Abundance and distribution of fish in the lower Mnembo River, Malawi-Mozambique

Endorheic Lake Chilwa is one of the most productive lakes for fisheries in Africa. High human population densities and agricultural practices in the Chilwa catchment have been linked to observed declines of the annual fish catch in the lake. The Mnembo River is a major inflow into Lake Chilwa which has received little scientific study to date. In 2003/2004, fish diversity, abundance and distribution were monitored monthly at three sites in the Mnembo River. Twelve fish species were collected, a subset of the fourteen fish species present in Lake Chilwa. Although Barbus spp. were the most abundant species sampled in the Mnembo, total biomass was higher for Labeo cylindricus (6709 and 10,434 g, respectively). Total biomass of Pareutropius longifilis (1741 g) and Brycinus imberi (1174 g) were also high in the river. Catches of Barbus and Labeo were highly correlated (r = 0.763). Compared with other inflows into Lake Chilwa (Likangala and Domasi), the Mnembo River appears to be less adversely influenced by human populations, with high abundance of Barbus and strong presence of the riverine species Labeo, Pareutropius and Brycinus.     

Histological assessment of selected tissues in tigerfish (Hydrocynus vittatus Castelnau, 1861) from the Sanyati Basin,Lake Kariba,Zimbabwe: a DDT-sprayed area

A pilot investigation was conducted in 2014 in the Sanyati Basin of Lake Kariba to ascertain whether long-term DDT spraying in the Kariba catchment had a negative effect on fish health. The aim was to assess the health of tigerfish, Hydrocynus vittatus, by means of histological analysis and to analyse water, sediment and tissue samples for bioaccumulated levels of chlorinated pesticides, including DDT. Eighteen tigerfish were collected by seine netting along the north-eastern shoreline of the Sanyati Basin in April 2014 and samples of their gill, liver, kidney, muscle and brain tissue were processed for histology and assessed using light microscopy. No detectable levels of DDT and/or its metabolites were found in the water or sediment samples and only a low concentration of p,p′-DDE in fish tissues. No major histological alterations were observed in the fish tissues. Consequently, there seems to be no risk of DDT exposure following the consumption of tigerfish from the Sanyati Basin of Lake Kariba. These results were unexpected, given the historical use of DDT within the current study area. It is recommended that these findings be compared with those from other regions of Lake Kariba.     

基于环境DNA技术的赤水河秋季鱼类多样性分布特征

赤水河是长江上游少有的仍保持自然流态的大型一级支流,是长江鱼类重要的繁衍场和珍稀物种的保护地,摸清其鱼类多样性现状及鱼类群落结构特征对赤水河水生态恢复评估极为重要。于2021年9月对赤水河流域开展了鱼类多样性、分布及其特征调查,全流域共设置52个采样点,采用环境DNA技术采集并研究了赤水河鱼类的组成及其分布。结果显示通过环境DNA方法共调查到鱼类6目18科62属77种,包含16种长江特有鱼类。以鲤形目为主,占总数的87.87%。赤水河鱼类食性以杂食性和肉食性鱼类为主,群落结构上,处于下层水环境鱼类较多;赤水河鱼类优势种为宽鳍鱲(Y=0.205)、西昌华吸鳅(Y=0.085)、麦穗鱼(Y=0.068)、乌苏拟鲿(Y=0.033)、云南光唇鱼(Y=0.027);赤水河上游和下游鱼类群落(P<0.01)和Shannon-Wiener指数差异均显著(P<0.05)。海拔、流速、pH、电导率和温度是影响赤水河鱼类多样性的主要环境因素。为环境DNA技术在赤水河鱼类多样性调查中的应用提供了探索性研究,将有助于赤水河生物多样性的保护。     

The diet of Herring Gulls (Larus argentatus) during winter and early spring on the lower Great Lakes

In the Great Lakes, the Herring Gull (Larus argentatus) is a prominent member of the aquatic bird community, and has been used to monitor spatial and temporal trends in contaminant levels. To understand more fully contaminant loading outside the breeding season, we analysed the contents of 1298 freshly regurgitated pellets and 179 fresh faeces, collected in March and early April 1978–83, and between late December and late February 1990–91, from the vicinity of breeding colonies in Lakes Ontario and Erie, the Niagara River, Detroit River, and south-eastern parts of Lake Huron. Most adult Herring Gulls from the Great Lakes population winter in these areas, but there is no published account of their food habits other than during the breeding season. Most pellets from colonies close to large urban centres contained remains of garbage, as well as various fish species. Small mammals, notably Deer Mice (Peromyscus maniculatus) dominated the early spring diet at Lake Huron colonies near agricultural areas. At all other sites fish predominated in pellets and faeces, but garbage items were also recorded regularly. The species of fish consumed varied regionally, probably reflecting local availability. In Lake Ontario, Rainbow Smelt (Osmerus mordax) and Alewife (Alosa pseudoharengus) occurred most frequently in samples, whereas Freshwater Drum (Aplodinotus grunniens) was the main fish prey in Lake Erie and the Detroit River. Dietary differences were apparent between years, within seasons, and amongst areas. While these may have reflected some real differences in food availability, interpretation of these results was confounded by various biases inherent in the sampling of pellets and faeces to determine diet in such an opportunistic species. Therefore, it would be unwise to draw rigid conclusions as to regional or seasonal differences in the diets of piscivorous birds, based upon analyses of diet from only a small sample of sites or years. Herring Gulls appear to feed mainly on fish and garbage in winter and early spring on the lower Great Lakes (much as during the breeding season), but any locally abundant food source is probably exploited opportunistically.     

长江安庆段江豚主要栖息地鱼类群落结构

长江皖河交汇处(皖河口)是安庆江段江豚主要的栖息地之一。为了解江豚主要栖息地鱼类群落结构,于2013年9月—2014年8月对皖河口及其附近4个断面逐月进行了鱼类调查。研究结果表明,共采集鱼类35种,与历史资料相比,鱼类物种多样性已经严重下降,并且小型化趋势明显。5个断面当中,皖河口鱼类种数最多,为27种,且以中上层鱼类餐和油餐为主要优势种;其余4个断面分别为16、20、19和14种,且多数断面以底层鱼类黄颡鱼和长须黄颡鱼为主要优势种。方差分析结果表明,皖河口渔获物的总数量和总重量与其他断面无显著差异,但总种数却显著高于断面1和5。对中上层、中下层和底层鱼类的进一步分析发现,5个断面的显著差异仅存在于中上层鱼类,且皖河口中上层渔获物的数量和重量均显著高于其他断面。由此推断,江豚选择皖河口作为主要栖息地可能主要由于其更加丰富的中上层鱼类资源。研究结果不仅有助于了解鱼类资源的变化,还对江豚的原地和迁地保护具有重要意义。     

Stream Fish Communities and Environmental Correlates in the Red River of the North, Minnesota and North Dakota

In the Red River of the North (Red River) drainage in Minnesota and North Dakota, there are strong east–west hydrological and chemical environmental gradients. Historical fish surveys indicated the presence of species with both widespread and restricted distributions, leading to unique fish communities in several streams. To determine the important physiochemical correlates of stream fish community structure, we partitioned 25 streams into 46 large reaches by ecoregion classification. The reaches were then characterized from sampling during 1962–1994 by the frequency of occurrence of 76 fish species and 12 landscape-level hydrologic and chemical factors. In canonical correspondence analysis, the first two axes explained 56% of the species–environment relationship, and indicated that coefficient of variation of mean monthly discharge, minimum discharge in May, and residue were the most important factors correlated with fish community composition. Important covariates of residue were specific conductance, dissolved sulfate, and total hardness of waters. Certain catostomids, Hypentelium nigricans and Moxostoma valenciennesi, cyprinids, Notropis anogenus and N. texanus, ictalurids, Ameiurus natalis, and percids, Etheostoma caeruleum and E. microperca, all correlated highly with habitats characterized by low-flow variability, high discharges, and low residue, conductivity, and hardness. Reaches with these characteristics included the Otter Tail River in the Red River Valley, North Central Hardwoods (NCH), and the Northern Minnesota Wetlands (NMW) ecoregions; the Pelican River in the NCH ecoregion; and the Red Lake River in the NMW ecoregion. The results of this analysis support the hypothesis that regional environmental conditions are important in structuring fish communities in northern streams. As conditions are altered in the future by anthropogenic factors at the landscape scale, our exploratory multivariate model can be used to predict fish community response and support conservation efforts aimed at preserving or restoring unique and/or rare small fishes in the Red River and other, similar stream systems.     

Natural sex change in the temperate protogynous Ballan wrasse Labrus bergylta

Wild Ballan wrasse Labrus bergylta were sampled monthly over 2 years in western Norway to identify the natural process of sex change in this species. Light microscopy of standard histological‐stained and immunohistochemistry‐treated gonad tissue showed that spermatogonial germ cells tended to proliferate around the periphery of the lamellae before filling into the slowly receding, apoptotic central areas of the lamellae. Sex change occurred following the breeding season. From July to September, fish were most often in an early state of gonadal transition (ET), characterized by degenerating previtellogenic oocytes and pockets of proliferating spermatogonia in the germinative epithelia. The majority of fish with late transitional gonads, that were typically dominated by spermatogenic cells, developing efferent ducts and the beginning of lobule formation, were found between October and November. Sex steroid profiles of fish representing the different sexual phases showed that breeding females had the highest concentrations of 17β oestradiol (E₂) and the lowest concentration of 11 ketotestosterone (11KT). Concentrations of E₂ decreased greatly in ET fish at the beginning of sex change and remained low in all subsequent phases. The opposite trend was demonstrated in 11KT profiles. Initial‐phase female fish had minimal concentrations of 11KT, but these increased during subsequent transitions. Sex change occurred most often in fish 34–41 cm total length (L_T) and the median of fish in the size‐frequency overlap of female and male fish was 36 cm L_T.     

珠江水系鱼类群落多样性空间分布格局

珠江是我国南方第一大河,是我国重要淡水渔业生产基地和水生生物资源基因库。珠江鱼类在维持生物多样性、提供鱼类种质资源方面举足轻重。但是到目前为止,关于其鱼类空间分布格局的研究甚少。特别是近几十年来各种水工建设和过度捕捞使得渔业资源急剧衰退,鱼类空间分布的研究显得尤为重要。2015年对珠江全流域13个站位进行了全面调查,共采集渔获物10119尾,隶属于94种72属17科。鲤科鱼类占显著优势,其次种类较多的依次为鲿科、鳅科。采用非度量多维标度排序(NMDS)方法对鱼类群落空间分布特征进行了分析,结果表明珠江鱼类被划分为3个类群,即以餐、南方拟餐、黄颡鱼等小型鱼类为主的中上游类群、以赤眼鳟、鲮鱼、广东鲂等中型鱼类为主的中下游类群和以罗非鱼为主的重要支流类群。同时发现中下游物种多样性高,上游及河口江段多样性低的格局。采用冗余分析方法(RDA)分析了鱼类多样性与环境因子的关系,发现年均气温、降雨量、年均径流量、河流宽度与透明度是珠江水系河流鱼类群落结构差异的主要影响因子,其中年均气温是影响鱼类群落分布的最关键因子之一。与历史资料对比后发现,珠江鱼类种类明显减少、空间分布也发生了巨大改变。研究是珠江水系野生渔业资源长期调查的一部分,研究结果将对渔业资源的多样性保护和可持续利用具有指导意义。     

小型水坝梯级开发对永宁河流域鱼类多样性的影响

永宁河是长江上游右岸的一级支流,其干、支流上共建有20余座小型水坝。为探究梯级水电站对鱼类多样性的影响,在永宁河流域设置共42个采样点,覆盖干支流及各个水坝,分别于2018年7月、10月和2019年1月、4月进行了四次鱼类资源调查。调查期间通过刺网、地笼、电捕等方法共采集到鱼类69种7332尾,隶属于4目13科54属,其中有长江上游特有鱼类13种,列入《中国脊椎动物红色名录》濒危和易危鱼类3种,国家二级重点保护鱼类岩原鲤(Procypris rabaudi)1种。Pinkas相对重要性指数(IRI)值较大主要为宽鳍鱲(Zacco platypus)、鲫(Carassius auratus)乐山小鳔鮈(Microphysogobio kiatingensis)等小型鱼类,29种鱼类的IRI值小于10;平均全长＜10cm的鱼类有24种3620尾,平均体重＜50g的鱼类有47种6493尾,鱼类规格较小,小型化严重。永宁河干流下游种类最多,多样性最高,干流中游鱼类数量最多。受自然环境以及水坝等的影响,永宁河的鱼类分布具有明显的空间差异。水坝类型对鱼类多样性有显著影响;而季节对鱼类多样性影响不显著。无水坝阻隔河段鱼类多样性著高于低头坝和高头坝阻隔河段;夏季的短距离洄游鱼类种数显著高于冬季和春季,但由于数量较少对鱼类多样性的季节性变化影响不明显。各种结果表明水坝阻隔对永宁河鱼类多样性和时空分布存在明显影响,为保护受小型水电站影响河流的鱼类多样性,有必要修复重要鱼类栖息地,适当拆除部分小型水坝,并科学开展增殖放流。     

The length-weight relationship of four fish species captured in the Ibicuí River,southern Brazil

Length-Weight relationship (LWRs) were estimated for four fish species occurring in the Ibicuí River drainage basin, southern Brazil. Samples were captured monthly during the spring and summer seasons (October 2018 to March 2019). The fish were caught with gillnets of different meshes (15, 20, 25, 30, 40 mm between adjacent nodes) and a trawl net (5 mm mesh between adjacent nodes) Eighteen excursions were realized in three sites, with a length of approximately 100 km, in third-order flux, all distributed in sub-basin Ibicuí River. The captured tools were installed at the end of the day (6 p.m.) and removed around 6 a.m. the next day. The present study provides the length-weight relationship for four species (Astyanax dissensos, Galeocharax humeralis, Hypostomus roseopunctatus e Hypostomus uruguayensis).     

长江口水域夏季鱼卵和仔稚鱼年间变化

基于2005年、2008年、2009年和2011年8月(夏季)在长江口水域(30°30'—31°45'N,121°15'—123°10'E)4个航次的浮游生物拖网资料,分析了长江口水域鱼卵和仔稚鱼的种类组成、数量分布特征及其年间变化。结果表明:4个航次采集的鱼卵和仔稚鱼鉴定到种的种类有17种,隶属于8目13科,以鲈形目种类最多,11种,其次是鲱形目,5种,其他各目种类均小于5种;种类数存在明显年间差异,2005年种类数最多(鱼卵3种,仔稚鱼8种),其次是2009年和2011年,2008年种类数最少(鱼卵1种,仔稚鱼5种)。优势种年间更替明显,长蛇鲻(Saurida elongata)、虾虎鱼(Gobiidae spp.)和中华小公鱼(Stolephorus chinensis)在2005年是优势种,2008年优势种为鳀鱼(Engraulis japonicus),2009年优势种为鳀鱼、寡鳞飘鱼(Pseudolaubuca engraulis)、虾虎鱼等,2011年虾虎鱼和小公鱼(包括小公鱼属未定种Stolephorus spp.和中华小公鱼Stolephorus chinensis)成为优势种。2005年鱼卵和仔稚鱼数量分布的密集区在嵊泗列岛附近水域,2008年鱼卵和仔稚鱼出现较少,未出现明显的数量密集区;2009年鱼卵数量较少,仔稚鱼数量较多,密集区主要分布在在长江口以外123°E附近水域;2011年鱼卵主要分布在在长江北支口门外附近水域,仔稚鱼在调查区内分布相对均匀。     

Breeding ecology of an amphidromous goby of the genusRhinogobius

Field observations of markedRhinogobius sp. DA (Dark type) individuals and monthly sampling in the Kashiwa River, Shikoku Island, Japan, indicated the breeding season of the species to be from mid-April to early July, peaking in May. Mark-and-recapture data showed that at least half of the females spawned more than once in one breeding season. Although eggs in male-guarded nests were all at the same developmental stage, their mean number exceeded that of pre-spawning yolk stage oocytes per female, suggesting that at least some guarding males received eggs from more than one female. The physical condition of both sexes deteriorated considerably during the breeding season, the hepatosomatic index of guarding males decreasing concurrently with the development of eggs. The decline in physical condition of guarding males was attributed mainly to their restricted feeding opportunities.     

繁殖期4种淡水鱼类化学预警行为及其与性腺指数的关联

化学预警信息（Chemical alarm cue,CAC）在鱼类捕食者-猎物关系中发挥重要作用,并与二者生存适合度密切关联。繁殖期鱼类的繁殖生理投入和化学预警响应均具有较高的能量需求,因而可能存在某种程度上的生存-繁殖的权衡（Trade-off）。选取高体鳑鲏（Rhodeus ocellatus,卵生,繁殖投入较低）、斑马鱼（Danio rerio,卵生,繁殖投入较高）、孔雀鱼（Poecilia reticulata,卵胎生,繁殖投入较高）和皮球鱼（Poecilia latipinna,卵胎生,繁殖投入很高）等繁殖方式各异、能量投入不同的4种淡水鱼类为实验对象,测定了繁殖IV期实验鱼对不同浓度的化学预警信息（Damage-released chemical alarm cues,DCAC）的行为响应模式,并探究了4种实验鱼的化学预警响应与其性腺指数（Gonadosomatic index,GSI）的关联。结果表明：（1）DCAC对4种实验鱼的空间分布、活跃状态、逃逸行为等大部分化学预警响应参数均有不同程度的影响（P<0.05）;（2）4种实验鱼GSI与其化学预警响应参数的变化无显著相关性（P>0.05）（除高浓度DCAC处理组皮球鱼GSI与底栖时间的变化负相关外）。研究回答了长期以来有关繁殖期鱼类化学预警通讯是否缺失的问题,证实了繁殖期不同繁殖生理投入/繁殖对策的4种淡水鱼类均有显著的化学预警响应,提示鱼类GSI与其化学预警响应程度通常不相关（仅高风险环境下繁殖生理投入很高的物种中可能呈现负相关）。     

大藤峡大坝蓄水对浔江鱼类群落的影响

2017年7月至2021年2月对浔江鱼类资源进行调查（每月调查一次）,以定制刺网、虾笼和钓钩为主要作业网具,结合相对重要性指数、鱼类丰度生物量比较（ABC）曲线、相似性分析、非度量多维尺度分析、生态网络和零模型等分析方法,探讨广西大藤峡大坝蓄水对浔江鱼类群落的影响。调查期间共采集鱼类77种,隶属7目19科63属。卷口鱼（Ptychidio jordani）、赤眼鳟（Squaliobarbus curriculus）、鲤（Cyprinus carpio）、粗唇鮠（Leiocassis crassilabris）的相对重要性指数（IRI）值为850.59-2347.23,表明它们是浔江优势种。大藤峡大坝蓄水后浔江鱼类群落发生了一系列变化：（1）鱼类群落相似性聚类分析显示,各年度间鱼类群落相似度均大于59.73%,总体呈现出时间相隔越远群落相似性越低的趋势。此外,鱼类种类数由69种下降为51种;（2）浔江鱼类群落受干扰程度随着时间的推移而增加,鱼类丰度生物量比较曲线（ABC曲线） W值由0.052降至-0.004。此外,基于浔江鱼类所构建的生态网络集散节点数不断减少,结构趋向于简单化,生态网络稳定性减弱;（3）基于时间生态位研究结果表明鱼类种间竞争加剧,时间生态位重叠增幅最大的种对是罗非鱼sp-东方墨头鱼以及卷口鱼-鲫等生态习性相近鱼类。（4）基于时间生态位重叠指数构建的零模型结果揭示了浔江鱼类群落构建取决于环境因素,大坝蓄水后浔江鱼类群落向竞争主导的随机分布发展格局转变。综上所述,大藤峡大坝蓄水对浔江鱼类群落产生较大的影响,亟需采取相应的保护措施。研究为后续浔江鱼类资源的保护和恢复工作以及大藤峡大坝运行的建议提供理论基础。     

Length–weight and length–length relationships of four native fish species from the Yalong River,China

Length‐weight and length‐length relationships were estimated for four native fish species from the Yalong River and its tributaries, China. A total of 976 specimens were collected monthly using trap nets and electric fishing in May 2013 and July 2015 to February 2016. This study presents the first references on LWRs (length–weight relationships) and LLRs (length–length relationships) for three species (Gymnocypris firmispinatus, Paracobitis variegatus and Euchiloglanis kishinouyei). Moreover, maturation length, absolute fecundity and predominant food items for the four species were also described in the study.     

River regulation and fish larvae: variation through space and time

1. Patterns in abundance and distribution of larval fish in a heavily regulated and a mildly regulated Australian lowland river were compared over four breeding seasons to gain some insight into how river regulation affects fish populations.
2. Larvae from a total of 13 species from nine families were recorded from the two rivers. The mildly regulated Broken River supported twice as many species as the heavily regulated Campaspe River. The two rivers shared three introduced species but only two native species. The dominant species in the Campaspe was not found in the Broken River.
3. The two most abundant species in the Campaspe were classified as `opportunists'. They are small, short-lived species, which spawn for up to 9 months, encompassing extremes in temperature and flow. The extended spawning period may place a subset of larvae in optimal conditions for recruitment and is hypothesised as being the key to the success of these species.
4. Most species spawned each year, despite large interannual variation in flow and temperature conditions. Poor recruitment over several decades, rather than a failure to spawn, is considered the most likely explanation for differences in the larval fish faunas between the two rivers.
5. The highly regulated section of the Campaspe River downstream of the regulating impoundment is thought to provide suboptimal habitat conditions for larvae relative to the less regulated downstream sections.
6. The timing of occurrence of larvae of the dominant species varied by breeding season and may be the result of flexibility in the timing of spawning.     

Length–weight relationships of three endemic fish species from the upper Yellow River,China

Length–weight relationships (LWRs) of three Chinese endemic fish species (Gymnocypris eckloni eckloni Herzenstein, 1891, Platypharodon extremus Herzenstein, 1891 and Triplophysa pseudoscleroptera (Zhu & Wu, 1981)) were analyzed, collecting from the upper Yellow River (Xunhua and Guide Counties, Qinghai Province). Totally 347 specimens monthly collected by gill nets with 40 mm mesh size and traps with 5 m length from August to October 2014, were used to estimate the relationship parameters. The allometric factor b values ranged from 2.96 in T. pseudoscleroptera to 3.33 in G. eckloni eckloni. The condition factor a values varies between 0.0063 and 0.0175 in three species. Three WLRs of fishes distributed in the upper Yellow River were firstly reported and will fill in some of the empty spaces on endemic species in the Fishbase.     

DNA barcoding and evaluation of genetic diversity in Cyprinidae fish in the midstream of the Yangtze River

The Yangtze River is the longest river in China and is divided into upstream and mid‐downstream regions by the Three Gorges (the natural barriers of the Yangtze River), resulting in a complex distribution of fish. Dramatic changes to habitat environments may ultimately threaten fish survival; thus, it is necessary to evaluate the genetic diversity and propose protective measures. Species identification is the most significant task in many fields of biological research and in conservation efforts. DNA barcoding, which constitutes the analysis of a short fragment of the mitochondrial cytochrome c oxidase subunit I (COI) sequence, has been widely used for species identification. In this study, we collected 561 COI barcode sequences from 35 fish from the midstream of the Yangtze River. The intraspecific distances of all species were below 2% (with the exception of Acheilognathus macropterus and Hemibarbus maculatus). Nevertheless, all species could be unambiguously identified from the trees, barcoding gaps and taxonomic resolution ratio values. Furthermore, the COI barcode diversity was found to be low (≤0.5%), with the exception of H. maculatus (0.87%), A. macropterus (2.02%) and Saurogobio dabryi (0.82%). No or few shared haplotypes were detected between the upstream and downstream populations for ten species with overall nucleotide diversities greater than 0.00%, which indicated the likelihood of significant population genetic structuring. Our analyses indicated that DNA barcoding is an effective tool for the identification of cyprinidae fish in the midstream of the Yangtze River. It is vital that some protective measures be taken immediately because of the low COI barcode diversity.     

Population dynamics of Rattus argentiventer, Rattus losea, and Rattus rattus inhabiting a mixed-farming system in the Red River Delta, Vietnam

Rodent pests cause significant damage to lowland irrigated rice crops in the Red River Delta of northern Vietnam. Data from a 4-year study were examined to look at the population dynamics of the ricefield rat, Rattus argentiventer (representing 50% of captures), the lesser ricefield rat, Rattus losea (30% of captures), and the black rat, Rattus rattus complex (9% of captures) that inhabit the irrigated mixed-cropping system. We tested the hypothesis that these rodent species were breeding in response to the availability of high-quality food provided by crops rather than in response to rainfall. The abundance of rodents fluctuated annually, with a main peak following the spring rice crop, and a secondary peak following the summer rice crop. There was a strong relationship between the monthly abundance of rats and rainfall, but a weak relationship between monthly rates of increase and rainfall. There were distinct peaks in breeding activity during the reproductive stages of the rice crops suggesting that changes in crop stages were more important than rainfall in this seasonal, but irrigated agroecosystem. The modal litter size for R. argentiventer was 8 (mean of 8.67±0.20 SE, range 2–16), where the mode for R. losea, was 7 (mean of 7.32±0.15 SE, range 3–14). Management of these species needs to be conducted prior to the onset of the main breeding seasons.