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E. A. G. Vidal and S. von Boletzky
16.5.1 Egg Collection and Transportation
Egg masses can be obtained from females spawning in captivity and collected from
the spawning grounds. In the second case, it entails careful selection of eggs in good
condition, following proper transportation. Embryos and paralarvae can also be produced by in vitro fertilization methods as demonstrated by D. pealeii (Crawford
2002). Studies that focus on aspects of embryonic development should acquire eggs
from captive females or in vitro fertilization, since fundamental information such as
the exact incubation time and the physical conditions the eggs were exposed to can
be obtained and controlled. When eggs are collected from the field, it is advisable
to get hold of them around stages 16–22 (i.e. late gastrulation stages). Collection of
eggs at early stages frequently results in death of the embryos if conditions during
transport and maintenance are not ideal, for instance, major oscillations in water
parameters (temperature, salinity, dissolved oxygen and pH) can lead to abnormalities and death of embryos (Marthy 1972). On the other hand, collection of eggs
at late stages (25–28) entails other problems. Mechanical disturbance may trigger
premature hatching and may cause mass hatching during transport. Additionally,
late-stage embryos metabolize at high rates and require more water and oxygen than
at early stages (Rosa et al. 2012). Thus, depletion of oxygen can occur rapidly causing mass premature hatching due to deterioration of water quality (Hanlon 1990).
Prematurely hatched paralarvae have not yet fully absorbed the outer yolk sack, a
crucial step prior to hatching; thus, the outcome from premature hatching is high
mortality of paralarvae (Boletzky and Hanlon 1983, Hanlon 1990), thus jeopardizing rearing trials.
The effects of transportation conditions on loliginid eggs are largely undervalued; however, when proper conditions are endowed the eggs can withstand long
transport times (~ 24 h, Yang et al. 1983a, b; Vidal et al. 2002a, 2005) at relatively
small shipping costs compared to juveniles and adults (Hanlon 1990). During transport, eggs should be conditioned in double plastic bags containing from 30 to 50 %
of oxygenated seawater with the remaining space filled with pure oxygen. To avoid
thermal shock, they should be slowly acclimatized to the temperature and salinity of
the rearing tanks at destination (1 °C h
−1
, Villanueva 2000b), especially if there is a
difference in any aspect of water quality. Hanlon (1990) provided detailed information on egg transportation and handling.
Eggs produce large amounts of ammonia and require high levels of dissolved
oxygen (Hanlon 1990), demanding pristine water quality and aeration. Excellent
hatching success has been obtained by carefully tying single collective capsules
(strands) or bunches of five to ten egg strands with nylon thread and suspending them in highly aerated water underneath the water inflow of the tanks and/or
maintaining an upwelling flow of water through the suspended eggs (Boletzky and
Hanlon 1983; Paulij et al. 1990; Villanueva 2000a; Vidal et al. 2002a). This simple
procedure exposes the eggs to adequate levels of oxygen that in combination with
high flow rates (Villanueva et al. 2003) and proper current speed inside the tanks
(Vidal et al. 2002a) maximize timely hatching. The aim of keeping egg strands in
E. A. G. Vidal and S. von Boletzky
16.5.1 Egg Collection and Transportation
Egg masses can be obtained from females spawning in captivity and collected from
the spawning grounds. In the second case, it entails careful selection of eggs in good
condition, following proper transportation. Embryos and paralarvae can also be produced by in vitro fertilization methods as demonstrated by D. pealeii (Crawford
2002). Studies that focus on aspects of embryonic development should acquire eggs
from captive females or in vitro fertilization, since fundamental information such as
the exact incubation time and the physical conditions the eggs were exposed to can
be obtained and controlled. When eggs are collected from the field, it is advisable
to get hold of them around stages 16–22 (i.e. late gastrulation stages). Collection of
eggs at early stages frequently results in death of the embryos if conditions during
transport and maintenance are not ideal, for instance, major oscillations in water
parameters (temperature, salinity, dissolved oxygen and pH) can lead to abnormalities and death of embryos (Marthy 1972). On the other hand, collection of eggs
at late stages (25–28) entails other problems. Mechanical disturbance may trigger
premature hatching and may cause mass hatching during transport. Additionally,
late-stage embryos metabolize at high rates and require more water and oxygen than
at early stages (Rosa et al. 2012). Thus, depletion of oxygen can occur rapidly causing mass premature hatching due to deterioration of water quality (Hanlon 1990).
Prematurely hatched paralarvae have not yet fully absorbed the outer yolk sack, a
crucial step prior to hatching; thus, the outcome from premature hatching is high
mortality of paralarvae (Boletzky and Hanlon 1983, Hanlon 1990), thus jeopardizing rearing trials.
The effects of transportation conditions on loliginid eggs are largely undervalued; however, when proper conditions are endowed the eggs can withstand long
transport times (~ 24 h, Yang et al. 1983a, b; Vidal et al. 2002a, 2005) at relatively
small shipping costs compared to juveniles and adults (Hanlon 1990). During transport, eggs should be conditioned in double plastic bags containing from 30 to 50 %
of oxygenated seawater with the remaining space filled with pure oxygen. To avoid
thermal shock, they should be slowly acclimatized to the temperature and salinity of
the rearing tanks at destination (1 °C h
−1
, Villanueva 2000b), especially if there is a
difference in any aspect of water quality. Hanlon (1990) provided detailed information on egg transportation and handling.
Eggs produce large amounts of ammonia and require high levels of dissolved
oxygen (Hanlon 1990), demanding pristine water quality and aeration. Excellent
hatching success has been obtained by carefully tying single collective capsules
(strands) or bunches of five to ten egg strands with nylon thread and suspending them in highly aerated water underneath the water inflow of the tanks and/or
maintaining an upwelling flow of water through the suspended eggs (Boletzky and
Hanlon 1983; Paulij et al. 1990; Villanueva 2000a; Vidal et al. 2002a). This simple
procedure exposes the eggs to adequate levels of oxygen that in combination with
high flow rates (Villanueva et al. 2003) and proper current speed inside the tanks
(Vidal et al. 2002a) maximize timely hatching. The aim of keeping egg strands in