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Bulletin of the Sea Fisheries Institute 2 (156) 2002 - CEEMaR

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52 K. FORMICKI, A. KORZELECKA-ORKISZ, M. BONIS£AWSKA, A. TAÑSKI, W. WAWRZYNIAK and A. WINNICKI<br />

number <strong>of</strong> movements [1min.]<br />

60<br />

50<br />

40<br />

30<br />

20<br />

10<br />

heart<br />

somatic<br />

0<br />

57 63 70 83 96 121 145 171<br />

time from fertilization [h]<br />

Fig. 4. Somatic and cardiac movements <strong>of</strong> herring Clupea harengus membras L. larvae<br />

during embryonic development.<br />

DISCUSSION<br />

The results obtained provided a fairly complete picture <strong>of</strong> <strong>the</strong> morphomechanical changes which<br />

take place during <strong>the</strong> embryogenesis <strong>of</strong> spring-spawning Baltic herring; some <strong>of</strong> <strong>the</strong>m, however,<br />

require additional discussion.<br />

The first important issue is <strong>the</strong> size and shape <strong>of</strong> <strong>the</strong> perivitelline space, which is created<br />

after activation and which determines <strong>the</strong> egg size. The sizes <strong>of</strong> eggs differ significantly and,<br />

unlike o<strong>the</strong>r salmonids, <strong>the</strong> difference in <strong>the</strong> size <strong>of</strong> <strong>the</strong> entire egg does not depend on <strong>the</strong> size<br />

<strong>of</strong> <strong>the</strong> egg cell (yolk sphere) which is <strong>the</strong> same in every egg from a given batch.<br />

The idea introduced by Zotin (1954) can be helpful in order to explain <strong>the</strong> mechanism<br />

which limits <strong>the</strong> size <strong>of</strong> <strong>the</strong> perivitelline space (amount <strong>of</strong> water absorbed by eggs). Zotin<br />

maintains that this mechanism involves only <strong>the</strong> increase <strong>of</strong> membrane resistance, which,<br />

following egg activation and hydration, also limits membrane plasticity. This explanation is<br />

acceptable since even small variations in <strong>the</strong> normal amounts <strong>of</strong> membrane-hardening enzyme<br />

released into <strong>the</strong> perivitelline space (Zotin 1961, Fisher 1963, Winnicki 1967b) may<br />

temporally shift <strong>the</strong> membrane hardening, while variations in <strong>the</strong> amounts <strong>of</strong> hydrophilous<br />

colloids responsible for water absorption (Bogucki 1930) can change <strong>the</strong> rate <strong>of</strong> water absorption.<br />

This may result in egg size variations. The above described mechanisms do not<br />

play a very important role in <strong>the</strong> egg development <strong>of</strong> o<strong>the</strong>r fish such as salmonids, for which<br />

<strong>the</strong> relative size and volume <strong>of</strong> <strong>the</strong> perivitelline space is relatively small and basically uniform,<br />

while <strong>the</strong> membranes <strong>the</strong>mselves are structurally solid and far less flexible (Winnicki<br />

and Domurat 1964). The phenomenon <strong>of</strong> <strong>the</strong> egg size diversity should be connected with <strong>the</strong><br />

primary structure and size <strong>of</strong> <strong>the</strong> membrane surface created during oogenesis, which, at <strong>the</strong><br />

moment <strong>of</strong> laying, is clearly corrugated and stretches during <strong>the</strong> egg hydration period (Winnicki<br />

1968).<br />

This idea is supported by <strong>the</strong> unusually spacious perivitelline space <strong>of</strong> <strong>the</strong> herring egg<br />

(Fig. 2e). In o<strong>the</strong>r fish, this area constitutes less than approximately 20% <strong>of</strong> <strong>the</strong> hydrated egg,

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