Changes in the fish egg strength dependent on the velocity with which the force is applied onto eggs

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Department of Fish Anatomy and Embryology, The Westpomeranian University

CHANGES IN THE FISH EGG STRENGTH DEPENDENT ON THE VELOCITY WITH WHICH THE FORCE IS APPLIED ONTO EGGS

Izabella Smaruj

Agata Korzelecka-Orkisz

Aleksander Winnicki

Krzysztof Formicki

ABSTRACT

egg pike kumz whitefish

We haw information, that factors to toughness eggs shell of the pike, kumz and whitefish at instant of their breakup stright hang from speed of the growth of power of the mechanical pressure on shell of the roe. There it is results fast stractces konformitions in membranes mikrostatis.

Key words: egg shell, egg membrane strength, velocity, European pike, trout, whitefish

INTRODUCTION

Egg membranes of the fish are semi-permeable structures that protect the egg cell (and later developing fish embryo) from the sudden changes (chemical, physical and biological) in the closest eggs surrounding during the first stage of reproduction which is embryogenesis.

One of the most important and on the same hand one of the most spectacular functions fulfill the egg membranes of fish (Hein 1907a, b, Gray 1932, Hayes 1942, Ignateva 1956, Ivanov 1956, Michajlova 1958, Zotin 1958, Zotin and Popov 1959, Winnicki 1967, Winnicki et al. 1970, Davenport et al. 1986, Iuchi et al. 1996, Winnicki et al. 2004, Sobociсski et al. 2005). It is not possible to make a straightforward and uniform conclusion based on the published work that discuss the case of the egg membrane behavior upon the pressure and force applied onto them in the natural environment as well as and perhaps most importantly in the context of the laboratory experimentation, where results show discrepancies. This is mostly applying to the forcing plane and the magnitude of the applied forcing onto the egg etc.

Just these observations lead us to make a decision to pay a closer attention to creeping of the egg during the application of the force and prior to the egg membrane breakage. We decided to try to answer whether and if so how the changes in the velocity of the measuring head onto the eggs influence the finite results of the egg membranes.

MATERIALS AND METHODS

Eggs of following fish were the subject of our experiments: European pike (Esox lucius L.), trout (Salmo trutta m. trutta L.) and common whitefish (Coregonus lavaretus L.), which were caught in the waters in the surrounding of Szczecin and later incubated in the lab Fish Anatomy and Embryology, The Westpomeranian University of Technology in Szczecin.

The mixture of the eggs from 5-7 females was fertilized using sperm from 3-6 males (“dry method”).

The fertilized eggs were kept and incubated in specially constructed experimental setups with water being constantly aerated. Water conditions were optimal for each fish species.

After fertilization of pike (24 hours), trout and common whitefish (5 days into the incubation) eggs strength was measured in samples of 20 eggs.

Velocities of the measuring head were: 1.0, 1.5, 2.5, 5.0, 7.5 and 10.0 mm/s.

Measurements were conducting using a strength measuring machine Zwick/Roell Z 2.5 with a regulated pressure in the units of force (F_max=200N) equipped in specialized software - testXpert II, which was recording the course of the test in a graphical format of the egg strength of the egg membranes (Fig. 1).

Fig 1 Instrumentation used to measure the mechanical strength of the egg membrane: Single eggs were first dried using tissue-paper and placed on the glass plate. Eggs prepared this way underwent a mechanical pressure

RESULTS

Results from our tests of the egg membrane strength show that, there is dependence between the increasing velocity of the measuring head when applying the forcing and the recorded egg membrane strength (when velocity increased the strength decreases) in case of all the studied species.

The strength tests of pike show the greatest strength of the egg membrane (3.7 N) is when the velocity was the lowest (1 mm/s). The velocity of 5mm/s was the threshold value after which the strength of egg membrane decreased down to 2.0 N (Fig. 2).

Data analysis for trout eggs show that the curve that describes the strength is similar to that for the pike egg membranes strength. The biggest strength is of a quite high value 18.1 N. When the velocity is 2.5 mm/s. When the velocity was 1.0, 1.5, and 2.5 mm/s egg membranes had a relatively high resistance to the mechanical pressure. Velocity of 5 mm/s and higher caused a decrease in the strength of the trout egg membranes down to 11 N (Fig. 3).

The results for the eggs of the common whitefish were slightly different. The greatest strength was 7.5N was for eggs when the head was moving with the velocity of 1.5 mm/s. Slightly smaller strength values were recorded when the velocity was 1.0 and 2.5 mm/s. With an increasing velocity (5 mm/s) of the measuring head the egg membrane strength suddenly decreased to 5 N just like it took place for eggs of pike and trout (Fig. 4).

Fig. 2 Strength of pike egg membranes after 24 hours from fertilization

Fig. 3 Strength of trout egg membranes during 5 days of the embryonic development

Fig. 3 Strength of whitefish egg membranes during 5 days of the embryonic development

SUMMARY AND CONCLUSIONS

Despite the interspecies differences in egg strength in case of the three fish species the trend that at one point when velocity of the measuring head increases the strength of the eggs decreases dramatically.

Based on the data from our tests we have two major conclusions. Firstly the differences in the egg membrane strength among the various fish species can be explained by variable egg membrane structure in each species which have been constructed according to the environmental conditions in which these fish live.

Trout, which is a reo- and lithophylic species, makes up its nest of the gravel and rocks, which can apply frequently a significant pressure onto the eggs. Hence their relative strength to the pressure to the mechanical damage which how it is shown by studies of Winnicki et al (1968) can resist the pressure on the order of kilograms.

The common whitefish lays eggs twice a year on the hard bottom covered by sand or gravel and rocks. These conditions also demand significant egg membrane strength when the moving water current pushes the substrate forward and applied hence pressure onto the eggs.

As an understandable phenomenon we acknowledge that the pike egg membranes are the weakest among the three fish species we covered in this study. Eggs of this fish are laid and develop on the underwater vegetation, where they are not exposed to mechanical damage of the hard rocky bottoms.

The most important however is the conclusion that the consistency of the method used in order to obtain the measurements the egg membrane strength is undeniably essential. Specifically the velocity of the applied forcing by the head of the instrument has an impact on the measured values of the egg membrane strength. When the velocity is high the egg membranes have no chance for a gradual stretching and shape shifting from the spherical to the cylindrical. The perivitelline fluid is not able to move to the peripheries of the flattened cylinder. The balance of the egg membrane strength and increasing as a result of increasing velocity forcing is disrupted which results in sooner egg explosion.

We think that this is caused by a set of quick conformational changes in the microstructure of egg membrane, its elasticity and springiness (Winnicki 1970), which is ultimately responsible for the egg membrane strength during the mechanical forcing onto it.

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