Rearing of African catfish (Clarias gariepinus) and vundu catfish (Heterobranchus longifilis) in traditional fish ponds (whedos): Effect of stocking density on growth, production and body composition

African catfish (Clarias gariepinus) (initial body weight: 34.8 ± 4.8 g) and vundu catfish (Heterobranchus longifilis) (initial body weight: 39.1 ± 8.2 g) fingerlings were stocked at densities of 4, 6 or 8 fish m^− 3 in traditional fish ponds (whedos) constructed in the floodplain of the Oueme River (South Benin, West Africa), for 70 days from March to June 2005. Fish were fed twice a day with 34% crude protein feed formulated with locally available ingredients. The effects of stocking density were evaluated in growth responses, gross production and body composition. Water quality variables were similar (p > 0.05) in all compartments. Temperature and pH were at the optimum level for fish. Dissolved oxygen ranged from 0.9 to 1.2 mg l^− 1 during the experiment and secchi disc transparency was low (< 14 cm). In both species, growth responses increased with the increasing density, significantly in African catfish stocked at density of 8 fish m^− 3 compared to the other densities (4 and 6 fish m^− 3) but not significantly in vundu catfish. Production data ranged from 3.1 ± 0.5 to 22.8 ± 4.5 t ha^− 1 year^− 1 in African catfish and from 6.1 ± 1.2 to 15.1 ± 3.1 t ha^− 1 year^− 1 in vundu catfish. Production increased with increasing stocking densities but only significantly (p < 0.05) between the density of 8 fish m^− 3 and the other densities. In both species, carcass fat increased with increasing density (p < 0.05) while carcass protein and moisture decreased (p > 0.05). These results are important because they indicate that, as far as growth rate and production are concerned, African catfish is more profitable than vundu catfish for culture at high density in whedo.     

Stimulating effects of pond water on digestive enzyme activity in the Pacific white shrimp, Litopenaeus vannamei (Boone)

Crude enzyme extracts were obtained from the digestive glands of Pacific white shrimp, Litopenaeus vannamei (Boone), reared in oligotrophic well water and eutrophic shrimp pond water to compare digestive enzyme activity between the two groups. Specific activities of serine protease, collagenase, amylase, cellulase, lipase and acid phosphatase were significantly higher (P < 0.01) in pond water‐reared shrimp (PW shrimp) than in well water reared‐shrimp (WW shrimp). For most enzymes assayed, specific activity was more than two times higher in PW shrimp, and cellulase activity was over six times higher. In contrast, chitinase activity was significantly higher (P < 0.001) in WW shrimp. Higher specific activity of most digestive enzymes in PW shrimp was probably due to natural productivity in the pond water that served as a source of organic substrates, and this increased activity may contribute to the growth‐enhancing effect of shrimp pond water.     

Comparison of food selection and growth performance of koi carp, Cyprinus carpio L., and goldfish, Carassius auratus (L.) in mono- and polyculture rearing in tropical ponds

To compare the effect of polyculture against conventional monoculture on ornamental carp production, investigations on food selection and growth performance of koi carp (K), Cyprinus carpio L. and goldfish (G), Carassius auratus (L.) were conducted in a 11‐week rearing experiment in two monoculture (100% K and 100% G) and five polyculture (90% K–10% G, 70% K–30% G, 50% K–50% G, 30% K–70% G and 10% K–90% G) conditions in tropical ponds. There were three replicates for each treatment. Environmental conditions and food availability were similar in all the treatments. Ivlev's electivity index showed that both fish species avoided phytoplankton and preferred cladocerans to other zooplankton groups (copepods and rotifers) in monotypic conditions. However, in the polyculture treatments, the positive electivity of goldfish towards cladocerans reduced significantly (P<0.05), while the percentage of copepods, rotifers and phytoplankton in the gut content increased. No significant differences in weight gain, specific growth rate and deformities were recorded at harvest for koi carp between the different treatments (P>0.05). Even the survival rate of koi carp recorded above 90% in all the treatments. However, the goldfish recorded significantly better weight gain, specific growth rate and survival in monoculture (100% G), compared with the polyculture treatments (P<0.05). Goldfish deformities were lowest (P<0.05) in the monoculture treatment (2.42%). The number of marketable fish above a set size limit of 4 g total weight was significantly higher in the two monoculture treatments, compared with the five polyculture treatments (P<0.05). Keeping in view of the dietary similarities of koi carp and goldfish, and the aggressive nature of koi carp in polyculture, it is suggested to refrain from polyculture of goldfish and koi carp until further documentations relating to optimum stocking density and management of polyculture of ornamental carps are available.     

盐碱池塘浮游动物的种类组成和生物量

１９９７年４月５日至１９９８年９月１日对山东高青盐碱池塘浮游动物的种类组成和季节变动进行了研究，结果表明，高青盐碱池塘含盐量变动于１.36-20g.G^-1，总碱度变动于２.4-72.mmol.L^-1,pH值８－９浮游动物主要是淡水盐种或喜盐种，一些是典型的盐水种，浮游动物优势种有团焰毛虫，双环栉毛虫，锥瓶口虫，瓜形膜袋虫，旋回侠盗虫和绿色前管虫（原生动物），褶皱臂尾轮虫，暗小异尾轮虫，萼花臂尾轮虫，角突臂尾轮虫，壶状臂尾轮虫，卜氏晶囊轮虫，简单前翼轮虫，角三肢轮虫和针族多肢轮虫（轮虫）微型裸腹和长肢秀体（枝角类），细巧华哲水蚤，近邻剑水蚤和台液温剑水蚤，（桡足类），无鱼对照池和新挖池塘的浮游动物生物量均较一般养鱼池塘的高。     

施肥对多盐水池塘浮游植物演替的影响

选择辽宁盘锦光合水产有限公司养殖基地为试验场所,于2002年春季4~5月进行试验。选择5个具有代表性的土池作为试验池,同时另选一土池作为对照池。研究相同N/P比值下不同施肥量对室外土池多盐水体的水化学和浮游植物群落、叶绿素a含量和初级生产力的影响,以及浮游动物对浮游植物的下行效应。共检出浮游生物42种。其中,浮游植物33种,浮游动物9种。浮游植物生物量高达288.2 mg.L-1,优势种为蛋白核小球藻(Chlorella pyrenoidesa)。叶绿素a含量为5.89~325.44μg.L-1。各池在第2次施肥后5~6天,叶绿素a含量达到高值,之后开始下降,8~9 d后恢复到原来水平。初级生产力均值为4.40 g(O2).m-2.d-1,呈低-高-低的变化,极值为1.25 g(O2).m-2.d-1和10.92 g(O2).m-2.d-1。以施N 2.0 mg.L-1、P 0.3 mg.L-1的4#池高峰期维持最长,施肥量的不同对浮游植物的生物量、种类数和种类组成影响较大。在北方地区的多盐水池塘,施氮磷混合肥能有效促进小球藻等藻类增长,达到定向培育的目的。     

虾塘沉积物—水界面的营养盐扩散通量及其在养殖季节的变化

以自行设计的方法测定了对虾养殖环境中沉积物-水界面的营养盐扩散通量。结果表明，营养盐自底质向养殖水体的扩散贯穿于整个对虾养殖季节；该扩散通量的最大值出现在养殖后期的有机质污染区，即投铒区；在污染区，养殖后期的扩散通量大大高于养殖前期，但在非污染区却未见其随养殖季节的明显差异；污染区的扩散通量始终高于非污染区，且随养殖时间的推移，该差异逐渐增大。此外，还比较了新、旧虾塘之间的营养盐扩散通量的差异。初步探讨了底质溶出营养盐对对虾养殖环境的影响。     

Growth patterns of reed (Phragmites australis): the development of reed stands in carp ponds

Reed stands exhibit apparent differences of stem diameter, shoot length, density, and invasiveness. In carp ponds, five characteristic growth patterns can be distinguished. These growth patterns are ontogenetic states of a time-dependent stand development. Invasive reeds with short shoots are found in newly occupied habitats. With continuing establishment of the stand, the shoots in the inner regions become taller and fewer, a growth pattern described as central reed. Later, only a few shoots with thick stems remain. Two alternative pathways of stand development exist: steep shore reed and reed tussocks. By mowing, the directional development of reed stands can be turned into a circulation of growth patterns. The growth patterns have implications for the selection of reed stand areas for conservation purposes.     

锯缘青蟹苗池微生态环境影响因素的初步探讨

通过对锯缘青蟹苗池微生态环境和水质环境的全过程检测,探讨了总菌数、弧菌数及弧菌数/总菌数的消长规律,并对苗种培育阶段涉及的各种外源因素及控制苗池微生态环境的相关手段的有效性作了初步的探讨。结果表明:苗池水体中总菌数在Z1~Z2少量添加水不换水阶段,呈相对稳定状态,进入Z3后总菌数逐渐增加,最高达3.5×106cfu/m l;弧菌数在Z1培育阶段出现2×102cfu/m l激增至5×104cfu/m l的峰值,第二峰值出现在Z5阶段,达6×105cfu/m l;弧菌数/总菌数比值在育苗起始时仅为0.4%,之后迅速升至30%~40%,在Z5阶段,由于弧菌数量急剧上升,达到50%的高比值;NH4-N与COD检测值在育苗过程中变动较大,两者与弧菌数/总菌数比值呈正相关关系。现行育苗方式中对苗池微生态环境产生影响的主要因素是苗种培育密度,海水、饵料的处理方式和抗生素;净化功能菌和蛭弧菌应用于育苗水体具有抑制弧菌繁殖的效果。     

淡水轮虫土池培育技术研究及应用

淡水轮虫是淡水水产动物育苗的优质饵料之一.在总结传统的土池水花鱼苗培育技术的基础上,确立了土池培育淡水轮虫的技术,旨在建立一种高效低耗的淡水轮虫培育技术.结果表明,在水温22 ～ 25℃下利用豆浆对浮游植物和轮虫进行同步培育,投入豆浆后第6天轮虫密度可达高峰期,所培育的轮虫高峰期时密度可达40 ～50个/ml.将培育的轮虫运用于花鱼骨和黄尾密鲴的苗种培育,取得了较好的效果.因此,在土池中进行淡水轮虫培育是可行的.该研究可使传统的淡水鱼苗培育技术更具有科学性和确定性,同时也可为工厂化的水产动物育苗提供优质、适口的生物饵料.     

池塘轮捕轮放高产高效养殖技术

轮捕轮放是提高养鱼产量的重要技术措施.该文介绍了池塘养殖轮捕轮放高产高效养殖技术,包括池塘选择、清塘、配套设备准备、苗种放养、投喂管理、日常管理、病害防治及成鱼收获等,并分析其经济效益.