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(RACE) DIVISION  (cont.)

Incubating Fertilized Arrowtooth Flounder Eggs

see figure caption for explanation

Figure 1. Arrowtooth flounder embryo from 4.5°C, 353 hours after fertilization.

Eggs from mature arrowtooth flounder (Atheresthes stomias) collected at two separate locations, were successfully fertilized at sea during the Winter Ichthyoplankton Survey on the NOAA ship Miller Freeman (cruise MF-03-02) and transported to the Kodiak Fisheries Research Center’s seawater laboratory facility for incubation in February 2003.  The objectives of this project were to incubate arrowtooth flounder eggs at three different temperatures and to describe progressive stages of the egg development and larval pigmentation after hatching (Fig. 1).

  picture of an egg incubator
Figure 2. Egg incubator.

Two separate batches of eggs were fertilized at different times on the Miller Freeman.  During the cruise, viable fertilized eggs were transferred into three refrigerators set at different temperatures (3.0°, 4.5,° and 6.0°C) and sampled every 2 hours until the blastodisc had formed.  The first batch of eggs reached this stage just before the cruise ended and were transported to the Kodiak Fisheries Research Center’s seawater laboratory facility 3 hours after docking 23 February 2003. The second batch of eggs was transported 24 February, after these eggs had developed to the same stage as the first batch before transferring to the lab.

  picture of a flow-through chilled seawater system

Figure 3. Flow-through chilled seawater system.

The fertilized eggs were immersed in 3.0°, 4.5°, and 6.0°C seawater using six incubators manufactured at the Kodiak Fisheries Research Center.  The egg incubators were created out of 1-foot sections of 10-inch diameter PVC pipe covered with 1.0 mm mesh at the base and suspended from the insulating cover floating on the surface of the tank with three-fourths of the incubator submerged in water (Fig. 2).  Chillers were used on two of the tanks to reduce the temperature of the circulating seawater to 3.0° and 4.5°C, while the water temperature in the 6.0° C tank was maintained using a 100-watt aquarium heater in combination with the seawater pumped into the tank (Fig. 3).  Calibrated temperature data loggers in each tank recorded water temperatures every 2 hours.  The developing eggs were kept in total darkness by covering the tops of the tanks with 5-mil black plastic sheeting, except during sample collection.  Samples of the egg stage advancement were collected every 6 hours until the eggs developed an early germ ring around the yolk, then every 12 hours until hatch.  The mesh at the base of the incubator was changed to 500 microns before the larvae hatched out of the eggs.

The two separate batches of fertilized eggs were successfully reared to hatching in the egg incubators.  The progressive stages of egg development in different water temperatures were collected and recorded (Fig. 1).  This data will be used to develop formulas to predict age at stage of arrowtooth flounder eggs at a range of temperatures and assist with the identification of arrowtooth flounder eggs captured in ichthyoplankton samples.

By Liz Chilton.


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