178
in T. platyurus has yet to be determined, of the two
light intensities used in this study, certainly 2500 lux
was better than 1500 lux.
The hatching progression observed when hydrated
cysts exposed to 4, 8, 12, 16 and 24 h of light were
returned to the dark indicates that, although 24 h of
light exposure may still be inadequate to maximally
trigger hatching, cysts do have a 'light memory'. In
nature, cysts situated at the mud/water interface, in
the turbulent conditions following a sudden rain may
need to overshoot a light signal threshold (determining
that they are in a suitable surface position) before they
'decide' to hatch. There is clearly a light/time or light
intensity/time combination.
DMSO is known to influence the Calcium (Ca2+)
pump (Romero, 1992). In the present study, 0.0375%
DMSO unexpectedly stimulated hatching over the control. It is possible that DMSO at this concentration
increased the permeability of the embryonic cells of
T. platyurus to Ca2+. Dumont et al. (1992) also believe
that Ca2+ inflow to the embryonic cells is a key factor
in cyst hatching. DMSO at low concentrations was not
toxic, and hatched nauplii did survive well subsequently. This indicates that in future work, it will be possible
to study the impact of non-polar compounds, such as
Ca2+ ionophore and others on hatching by dissolving
them in a suitable DMSO-water mixture.
Glycerol improved hatchability at a concentration
of 0.0125%. Glycerol, an osmotically active metabolite produced by the embryo, is responsible for mechanically breaking the tertiary shell in Artemia sp. (Clegg,
1964) and in Chirocephalus diaphanus (Hall & MacDonald, 1975). The increased hatchability of T. platyurus at low quantity of glycerol corroborates earlier
findings of Munuswamy (1989) on Streptocephalus
dichotomus cysts. A lowered hatching at higher concentrations of glycerol, conversely, might be due to
an increase in the viscosity of the medium and perhaps to the rapid development of fungi and baeteria.
Though glycerol, accumulated inside the cysts, aids
the embryo to rupture the shell, its role in hatching
when added externally is indeed not known.
Acknowledgments
We thank Dr Dallas Weaver and Dr Denton Belk, USA,
for the cysts of T. platyurus. One of us (G. M) was
supported by the ICSC- -World Laboratory, Switzerland.
References
Belk, D., 1972. The biology and ecology of Eulimnadia untiei (Conchostraca). Southwest. Nat. 16: 297-305.
Bishop, 1. A., 1967. Some adaptation of Limnadia stanieyana King
(Crustacea:Branchiopoda:Conchostraca) to a temporary fresh
water environment. 1. animo Ecol. 36: 599-609.
Clegg, J. S., 1964. The control of emergence and metabolism by
external osmotic pressure and the role of free glycerol in developing cysts of Artemia salina. J. expo BioI. 41: 879- -892.
Dumont, H. J., P. Casier, N. Munuswamy & C. De Walsche, 1992.
Cyst hatching in Anostraca accelerated by retinoic acid, amplifled by calcium ionophore A 23187, and inhibited by Calciumchannel blockers. Hydrobiologia 230: 1-7.
Hall, R. E. & L. J. MacDonald, 1975. Hatching of the anostracan
branchiopod Chirocephaius diaphanus Prevost. I. Osmotic process and the possible role of glycerol. Hydrobiologia 46: 369375.
Hempel-Zawitkowska, J., 1970. The influence of strong ultraviolet
radiation on hatchability of Triops cancire.fcJrmis (Bosc.) eggs.
Pol. Arch. Hydrobiol. 17: 483-493.
Mitchell, S. A., 1990. Factors affecting the hatching of Streptocephaius macrourus Daday (Crustacea:Eubranchiopoda) eggs.
Hydrobiologia 194: 13-22.
Munuswamy, N., 1989. Aquaculture of sweetwater Anostraca.
Report to the Belgian Administration for Development and Cooperation, 76 pp.
Pancella, 1. R. & R. G. Stross, 1963. Light induced hatching of
Daphnia resting eggs. Chesapeake Sci. 4: 135-140.
Pressman, B. c., 1976. Biological applications of Ionophores. Ann.
Rev. Biochem. 45: 501-530.
Romero, P. J., 1992. Inhibition of the human erythrocyte calcium
pump by dimethyl sulfoxide. Cell Calcium 13: 659-667.
Shan, R. K., 1970. Influence of light on hatching resting eggs of
chydorids (Cladocera). Int. Rev. ges. Hydrobiol. 55: 295-302.
Sorgeloos, P., 1973. First report on the triggering effect of light on
the hatching mechanism of Artemia salina dry cysts. Mar. BioI.
22: 75-76.
Van der Linden, A, 1989. Light induced development of Artemia
cysts. Ph. D. thesis to the University of Antwerpen, Belgium,
155 pp.
Vanhaecke, P., A. Cooreman & P. Sorgeloos, 1981. International
study on Artemia. Xv. Effect of light intensity on hatching rate
of Artemia cysts from different geographical origin. Mar. Ecol.
Prog. Ser. 5: 111-114.
in T. platyurus has yet to be determined, of the two
light intensities used in this study, certainly 2500 lux
was better than 1500 lux.
The hatching progression observed when hydrated
cysts exposed to 4, 8, 12, 16 and 24 h of light were
returned to the dark indicates that, although 24 h of
light exposure may still be inadequate to maximally
trigger hatching, cysts do have a 'light memory'. In
nature, cysts situated at the mud/water interface, in
the turbulent conditions following a sudden rain may
need to overshoot a light signal threshold (determining
that they are in a suitable surface position) before they
'decide' to hatch. There is clearly a light/time or light
intensity/time combination.
DMSO is known to influence the Calcium (Ca2+)
pump (Romero, 1992). In the present study, 0.0375%
DMSO unexpectedly stimulated hatching over the control. It is possible that DMSO at this concentration
increased the permeability of the embryonic cells of
T. platyurus to Ca2+. Dumont et al. (1992) also believe
that Ca2+ inflow to the embryonic cells is a key factor
in cyst hatching. DMSO at low concentrations was not
toxic, and hatched nauplii did survive well subsequently. This indicates that in future work, it will be possible
to study the impact of non-polar compounds, such as
Ca2+ ionophore and others on hatching by dissolving
them in a suitable DMSO-water mixture.
Glycerol improved hatchability at a concentration
of 0.0125%. Glycerol, an osmotically active metabolite produced by the embryo, is responsible for mechanically breaking the tertiary shell in Artemia sp. (Clegg,
1964) and in Chirocephalus diaphanus (Hall & MacDonald, 1975). The increased hatchability of T. platyurus at low quantity of glycerol corroborates earlier
findings of Munuswamy (1989) on Streptocephalus
dichotomus cysts. A lowered hatching at higher concentrations of glycerol, conversely, might be due to
an increase in the viscosity of the medium and perhaps to the rapid development of fungi and baeteria.
Though glycerol, accumulated inside the cysts, aids
the embryo to rupture the shell, its role in hatching
when added externally is indeed not known.
Acknowledgments
We thank Dr Dallas Weaver and Dr Denton Belk, USA,
for the cysts of T. platyurus. One of us (G. M) was
supported by the ICSC- -World Laboratory, Switzerland.
References
Belk, D., 1972. The biology and ecology of Eulimnadia untiei (Conchostraca). Southwest. Nat. 16: 297-305.
Bishop, 1. A., 1967. Some adaptation of Limnadia stanieyana King
(Crustacea:Branchiopoda:Conchostraca) to a temporary fresh
water environment. 1. animo Ecol. 36: 599-609.
Clegg, J. S., 1964. The control of emergence and metabolism by
external osmotic pressure and the role of free glycerol in developing cysts of Artemia salina. J. expo BioI. 41: 879- -892.
Dumont, H. J., P. Casier, N. Munuswamy & C. De Walsche, 1992.
Cyst hatching in Anostraca accelerated by retinoic acid, amplifled by calcium ionophore A 23187, and inhibited by Calciumchannel blockers. Hydrobiologia 230: 1-7.
Hall, R. E. & L. J. MacDonald, 1975. Hatching of the anostracan
branchiopod Chirocephaius diaphanus Prevost. I. Osmotic process and the possible role of glycerol. Hydrobiologia 46: 369375.
Hempel-Zawitkowska, J., 1970. The influence of strong ultraviolet
radiation on hatchability of Triops cancire.fcJrmis (Bosc.) eggs.
Pol. Arch. Hydrobiol. 17: 483-493.
Mitchell, S. A., 1990. Factors affecting the hatching of Streptocephaius macrourus Daday (Crustacea:Eubranchiopoda) eggs.
Hydrobiologia 194: 13-22.
Munuswamy, N., 1989. Aquaculture of sweetwater Anostraca.
Report to the Belgian Administration for Development and Cooperation, 76 pp.
Pancella, 1. R. & R. G. Stross, 1963. Light induced hatching of
Daphnia resting eggs. Chesapeake Sci. 4: 135-140.
Pressman, B. c., 1976. Biological applications of Ionophores. Ann.
Rev. Biochem. 45: 501-530.
Romero, P. J., 1992. Inhibition of the human erythrocyte calcium
pump by dimethyl sulfoxide. Cell Calcium 13: 659-667.
Shan, R. K., 1970. Influence of light on hatching resting eggs of
chydorids (Cladocera). Int. Rev. ges. Hydrobiol. 55: 295-302.
Sorgeloos, P., 1973. First report on the triggering effect of light on
the hatching mechanism of Artemia salina dry cysts. Mar. BioI.
22: 75-76.
Van der Linden, A, 1989. Light induced development of Artemia
cysts. Ph. D. thesis to the University of Antwerpen, Belgium,
155 pp.
Vanhaecke, P., A. Cooreman & P. Sorgeloos, 1981. International
study on Artemia. Xv. Effect of light intensity on hatching rate
of Artemia cysts from different geographical origin. Mar. Ecol.
Prog. Ser. 5: 111-114.