Page 13 - World Aquaculture Magazine - March 2011

World Aquaculture 11
New concepts for hatching quality
and evaluation of brine shrimp Artemia
(Crustacea: Anostraca) cyst
Alireza Asem1
The cysts of brine shrimp Artemia are widely used in
the aquaculture industry (Sorgeloos 1980, Sorgeloos et al.
1998, Sorgeloos et al. 2001). They are produced commer-
cially by culturists in many places or harvested from their
natural habitat, such as the Great Salt Lake (Van Stappen
2003). Irrespective of the fact that each species or popula-
tion has its own unique characteristics, the processing of
Artemia cysts is an important factor in price determina-
tion. Thus, different definitions have been developed for
the evaluation of the hatching quality of Artemia cysts.
Those hatching percentage, hatching efficiency, hatching
rate, hatching synchrony and hatching output (Sorgeloos
et al. 1978, Van Stappen 1996).
• Hatching Percentage: The number of nauplii that can be
produced under standard hatching conditions from 100
full cysts; this criterion does not take into account cyst
impurities, such as cracked shells, sand or salt, and refers
only to the hatching capacity of the full cysts.
• Hatching Efficiency: Number of nauplii that can be
produced from 1 g of dry cyst product under standard
hatching conditions.
• Hatching Rate: The time period for full hatching from
the start of incubation (hydration of cysts) until naup-
lius release (hatching), at a number of time intervals.
• Hatching Synchrony: Time lapse during which most
nauplii hatch, i.e. Ts = T90-T10.
• A high hatching synchrony ensures a maximal number
of instar I nauplii available within a short time span; in
case of poor synchrony the same hatching tank needs
to be harvested several times in order to avoid a mixed
instar I-II-III population when harvesting at T90.
• Hatching Output: Dry weight biomass of nauplii that
can be produced from 1 gram dry cyst product incubated
under standard hatching conditions; best products yield
about 600 mg nauplii/g of cysts. The calculation is made
as follows: hatching efficiency x individual dry weight of
an instar I nauplius.
These concepts are used in Artemia based on research
(Vanhaecke et al. 1981,Vanhaecke and Sorgeloos 1982,
Drinkwater and Crowe 1991, Triantaphyllidis et al. 1993,
Van Stappen et al. 2003, Saygi 2004, Kara et al. 2004, Abat-
zopoulos et al. 2006) and as quality determining factors for
economic purposes (Vanhaecke and Sorgeloos 1983).
All five definitions, but in particular hatching percent-
age and hatching efficiency, have major roles in cyst quality
determination. The major issue is that these definitions can
provide a real role in cyst quality only where there is a suit-
able processing of cysts. Sometimes, cysts have a high per-
centage of shells and are cracked. Although freshwater-sat-
urated brine technology is used for purification of Artemia
(Baert et al. 1996, Treece 2000), in some cases the method is
not efficient in separating shells and cracked cysts of from
full Artemia2 cysts. Present definitions and calculations are
unable to determine the percentages of shell content and
cracked cysts in samples.
In determining hatching percentage after decapsulation
of cysts, the shells and cysts with undeveloped embryos are
deleted. Most of the cracked cysts disintegrate during the
first 3-4 hours after hydration, but they are included as part
of the cyst batch. Even hatching efficiency is unable to deter-
mine quality of cysts, because it depends on their diameter
(Asem et al. 2007). Moreover, because shells and cracked
cysts are eliminated at the end of determining the hatch-
ing percentage, it doesn’t seem unexpected for the cyst mass
containing shells and cracked cysts to show a high percent-
age of hatching.
This article delineates six new concepts and definitions
for examining the quality and evaluation brine shrimp cysts
that can accurately show the hatching percentage, cyst qual-
ity and purification effectiveness.
New Concepts and Their Formulas
Since hatching percentage can’t clearly provide cyst qual-
ity because cracked cysts are disintegrated in the first 2-3
hours after hydration and the shells are finally removed by
sodium hypochlorite. Therefore, it is suggested the title per-
centage of false hatching (FH) should be substituted for
hatching percentage.
1. Percentage of Potential hatching (%PH): the num-
ber of larvae harvested from 100 shells, perfect and
cracked cysts.