The Early Life History of Fish

Rapp. P.-v. Réun. Cons. int. Explor. Mer, 191: 400-408. 1989 The role of barosensitivity in the control of migrations of larval and juvenile sole (Solea solea L.): influence of pressure variations on swimming activity and orientation C. Macquart-Moulin, C. Castelbon, G. Champalbert, D. Chikhi, L. Le Direach-Boursier, and G. Patriti Macquart-Moulin, C., Castlebon, C., Champalbert, G., Chikhi, D., Le Direach- Boursier, L., and Patriti, G. 1989. The role of barosensitivity in the control of migrations of larval and juvenile sole (Solea solea (L.)): influence of pressure variations on swimming activity and orientation. - Rapp. P.-v. Réun. Cons. int. Explor. Mer, 191: 400-408. Pressure variations from 0.5 to 50% of the reference pressure (0-1500 mb) were applied in total darkness suddenly or in cycles varying in period from 4 sec to more than 12 h. In juveniles, swimming activity and the amount of upward swimming increased during pressure decreases (sudden or progressive), during cyclic pressure variations simulating tide effects, and also during cyclic variations of low amplitude and very short period simulating wave effects in shallow areas. Larvae and juveniles reacted in the opposite sense from juveniles when they were subjected to sudden pressure variations, but reacted in the same sense when they were subjected to cyclic variations simulating waves. C. Macquart-Moulin, C. Castelbon, G. Champalbert, D. Chikhi, L. Le Direach- Boursier, and G. Patriti: Centre d’Océanologies de Marseille, Faculté des Sciences de Luminy, Case 901, F-13288 Marseille Cédex 9, France. Introduction In benthic or hyperbenthic animals whose behaviour is not very different from that of the sole after meta This paper summarizes the first results of a study sup morphosis, barosensitivity may be involved in the con ported by a French national programme on the recruit trol of several kind of movements, especially in the ment of some marine species including the sole, Solea intertidal zone and in estuaries. These are: solea (L.). In the sea, young sole are subjected to different kinds of hydrostatic pressure changes: (1) cyc 1. Movements due to waves if animals are sensitive to lic and progressive pressure changes caused by the tidal small and sudden pressure changes. Waves at the sea cycle, during which the amplitude does not exceed one surface induce pressure variations on the bottom. bar; (2) cyclic pressure changes of short period and The depth range influenced by these variations small amplitude caused by waves in shallow waters; (3) depends on wave amplitude and wave length. sudden changes related to vertical migration during 2. Ebb transport when a pressure decrease induces pelagic swimming and (4) changes caused by animal increased swimming activity. movements. 3. Flood transport when a pressure increase induces During the last decades, several studies have shown active swimming. the great sensitivity of several species of aquatic animals 4. Tidal swimming in all directions for species stimu to small hydrostatic pressure variations (Hardy and lated during pressure increase or decrease. Bainbridge, 1951; Enright, 1962; Qasim et al., 1963; Rice, 1964; Morgan, 1972; Blaxter, 1978). The most Many authors such as Dijkgraaf (1942), Qasim et al. frequent reaction in planktonic animals, including soleid (1963), Rice (1964), McCutcheon (1966), Blaxter and larvae, is an upward movement when the pressure is Tytler (1972), Gibson (1982) have studied pressure sen increasing and a downward movement (active or not) sitivity of fish including pleuronectiforms (especially when the pressure is decreasing. These two reactions plaice and dab). Adults or larvae with a swimbladder may regulate the depth at which the animals swim. can be particularly barosensitive: thus, a pressure 400 increase of 5-10 mb induces upward swimming in Blen- Material and methods nius pholis larvae (Qasim et al., 1963) and different behavioural or physiological responses were observed In order to determine changes in behaviour occurring for variations of similar amplitude (0.5-1%) in several during development, experiments were carried out on fishes such as cod, haddock, minnow, trout, and gold 3-5 mm larvae and juveniles of different stages (1- fish. The barosensitivity of adults or larvae without a 4 cm). Most animals came from a hatchery on the French swimbladder (most pleuronectiforms) is known to be Atlantic coast at Brest, but a few were caught at night smaller, nevertheless Pholis gunnelus larvae react to in the Mediterranean plankton. They were maintained pressure increase of 25 mb and the dab exhibits a cardiac in the laboratory at constant temperature (14°C) under response for a A p/p less than 1%; that means a sen atmospheric pressure and exposed to a natural light sitivity similar to the sensitivity of fish with swimbladders cycle. Each day, but at different times, they were fed (Blaxter and Tytler, 1972). on Artemia nauplii. For each experimental set, 80 larvae This study is an attempt to establish the effects of or 10-15 juveniles were used. Animals were not fed these different kinds of pressure changes on swimming during the experiments. activity, orientation, and migratory processes of larval Special actographs were built for this study. Each and juvenile sole. Most experiments deal with pressure consisted of a dark temperature-controlled chamber cycles whose amplitude and period are within the range inside which was a cylindrical tank (50 cm in height, normally encountered in the sea, such as variations 14 cm in diameter) fitted with two sets of three photo induced by waves or tides, but some experiments with electric infra-red barriers mounted on a circular frame sudden pressure changes were carried out. (Fig. 1). The bottom of the tank was covered with a 2- 4 cm layer of sand. relating arm experimental chamber Mercury Reservoir 14 cm — insulating wa W a t e r Membrane Figure 1. Actograph and pressure device: cyclic pressure changes inside the experimental tank are produced by monitoring a mercury reservoir attached to a rotating-arm set in action by a motor. 401 The device producing pressure variations was adapted fidence interval (at 95 or 99%) of the regression line from Morgan’s (Morgan et al., 1964) and Gibson’s calculated with the points of a new spectrum set with a (1982) apparatus. It consisted of a mercury reservoir similar method after randomization of these same data. connected to the experimental tank by means of a silicon pipe and a device with a membrane insulating the tank Results water from the water in contact with the mercury. The mercury reservoir was attached to a rotating arm driven In total darkness, larvae and juveniles exhibit an by an electric motor that was completely isolated from endogenous circadian rhythm of swimming activity, the actograph chamber. The amplitude of the pressure maximum activity occurring in the evening and mini changes could be adjusted by changing the position of mum in the morning (Champalbert and Castelbon, the attachment point on the rotating arm. 1989). Two kinds of motor were used: a variable fast speed motor giving periodic variations similar to those of Sudden variations waves (from 2 to 15 sec), and a constant speed motor giving 12 h periodic cycles, equivalent to tidal cycles. Larvae Movements of fish broke the light beams and the num Since light had little effect on the vertical movements ber of interruptions was recorded per unit time on a of the young sole under experimentation, direct obser printing counter. These counts were used as a measure vation of behaviour was made. When pressure was of swimming activity. Movements were recorded in increased to 100 mb in larvae 3, 9, and 13-d-old (i.e. 3- total darkness in order to eliminate possible interactions 5 mm) an immediate increase in the amount of upward between reactions to pressure and light. Some experi swimming was observed. This effect stopped as soon ments were carried out in total darkness and without as the pressure change ceased. After every pressure pressure variations in order to determine the circadian decrease there was a passive sinking toward the bottom. rhythm and the timing of peaks of activity. The acto These short-term responses were visible to the naked graph only records activity near the surface and bottom eye but were not obvious on the actograms. of the tanks. The analysis of rhythmic movements and the deter Juveniles mination of the period of the oscillatory components After metamorphosis, direct observation becomes dif was that adapted by Williams and Naylor (1978) and ficult because light influences juvenile behaviour Macquart-Moulin and Castelbon (1983) from Enright’s (Champalbert and Castelbon, 1989). Nevertheless, in periodogram method (1965). The periodogram rep the youngest stages subjected to sudden pressure resents the amplitude spectrum of relative variability or changes, a few brief reactions were sometimes observed, “variation coefficient” (standard deviation divided by because their duration was long enough to appear on the mean) of the means calculated on data arranged the actograms. In very young juvenile stages, (about according to the Buys-Ballot table. The periodogram 10 mm), both increase and decrease of pressure induced significance was tested with the upper limit of the con intense swimming activity (Fig. 2). The threshold of this mb 2000-n 1500_ 1000- T i m e of d a y Figure 2. Juveniles 10 mm long: activity (interruptions of infra-red beam as a function of time) at the surface of 8 animals subjected to successive pressure increases and decreases. Reference pressure = 1 atm + 500 mb; Ap = 100 mb. 402 mb 210«-. 1500 - 1 0 0 0 - 2 0 0 - Figure 3. Juveniles 14 mm long: activity (interruptions of infra-red beam as a function of time) at the surface of 10 animals subjected to successive pressure 0- increases and decreases.

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