得到全长为532 bp的cDNA片段,其开放阅读框(ORF)与GenBank中登录号为HQ897688.1的MdL-II基因全序列同源性为95%。将MdL-II ORF序列插入到pET-32a(+)表达载体中成功构建重组质粒,其表达产物经十二烷基磺酸钠-聚丙烯酰胺凝胶电泳(SDS-PAGE)分析,结果显示约在34 ku处出现表达条带且与目的蛋白大小相符。当诱导温度为37℃,IPTG浓度为0.6 mmol/L时可获得大量可溶性Trx-MdL-II融合蛋白,纯化融合蛋白并进一步检测该蛋白的抑菌活性,结果表明融合蛋白对大肠杆菌和链球菌均有抑菌作用,且对大肠杆菌的抑菌作用相对较强。     

Diet overlap between young-of-the-year perch, Perca fluviatilis L., and burbot, Lota lota (L.), during early life-history stages

Abstract –  The diet overlap between young-of-the-year (YOY) perch and burbot in the pelagic zone of Lake Constance during spring and summer was investigated in relation to gape size limitation. Because perch were larger and grew faster than burbot during their early life history, perch overcame gape size limitation for various zooplankton taxa earlier than burbot. The interspecific diet overlap between perch and burbot decreased continuously until June, but increased slightly, when burbot became able to feed on large daphnids by the beginning of July. All zooplankton taxa could be found within perch stomachs by the middle of June, when perch overcame gape size limitation for large cladocerans. However, there was an increasing tendency for individual diet specialisation of perch, as the similarity between individual perch stomach contents decreased. In contrast, the similarity between individual burbot stomach contents remained at almost 50% until the end of August, indicating that all burbot rely on cyclopoid copepods during their entire pelagic life-history stage. Because by July YOY perch are more abundant by one order of magnitude in the pelagic zone than burbot, YOY perch may be more affected by intraspecific competition than by interspecific competition with burbot. Burbot, on the other hand, may evade strong competition with YOY perch by performing diel vertical migrations, thus being restricted to feed on migrating zooplankton prey.     

Testicular development and serum profiles of steroid hormone levels in captive male Pacific herring Clupea pallasii during their first maturational cycle

The present study investigates the relationship between testicular development and serum steroid hormone levels in captive Pacific herring Clupea pallasii during the first reproductive cycle. The maturity of the testis was divided into five periods based on histological observation. These are early spermatogenic stage (April to July), mid-spermatogenic stage (August to November), late spermatogenic stage (December to March), functional maturation stage (early April) and spent stage (late April). The pattern of seasonal change in gonadosomatic index (GSI) clearly reflected testicular maturity. 11-Ketotestosterone (11-KT) levels increased from October to a peak level (6.58 ± 1.87 ng/mL) in January, and were maintained at this level until March. In contrast, testosterone levels were consistently low, less than 1 ng/mL, at all times. These results suggest that 11-KT is the predominant androgen that controls spermatogenesis in this species. 17,20β-Dihydroxy-4-pregnen-3-one (DHP) showed a single sharp peak (3.38 ± 0.35 ng/mL) in early April of the second year, suggesting that milt production is induced by DHP as in some other teleost species.     

三种饲料单独及组合投喂对多鳞白甲鱼仔鱼生长及存活率的影响

本研究旨在探讨商品饲料、黑水虻粉、裂殖壶藻粉单独及其组合投喂对多鳞白甲鱼仔鱼生长及存活率的影响。将1350尾出膜后5 d的健康多鳞白甲鱼仔鱼随机分为3组,每组3个重复,进行两个阶段为期25 d的饲养试验,前10 d为第一阶段,分别单独饲喂3种饲料,后15 d为第二阶段,向黑水虻粉、裂殖壶藻粉组饲料等比补充商品饲料进行饲喂。结果发现,生长方面,商品饲料组在两个阶段均保持最佳;黑水虻组在第一阶段短期内(前5 d)全长及体质量均最大,第二阶段15 d时体质量出现一定程度负增长(-26.93%),而后恢复增长;裂殖壶藻粉组第一阶段生长表现最差,第二阶段出现一定程度负增长(-10.51%),而后恢复,最终生长情况优于黑水虻粉组。成活率方面,整体成活率商品饲料组最高(85.66±4.51)%,裂殖壶藻粉组次之(72.67±11.57)%,黑水虻粉组最低(60.0±16.17)%;分阶段看,第一阶段裂殖壶藻粉组最高(96.44±2.04)%,其次为商品饲料(91.11±3.08)%,黑水虻粉组最低(85.78±2.77)%,第二阶段商品饲料组最高(85.66±4.51)%,裂殖壶藻粉组次之(75.34±10.24)%,黑水虻粉组最低(69.59±16.79)%。研究表明,本试验条件下,商品饲料作为多鳞白甲鱼仔鱼开口饲料,其生长效果最佳,而裂殖壶藻粉在保持较高存活率方面效果较为明显。今后应进一步研究黑水虻粉及裂殖壶藻粉在饵料中的配比及应用方式。