Fluidized Bed Hatcher

Instructions and Notes:

 

Introduction:

 

Fluidized bed hatchers are designed for developing zebra fish embryos with minimal stress on the developing embryo and automatic removal of any non-developing embryos. They consist of an up-flow tube where water entering underneath a small bed of glass bead media causes the bed to expand and fluidize.  With proper adjustment of the flow rate, zebra embryos will fluidize on top of this fluidized glass bead media.  This procedure effectively suspends the developing embryos in a uniform up-flow of clean water, which removes the waste products from the developing embryo while providing oxygen.  Non-viable eggs tend to swell up and are removed by the up-flowing water.  These units are designed to handle 1 to 2000 zebra embryos at a time.

 

Installation:

 

The FBH consists of a vertical fluidizing column and a horizonal discharge piece that hangs on the side of a standard rack tank from either Aquaneering, Inc. or Aquatic Habitats, Inc.  Fluidization is achieved by introducing water into the media via a pipette used as probe. 

 

The flow rate to the probe must be very constant and well regulated.  With very low flows in real fish systems, there is always the possibility of small particles blocking small orifices.  This unit is equipped with a fixed turbulent flow device for flow control, which is less sensitive to small particles than a small valve or orifice.  This device uses a long internal path rather than a small orifice for flow control.  Different system pressures will require different flow control devices to attain the correct level of flow rate.  The internal control element is changeable, and three different flow resistances are provided in the kit. 

 

The water inlet manifold also has a small ball valve, which can be used when the system pressure is abnormally low or when you want to flush larva out of the column.  The manifold can be connected via 1/4 OD tubing to the system water supply. 

 

The water inlet probe is centered in the column with a 1 hole rubber stopper.  These stoppers have been leached to reduce the levels of toxins to the point of passing bioassay with zebra larva, although the stoppers are always above the water, so they would not pose a problem anyway.

 

 

A common practice in using this system is to setup a standard rack tank with a fine mesh screen (300µ screen) on the discharge.  Air injection behind the screen is advised to help keep the screen clean and eliminate any oxygen problem without adding turbulence to the tank.

 

 

 

 

 

¥ Add about 3" of media to the column, then mount the column on the tank.  More media can be added when there are fewer than 100 embryos.  The deeper media can make a more stable bed with less turbulence reaching the eggs.

 

¥ Insert the probe and adjust the water flow (change the turbulent flow controls to the correct size for your system pressure).  The media should expand about 20 to 30% in volume.

 

¥ Make sure the probe is centered when adjusting the flow rate. 

 

¥ Remove the probe and add the embryos. 

 

¥ Reinsert the probe with the water flowing and get both the media and the embryos fluidized.  If you have a large batch of embryos with a high percentage of non-viable embryos, it is advisable to run a slightly higher flow rate and higher fluidization expansion on the eggs. This will minimize the impact of the non-viable embryos and associated bacteria on the viable embryos.  By being very careful about the flow rates, it is possible to get a good hatch with < 50% viable embryos without manual separation. 

 

¥ Check the level of fluidization (which is a measure of the flow rate).  A piece of tape on the tube with a mark works well.

 

¥ Check daily to make sure the flow has stayed constant. 

 

Notes:

 

The extra turbulent flow control units provided with each unit can be used to obtain a low flow rate into the larval tank.  When feeding live food, you need a low water exchange rate of about 1 to 5 hr to prevent too much food loss.  When you have an air-line behind the screen, you won't have a low oxygen problem with low water exchange rates.

 

After hatching, some of the larva will want to stay in the hatcher.  The ball valve can be used to increase the flow and flush them out into the tank. 

 

The tank into which the larva are discharged must have a clean water surface.  Having a drip of water into the tank will help clean the surface.