环境变化对湿地植物根系的影响研究

湿地生态系统具有独特的水文特征和潜育化土壤环境,湿地植物在生长过程中往往表现出独特的环境适应机制。根系作为植物重要的功能器官,是湿地植物群落与周围环境实现物质循环与能量流动的关键纽带,在发挥植物的生态功能及维持生态平衡中具有重要作用。因此,近年来植物根系生理生态研究越来越受到关注。从湿地植物根系在植物生长及湿地生态系统中的作用出发,综合论述环境因子对湿地植物根系的影响及作用机制,着重评述近年来水分条件、土壤盐分、土壤养分、有毒有害物质以及其他因子对湿地植物根系生理生态特征的影响等方面的研究进展和亟待解决的问题,指出湿地植物根系研究将是湿地生态学的重要研究方向。     

水分对湿地生态系统不同植被类型土壤种子库的影响

探讨退化河流湿地生态系统不同植被类型土壤种子库对水分变化的响应机制，了解植物群落的演替规律和退化驱动力，可为退化湿地的保护和生态恢复提供参考。通过水分控制实验（干旱、湿润和积水），在妫水河流域自然湿地生态系统五种不同植被类型的表层土样上开展土壤种子库的萌发实验。结果表明，不同的植被类型对于水分变化的响应模式明显不同。根据其植被特征可分为三类：（1）对于以中旱生植物为主的林下杂类草群落，随着水分的增加其植物种类和数量明显增多。相比较干旱处理，积水处理组植物种类和数量增加的幅度分别为43.8%和249.5%，其中湿生植物明显增多；多样性指数的分析也表明积水处理组其多样性较干旱处理组更高。（2）对于湿生/水生的欧地笋杂类草、芦苇杂类草和芦苇优势种群落，其表现为湿润处理时单位面积物种数和植物密度最低，而干旱和积水处理皆高于湿润处理；多样性水平则呈现随水分增加而降低的趋势。（3）水生的香蒲优势种群落则呈现和林下杂类草群落相反的结果，随水分增加其植物种类明显下降、多样性水平显著降低，但植物数量随水分的增加而呈增加趋势、最大增幅为137.6%。在植物群落组成和相似度方面，本文涉及的五种植被类型皆有其特定的优势植物及结构组成，并和其他植被类型有较高或较低的相似性，并呈现出对于不同水分条件的适应特异性。本研究表明，水分因子在植物群落的发生和演替中起重要作用，是湿地生态系统植被类群演替的重要外在环境因素。     

南水北调北京段大宁水库消落带植被分布特征及多样性

为探究南水北调中线北京段大宁水库消落带植被的分布特征及多样性,2019年6月对水库消落带典型区域(水位高程46～61 m)开展植被调查,并基于重要值、多样性指数和线性拟合统计方法,探讨消落带植被物种的组成、分布特征及生活型。结果显示:(1)研究区内共发现植被19科、37属、45种,以菊科、蓼科、藜科、莎草科、萝藦科和禾本科的种类较多,绝大部分是单属单种植物;出现频率35%以上的植物仅有2种,为灰绿藜(Chenopodium glaucum)和小飞蓬(Conyza canadensis),占植物总数53%的植被出现频率低于5%;(2)聚类分析表明,大宁水库消落带群落可划分为绵毛酸模叶蓼+小飞蓬、芦苇+朝天委陵菜、狗尾草+假还阳参共计3个群落类型,46～50 m、50～55 m、55～61 m水位区段的主要群落分别为绵毛酸模叶蓼+酸模叶蓼、苘麻+艾蒿、狗尾草+葎草+茵陈蒿;(3)消落带植被的平均株高、总盖度及物种多样性指数(丰富度、Shannon-Wiener多样性、Pielou均匀度、Simpson优势度)均表现为随水位梯度升高而增加;(4)按照3级植物生活型的分类方式,将库区消落带植被分为9种生活型,涵盖3种1级生活型(木本、半木本、草本)和6种2级生活型(乔木、灌木、半灌木、一年生草本、多年生草本、水生植物),草本类(89.19%)木本类(5.41%)半木本类(4.05%),说明草本类是消落带植被群落的主要建群种,且一年生草本(58.1%)是主要优势生活型。     

三峡水库运行对汉丰湖湿地植物群落及生境的影响

2012年9月和2013年9月对汉丰湖湿地5个断面的生境和植物群落特征进行了调查,分析了三峡水库运行对汉丰湖湿地植物群落及土壤生境的影响。结果表明,维管束植物共计59种,隶属于26科、20属,其中菊科、禾本科和蓼科种类较多;群落结构以草本植物为主,其中一年生草本植物占54.2%,多年生草本植物占37.3%;植物群落鲜重、高度和盖度平均值(范围)依次为2 031.5(488.3~6 586.1)g/m2、59.2(19.6~102.2)cm、109%(23%~201%);土壤容重、pH、有机质、有效氮、有效磷和有效钾的平均值(范围)分别1.32(1.00~1.60)g/cm3、8.15(6.83~8.59)、10.03(1.40~22.5)g/kg、29.37(6.00~94.38)mg/kg、12.18(1.33~59.37)mg/kg和46.13(2.50~219.00)mg/kg;重要值较大的有狗牙根(22.84±5.78)、牛鞭草(16.38±13.27)、马唐(11.10±12.27)、无芒稗(10.83±3.64)和狗尾草(9.56±5.38);主要环境影响因子为土壤pH值和有效钾含量。     

刺苦草对铜胁迫的耐受性及其恢复能力研究

采用沉水植物对低浓度铜(Cu)污染的水体进行生态修复被认为是一种经济、安全、有效的方法。以鄱阳湖分布较为广泛的刺苦草(Vallisneria spinulosa)为研究对象,设置4个Cu~(2+)添加梯度,对照组(CK)为(0.007±0.012)mg/L,试验组(T1)为(0.400±0.026)mg/L,试验组(T2)为(0.830±0.010)mg/L,试验组(T3)为(1.697±0.055)mg/L;处理1周后彻底换水,使其进行为期2周的恢复生长,探究铜胁迫及解除后刺苦草地上部分、地下部分生长状况的变化及其对Cu~(2+)的富集效果。结果显示,不同浓度Cu~(2+)处理对刺苦草生长产生了严重的胁迫作用,试验组地上部分长度、鲜重和叶绿素含量均显著低于对照组;刺苦草对水体Cu~(2+)的去除率在前4d平均为63%,各处理组水体Cu~(2+)含量均显著下降;刺苦草地上部分Cu~(2+)含量随水中Cu~(2+)含量的增加而显著上升,T3组刺苦草地上部分Cu~(2+)含量达到(3.68±0.32)mg/g,约为T1处理组的6.4倍,地下部分Cu~(2+)含量则没有显著差异;刺苦草Cu~(2+)化学计量内稳性较差,其指数(1/H)约为1.09。在解除Cu~(2+)胁迫后的恢复阶段,T1、T2和T3地上部分Cu~(2+)含量相对于胁迫阶段分别下降了43.04%、92.12%和86.00%,地下部分分别下降了57.91%、42.70%和33.81%,而刺苦草鲜重、叶绿素含量及地下部分Cu~(2+)含量则没有显著差异。研究表明,刺苦草是一个较理想的Cu~(2+)超富集植物,铜胁迫解除后具有一定的恢复能力。     

不同耐盐植物人工湿地净化养殖外排水效果

为了探究不同耐盐植物对海水养殖外排水的去污效果,选取了芦苇(Phragmites australis)与互花米草(Spartina alterniflora)为湿地植物,细沙、蛭石和珊瑚石为基质,构建了2套复合垂直流人工湿地系统。对比分析了2种挺水植物的耐盐性及对海水养殖外排水中氨氮(NH_4-N)、亚硝态氮(NO_2-N)、硝态氮(NO_3-N)、高锰酸钾指数(COD_(Mn))和磷的净化效果。结果显示,芦苇耐盐度最高为20,而互花米草在盐度35以下均能正常生长,芦苇和互花米草湿地系统对NH_4-N的平均去除率分别为(85.48±0.50)%和(95.01±1.18)%,对COD_(Mn)平均去除率分别为(57.74±4.40)%和(72.84±2.64)%。互花米草湿地系统对NH_4-N和COD_(Mn)的平均去除率高于芦苇湿地,分别高9.53%和15.01%,差异性显著(P0.05)。互花米草和芦苇湿地系统对磷酸盐和总磷(TP)的去除率为40.00%~50.00%,差异性不显著(P0.05)。研究表明,在高盐胁迫下,互花米草生长状况和对无机氮(DIN)和COD_(Mn)的去除效果均优于芦苇,2种植物对磷酸盐和TP的去除率差异不明显。     

基于人工湿地的海水池塘循环水养殖系统构建与运行效果研究

为有效调控高密度海水养殖池塘的水环境状况,构建了以人工湿地为核心的"鱼-虾-贝-草"海水池塘循环水养殖系统。通过比较人工湿地连续流与间歇流,以及种植盐角草(Salicornia europaea)和互花米草(Spartina alterniflora)时的净化效率,研究适用于海水池塘养殖系统的人工湿地运行方式及植物种类。通过比较不同养殖模式下池塘水质及养殖对象生长情况,分析人工湿地对养殖池塘水体的调控效果,探讨循环养殖模式对池塘产量的提升效果。结果显示:人工湿地间歇运行时(水力负荷为300 mm/d),其净化效率相比于连续运行有显著提升;盐角草湿地出水中的氮、磷质量浓度显著低于互花米草湿地;虽然排、换水频率有较大差异,循环养殖模式与传统养殖模式下养殖池塘水体氨氮(NH~+_4-N)和亚硝酸盐氮(NO~-_2-N)质量浓度均处于较低水平;采用基于湿地循环水处理的文蛤(Meretrix meretrix)和脊尾白虾(Exopalaemon carinicauda)分池组合混养模式能进一步提高脊尾白虾的单位面积产量,并有效控制养殖废水排放。研究表明:基于人工湿地的海水池塘循环水养殖系统具有较强的环境效益,可为江苏地区海水池塘养殖业的健康发展提供参考。     

“鱼-植物”共生模式下不同植物根际细菌多样性及群落结构研究

为研究“鱼-植物”共生模式下不同植物根系细菌多样性及群落结构与水体中氮、磷含量的关系,分别剪取定植于浮床中的水稻(Oryza sativa)、茨菰(Sagittaria sagittifolia)、水蕹菜(Ipomoea aquatica)、水芹菜(Oenanthe javanica)和苏丹草(Sorghum sudanense)根系,经PBS(p H=7.4)缓冲液漂洗、摇床震荡和离心富集根系土壤等处理后,利用高通量测序技术测定根系细菌群落多样性,同时采集植物种植区水样,分析有关水质指标。结果表明,不同植物在“鱼-植物”共生模式下根系细菌OTU绝大部分为特有类型,彼此间差异极大,水蕹菜的OTU数最多,苏丹草最少;聚类分析结果表明,苏丹草与其他四种植物差异大,而茨菰和水稻聚于一个分支,说明试验植物间的OTU相似性较高。不同种类植物根系细菌群落组成均匀度低,不同种类菌群差异较大;通过水质与根系细菌菌群关联分析发现,Planctomycetaceae等14科、Rhodobacter等14属与水体中的N、P含量呈显著(P<0.05)或极显著相关性(P<0.01)。为提高共生植物对...     

利用人工湿地处理池塘养殖废水效果分析

构建表面流和水平潜流人工湿地系统处理水产养殖池塘排放的废水,以减少水产养殖废水对周围水域环境的污染.结果表明,经湿地净化处理后,养殖废水中总氮、总磷、CODMn、氨氮分别从2.32、0.50、14.88、0.61 mg/L降至0.98、0.18、9.72、0.30 mg/L,叶绿素a从369.6 μg/L降至61.78 μg/L,水质明显得到净化.湿地植物存活时组织氮、磷含量明显高于死亡时,湿地植物死亡时梭鱼草、黄菖蒲、小香蒲的组织氮含量分别仅为存活时的18.8%、26.8%、38.1%.湿地植物死亡时收割可去除氮、磷含量分别为11.68 g/m2和4.81 g/m2,再力花去除氮、磷能力最强.在湿地植物死亡前收割能够提高湿地植物吸收所贡献的净化率.     

生化尾水胁迫下湿地植物生理特性变化

检测植物处理污水厂生化尾水的效果和分析植物生理生长特性,为西北干旱半干旱地区人工湿地污水处理系统合理配置土著湿地植物提供理论依据。在复合垂直流-水平流人工湿地中种植芦苇和香蒲,生活污水处理装置的二级生化出水胁迫,植物移栽成活后和收割之前分别检测植物的生理、生长指标和光合参数。结果表明,COD_(Cr)、NH~+_4-N、TN、TP的去除率,种植植物期间分别为79.32%、85.69%、82.17%、91.76%,植物收割后分别为71.34%、58.45%、60.49%、89.86%;芦苇最高株高达到380 cm,香蒲最高株高达到320 cm;地上部分生物量香蒲最高达到4.15kg,芦苇最高达到7.55 kg;香蒲的净光合速率(P_n)分别增加了6.35%、3.99%、22.39%,芦苇的净光合速率(P_n)则分别增加了42.20%、5.26%、8.96%。2种湿地植物在污水胁迫下表现出一定的防御能力,但是抗污能力存在一定的差异。     

Association between the interannual variation in the oceanic environment and catch rates of bigeye tuna (Thunnus obesus) in the Atlantic Ocean

The environmental processes associated with variability in the catch rates of bigeye tuna in the Atlantic Ocean are largely unexplored. This study used generalized additive models (GAMs) fitted to Taiwanese longline fishery data from 1990 to 2009 and investigated the association between environmental variables and catch rates to identify the processes influencing bigeye tuna distribution in the Atlantic Ocean. The present findings reveal that the year (temporal factor), latitude and longitude (spatial factors), and major regular longline target species of albacore catches are significant for the standardization of bigeye tuna catch rates in the Atlantic Ocean. The standardized catch rates and distribution of bigeye tuna were found to be related to environmental and climatic variation. The model selection processes showed that the selected GAMs explained 70% of the cumulative deviance in the entire Atlantic Ocean. Regarding environmental factors, the depth of the 20 degree isotherm (D20) substantially contributed to the explained deviance; other important factors were sea surface temperature (SST) and sea surface height deviation (SSHD). The potential fishing grounds were observed with SSTs of 22–28°C, a D20 shallower than 150 m and negative SSHDs in the Atlantic Ocean. The higher predicted catch rates were increased in the positive northern tropical Atlantic and negative North Atlantic Oscillation events with a higher SST and shallow D20, suggesting that climatic oscillations affect the population abundance and distribution of bigeye tuna.     

Growth performance,digestive enzyme activity and immune response of Japanese sea bass,Lateolabrax japonicus fed with fructooligosaccharide

In this experiment, a feeding trial was performed to determine the effects of fructooligosaccharide (FOS) on growth performance, digestive enzyme activity and immune response of Japanese sea bass, Lateolabrax japonicus juveniles (initial weight 38.3 ± 0.5 g), and the fish were examined following feeding with six levels of FOS (0, 0.5, 1, 2, 4 and 6 g/kg) for 28 days. Significant enhancement of weight gain (WG) and specific growth rate (SGR) was found in fish fed 1 g/kg FOS incorporated diets (p < .05), while the feed conversion ratio (FCR) in the 1, 2 g/kg FOS groups reduced significantly compared with the control (p < .05). Besides, the crude lipid in the 4, 6 g/kg FOS groups increased significantly compared with the control (p < .05). On the other hand, the erepsin and lipase activities significantly elevated in intestine of fish fed 2 g/kg FOS (p < .05) and the lysozyme activity in serum of fish fed 2 g/kg FOS were significantly higher than that in the control (p < .05). Moreover, the alkaline phosphatase activities in serum of fish fed 0.5, 1, 2 g/kg FOS were significantly higher than in control (p < .05). Regression analysis showed that the relationships between dietary FOS levels and either SGR, FCR, erepsin or lysozyme activities were best expressed by regression equations, and the optimal inclusion levels are 1.37, 1.80, 3.06, 3.11, 1.93 and 1.80 g/kg for SGR, FCR, erepsin, lipase, lysozyme and total superoxide dismutase activities, respectively. Overall, this study revealed that FOS incorporated diets could beneficial for L. japonicus culture in terms of increasing the growth, digestion and immune activities. Under the present experimental condition, the optimal supplementary level of FOS in the diet of L. japonicus is 1–3 g/kg.     

Protein and amino acid composition from the mantle of juvenile O ctopus vulgaris exposed to prolonged starvation

Protein and amino acid composition of the mantle of juvenile O ctopus vulgaris (Cuvier, 1797) during fasting for 27 days were determined. Average protein content of octopus mantle was of 711.19 ± 46.80 g kg^?1 DW, and it decreased with increasing fasting days. The non‐essential amino acids content was higher (486.18 ± 11.08 g kg^?1 protein) than essential amino acids (425.82 ± 9.15 g kg^?1 protein) at the start of the experiment (unstarved animals). The results suggest that the amino acid profile of the mantle where the most abundant amino acids are Arg, His, Lys, Gly, Leu and Pro could indicate a prolonged fasting condition (>20 days) or poor nutrition of O . vulgaris. This study supports the idea of using mantle for metabolic needs of starved O . vulgaris suggesting that the degradation pathway of amino acids to pyruvate and tricarboxylic acid cycle intermediates was favoured contrary to the degradation pathway of ketogenic amino acids. Special considerations should be taken concerning Thr, Ile, Ser, Ala, Asx (Asp, Asn), Glx (Glu, Gln) (because of their fast intake) and Lys and His (due to their stable contents) during a prolonged period of fasting.     

Involvement of gonadal steroids in final oocyte maturation of white perch (Morone americana) and white bass (M. chrysops): in vivo and in vitro studies

Plasma estradiol-17 (E₂), testosterone (T), 17,20-dihydroxy-4-pregnen-3-one (DHP) and 17,20,21-tri-hydroxy-4-pregnen-3-one (20-S) levels were measured by radioimmunoassay (RIA) in white perch (Morone americana) and white bass (M. chrysops) that were induced to undergo final oocyte maturation (FOM) with human chorionic gonadotropin (hCG). Plasma DHP levels increased in females of both species in association with oocyte germinal vesicle migration (GVM) and germinal vesicle breakdown (GVBD) and decreased thereafter. Plasma 20-S levels also increased with oocyte GVM in white bass, but were several-fold lower than DHP levels. Circulating E₂ and T levels were greatest during GVM and GVBD in both species and decreased to low levels during oocyte hydration and ovulation. Follicles from white perch and white bass which received a priming injection of hCG in vivo, produced both DHP and 20-S in vitro after exposure to hCG and their oocytes underwent GVBD. Ovarian incubates from unprimed fish of either species produced only E₂ and T and their oocytes did not complete GVBD. Oocytes from unprimed bass, but not perch, matured when follicles were exposed to hCG in vitro. Both trilostane and cycloheximide blocked in vitro production of DHP and 20-S and oocyte GVBD by white perch follices. DHP and 20-S were equipotent inducers of FOM in the GVBD bioassay. None of several other structurally-related steroids tested were effective within a physiological range of concentrations. These results indicate a role for DHP and 20-S in the control of FOM in white perch and white bass.     

Cardiac,ventilatory and metabolic responses of two ecologically dissimilar species of fish to waterborne cyanide

Changes in heart rate, ventilatory activity and oxygen consumption were determined in trout (Salmo gairdneri) and brown bullhead catfish (Ictalurus nebulosus) during exposure to a steadily increasing concentration of waterborne cyanide selected to produce death in 8–9 hours for each species. The lethal cyanide concentration for the bullheads was an order of magnitude higher than for trout. Trout developed an immediate and gradually increasing bradycardia throughout the exposure period. Cyanide produced tachycardia in the bullhead followed by a gradual onset of bradycardia as the concentration of cyanide was raised. Pericardial injection of atropine (a muscarinic cholinergic antagonist) indicated that bradycardia in the trout was due initially to increased vagal tone but later due to the direct effect of cyanide on the heart. Hyperventilation in the trout persisted throughout the exposure period, although the rate and amplitude fluctuated and was variable between individual fish. During the last hour of exposure (highest cyanide concentration), ventilation was characterized by rapid, shallow breaths followed by a sudden respiratory arrest. The bullheads exhibited hyperventilation during the first 3 hours of exposure followed by a gradual, linear drop in ventilation rate and amplitude until death occurred. Cardiac and ventilatory responses in both species were attributed to stimulation of central and peripheral chemoreceptors by cyanide. Evidence is presented which suggests the initial response in the bullheads was due, at least in part, to gustatory stimulation by the cyanide. Oxygen consumption of the trout remained above pre-exposure levels for the majority of the test period. Oxygen consumption in the bullhead paralleled the changes in heart and ventilatory rates. Whole-body lactate levels of fingerlings of both species during cyanide exposure were measured to estimate the extent of anaerobiosis. Whole-body lactate levels were much greater in the bullheads than the trout, indicating a higher capacity for anaerobiosis, possibly due to a greater fuel supply. Overall, the trout responded to cyanide in a manner similar to that produced by environmental hypoxia whereas the bullheads experienced a gustatory stimulus which masked the hypoxia-like response.     

An overview of stress physiology of fish transport: changes in water quality as a function of transport duration

This study brings an integrated analysis about the relationship between water deterioration and its physiological consequences in live fish transport. The analysis was focused on the transport water and its deterioration, and physiological challenges imposed on the fish. Usual commercial handling procedures employed to mitigate fish stress during transport were discussed. Future topics of research for the establishment of safer fish transport protocols were proposed. Transport was classified into short (≤8 h) or long transport (>8 h). The main issue in short transports should be the prevention of water pH reduction, while in long transports it is the increase in ammonia. Plasma cortisol is the most employed marker for stress and is acutely elevated upon short episodes of transport, but remains elevated even in long‐transport events. Plasma glucose is perhaps a better marker for handling stress. Plasma lactate, pH, osmolality CO₂ and ions should be more often evaluated. Plasma Na⁺ and Cl^‐ are very useful markers of acidosis, due to their respective exchange for H⁺ and , for acid–base regulation. The establishment of species‐specific transport protocols should be preceded by such combined analyses of water and physiological parameters.     

Are hatchery‐reared abalone naïve of predators? Comparing the behaviours of wild and hatchery‐reared northern abalone,Haliotis kamtschatkana (Jonas, 1845)

Abalone populations have declined worldwide, generating interest in enhancement using hatchery‐reared individuals. In many cases, such restoration efforts have met with limited success due to high predator‐induced mortality rates. Furthermore, the mortality rates of outplanted hatchery abalone are often considerably higher than for wild individuals. This study uses northern abalone (Haliotis kamtschatkana) as a case study to determine whether hatchery‐reared abalone behave differently than their wild counterparts. In the field, outplanted hatchery‐reared abalone were significantly less responsive than wild abalone, in terms of number of abalone responding and intensity of response, to nearby movement and to physical contact with an inert probe. Also, when encountering a cue to which all abalone responded (a seastar predator), hatchery‐reared individuals remained subdued. Anti‐predator behavioural deficits in hatchery‐reared abalone were more pronounced in 4‐year‐old individuals than in 1‐year‐old individuals, suggesting an influence of either age or amount of time spent in the hatchery environment. These behavioural differences are expected to increase the vulnerability of hatchery‐reared abalone to predators, and are likely a major cause of their elevated predator‐induced mortality when outplanted.     

Effects of cadmium on the kinetics of calcium uptake in developing tilapia larvae, Oreochromis mossambicus

The toxic effects of Cd²⁺ on Ca²⁺ influx kinetics in developing tilapia (Oreochromis mossambicus) larvae were evaluated. Addition of 20 µg l^-1 of Cd²⁺ to the environment of 0 and 3 day-old larvae competitively inhibited the Ca²⁺ uptake within 4h resulting in a great increase in K_m values for Ca²⁺ influx (19.3 and 17.4 fold, respectively) as compared with their respective controls. Consequently, the actual Ca²⁺ influx of larvae in solutions of 0.2 mM Ca²⁺ are suppressed by 32–45%. Also, 3 day-old larvae were more sensitive to internally accumulated Cd²⁺ than 0 day-old larvae. Although the Ca²⁺ influx in 0 and 3 day-old larvae may be restored to the levels of their respective controls with 24h of being transferred to a 20 µg l^-1 Cd²⁺ solution, total body Ca²⁺ content was significantly reduced in 3 day-old larvae. Increased Ca²⁺ uptake efficiency ensures sufficient Ca²⁺ for normal growth. However, rapid increase in Ca²⁺ influx after hatching also leads to higher Cd²⁺ uptake. Exposure to Cd²⁺ will lead to a drop in body Ca²⁺ content resulting in retardation of larval growth. Therefore, we conclude that if Ca²⁺ uptake is interfered with at this critical stage of development, larvae will not be able to maintain normal levels of body Ca²⁺ and will show signs of Cd²⁺ poisoning.     

Migratory dynamics of stream-spawning longnose gar (Lepisosteus osseus)

Abstract– Literature evidence suggests that lake-dwelling longnose gar (Lepisosteus osseus) enter tributary streams to spawn, Until the present study, the dynamics of this breeding migration had never been investigated quantitatively. During the summers of 1991 and 1992, longnose gar were captured as they entered Weaubleau Creek, Missouri, a tributary of Harry S. Truman Reservoir. The in-stream spawning migration began in early April and ended in late May, and was positively correlated with stream flow and water level, and negatively correlated with water temperature. In-stream residence times ranged from 15 to 94 days, with males exhibiting longer residence times than females. Once in-stream, longnose gar travelled as far as 10 km upstream and occupied certain pools at greater relative frequencies. Although the reason for this preferential utilization is not completely understood, it may relate to pool depth and riffle proximity. Longnose gar disperse from the spawning stream great distances, with gar captured in Weaubleau Creek being recaptured up to 48 km away. This information should provide fisheries biologists the means to consider the reproductive ecology of this species in their conservation and management decisions.     

Nutritional regulation of hepatocyte fatty acid desaturation and polyunsaturated fatty acid composition in zebrafish (Danio rerio) and tilapia (Oreochromis niloticus)

The desaturation and elongation of [1-¹⁴C]18:3n-3 was investigated in hepatocytes of the tropical warm freshwater species, zebrafish (Danio rerio) and Nile tilapia (Oreochromis niloticus). The hepatocyte fatty acid desaturation/elongation pathway was assayed before and after the fish were fed two experimental diets, a control diet containing fish oil (FO) and a diet containing vegetable oil (VO; a blend of olive, linseed and high oleic acid sunflower oils) for 10 weeks. The VO diet was formulated to provide 1% each of 18:2n-6 and 18:3n-3, and so satisfy the possible EFA requirements of zebrafish and tilapia. At the end of the dietary trial, the lipid and fatty acid composition was determined in whole zebrafish, and liver, white muscle and brain of tilapia. Both zebrafish and tilapia expressed a hepatocyte fatty acid desaturation/elongation pattern consistent with them being freshwater and planktonivorous fish. The data also showed that hepatic fatty acid desaturation/elongation was nutritionally regulated with the activities being higher in fish fed the VO diet compared to fish fed the FO diet. In zebrafish, the main effect of the VO diet was increased fatty acid Δ6 desaturase activity resulting in the production of significantly more 18:4n-3 compared to fish fed the FO diet. In tilapia, all activities in the pathway were greater in fish fed the VO diet resulting in increased amounts of all fatty acids in the pathway, but primarily eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3). However, the fatty acid compositional data indicated that despite increased activity, desaturation of 18:3n-3 was insufficient to maintain tissue proportions of EPA and DHA in fish fed the VO diet at the same level as in fish fed the FO diet. Practically, these results indicate that manipulation of tilapia diets in commercial culture in response to the declining global fish oil market would have important consequences for fish fatty acid composition and the health of consumers. Scientifically, zebrafish and tilapia, both the subject of active genome mapping projects, could be useful models for studies of lipid and fatty acid metabolism at a molecular biological and genetic level. This revised version was published online in August 2006 with corrections to the Cover Date.