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 12
Issue 4
Korzelecka-Orkisz A. , Bonisławska M. , Pawlos D. , Szulc J. , Winnicki A. , Formicki K. 2009. MORPHOPHYSIOLOGICAL ASPECTS OF THE EMBRYONIC DEVELOPMENT OF TENCH TINCA TINCA (L.), EJPAU 12(4), #21.
Available Online: http://www.ejpau.media.pl/volume12/issue4/art-21.html


Agata Korzelecka-Orkisz1, Małgorzata Bonisławska2, Dorota Pawlos3, Joanna Szulc1, Aleksander Winnicki4, Krzysztof Formicki5
1 Division of Hydrobiology, Ichthyology and Biotechnology of Biotechnology of Reproduction, West Pomeranian University of Technology in Szczecin, Szczecin, Poland
2 Department of Aquatic Sozology, West Pomeranian University of Technology in Szczecin, Szczecin, Poland
3 Westpomeranian Research Centre, IMUZ Szczecin
4 Department of Fish Anatomy and Embryology, West Pomeranian University of Technology, Szczecin, Poland
5 Division of Hydrobiology, Ichthyology and Biotechnology of Biotechnology of Reproduction,
West Pomeranian University of Technology in Szczecin, Szczecin, Poland



Effects of temperature (10; 14; 20; 24; 30°C) on the duration and course of embryogenesis, embryo movements in tench Tinca tinca (L.) were observed vertically and horizontally using two set-ups, each consisting of a microscope, digital camera, monitor, video recorder, and a computer. The results showed that small tench eggs including the eggs cells of v = 0.49 ±0.4 mm3, had sticky egg shell, whose external part had an irregular structure and a few openings that closed rather quickly upon hydration. However, on the internal part of the shell there were oval pores present throughout the entire embryogenesis. During the embryogenesis, which at 24°C lasted approximately 840 H° following observations were made: sideways situated germinal disc due to the lack of the lipid droplet was a characteristic for the cyprinid fishes; yolk sac was divided after approximately 415 H° into two parts; specific somatic and "trembling" embryo movements. Right after the hatching the individuals whose mean length was 3.49 ±0.54 mm had a small (v = 0.21 ±0.15 mm3) yolk sac. The early stage embryogenesis was retarded in the temperatures that were too low.

Key words: tench Tinca tinca (L.), embryogenesis, egg, embryonic morphometry.


Tench is a common fish, spanning entire continent of Europe, as well as Siberia, east of the Lena River, Transcaucasian states, and a part of Asia Minor (Anatolia). It has been introduced to both Americas, Africa, Australia, and New Zealand.

Tench has portion spawning from the end of May till August. Spawning occurs in shallow, muddy sites. Aquatic vegetation is a requirement in the spawning ground of a tench and favourable temperature ranges between 19 and 20°C [11,12,13,16]. The number of portions depends on the temperature during the ovary maturation cycle [2,30].

Tench females deposit up to 9.00x105 eggs (averaging around 3.60 – 4.00×105). Small roe (1.00–1.90 mm in diameter) [10,16,20,24] contains 0.79 –1mm egg cell [13,20]. The egg-shell is covered by a sticky envelope, which enables its attachment to either vegetation or to each other. Therefore the eggs are clustered into lumps of several grains [30].

The duration of tench's egg incubation decreases exponentially with the increase of temperature. The incubation can take 165 hours at 15°C ; 70 hours at 18–19°C and can be as short as 30 hours at 28°C, or 22.5 hours at 31.5°C [15,7].

According to Kokurewicz [11] the incubation temperatures lower (8.5–19°C) or higher (24–30.2°C) than the optimum range, translate into smaller-size larvae and a higher frequency of teratological cases.

Rezničenko et al. [21] and Geldhauser [7] studied the effect of constant temperatures within the range of 10–35°C on the embryonic development of tench. Both 10°C and 35°C turned out in that study to be lethal with the embryogenesis progressing only at first few steps. These studies demonstrated that the optimal temperatures, which were in the range of 22–25°C, ensured proper development and resulted in hatched individuals having the highest values of condition factors (> 94% ) [7,21].

Rezničenko et al. [21] reported that the developing roe of tench could be ecologically adapted to the diel variation of the water temperatures. A short exposure to the unfavourable temperature, occurring within 24-h cycle, did not exert harmful effect on the eggs, which could be contrasted with the findings in laboratory study of a long term exposure effect [21].

The aim of this study was revealing the biological sense of the observed phenomena through presenting the relationships, reciprocal actions, and regularities occurring between specific morphological-, mechanical-, and physiological processes and highly variable different thermal condition of the environment where the natural reproduction takes place. Specific objectives were: a structure of egg shell, distribution and morphometrics eggs and larvae, embryo movements.


This study was carried out in a spring (May – June) in the laboratory of the Department of Fish Anatomy and Embryology, The West Pomeranian University of Technology in Szczecin. The eggs and sperm of tench were obtained from hormonally-stimulated (Ovopel) brood fish (3 female body weight of – 400–500 g; 3 male 350–450 g) from the lake (North-western Poland).

Egg shell
Shortly after the fertilization and before hatching the eggs were preserved in 4% formaldehyde for 4 days. Samples were dehydrated in the alcohol sequence, following the acetone. They were dried using the critical liquid CO2.

Samples were later mounted to the base and saturated with a thin layer of gold and palladium. Preparations were observed using the scanning microscopy (JEOL JSM 6100). Obtained images were used further in the data analysis.

Fertilised eggs were placed in the basket containers and placed in the aquaria with constant temperature maintenance [4]. Temperature was monitored constantly in order to calculate the number of degree-hours (H°) and recorded using a four-channel electronic temperature recorder AKO 15710. The daily temperature deviations did not exceed 0.1°C.

The eggs were incubated at 5 temperature regimes: 10 ± 0.1°C, 14 ± 0.1°C, 20 ± 0.1°C, 24 ± 0.1°C, and 30 ± 0.1°C.

The developing embryos were observed vertically and horizontally using two set-ups, each consisting of a microscope Nikon, digital camera CCD Sony, TV monitor, VCR, and a computer [27].

The measurements of the embryos and the dynamics specific for all body parts were recorded and later analyzed using Multiscan v.13.01. software (Computer Scanning System, Ltd. Poland).

Eggs and larvae morphometrics
Pictures of the 50 developing eggs (after egg activation and hydration) were subjected to image analysis using MultiScan v. 13. 01. The measurements included two diameters of each egg (longer one and shorter one) (± 0.01 mm) and the egg cell [1]. Mean values of the measurements were used for the calculation of the egg and egg cell: volume (V = 4/3 πr3), surface area (S = 4 πr2), and the coefficient S/V ratio (surface area to volume).

Images of the newly-hatched (11 individuals from each temperature regime) larvae were video recorded. Subsequently total length (longitudo totalis – l.t.) as well as its bipartite yolk sac (length, l1 and l2; height, h1 and h2) of each larva were measured. The yolk sac volume (V) was assumed to be a sum of the volumes of elongated ellipsoid (Ve) and a cylinder (Vc) [3,4]:

V = Ve+Vc

V = (π/6·l1·h12) + [π·(h2/2)2·l2] (mm3)

l1 – length of first part of yolk sac (ellipsoid) (mm),
h1 – height of first part of yolk sac (ellipsoid) (mm),
l2 – length of second part of yolk sac (cylinder) (mm),
h2 – height of second part of yolk sac (cylinder) (mm).

Data analysis
The results obtained were processed using the following statistical tests (Statistica 7.1 PL software, StatSoft Poland):


The study, was involved observations of the embryogenesis of tench in two plains- vertical and horizontal, demonstrated that the embryonic development of this fish follows the general sequence of events, characteristic for cyprinid fishes.

The tench embryogenesis was precisely described at 24°, temperature within the optimum range of this fish (Table 1). In addition Table 1 depicts the embryogenesis of tench in various temperatures.

Table 1. The course of embryogenesis (selected stages) of tench and its duration at different temperatures (degree hours)

Phases of development

Temperature [°C]





4 blastomeres





16 blastomeres





Multicellular blastula





Started gastrulation





Epiboly 1/2





Blastopore closure





First myomeres




First somatic movements




Formation of eye lenses




Heart beat




Pigment of eyes




Pigment of head and body




50% of hatch




Number of hours of incubation




Egg shell
Post fertilization there were visible irregularly structured few openings, which closed off rather quickly during the hydration of an egg. During the progressing embryogenesis, on the surface of the external egg shell few bacteria were observed  (Fig. 1a). Their density increased prior to hatching up to 24 cells per 100 µm2.

Fig. 1. Egg shell (embryo just prior to hatching): a. Internal surface of egg, b. External surface of egg shell

The internal membrane site was at all time equipped with numerous oval pore openings (70 per 100 µm2). Their diameters were following: 0.3 µm (longer) and 0.18 µm (shorter) (Fig. 1b).

The post activation water intake by the eggs lasted approximately 15 minutes. The perivitelline space, formed as a result of this process, and took up some 50% of the egg volume (Fig. 2a, b).

Fig. 2. Formation of the perivitelline space: a. 3 minute after activation (view from top), b. formed reception mound (lateral view)

The mean volume of swollen egg was approximately 0.93 ± 0.1 mm3, while the volume of the yolk sphere was 0.49 ± 0.4 mm3. The differences between the largest- and the smallest eggs reached nearly 60%. Those differences for the egg cells exceeded 70% (Fig. 3).

Fig. 3. Volume distribution in egg cells of tench egg

Coefficient S/V ratio (surface area to volume) was very favourable and it amounted to 4.95 ± 0.18 for the eggs and 6.10 ± 0.19 for the egg cells (Table 2).

Table 2. The size and surface area of 50 eggs and egg cells of tench ( ± SD)


Diameter [mm]

Surface area (S)[mm2]

Volume (V) [mm3]

S/V ratio


1.21 ± 0.04

4.60 ± 0.33

0.93 ± 0.10

4.95 ± 0.18

Egg cells

0.97 ± 0.03

2.99 ± 0.17

0.49 ± 0.04

6.10 ± 0.19

There were no structural lipids in the form of droplets inside the tench eggs and therefore the germinal disc slid sideways as far as it was permitted by the width of the perivitelline space.

Very thin egg shell was covered by the layer of a sticky substance.

The course of embryogenesis in tench
After approximately 35 minutes there was ectoplasm on the animal pole, which then became the germinal disc.

The first cleft appeared 45 minutes after fertilization (Fig. 4a), and the next one 75 min late (Fig. 4b). Eight blastomeres are visible in 90 minutes post-activation. The first blastomers were regular and large in relation to the yolk sphere. The stage of blastula appeared at 70 H° (Fig. 4c).

Fig. 4. Embryonic development of tench: a. stage of 2 blastomeres, b. stage of 4 blastomeres, c. blastula, d. gastrulation – 1/3 epiboly, e. embryo; metamerisation visible in the thoracic part

Gastrulation started after 104 H° (Fig. 4d) and ended after 224 H°, when the outline of the developing body of an embryo was already visible. The blastopore closed off at 254 H°.

Organogenesis. The head became distinctly visible after 248 H°, while the first myomeres in the thickening thoracic part appeared at 296 H° (Fig. 4e). At the same time eye cups were formed. Lenses were visible slightly later (at 344 H°).

After 444 H° the embryo executed its first somatic movements at the frequency of 1–2 contractions per minute. Those first movements were single, short-range contractions of the trunk. In time, the frequency of the body movements increased up to 5 per min (at 608 H°) and also their extent widened to the whole body (Fig. 5).

Fig. 5. Embryonic motorics of tench incubated at 24°C
Q – quasi-peristaltic ectoplasm movements (the shield is formed),
P – pulsate caudal part the yolk sac, S – somatic movements, H – heart beats, E – eyeballs movements, T – "trebling of embryo"

The first evidence of the eye pigment appeared at 580 H°. Shortly after, the heart primordial started to work at 18 contractions per minute (Fig. 6) increasing at about  752 H° to 70–80 beats per minute. When the heart became more active the number of body movements decreases to 3 or less per minute. At this stage of the development the pigment along the body became apparent, and the eye pigment was well defined.

Fig. 6. Somatic contractions and the heart beat at various temperatures

Before the hatching, the embryo started visibly "trembling". This type of movements consisted of few (3–4) series of short vibrations within some 10 min.

At 415 H° the yolk sphere was divided into 2 parts:

The timing of the embryogenesis was not equal (Fig. 8). As expected its duration was the longest at the lowest temperature (20°C) and the shortest – at the highest temperature (30°C). The tested temperature regimes of 10 and 14°C turned out to be too low and the embryogenesis at 10°C stopped at the stage of 2 blastomeres, while at 14°C – it ceased at the moment of blastopore closure.

Fig. 7. Formation of two parts of the yolk sac: a. formation of the narrowing, b. caudal part distinctly visible

Fig. 8. The course of embryogenesis (selected stages) of tench and its duration at different temperatures

The first hatching event occurred at 704 H°, while the most hatching was observed 124 H° later (24°C) (Table 1). The majority of larvae hatched head – first and their anterior part protruded outside. Subsequently, after a period of immobility, the embryo bending strongly its body and tail, widened the opening and vacated the egg shell completely. Among the eggs incubated at 20°C, 50 % of hatching occurred post 886 H°, however at 30°C it occurred only after 760 H° (Table 1).

Table 3. Characteristics of tench larvae after hatching from eggs incubated at different temperatures  ( ± SD)

Larvae characteristics

Temperature [°C]




% survival




Total length (mm) (ANOVA p<0.01)

3.29 ± 0.62a

3.49 ± 0.54a

3.36 ± 0.17a

Yolk sac volume (mm3) (ANOVA p<0.01)

0.21 ± 0.18a

0.21 ± 0.15a

0.22 ± 0.52a

Immediately after hatching the specimens measured on average 3.49 ± 0.54 mm and their yolk sac was small, taking up 0.21 ± 0.15 mm3 (Table 3; Fig. 9). Larvae that hatched from the eggs incubated at 20°C and 30°C were not statistically different from those hatched from eggs incubated at 24°C of their body length and their yolk sac volume (Table 3). Newly hatched tench larvae attached themselves to the aquarium walls using the secretion from their cement gland.

Fig. 9. Newly hatched larva


The specificity of the hydrological conditions, accompanying the tench reproduction, outlines the range- and determines the picture of morpho-physiological adaptations, necessary to secure undisturbed and regular course of embryogenesis. Such adaptations guarantee, not only the survival of populations of this species in their current habitats, but also in new ecological niches, acquired either in the course of natural expansion of a stocking action, as has been mentioned earlier in the introduction.

A very important, or possibly even the most important, factor exerting a significant pressure on the course of embryogenesis of tench is the ambient temperature.

Tench spawns at the times when highest water temperatures occur, which coincides with the longest day in places of tench's geographical distribution. Such strategy could be intended to minimize the time period (measured in thermal units) of a forced confinement in the small space of an egg. The time of massive hatching of tench also coincides with the highest abundance of the food items which are the phytoplanktonic organisms suitable for the hatchlings. During that time it stays light during the day for the longest, which favours the photosynthetic rates as well as generally the reproduction of phytoplankton, and high dissolved oxygen level in the water which is necessary for the larvae respiration.

The thermal conditions of the water bodies, where the tench reproduces and the selection of the time period of the spawning, contribute to the fact that the eggs of this fish are relatively small, being one of the World's smallest piscine eggs. The tench eggs show a number of morpho-physiological features ensuring undisturbed embryogenesis:

Coefficient – S/V ratio of an egg in our study was high and therefore very favorable from the point of view of the egg's respiratory efficiency [5].

In case of tench, unlike the other cyprinids, closing of the blastopore, which marks the end of time of the process when the embryo grew around the yolk, has been observed to come later, when the body shape is clearly distinguishable, and the head begins to separate from the rest of the body. This has been previously described by Peňaź et al. [20], who made a case that at this particular time in the embryogenesis the eggs were especially fragile and sensitive to potentially harmful external environmental factors, which could hence contribute to a greater mortality at this stage.

Yolk sac was bipartite, characteristically for the cyprinid fishes [28]. The caudal part of the sac, shortly after its formation, started to execute quasi-peristaltic, rhythmic contractions stirring the surrounding fluid.  Such movement contributed to a better oxygen supply of the embryo long time before the heart was formed and could assume its duties. The bipartity of the yolk sac thus constituted a morpho-physiological adaptation vital for the early embryogenesis.

In the subsequent development, the posterior part of the sac extended along with the quickly growing caudal part of the embryo and after the resorption of the yolk, it transformed into the posterior part of the body cavity of the larva.

Our study had confirmed and solidified the notion that the optimal temperatures for the embryonic development of tench fall into the range of 20–24°C. Such temperatures support a substantial pace of the metabolism of living organisms and are associated with increased oxygen demand. This fact influenced, among other things, the small size of eggs and egg cells. The small size ensures an S/V ratio that benefits towards respiratory effectiveness of the egg shell, and hence the body of an embryo itself.

The small size of the eggs enabled a relatively high absolute fecundity and the possibility of performing multiple sexual acts (portion spawning). Such adaptations secure the "survival" of the population, even during unfavorable events of fluctuating hydrological conditions on the spawning grounds that might adversely affect the chances of some portions of roe to develop.

The embryonic motorics of tench show close similarities to that of other cyprinid fishes, with the provision that the quasi-peristaltic movements are distinctly pronounced only within the period of cleavage and only in the pulsation of the caudal part of the yolk sac [14].

Observed by us, phenomenon of the embryo's diminishing somatic motorics in favour of the heart muscle's increasing motorics could be explained by a need for sustaining energy. Before the formation of the closed circulation system, the somatic movements promoted the "mixing" of the internal environment. When the heart assumed its function, the energy expenditure related to no – longer necessary somatic movements would jeopardise tight energy budget of an embryo in the situation of an increased oxygen demand, caused by the progressing organogenesis.

Shortly, before the hatching a peculiar series of somatic trembling in the embryo was observed. That trembling could most likely be associated with the process of hatching. Larvae could break through the egg shell due to enzymatically stimulated shell perforation. This enzyme is released by the hatching gland [6,8,9,25,26,29,31].


  1. Eggs of tench are small and they are protected by a sticky shell equipped on its exterior with appendages which enable their attachment to the substrate.

  2. Tench alike other cyprinids have sideways allocated germinal disc due to no lipid droplet; the yolk sac is divided.

  3. The optimal temperature range assuring tench's proper development and low mortality is 20–24°C.

  4. Incubation temperatures equal to 14°C had stopped the embryogenesis, however temperature when too high increased the mortality among developing embryos.


  1. Bartel R., 1971. Pomiary średnicy jaj pstrąga tęczowego (Salmo gairdneri Rich.) [Measurements of diameter of the eggs of rainbow trout (Salmo gairdneri Rich.)]. Rocz. Nauk. Rol. 93-H-3, 7–17 [in Polish].

  2. Barus V., Oliva O., 1995. Mihulovci (Petromyzontes) a ryby (Osteichthyes) [Lampreys (Petromyzontes) and fishes (Osteichthyes)] Vol. 2. Academia, Praha. 80-89 [in Czech].

  3. Blaxter J.H.S., G. Hemple., 1963. The influence of egg size on herring larvae   (Clupea harengus). J. Cons. Int. Explor. Mer., 28, 211–240.

  4. Bonisławska M., 2001. Wpływ temperatury na tempo i przebieg embriogenezy u ryb [Temperature effects on the rate and course of embryogenesis in fish]. PhD Thesis, Agric. Univ. Szczec. [in Polish].

  5. Bonisławska M., Winnicki A., 2000. Duration of embryonic development and S/V (surface/volume) coefficient in fish eggs. Arch. Ryb. Pol., 8 (2), 161–69.

  6. Bourdin J., 1926. Le mécanisme de l'éclosion chez les Téléostéens. IV. Physiologie du liquide périvitellin des oeufs de Téléostéens á l'éclosion [The physiology of the vitellus liquid eggs of Teleostei during the hatching time]. Comptes Rendus Academie de Sciences 95, 1242–1243 [in French].

  7. Geldhauser F., 1995. Some aspects of embryonic and larval development of tench (Tinca tinca (L.)). Pol. Arch. Hydrobiol. 42, 1–2, 87–95.

  8. Gray J., 1932. The osmotic properties of the eggs of the trout (Salmo fario). Brit. J. Exptl. Biol. 9 (3), 277–299.

  9. Hayes F.R., 1942. The hatching mechanism of salmon eggs. J. Exp. Biol. 83, 257–373.

  10. Kennedy M., Fitzmaurice P., 1970. The biology of the tench Tinca tinca (L.) in Irish waters. Proc. Roy. Irish Acad., Sect B, 69 (3),31–82.

  11. Kokurewicz B., 1970. The effect of temperature on embryonic development of Tinca tinca (L.) and Rutilus rutilus (L.). Zool. Pol. 20 (3), 317–337.

  12. Kokurewicz B., 1971. Warunki termiczne a rozród niektórych gatunków ryb. [Thermal conditions versus reproduction of some fish species]. IRŚ Olsztyn, Zakład Upowszechniania Postępu  47, 1–16 [in Polish].

  13. Kokurewicz B., 1981. Effect of different thermal regimes on reproductive cycles of tench Tinca tinca (L.). Part VII. Embryonic development of progeny. Pol. Arch. Hydrobiol. 28 (2), 243–256.

  14. Korzelecka A., 1999. Motoryka embrionalna u ryb kostnoszkieletowych. [Embryonic motorics of teleost fishes]. PhD Thesis, Agricult. Univ. Szczec. [in Polish].

  15. Kouřil J., Peňáz M., Prokes M., Hamáčková J., 1988. Vpliv teploty vody na délku inkubaćní doby a líhnivost jiker lína obecného [Effects of water temperature on incubation period and hatchability in tench eggs]. Bull. VURH Vodnany, 1, 3–9 [in Czech].

  16. Kryzanovski S.G., 1949. Ekologo-morfologičeskie zakonomiernosti razvitia karpovyh, v'ûnovyh i somovyh ryb (Cyprinoidei i Siluroidei) [Eco-morphological principles of the development of cyprinid, cobitid and siluroid fishes]. Tr. Inst. Morf. Ziv. AN SSSR Moskwa – Leningrad 1, 5–338 [in Russian].

  17. Lindroth A., 1946. Zur Biologie der Befruchtung und Entwicklung beim Hecht [The biology of the fertilization and development of the pike]. Institute of Freshwater Research at Drottningholm rep. 24, 1–173 [in German].

  18. Morrison C., Bird C., O'Neil D., Leggiardo C., Martin-Robichaud D., Rommens M., Waiwood K., 1999. Structure of the egg envelope of the haddock, Melanogrammus aeglefinus, and effects of microbial colonization during incubation. Can. J. Zool. 77, 890–901.

  19. Patzner R.A., Glechner R., 1996. Attaching Structures in. Eggs of Native Fishes. Limnologica 26 (2), 179–182.

  20. Peňaź M., Wohlgemuth E., Hamáčková J., Kouřil J., 1981. Early ontogeny of the tench, Tinca tinca L. Embryonic  period. Folia Zool. 30 (2), 165–176.

  21. Rezničenko P.N., Gulidov M.V., Kotlarevskaâ N.V., 1968. Vyzivanie ikry lina Tinca tinca (L.) pri postoânnyh temperaturah ikubaci [Survival of tench roe (Tinca tinca (L.)) under constant temperatures of incubation]. Vopr. Ichtiol. 8(3), 492–499 [in Russian].

  22. Stanisz A., 1998. Przystępny kurs statystyki w oparciu o program STATISTICA PL na przykładach z medycyny [A user-friendly course of statistics based on STATISTICA PL software, using medical examples]. StatSoft Polska, Kraków. [in Polish].

  23. Tański A., Korzelecka A., Bonisławska M., Winnicki A., Formicki K., 2000. New data on morphomechanical changes during embryogenesis of pike (Esox lucius L.). Folia Univ. Agric. Stetin. 214, Piscaria (27), 207–213.

  24. Virbickas S., 1969. Lynaas Lietuvoje [The tench of Lithuania]. Leidykla "Mintis", Vilnius, 86pp [in Lithuanian].

  25. Winnicki A., 1968. Rola i właściwości osłonek jajowych ryb łososiowatych [The role and characteristics of egg shells of salmonid fishes]. WSR, Olsztyn, DSc Thesis [in Polish].

  26. Winnicki A., Stańkowska-Radziun M., Radziun K., 1970. Structural and mechanical changes in the membranes of Salmo gairdneri Rich. during the period of hatching of the larvas. Acta Ichthol. Piscat.1, 7–18.

  27. Winnicki A., Korzelecka A., 1997. Morphomechanical aspects of the development of the bleak (Alburnus alburnus L.). Acta Ichthol. Piscat. 27( 2), 17–27.

  28. Winnicki A, Korzelecka A., Bonisławska M., Formicki K., 2001. Bipartity of yolk sac in cyprinid embryos. Arch.  Pol. Fish. 9(2), 279–286.

  29. Wintrebert P., 1912. Le mécanisme de l’éclosion chez la truite arc-en-ciel [Hatching mechanism of the rainbow trout]. Comptes Rendus Academie de Sciences 72, 724–727 [in French].

  30. Załachowski W., 1997. Ryby [Fishes]. PWN, Warszawa [in Polish].

  31.  Zotin A.J., 1961. Otnositel’naâ plodovitost’ i razmiery ryb [Fecundity and sizes of fish]. Vopr. Ichtiol. 1, 2 (19), 307–313 [in Russian].


Accepted for print: 26.11.2009

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

Małgorzata Bonisławska
Department of Aquatic Sozology, West Pomeranian University of Technology in Szczecin, Szczecin, Poland
Kazimierza Królewicza 4B
71-550 Szczecin
email: Malgorzata.Bonislawska@zut.edu.pl

Dorota Pawlos
Westpomeranian Research Centre, IMUZ Szczecin
Czesława 9, 71-504 Szczecin, Poland

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

Aleksander Winnicki
Department of Fish Anatomy and Embryology,
West Pomeranian University of Technology,
Szczecin, Poland
K. Królewicza 4, 71-550 Szczecin, Poland

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

Responses to this article, comments are invited and should be submitted within three months of the publication of the article. If accepted for publication, they will be published in the chapter headed 'Discussions' and hyperlinked to the article.