Electronic Journal of Polish Agricultural Universities (EJPAU) founded by all Polish Agriculture Universities presents original papers and review articles relevant to all aspects of agricultural sciences. It is target for persons working both in science and industry,regulatory agencies or teaching in agricultural sector. Covered by IFIS Publishing (Food Science and Technology Abstracts), ELSEVIER Science - Food Science and Technology Program, CAS USA (Chemical Abstracts), CABI Publishing UK and ALPSP (Association of Learned and Professional Society Publisher - full membership). Presented in the Master List of Thomson ISI.
Volume 14
Issue 4
Available Online: http://www.ejpau.media.pl/volume14/issue4/art-08.html


Adam Tański1, Agata Korzelecka-Orkisz1, Leon Grubi¹ię2, Vjekoslav Tičina2, Joanna Szulc1, Krzysztof Formicki3
1 Division of Hydrobiology, Ichthyology and Biotechnology of Biotechnology of Reproduction, West Pomeranian University of Technology in Szczecin, Szczecin, Poland
2 Institute of Oceanography and Fisheries Split, Croatia
3 Division of Hydrobiology, Ichthyology and Biotechnology of Biotechnology of Reproduction,
West Pomeranian University of Technology in Szczecin, Szczecin, Poland



The effect of static magnetic field on the choice of direction of movement of sea bass (Dicentrarchus labrax) and sea bream (Sparus aurata) fry in a research setting, in which the fish had the option of swimming to one of four chambers at whose entrance magnetic field higher than the Earth's magnetic field was generated. Results on research on sea bream fry show significant correlations between the choice of direction of movement and the level of generated magnetic field. No such response was noted in the case of sea bass fry. These results suggest that some species of fish, despite inhabiting a very characteristic, environment of which the Adriatic coast is, where there is stratification of salinity and temperature and within which migrations of sea bream and sea bass to reproduction and feeding grounds take place, show changes in the direction of movement under the influence of artificially generated magnetic field, and most probably are guided by changes in magnetic field gradient during migrations.

Key words: Adriatic Sea, directional responses, fish fry, magnetic field, sea bream, sea bass .


European sea bass (Dicentrarchus labrax) and sea bream (Sparus aurata) play a significant important role in the Mediterranean mariculture [1, 2]. In 2008, 102 765 tons of sea bass valued at 526 million EURO and 129 343 tons of sea bream valued at 475 million EURO were produced [3].

Sea bream as a coastal bathypelagic species inhabit the Mediterranean Sea along the eastern shore of the Atlantic Ocean, from Britain to Senegal, and also occasionally the Black Sea [4, 5]. This species also occurs in coastal lagoons and estuaries [6]. Before spawning, the adults are sensitive to low temperatures that is why in autumn they migrate towards open sea. Reproduction of these species occurs at considerable distance from shore, where hatching of larvae occurs between October and December. In early spring, the fry migrate to the coastal waters, where they finds a rich trophic varieties and milder temperature conditions [7].

Traditional extensive farming of sea bream in the lagoons make use of the trophic migration of fry to the coastal lagoons [8, 9]. Suau and Lopez [10] carried out experimental studies on the migration of this species from coastal lagoons towards the sea, while studies on the migration from the open sea towards the coastal zone in the Italian waters were carried out by Bullo [11]. Similar studies were conducted off the coast of northern Africa by Heltd [12] and off Egyptian coast by Ben-Tuvia [13]. In France, studies were carried out on trophic migrations of sea bream fry from open waters to shallow fertile lagoons and river estuaries, where catches were dominated fish of age 0+ and 1+, while older individuals migrated to open waters of the Gulf of Lyon [14]. Sea bream leave the estuaries and lagoons when they are one year old, but some as later as when they are two years [15].

Sea bass, as well as sea bream, inhabit the Mediterranean Sea, along the eastern shore of the Atlantic Ocean from Great Britain to Senegal and the Black Sea [4, 16]. This species is more tolerant to variable salinity and temperature than the sea bream [17]. Hence the reason it also occurs occasionally in the Baltic Sea [18,19] Seasonal trophic migrations appear already in earlier developmental stages of sea bass, just like the sea bream [20, 21] and reproduction migrations during spawning of mature individuals [8, 9]. Yong sea bass migrate to the estuaries [20, 22] where they often constitute the most numerous group of fish species [23].

Since 2000, CEFAS (Centre of Environment, Fisheries and Aquatic Science, England), BASS (Bass Anglers Sport Fishing Society, England), IFREMER (The Institut Français pour la Recherche et l'Exploration de la Mer, Brest Centre, France) in cooperation with fishermen have been running a program of marking and monitoring the migration of adult sea basses in the waters of north-west Europe. For the sea bass, in the area of England and Wales, spawning autumn migrations are in the southerly and westerly direction, while spring trophic migrations are to the north and east [24, 25].

Migrations of many species of fish, in particular the mechanisms by which they are guided has for years been of great interest among biologists. Both catadromous and anadromous fish use, inter alia, the Earth's magnetic field for space orientation during migration [26, 27, 28, 29, 30]. Space orientation is used by animals migrating over long distances, where usually their target is beyond the range of sensory perception [31]. The ability to respond to and use magnetic field during migration over long distances are possessed by such fish as chinook salmon (Oncorhynchus tschawytscha), keta (Oncorhynchus keta) [32, 33] yellowfin tuna (Thunus albacares) [34], as well as Atlantic salmon (Salmo salar) [35], sea trout (Salmo trutta m. trutta) [36] and eel (Anguilla anguilla) [37]. Even fish species not commonly considered to be migratory have been found to response to magnetic field. Studies carried out on ide (Leuciscus idus), northern pike (Esox lucius) and sunbleak - (Leucaspius delineatus) fry have clearly demonstrated that generated magnetic field influences the directional responses of these fish [38]. There are also ongoing research studies on the effects of static generated magnetic field on gametes, embryos and larvae of various species of fish [39, 40, 41, 42, 43].

Despite the numerous scientific studies on the biology of sea bass and sea bream as well as the fact that these species occupy a leading role in marine aquaculture in Europe, little is known about the eventual environmental factors, by which these species are guided during migratory behaviors [7]. One of such factor is the natural magnetic field.

The aim of the research studies presented in the paper was to verify whether sea bass (Dicentrarchus labrax) and sea bream (Sparus aurata) fry show directional response to magnetic field that could be used by the fish during fry migration in the natural environment in the Adriatic.


Experiments were conducted in June 2008 in the Institute of Oceanography and Fisheries, Croatia. 1.5 grams of fry of sea bream (Sparus auratus) and sea bass (Dicentrarchus labrax), harvested in May, constituted the research material - after migration from spawning grounds to the coast. The fish were harvested using fishing gear and placed in fish transporting basins, with fresh sea water in the place from where they were caught. The fish, upon harvesting, were transported to the experimental laboratories, at the Institute of Oceanography and Fisheries, where they were placed in rotary pools, volume 5 m3, in open circuit - the tanks were fed with water drawn from the Adriatic. The water, in addition, was aerated.

Specially constructed unit, in the shape of a square with sides measuring 100 cm in length and 10 cm in high, was used to study the behavior of larvae in response to static magnetic field (Fig. 1).

Figure 1. A experimental setup for studying the behavior of fish under magnetic field, M - chamber at whose entrance a magnetic field of intensity 0.2 mT was generated, K - control, A – arena.

At the centre of the square was a circular arena, diameter 40 cm, with four passages 15 cm in width leading to it and at whose entrances screens (gorges) forming a 1.5 cm gap hindering the withdrawal of fish were fixed. The entrances to the passages were arranged in accordance with the geographically directions - north (N), south (S), west (W) and eastern (E). The unit (walls, floor, screens) were made of opaque plexiglas and glass taped with dull foil. During the experiments, the temperature was maintained at a constant level that corresponded to prevailing Adriatic Sea water temperature in June, 20°C (±0.5°C).

To eliminated any possible influence from other physical stimuli (e.g. light) on the choice of direction by the fish, the whole unit, during the experiments, was shielded with a dark opaque folio (circular curtain).

The bottom of the unit was lit by two 35W fluorescent lamps on which milky plexiglass veil were placed, in order to disperse radiation and obtain a homogeneous lighting without shadows. At some 2 m above the test kit a digital camera, Sony DCR – DVD109E, connected to a computer was mounted, with this is was possible to continuously monitor the behavior of the fry, and record the images on a computer disk for later detailed analysis.

At the entrance to the passageways, on opposite sides of the circular arena, magnetic field was generated using permanent magnets, in such a way that the magnetic field intensity at the slot through which fish pass to the center of the passage was 0.2 mT (Fig. 2).

Figure 2. Entrance to the passage leading to the chamber in the research setting, M – magnet.

Magnets arranged in such a way that the magnetic field lines generated by the magnets coincided with the natural geomagnetic field lines. That is why the magnets were positioned at the entrance to the passage facing in the E and W direction. The remaining two passages arranged in the S and N direction acted as control - dummy rubber magnets were placed at their entrance. Magnetic field intensity was measured using hallotron gaussmeter HTM-12m (Institute of Telecommunications and Acoustics, Wroclaw University of Technology).

Sea bream and sea bass fry - 7 each - were transferred from pools, fed with sea water in open circuits, to the research unit center, where the fry were placed in a bottomless cylinder. After 20 minutes acclimation period, during which the fish settled down after moving to the research unit, through a hole at the top of unit cover, the cylinder was carefully vertically lifted up, using line invisible to fish, hence freeing the fish (a proper moment for starting the experience).

The experiment was repeated 18 times, each time recording the behavior of each of the seven sea bream fry and 20 repetitions of experiment with seven sea bass fry. The behavior of the fish was continuously monitored on a computer screen, saving the results on a disk. After 30 minutes from the time the fish were allow to freely move within the experimental arena, the number of individuals in the chambers at whose entrance magnetic field (0.2 mT) was generated and in the chambers at whose entrances was the natural magnetic field, and the number of individuals that remained in the arena and did not swim to any of the chambers. The results obtained were statistically analyzed using Statistica PL v. 9.0 program using the Pearson chi-square test for qualitative variables and observed and expected frequencies.


Experiments were conducted on a total of 266 individuals of the two experimental fish species. For the experimental group setting, the number of fish that entered individual chambers under generated magnetic field (0.2 mT) in the experiment with sea bream fry: chamber to the east (E) - 37 individuals, west (W) - 45 individuals. For the control setting, chambers where the entrance was acted upon by natural magnetic field: chamber to the south (S) - 11 individuals and north (N) – 27 (Fig. 3). Six fish remained in the arena as non-oriented.

Figure 3. Directional responses of sea bream fry in the experimental setup. Frequencies observed and expected Chi Square = 21.46667 df = 3
p = 0.000084

In the second experiment with sea bass individuals, 44 and 31 individuals respectively swam to the chambers, at whose entrance permanent magnets were placed, to the east (E) and western (W). 29 and 35 individuals respectively swam to the control passages – to the south (S) and north (N) (Fig. 4). One individual, representing 0.71%, remained in the arena.

Figure 4. Directional responses of sea bass fry in the experimental setup. Frequencies observed and expected Chi Square = 3.820144 df = 3
p = 0.281554

Comparing the results in terms of choice by the fish to swim to different planes - control north-south meridional plane (NS), along which only the Earth's magnetic field acted, and the east-west longitudinal plane (EW), along which generated magnetic field of intensity 0.2 mT acted, it can be observed that 38 sea bream individuals swam to the setting with natural magnetic field - control - NS plane, and 82 individuals to the chambers with generated magnetic field, in the EW plane (Fig. 5). Six non-oriented fish remained in the arena.

Figure 5. Directional responses of sea bream fry in the experimental setup in W-S and E-W planes. Chi square = 16.13333 df = 1
p = 0.000059

Summary of data in the same system of planes showed that 64 sea bass fry swam to the control chambers in the north-south (N-S) plane, while 75 individuals swam to at the chambers in the east-west (E-W) plane, at whose entrance magnetic field of intensity 0.2 mT was generated (Fig. 6). One individual remained in the experimental arena.

Figure 6. Directional responses sea bass fry in the experimental setup in W-S and E-W planes. Chi Square = 0.8705036 df = 1
p = 0.350817


The experimental results points to a significant correlation between the choice of the direction of movement of sea bream fry (swimming to various chambers) and applied magnetic field of intensity 0.2 mT at the entrance to these chambers. 29.37% and 35.71% of the fish swam to the chambers at whose entrance magnetic field of intensity 0.2 mT acted, and for the remaining two chambers - control 8.73% and 21.43%. Only 4.76% of the sea bream fry surveyed did not swim to any of the chambers. The differences are statistically significant.

No significant correlation was noted in the case of sea bass fry. Studied fry swam to individual chambers in similar proportion - 31.43% and 22.14% of the fry swam to the chambers with elevated magnetic field - 0.2 mT, while 20.71%, and 25, 00% of them swam to the control setting (Earth's magnetic field). Only 0.71% of the studied sea bass fry did not swim to any of the possible passages. No statistically significant differences observed.

Effect of magnetic fields on fish has been demonstrated in all of the fish organogenesis phases. Studies carried out on salmon, sea trout, rainbow trout (Oncorhynchus mykiss), vendace (Coregonus albula), northern pike and rudd (Scardinius erythrophthalmus) embryos, which were exposed to action of generated static magnetic field, show that they exhibit significant differences in the positioning of the body's axis of symmetry in a north - south direction [44, 45]. This is connected with directed quasi peristaltics of periblast in the early stages of organogenesis and corrective meridionally-latitudinal movement waves of the protoplasm, which, combined with the effects of static magnetic field at the early stages of embryonic development, cause spatial orientation of the embryo inside the egg chorion [46].

The effect of magnetic field at the early development stages has also been confirmed by exposing developing eggs of carp and pike to magnetic field. In experimental embryos there was an observed increased in the heart rate that was preceded by a slight slowdown. Magnetic field also resulted in acceleration of motility of the pectoral fins in newly hatched larvae, in which the fins have respiratory function [39]. Also, sea trout hatched larvae and fry, placed in settings offering choice of direction of movement, often chose the path of movement towards passages at entrance of whose generated magnetic field of value higher than the natural magnetic field acted [38]. In examining responses of adult fish in water column on choice of direction of movement and swimming to fishing gear traps it has been demonstrated that larger catches were associated with the use of magnetic field at the entrance to the fishing gear [36].

Particles of magnetite (Fe3O4), most likely responsible for orientation ability, were detected [35] in the body of some migratory fish species – at head of yellowfin tuna [47], in the trunk of the chinook salmon (Oncorhynchus tschawytscha (Walb)) and keta [32, 33], in the skull of the eel [37] and in the lateral line of Atlantic salmon. To date, no studies aimed at detecting magnetic material in sea bream and sea bass body have been carried out, however, it can be assumed that since traces of magnetite, or magnetic material have been detected in many species of fish, then perhaps it also occurs in sea bream and sea bass. Latest theory to explain the mechanism of perception of magnetic field points to the existence of mechanical connections between crystals in the cells, and ion channels in the membranes, which can mechanically open or close, bring changes of its position of magnetite crystals under the influence of magnetic field [48, 49].

The change in behavior of sea bream and sea bass fry under generated magnetic field require an explanation. In the sea bream fry choice of direction of movement towards chambers with generated magnetic field compared to natural magnetic field differ significantly, while in sea bass fry generated magnetic field at the entrance to the chambers did not lead to significant changes in the behavior of fry. The differences in the behavior of individual species may depend on prevailing ontogenesis period. It may also be assumed that directional responses in magnetic field of sea bream fry exist throughout ontogeny, while in sea bass fry this sensitivity is greatly weaken or even eliminated after moving to the feeding grounds. It could be that in the case of sea bass fry clues provided by the changes in the physical and chemical properties of water, depending on the distance from the shore, predominate in choosing the direction of movement. These changes, mainly temperature and salinity could, in the sea bass fry, play significant role than the magnetic field in choosing the direction of movement.

From the results of experimental studies conducted it can be concluded that sea bream fry are sensitive to changes in the magnetic field and show significant differences in behavior – in choosing direction of movement.


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Accepted for print: 21.12.2011

Adam Tański
Division of Hydrobiology, Ichthyology and Biotechnology of Biotechnology of Reproduction,
West Pomeranian University of Technology in Szczecin, Szczecin, Poland
K. Królewicza 4
71-550 Szczecin
email: adam.tanski@zut.edu.pl

Agata Korzelecka-Orkisz
Division of Hydrobiology, Ichthyology and Biotechnology of Biotechnology of Reproduction,
West Pomeranian University of Technology in Szczecin, Szczecin, Poland
K. Królewicza 4
71-550 Szczecin
email: Agata.Korzelecka-Orkisz@zut.edu.pl

Leon Grubi¹ię
Institute of Oceanography and Fisheries Split, Croatia

Vjekoslav Tičina
Institute of Oceanography and Fisheries Split, Croatia

Joanna Szulc
Division of Hydrobiology, Ichthyology and Biotechnology of Biotechnology of Reproduction,
West Pomeranian University of Technology in Szczecin, Szczecin, Poland
K. Królewicza 4
71-550 Szczecin

Krzysztof Formicki
Division of Hydrobiology, Ichthyology and Biotechnology of Biotechnology of Reproduction,

West Pomeranian University of Technology in Szczecin, Szczecin, Poland
K. Królewicza 4
71-550 Szczecin
email: Krzysztof.Formicki@zut.edu.pl

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