加速流对鲢、鳙幼鱼下行过程中游泳行为的影响

研究以具有下行洄游需求的鲢(Hypophthalmichthys molitrix)、鳙(Aristichthys nobilis)幼鱼为实验对象, 分别在2种不同流态加速流(Ⅰ: 22—55 cm/s, Ⅱ: 25—60 cm/s)中进行下行实验, 对实验鱼在2种加速流中的游泳行为(下行率、下行方式及各区域游泳时间)进行定量分析并利用游泳停留时间百分比F_t衡量其偏好水流速度。结果显示: 加速流下鲢、鳙均表现出了直接下行与非直接下行两种行为。其中加速流Ⅰ中鲢、鳙直接下行率分别为35.71%、30.00%, Ⅱ中分别为45.83%、59.09%。非直接下行的鲢在2种加速流中小于30 cm/s流速区域的停留时间显著高于其他区域(P<0.05), 即鲢在实验条件下的偏好水流速度范围为小于30 cm/s; 非直接下行的鳙在加速流Ⅰ中小于30 cm/s及50—55 cm/s流速区域的停留时间显著高于其他区域(P<0.05), Ⅱ中小于30 cm/s流速区域的停留时间显著高于其他区域(P<0.05), 即鳙本实验条件下偏好水流速度范围为小于30 cm/s。将2种加速流流速相同区域合并分析发现鲢、鳙在小于30 cm/s和50—55 cm/s流速区域的停留时间存在显著性差异(P<0.05), 中间及高流速区域无明显性差异(P>0.1)。研究表明: 加速流对鲢、鳙下行游泳行为产生了影响且2种鱼在下行通过方式和偏好流速选择上存在一定的种间差异性。

THE EFFECT OF ACCELERATING FLOW ON SWIMMING BEHAVIOR OF JUVENILE ARISTICHTHYS NOBILIS AND HYPOPHTHALMICHTHYS MOLITRIX DURING DOWNSTREAM MIGRATION

Accelerating flow generally exists during fish downstream migration passage, which will affect swimming behavior of individual fish. In this study, the swimming behavior of juvenile silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis) during downstream migratory were tested under two types of accelerating flows (Ⅰ: 22—55 cm/s, Ⅱ: 25—60 cm/s). The objective of this experiment was to quantify the swimming behavior, including downstream pass rate, the way of downstream movement, and the time spent in each area. The preferred flow velocity was measured by the percentage of residence time (F_t). The result showed that the fish performed two kinds of downstream behavior in accelerating flow, which were " direct” and " non-direct”. The direct downstream rate of silver carp and bighead carp were 35.71% and 30% in Ⅰ, and 45.83% and 59.09% in Ⅱrespectively. During the non-direct downstream movement, silver carp spent significantly longer time in the flow less than 30 cm/s under both I and II flow conditions (P<0.05), which indicated that the preferred water velocity of silver carp in the tests was less than 30cm/s. The time spent by bighead carp was significant longer in the flow velocity less than 30 cm/s and 50—55 cm/s under flow conditionⅠ than in flow with other velocity (P<0.05), and under flow condition II, the time was longer in the flow velocity less than 30 cm/s (P<0.05), which implicated that the preferred water velocity of bighead carp in the test was less than 30 cm/s. Based on the results from two types of accelerating flow conditions, it showed that there was significant difference (P<0.05) in the residence time between silver carp and bighead carp in the flow with velocities less than 30 cm/s and 50—55 cm/s, but there was no significant difference (P>0.1) in medium and high velocity conditions. The study demonstrated that the accelerating flow can affect the swimming behavior of individual fish during downstream migration, and there is some interspecific difference in the ways of downstream migration and preferred velocity between silver carp and bighead carp.