不同孔距固定气泡幕对黑鲷的阻拦效果

THE INTERCEPTING EFFECTS OF BUBBLE CURTAINS WITH DIFFERENT AIR-HOLE SPACING ON SPARUS MACROCEPHALUS

于1987年3月一1988年1月，在室内水池中观测孔径为0．smm，孔距分别为工工5．07.5，10.0，20.0cm5种固定气泡幕的视觉特征和声学特征；对其中孔距分别为5.0，10．0和20．0cm3种气泡幕对黑鲷的阻拦作用予以重点分析研究，以期探讨适合阻拦黑鲷的最适孔距。结果表明，这3种气泡幕对黑鲷都具有明显的阻拦作用，平均阻拦率分别为75．l％，55．5％和54．5％；其中，以5.0cm孔距的气泡幕阻拦效果最好，与其他两种气泡幕的阻拦率差异极显著（P＜0.01），而孔距为10．0cm和20.0cm气泡幕之间的阻拦效果无显著差异。该种鱼对3种气泡幕均无明显的适应现象。

In order to investigate the intercepting effects of immovable bubblecurtains (IBC) with different air-hole spacing on black porgy (Sparus macrocephalus),indoor experiments were conducted from l987 to l988' The visual and acousticcharacteristics of IBC with a 0.5mm air-hole diameter and different air-hole spacingwere recorded, described and analyzed. The air-hole spacing of each IBC was 2.5,5.0, 7.5, l0.0 and 20.0cm and only the intercepting effeets of the IBC with 5.0, 10.0and 20.0cm air-hole spacing on the fish were studied. The IBC were constructedfrom a hard polyethylene pipe (l7.5 mm i,d'), fixed on the bottom middle of anexperimental tank, from which colunms of bubbles escaped through a series of holes(0.5mm, i.d.) located on the upper side of the pipe at regular intervals. Compressedair with 0.25kg /cm2 was supplied by a compressor (Model: Al301, Japan)- Theacoustic frequency spectra of bubble curtains on the bottom and on the surfaee wererecorded using a HP-3582A spectrum analyzer at 20 cm from the central buble cur-tain. The experimental tank (3.5 m long, 2.5 m wide, and 0.8 m deep), filled withseawater with 3.5 m diaphaneity, was surrounded with black cloth. The tank top wasuniformly illtalnated with fluorescent lamps giving 86 lx on the central surface. Theexperimental fish, 8.0 - l3.5 cm in body -length, were maintained in the laboratoryfor l - 2 days prior to test. Twenty-five fish in good conditions were randomly se-lected and divided into five groups to be tested in each IBC experiment. The five se-lected fish were put in the experimental tank and allowed to acclimate the newenvironment for l2- 24h prior to test. Each experiment was carried out by dividinginto two testing sections, the aeration experiment and the control experiment (noIBC). The observation period of each section was l h. The control experiment was performed randonily before or after the aeration experiment. Three replicates were succes-sively carried out for each fish group. For all the experiments, the behaviors of fishwere recorded with a CC- l500 television camera mounted over the tank and avideo-tape, for subsequent analysis. The time at which fish passed through the bubble curtain or the air pipe and the number of passage were registered readily. TheIBC appear to be a bubble wall when the air-hole spacing is 5.0cm or 2.5 cm- Thebubble columns of IBC were distributed uniformly- When the air-hole spacing increases to 7.5cm, l0.0cm or 20.0cm, the IBC appear to be a bubble barrier, ratherthan a bubble wall, and the bubble columns of IBC became sparse. In all acoustic fre-quency spectrums of these five IBC, eith recorded in surface or bottom, there weretwo acoustic pressure peaks, one in low frequency area (below l kHz), and the otherin high frequency area (3 - 9kHz). The acoustic pressure of IBC recorded in surfacewas lower than that in bottom. The acoustic pressure both in the low and high fre-quency areas dropped with the decrease or increase in air-hole spacing. In the lhcontrol experiinent, the average numbers of passage through the air pipe were 448,7l5, 3l4 for 5.0, l0.0 and 20.0cm, respectively. Fish behavior changed distinctly sinceIBC existed. Their swiedng became faster than that in the control experiment andaverage numbers of passage through the bubble curtain in l h aeration experiment de-creased to ll7, 304, ll4 for 5.0, l0.0 and 20.0cm, respectively. Sighficantintereepting effects of these three IBC on the fish behaviors were observed, bu theseIBC were not complete obstacles to black porgy. The average obstructing rates were75.l%, 55.5% and 54.5% for 5.O, l0.0 and 20.0cm air-hole spacing, respectively.The results demonstrate that the intercepting effects of IBC are affected siginficantlyby the air-hole spacing. There are sighficant differences between the obstructing rateof 5.0cm IBC and that of l0.0cm or 20.0cm (P<0.0l). However, theer is nosignificant difference between l0.0cm and 20.0cm (P>0.05)- In addition, black porgyhas no marked adaptation to these IBC.