鱼类游泳速度分类方法的探讨

游泳速度是评价鱼类游泳能力的重要指标。本文对常用的几种鱼类游泳速度概念和分类方法进行了总结。目前,以时间长度作为分类标准可将游泳速度分为巡航游泳速度(Cruising swimming speed,T200min)、长时游泳速度(Prolonged swimming speed,200minT20s)、冲刺游泳速度(Burst swimming speed,T20s)3类。但由于时间长度的选择缺乏令人信服的依据,很多学者并未遵循这一时间界定标准进行各类试验,致使游泳速度的界定出现混乱,从而使以时间长度作为分类依据的方法失去意义。作者综合多数学者的研究方法,以鱼类的游泳状态作为依据,重新对鱼类游泳速度进行分类,并在这一分类基础上拓展引申出最大探顶游泳速度这一新概念,并对其推求方法和实际意义进行了探讨。根据新的分类方法,鱼类游泳速度主要分为5大类:最优巡航速度(Optimum swimming speed)、最大续航速度(Maximum sustained swimming speed)、临界游泳速度(Critical swimming speed)、最大探顶游泳速度(Maximum domed swimming speed)、冲刺游泳速度(Burst swimming speed)。其他游泳速度概念基本可以按照上述分类进行归并。借助最大探顶游泳速度这一概念,作者进一步探讨了其与最大续航速度、临界游泳速度3者之间的联系,认为在某种程度上这3种游泳速度作为评价鱼类游泳能力的指标具有一致性。     

与鱼道设计相关的鱼类游泳行为研究

在鱼类生境遭受破坏，渔业资源日益减少的今天，修建鱼道等过鱼设施已成为减缓水利工程建设所致不利影响的重要举措。纵观世界各国，早期的鱼道建设往往因为缺乏对鱼类的了解而最终成为摆设。我国的鱼道建设起步晚，其再度兴起需要更可靠的生物学信息。鱼类的游泳能力及行为关系着鱼道设计的各个方面，决定着设计的成败。文章针对鱼道设计，综述了国内外几十年来鱼类游泳行为的研究成果。鱼类的游泳速度可分为三类，即持续游泳速度，耐久游泳速度和突进游泳速度，其中与鱼道设计密切相关的是后两者。影响鱼类游泳速度的因素既有生物个体因素也有环境因素，主要包括摆尾频率、体长、疲劳时间、温度及耗氧量等。文章最后简述了鱼类行为学在鱼道设计中的应用。我国针对过鱼设施建设的鱼类行为学研究极少，总结国外的研究方法和经验成果可为我国的过鱼设施建设提供生物学基础，促进该领域的发展。     

鳙幼鱼4种典型游泳状态特性研究

在23±0.5℃水温条件下,利用游泳行为测试水槽分析早期发育阶段鳙幼鱼（Hypophthalmichthys nobilis）（5.0～9.0cm,2.5～11.5g）游泳行为特性与水流流速变化的响应关系。结果表明该体长范围鳙幼鱼的平均临界游泳速度为0.468±0.161m/s;平均突进游泳速度为0.672±0.154m/s,且绝对临界游泳速度和绝对突进游泳速度均随体长的增加而线性增加,相对突进游泳速度随体长的增加而线性减小;绝对突进游泳速度与绝对临界游泳速度存在如下关系： ;在测试突进游泳速度中鱼类游泳行为随水流流速变化存在4种游泳状态相互穿插（顶流前进、顶流后退、顶流静止、顺流而下）,根据鱼类运动过程中的四个阶段分别对应的4种游泳状态,得到以鳙幼鱼为过鱼对象的鱼道池室主流流速为16.0～46.5cm/s;对于鱼道高流速区的竖缝、孔口等最佳流速应为46.5～85.4cm/s。本研究成果补充了四大家鱼游泳特性指标,为四大家鱼资源保护、鱼类洄游通道建设提供参考依据。     

鲢幼鱼游泳能力及游泳行为的试验研究

为了探究四大家鱼的游泳能力,指导鱼道水力学设计,提高鱼道过鱼成功率,增殖鱼类资源总量,以四大家鱼之一的鲢(Hypophthalmichthys molitrix)为试验对象,研究其游泳能力及游泳行为。在(30±1)℃水温下,采用流速递增法,鲢的体长7.3~16.8 cm,体重6.10~66.50 g,按体长将鲢分为(8.17±0.59)cm、(10.09±0.53)cm、(11.84±0.67)cm、(13.94±0.68)cm、(15.90±0.64)cm共计5个试验组。结果表明,鲢的临界游泳速度为52~100 cm/s,相对临界游泳速度为5.90~7.14 BL/s,摆尾频率为98.7~432.2次/min。鲢的临界游泳速度随体长增加而增大,其线性拟合方程为Ucrit=4.908L+17.63(R2=0.998);其相对临界游泳速度随体长增加而减小,线性拟合方程为U'crit=-0.130L+8.025(R2=0.979);在整个试验过程中,根据鱼类对水流速度的游泳行为响应,鲢摆尾频率随水流速度的增大而增加,两者呈线性关系;在相同流速下,较长个体鲢的摆尾频率显著小于较小的个体。     

美国红鱼游泳体能分配模型及其在海区选址中的应用

以深水网箱养殖的美国红鱼为研究对象,通过研究其游泳时主要能量物质和代谢产物的变化规律,构建美国红鱼的游泳体能分配模型,最后结合特定的潮流规律,建立养殖海区最大潮流选择的理论方法。结果显示,美国红鱼游泳过程中,血糖浓度会显著提高,肌糖原有少量减少,肝糖原会显著降低,鱼类游泳接近疲劳时,肝糖原浓度亦接近耗尽;美国红鱼以较高速度游泳过程中,血乳酸和肌乳酸浓度会有较明显的增加,表明美国红鱼游泳过程伴随着无氧呼吸和有氧呼吸两种能量物质代谢过程。本实验提出以肝糖原浓度作为判定鱼类持续游泳能力的重要指标,并建立了基于肝糖原储能消耗的美国红鱼游泳体能分配模型。最后基于美国红鱼体能分配模型,结合养殖海区潮流规律,提出了美国红鱼养殖海区最大潮流流速选择的计算方法。研究表明,本实验提出的鱼类游泳体能分配模型构建方法以及鱼类养殖海区潮流选择论证方法,可为相关研究提供新的途径,为深水网箱、浅海围网等海洋养殖模式的海区潮流选址提供科学的参考依据。     

应用于鱼道设计的新疆木扎提河斑重唇鱼的游泳能力测试

为了探究斑重唇鱼的游泳能力，给过鱼设施设计和鱼类游泳行为学研究提供基础参数，本研究以木扎提河野生斑重唇鱼(全长TL=12~16 cm)为研究对象，测定了其在(16.6±1.6) ℃水温下的感应流速、临界游泳速度、爆发游泳速度及持续与耐久游泳能力。结果显示，斑重唇鱼感应流速为(0.18±0.02)m/s，相对感应流速为(1.40±0.23) BL/s (BL为体长)；临界游泳速度为(1.02±0.15) m/s，相对临界游泳速度为(8.58±1.65) BL/s；爆发游泳速度为(1.39±0.17) m/s，相对爆发游泳速度为(10.92±1.86) BL/s；最大持续游泳速度为0.87 m/s，最大耐久游泳速度为1.37 m/s，与平均爆发游泳速度相近。其持续游泳时间与流速呈负相关(${\rm lg}T = - 5.136{{X}} + 8.504$)。当以斑重唇鱼为主要过鱼对象时，建议为吸引鱼类进入鱼道，进口流速设计为1.02~1.39 m/s，休息池主流设计为0.20~1.02 m/s，鱼道竖缝处流速宜低于0.85 m/s。鱼道长度为1 000 m时，鱼道内平均水流速度应低于0.78 m/s。本研究结果可为新疆木扎提河流域鱼类游泳能力研究提供参考，对保护日益减少的鱼类资源具有重要意义。     

禁食对8种幼鱼游泳运动能力的影响

为了探究不同种类幼鱼在禁食胁迫下的游泳能力 , 本研究以青鱼 (Mylopharyngodon piceus)、草鱼 (Ctenopharyngodon idellus)、鲢(Hypophthalmichthys molitrix)、鳙(Aristichthys nobilis)、鲫(Carassius auratus)、长薄鳅(Leptobotia elongata)、泥鳅(Misgurnus anguillicaudatus)、台湾泥鳅(Paramisgumus dabryanus ssp.) 8 种幼鱼为对象, 采用流速递增法测定了不同禁食时间(0 d、2 d、5 d、10 d、15 d)条件下 8 种鱼类的感应流速(U_ind)、临界游泳速度(U_crit)、爆发游泳速度(U_burst)。结果表明: 8 种鱼类游泳能力均为感应流速＜临界游泳速度＜爆发游泳速度。感应流速平均值的变化范围在(6.12~12.78) cm/s, 其中草鱼、鲢和鳙的感应流速较接近且对流速的感应较敏感, 感应流速为 4.75~7.75 cm/s。8 种实验鱼的游泳速度存在显著差异(P＜0.05), 其中青鱼和长薄鳅的临界游泳速度和爆发游泳速度最高, 分别为(121.65±3.19) cm/s、(143.48±5.77) cm/s、(85.08±3.23) cm/s、(132.68±8.52) cm/s, 游泳能力较差的为台湾泥鳅[(19.28±1.90) cm/s、(31.53±2.14) cm/s]。禁食对感应流速的影响不显著(P＞0.05), 但实验鱼的临界游泳速度和爆发游泳速度随禁食时间的延长呈线性下降, 其中临界游泳速度的下降幅度较爆发游泳速度更为显著 (P＜0.05)。在禁食 0 d 和 2 d 时, 实验鱼的临界和爆发游速无显著差异(P＞0.05); 禁食 5 d 时, 两者开始呈现下降趋势; 禁食 5 d 后, 临界和爆发游速分别下降了 13%~51%和 9%~39%。禁食 10 d 后, 临界和爆发游速分别下降了 29%~70%和 20%~55%, 其中 10 d 禁食期间的游泳速度降低幅度最为显著。因此, 禁食 10 d 是影响鱼类游泳能力的关键时期。禁食对幼鱼的感应流速无显著影响, 但临界游泳速度和爆发游泳速度受禁食时间影响明显, 且禁食时间越长, 游泳能力下降越显著。此外, 临界游泳速度与爆发游泳速度之间的差异可能源于不同游泳方式在能量消耗方面的差异。     

鲢幼鱼非疲劳贴网及姿态转换行为研究

流速是影响鱼类生存与繁衍栖息的重要因子。为了了解鱼类在中等流速区的游泳行为,探究其对水流的适应特征,利用鱼类游泳能力测定装置,以鲢(Hypophthalmichthys molitrix)幼鱼[体重(9.82±3.81) g,体长(8.56±1.11) cm)]为对象,采用递增流速法,分析了游泳过程中的非疲劳贴网行为与姿态转换行为。结果表明,在22℃水温条件下,鲢幼鱼平均相对临界游泳速度(critical swimming speed,U_(crit))相比其体长(body length,BL)为(6.00±0.93)BL/s;其非疲劳贴网速度(no-fatigue impingement speed,U_(imp))与临界游泳速度呈线性正相关,U_(crit)=1.03 U_(imp)+1.26 (R~2=0.86,P0.01);姿态转换速度(gait transition speed,U_(tran))与临界游泳速度呈线性正相关,U_(tran)=0.59 U_(crit)+1.55 (R~2=0.43,P0.01);非疲劳贴网速度与姿态转换速度呈线性正相关,U_(tran)=0.51U_(imp)+2.72 (R~2=0.41,P0.001)。在中等流速范围内(2～4 BL/s),实验鱼摆尾频率(tail beat frequency, TBF)和单次摆尾周期前进距离(stride length, SL)均随流速增加而增大。首次出现非疲劳贴网的流速为4.62 BL/s,流速增至5.08 BL/s时出现姿态转换行为。发生姿态转换后,TBF开始下降,而SL随流速增加快速增大。研究显示,鲢幼鱼非疲劳贴网行为对游泳能力和姿态转换速度有显著影响,且非疲劳贴网行为与姿态转换行为之间也存在相互影响。研究结果可为自然环境中鱼类生态行为研究、鱼类资源保护及渔业管理提供参考。     

异齿裂腹鱼游泳能力初探

为了摸清雅鲁藏布江特有种异齿裂腹鱼(Schizothorax oconnori)的游泳能力,以野生鱼种为实验对象,通过丹麦Loligo System公司的环形试验水槽测试了异齿裂腹鱼的临界游泳速度、突进游泳速度和持续游泳速度。结果显示,异齿裂腹鱼的临界游泳速度随体长的增大而增加,相对临界游泳速度随体长的增大而减小,其临界游泳速度与体长的关系为Y1=-39.369+13.23X-0.371X2+0.004X3(Y1是绝对临界游泳速度,X为体长)。突进游泳速度随体长的增加而近似呈线性递增趋势,而相对突进游泳速度随体长的增大而减小。在三个固定流速(60cm/s、80 cm/s、100 cm/s)下,初步确定60 cm/s为异齿裂腹鱼的持续游泳速度,80 cm/s、100 cm/s为耐久游泳速度。研究成果以期为青藏高原地区鱼类行为学的研究提供基础资料,为鱼道等过鱼设施的设计提供参考资料。     

鲢鳙幼鱼临界游泳速度的比较研究

通过比较不同鱼类的游泳能力,为鱼道建设和鱼类行为学研究提供基础资料。在(20±1)℃水温下,使用丹麦Loligo System公司的鱼类行为视频跟踪系统,采用Brett流速递增法,以鲢(Hypophthalmichthys molitrix)和鳙(Aristichthys nobilis)为研究对象,体长作为划分依据,分别测定不同体长组鲢鳙临界游泳速度。结果表明:(1)鲢鳙绝对临界游泳速度随着体长的增加而增大,相对临界游泳速度随着体长的增大而减小,鲢体长与绝对临界游泳速度拟合方程为:Y1=0.10X21-0.11X1+55.86(R2=0.85),与相对临界游泳速度拟合方程为:y1=0.02x21-0.87x1+12.86(R2=0.94),鳙体长与绝对临界游泳速度拟合方程为:Y2=0.03X32-1.29X22+21.04X2-29.21(R2=0.85),与相对临界游泳速度拟合方程为:y2=0.02x22-0.87x2+14.81(R2=0.98);(2)相近体长组鲢(10.11±0.24)cm和鳙(10.78±1.34)cm临界游泳速度分别为(65.50±2.08)cm/s和(80.89±4.03)cm/s,可知鳙鲢,且差异性显著(P0.05);(16.90±0.55)cm鲢和(15.39±0.62)cm鳙的临界游泳速度为(83.92±3.03)cm/s和(91.62±3.54)cm/s,无显著性差异(P0.05);(3)通过比较鲢鳙临界游泳速度与突进游泳速度能力,发现鲢的突进游泳速度大于鳙,而临界游泳速度小于后者,可知鲢鳙有氧运动和无氧运动能力之间存在权衡作用,临界游泳速度与突进游泳速度不一定呈现正相关关系。鱼类能否顺利完成上溯需求取决于鱼道内水力条件和自身游泳能力。     

北盘江2种典型增殖放流鱼类突进游速研究

长臀（Cranoglanis bouderius）和白甲鱼（Onychostoma sima）是目前北盘江主要放流鱼类,但这2种鱼的放流效果差异较大。由于鱼类的突进游速在一定程度上影响增殖放流的效果,故试验采用自制测试装置,用递增流速法测试了2种鱼的突进游速。结果显示,白甲鱼的突进游速大于长臀,且2种鱼的突进游速均随体长增加而近似线性增大;而相对突进游速则随着体长的增加而近似线性减小。研究结果可为北盘江鱼类增殖放流和放流效果评估,以及日后北盘江的拦鱼、诱鱼、集鱼船等鱼类资源保护措施的实施提供参考。     

水温、盐度和溶氧对红鳍东方鲀幼鱼游泳能力的影响

为了考查水温、盐度和溶氧对红鳍东方鲀(Takifugu rubripes)幼鱼游泳能力的影响,测定了其在不同水温[15.2、20.2、25.6(对照)和30.4℃]、盐度[0、10、20、32(对照)和40]和溶氧[2.14、4.10、5.81和7.36 mg/L(对照)]条件下的临界游速和最大游速。结果表明,水温和溶氧含量均显著影响实验鱼的临界游速和最大游速(P0.01)。随水温和溶氧含量升高,实验鱼的临界游速和最大游速均逐渐增加。水温(T,℃)与临界游速(U_(crit),cm/s)和最大游速(U_(max),cm/s)均呈二次函数关系,关系式分别为U_(crit)=-0.095T 2+5.450T-47.79,R~2=0.995(P0.01)和U_(max)=-0.018T 2+2.204 T-12.27,R~2=0.981(P0.01)。溶氧含量(DO,mg/L)与临界游速和最大游速也均呈二次函数关系,关系式分别为U_(crit)=0.230DO2+1.561DO+5.84,R~2=0.995(P0.01)和U_(max)=-0.806 DO2+11.10DO-3.919,R~2=0.985(P0.01)。不同盐度下实验鱼的临界游速和最大游速与对照组均无显著差异(P0.05)。结论认为,低温和缺氧会降低红鳍东方鲀放流苗种的游泳能力,进而降低其放流后的捕食成功率,提高被捕食概率。     

不同营养状况对鲫鱼偏好游泳速度的影响

为考察不同营养状况对鲤科鱼类偏好游泳速度的影响,本研究以鲫鱼(Carassius auratus)为实验对象,(25±1.0)℃条件下设置3个不同营养状况实验组:对照组(禁食48 h)、饱食组(饱食)和饥饿组(饥饿14 d),将单尾实验鱼置于梯度流速选择仪(流速范围为11.86~65.45 cm/s,等距离划分为5个流速区域,从第一到第五流速区域流速连续增加)中拍摄1 h,采用Ethovision XT9软件分析视频资料并计算实验鱼在不同流速区域平均进入频次(F,次)、单次进入停留时间(T,s/次)和平均停留时间百分比(P_t,%)等流速选择行为指标。结果显示,对照组和饱食组的F值随水流速度上升而增加,对照组的T值不同流速区域间无差异(P0.05),而饱食组第三和第四流速区域T值均显著大于其他流速区域(P0.05),因此两实验组第三和第四流速区域的P_t均显著大于其他流速区域,其偏好游泳速度为20.12~41.30 cm/s。饥饿组流速偏好行为出现表型分化,I型实验鱼在第一流速区域P_t和T值显著大于其他流速区域(P0.05),各流速区域的F值均显著小于其他实验组(P0.05),故I型实验鱼的偏好游泳速度为11.86~15.18 cm/s。而II型实验鱼则与对照组相似,在第三和第四流速区域Pt均显著大于其他流速区域(P0.05),故II型实验鱼的偏好游泳速度为20.12~41.30 cm/s。结果表明,饱食不影响鲫鱼的偏好游泳速度,可能是饱食不影响鲫鱼的游泳能力所致,但饱食组在各流速区域间的出入频次减少而停留时间有所增加。饥饿后鲫鱼偏好游泳速度出现表型分化,I型实验鱼的偏好游泳速度降低,而II型实验鱼则无明显变化,I型和II型实验鱼偏好游泳速度的差异可能是由于在饥饿条件下二者能量节约和游泳功能维持的策略不同。     

5种鱼类标志对草鱼临界游泳速度的影响

采用被动整合雷达标志法(PIT)、切鳍标记、荧光标记、超声波标志和T型标志这5种标志方法对草鱼(Ctenopharyngodon idellus)进行标记后,测定其临界游泳速度,研究5种不同标记对草鱼游泳能力的影响。将试验草鱼按不同体长分为3组:15~18 cm,18~21 cm,21~25 cm,每个体长组均设置对照组,并分别进行以上5种鱼类标志,测量标志后草鱼的绝对临界游泳速度和相对临界游泳速度。采用SPSS17.0统计软件进行数据的分析比较。研究结果表明,随着体长增加,草鱼的绝对临界游泳速度增大,相对临界游泳速度减小;超声波标志对3个体长组草鱼的临界游泳速度均有极显著影响(P0.01),标志后草鱼绝对临界游泳速度分别下降18.72%、16.40%、23.15%,相对临界游泳速度分别下降18.95%、17.78%、21.86%;T型标志对15~18 cm体长组草鱼的临界游泳速度有极显著性影响(P0.01),标志后草鱼绝对临界游泳速度下降8.35%,相对临界游泳速度下降9.30%,对体长大于18 cm的草鱼无显著性影响;PIT标志、切鳍标记和荧光标记对这3个体长组草鱼的临界游泳速度均无显著性影响(P0.05)。     

A new device for monitoring the activity of freely swimming flatfish, Japanese flounder Paralichthys olivaceus

ABSTRACT:   The tail beat and activity behavior of four captive Japanese flounder Paralichthys olivaceus , were monitored with acceleration data-loggers while the fish swam in an aquarium. Depth, swimming speeds and two-axis acceleration data were collected continuously for approximately 20 h per fish. Simultaneously, the swimming behaviors of the fish were filmed at different angles. Using the specific characteristic of the acceleration profiles, in tandem with other types of data (e.g. speed and depth), four behavioral patterns could be distinguished: (i) 'active' swimming; (ii) burying patterns; (iii) 'inactive' gliding; and (iv) lying on the bottom. Tail beat frequency ranged from 1.65 ± 0.47 to 2.04 ± 0.25 Hz (mean ± SD; n  = 4). Using the relationship between tail beat frequency and swimming speed, the 'preferred' swimming speed of the fish was estimated to be between 0.6 and 1.2 body lengths (BL)/s. Additionally, fish rarely swam faster than 1.2 BL/s. This study shows that the acceleration data-loggers represent a useful and reliable system for accurately recording the tail beat of free-ranging fish and estimating flatfish behavior.     

Swimming ability and differential use of velocity patches by 0+ cyprinids

Abstract– The ability of chub, dace and roach to resist displacement in a laboratory channel was not only controlled by species-specific swimming ability, but also by the fishes'ability to locate areas of reduced velocity. Dace were better able to withstand high velocities than roach. Chub were better at locating slow flowing patches than either roach or dace throughout their early development. Only chub larvae shifted towards slower flowing patches as velocity increased. All juveniles shifted to slower flowing patches at high velocities.     

Detection efficiency of multiplexed Passive Integrated Transponder antennas is influenced by environmental conditions and fish swimming behaviour

Abstract –  The efficiency of a Passive Integrated Transponder (PIT)-tag detection system was tested during a 23-day experiment using a permanent digital video to record the passage of fish through multiplexed antennas. Coupling video to the PIT system allowed the detection of error sources and the correction of erroneous data. The efficiency of the detection system and its variation were investigated according to fish swimming speed, direction of movement and individual fish behaviour. Influence of time and environmental conditions on detection results were also checked. The PIT tag system was 96.7% efficient in detecting fish. Upstream movements were better detected (99.8%) than downstream movements (93.7%). Moreover, results showed that efficiency rate was not stable over the experiment; it was reduced on stormy days. Several sources of errors were identified such as sub-optimal orientation of the PIT tag relative to the antenna plane, the influence of fish swimming speed, individual fish behaviour and influence of environmental conditions.     

Undulatory fish swimming: from muscles to flow

Undulatory swimming is employed by many fish for routine swimming and extended sprints. In this biomechanical review, we address two questions: (i) how the fish's axial muscles power swimming; and (ii) how the fish's body and fins generate thrust. Fish have adapted the morphology of their axial musculature for high power output and efficiency. All but the superficial muscle fibres are arranged along curved trajectories, and the myomeres form nested cones. Two conflicting performance goals shape the fibre trajectories of the axial muscles. Maximum power output requires that all fibres contract uniformly. In a bending fish, uniform contraction in a single myomere can be ensured by curved fibre trajectories. However, uniform strain is only desirable if all muscle fibres have the same contractile properties. The fish needs several muscle‐fibre types that generate maximum power at different contraction speeds to ensure effective muscle power generation across a range of swimming speeds. Consequently, these different muscle‐fibre types are better served by non‐uniform contractions. High power output at a range of swimming speeds requires that muscle fibres with the same contractile properties contract uniformly. The ensuing helical fibre trajectories require cone‐shaped myomeres to reduce wasteful internal deformation of the entire muscle when it contracts. It can be shown that the cone‐shaped myomeres of fish can be explained by two design criteria: uniform contraction (uniform strain hypothesis) and minimal internal deformation (mechanical stability hypothesis). So far, only the latter hypothesis has found strong support. The contracting muscle causes the fish body to undulate. These body undulations interact with the surrounding water to generate thrust. The resulting flow behind the swimming fish forms vortex rings, whose arrangement reflects the fish's swimming performance. Anguilliform swimmers shed individual vortex rings during steady swimming. Carangiform swimmers shed a connected chain of vortex rings. The currently available sections through the total flow fields are often not an honest representation of the total momentum in the water – the wake of carangiform swimmers shows a net backward momentum without the fish accelerating – suggesting that our current picture of the generated flow is incomplete. To accelerate, undulatory swimmers decrease the angle of the vortex rings with the mean path of motion, which is consistent with an increased rate of backward momentum transfer. Carangiform swimmers also enlarge their vortex rings to accelerate and to swim at a higher speed, while eel, which are anguilliform swimmers, shed stronger vortex rings.     

Effects of size and sex on swimming performance and metabolism of invasive mosquitofish Gambusia holbrooki

In freshwater ecosystems, abiotic factors such as flow regime and water quality are considered important predictors of ecosystem invasibility. The aim of this study was to investigate the critical swimming capacity and metabolism of the eastern mosquitofish, Gambusia holbrooki, focusing on sex and size effects, to evaluate the influence of water flow on its invasive success. Specimens of mosquitofish were captured from the Ter Vell lagoon (L'Estartit, north‐eastern Spain) in July 2014, and we measured the critical swimming speed (U_crit) and oxygen consumption of individual fish (30 females and 30 males) using a mini swim tunnel. The mean U_crit of this poeciliid fish was estimated at 14.11 cm·s^?1 (range = 4.85–22.26), which is lower than that of many other fishes of similar size and confirms that this species is limnophilic and its invasive success might be partially explained by hydrologic alterations. However, the U_crit and maximal metabolic rate vary markedly with fish size and sex, with males having much higher values for the same body mass, and thus probably being more resistant to strong water flows. Multiple regression models illustrate that multivariate analyses might increase the predictive power and understanding of swimming performance and metabolic traits, compared to results from conventional simple regressions.