In situ study on effect of food competition on diet shifts and growth of silver and bighead carps in large biomanipulation fish pens in Meiliang Bay, Lake Taihu

Silver and bighead carps were cultured in large fish pens to reduce the risks of cyanobacterial bloom outbreaks in Meiliang Bay, Lake Tauhu in 2004 and 2005. Diet compositions and growth rates of the carps were studied from April to November each year. Both carp species fed mainly on zooplankton (> 50% in diet) in 2004 when competition was low, but selected more phytoplankton in 2005 when competition was high. Silver carp had a broader diet breadth than did bighead carp. Higher densities and fewer food resources increased diet breadths but decreased the diet overlap in both types of carps. It can be predicted that silver and bighead carps would be released from diet competition and shift to feed mainly on zooplankton at low densities, decreasing the efficiency of controlling cyanobacterial blooms. Conclusively, when silver and bighead carps are used to control cyanobacterial blooms, a sufficiently high stocking density is very important for a successful practice.

摄动有限差分方法研究进展

摄动有限差分(PFD)方法,既离散微商项也离散非微商项(包括微商系数)，在微商用直接差分近似的前提下提高差分格式的精度和分辨率。PFD方法包括局部线化微分方程的摄动精确数 值解(PENS)方法和摄动数值解(PNS)方法以及考虑非线性近似的摄动高精度差分(PHD)方法。论述了这些方法的基本思想、具体技巧、若干方程(对流扩散方程、对流扩散反应方程、双 曲方程、抛物方程和KdV方程)的PENS、PNS和PHD格式，它们的性质及数值实验。并与有关的数值方法作了必要的比较。最后提出值得进一步研究的一些课题。

摄动有限差分(PFD)方法的数值计算

利用数值摄动的思想发展了对流扩散(CD)方程的摄动有限差分(PFD)格式，局部线化可获得摄动准确解(PENS)格式。把格式中的指数函数按网格雷诺数的幂级数展开，能够给出PENS格式的各阶近似，即各阶PFD格式。文中构造了一维CD方程的PENS及二阶PFD格式以及二维CD方程的二阶PFD格式，并利用二阶精度的PFD格式计算了一维CD方程、方腔流动和前、后台阶绕流流动等算例。计算给出了准确度较高的数值结果。

In situ study on the control of toxic Microcystis blooms using phytoplanktivorous fish in the subtropical Lake Taihu of China: A large fish pen experiment

Three large fish pens (0.36 km(2) of each) stocked with silver and bighead carp were set up in Meiliang Bay for controlling toxic Microcystis blooms. The responses of plankton communities and food consumption of silver and bighead carp were studied. Crustacean zooplankton were significantly suppressed in the fish pens. Total phytoplankton biomass, Microcystis biomass and microcystin concentration were lower in the fish pens than in the surrounding lake water, but the difference was not statistically significant. The present stocking density of silver plus bighead carp (about 40 g/m(3) in July) was likely too low to achieve an adequate control of Microcystis. Silver carp fed mainly on phytoplankton but bighead carp mainly on zooplankton: mean zooplankton contribution in the gut was 31.5% for silver carp and 64.7% for bighead carp. Compared with previous studies, both carp species preyed upon more zooplankton because of the abundant food resource. Daily rations of silver and bighead carp were estimated by Egger's model in the main growing season. Filtration rate was calculated from the daily ration and the density of plankton in the lake. During May-October, filtration rates of silver and bighead carp for phytoplankton were 0.22-1.53 L g(-1) h(-1) and 0.02-0.68 L g(-1) h(-1), respectively, and filtration rates for zooplankton were 0.24-0.44 L g(-1) h(-1) and 0.08-1.41 L g(-1) h(-1), respectively. Silver carp had a stronger ability of eliminating phytoplankton than bighead carp. To achieve a successful bioniampulation with a minimum effect of ichthyoeutrophication, the stocking proportion of bighead carp should be controlled in the future practice. (c) 2007 Elsevier B.V All rights reserved.

Seeding nets with neutral spores of the red alga Porphyra umbilicalis (L.) Kutzing for use in integrated multi-trophic aquaculture (IMTA)

Nets in traditional Porphyra mariculture are seeded with conchospores derived from the conchocelis phase, and spend a nursery period in culture tanks or calm coastal waters until they reach several centimeters in length. Some species of Porphyra can regenerate the foliose phase directly through asexual reproduction, which suggests that the time, infrastructure, and costs associated with conchocelis culture might be avoided by seeding nets with asexual spores. Here, we present work from a short-term mariculture study using nets seeded with asexual spores (neutral spores) of a native Maine species of Porphyra. Porphyra umbilicalis (L.) Kutzing was selected for this proof of concept research because of its reproductive biology, abundance across seasons in Maine, and evidence of its promise as a mariculture crop. We studied the maturation, release, and germination of the neutral spores to develop an appropriate seeding protocol for nets, followed by development of a nursery raceway to provide an easily manipulated environment for the seeded nets. Neutral spores were produced throughout the year on the central Maine coast,however, there was a temporal variability in the number and survival of released neutral spores, depending upon thallus position in the intertidal zone. Small thalli were strictly vegetative, but most thalli reproduced by neutral spores- sexual reproduction was absent. Neutral spores germinated quickly at 10 and 15 'C, but germination was delayed at 5 degrees C. Unlike some algal zygotes and spores, neutral spores of R umbilicalis required light to germinate; however, irradiances of 25 and 100 mu mol photons M-2 S-1 were equally sufficient for germination. Rafts of seeded nets were deployed in Cobscook Bay, Maine, at two distances from salmon aquaculture pens and at a control site on a nearby, fallow aquaculture site (no salmon). There was no difference in nitrogen content of harvested thalli; however, both the density and the surface area of harvested thalli were different among the sites. The possible causes of these differences are discussed in the context of potential use of P umbilicalis in IMTA. (C) 2007 Elsevier B.V. All rights reserved.