FACTORS INFLUENCING EGG VIABILITY

From: Samuel R. Chapman

To: aqua-l@upei.ca

Sent: January 23, 2000

QUESTION:

I operate a hatchery in the state of Maine, USA, that produces American shad Alosa pseudoharengus for a state sponsored restoration program. East coast, USA, American shad restoration efforts depend heavily, but not completely, on eggs collected from spawning adults caught in nets on the spawning grounds. The number of eggs available is the main bottleneck in the collective east coast restoration effort. Increasing overall egg % viability would enhance all hatchery efforts. The viability in the eggs from the netted shad can range from 5% to 90%. Our average is about 55%. One trial using 45% saline water in the fertilization process, when compared to river water, showed a marked improvement in % viability. We need to test this technique, in a qualified way in the upcoming season. I have located published papers that offer different reasons why this might work for several fish species other than shad. That's ok. I'm looking for a base of information I can utilize as a starting point. I would appreciate your assistance in locating more techniques, published articles and information that indicate factors that do or might affect egg viability. My expectation from this input is to be able to incorporate some "new" methods and increase our overall viability by a few %.

American shad are anadromous. They spawn in swiftly running riverine conditions, usually between the hours of 7:00 PM to 11:00 PM. They are spring spawners, most active between 17 degrees C to 22 degrees C. By the time the rivers hit 24 degrees C the spawning run is over. The eggs are usually processed either on the net boat or on the river banks. Eggs are allowed to water harden 1.5 hr, then packaged, 5 liter of eggs plus 5 liters of water, inside plastic bags with an oxygen atmosphere. Then the bags are placed in insulated boxes for shipment to the hatcheries. The eggs may be in the shipping containers 7-10 hours depending on hatchery location. Upon receipt in the hatchery the viable eggs are usually well into a capped stage with cells not yet beginning to envelop the yolk. The eggs are disinfected with 50 ppm iodine solution at pH 7. They are slowly acclimated, +/- 0.5 degree C, to hatchery water. Normally egg viability does not degrade after the eggs go into the incubation system.

Sam Chapman

Waldoboro Shad Hatchery

50 Bremen Road

Waldoboro, Me 04572

USA

Tel: 1-207-832-7548

Fax: 1-207-832-7831

E-mail: samchap@ime.net

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COMMENTS 1:

I'm unclear if you are spawning alewife, Alosa pseudoharengus, as your message stated, or American shad, Alosa sapidissima, also as your message stated. You either used the incorrect scientific name or the incorrect common name. My recommendations would be different for the different species.
If you really mean the smaller alewife, I'd suggest you try moving
prespawning adults to the new restoration waters. American shad adults are difficult to move successfully (even with using round tanks with pump induced circular currents) and generally are strip-spawned at the bank as you described it. Check with Dick St. Pierre of the US Fish and Wildlife Service to get descriptions of his techniques, developed many years ago in Susquahanna River American shad restoration efforts. You can get his address from any USFWS office.
I would make two general suggestions however. (1) Water harden the eggs on the bank and not the boat as the boat bouncing can be part of your problem. And (2) It is also important to remember that American shad are incremental spawners. If you are stripping the females aggressively you are probably getting more eggs than are ready to be fertilized. No matter what you do at that point the (not ready) eggs will not develop beyond the first or second cell division. Also there was considerable difference between the success of early vs. late season spawners, as I remember my data on reintroducing American shad to the Savannah River in the mid-80's. I suggest you don't get too anxious to fill up your hatching jars early in the run, but space the effort out over the entire run. And don't try to get too many ova from any one female. Poor genetic variability as well as expending effort on immature ova. One last item. When you dry fertilize the ova don't just mix the sperm from more than one male into a bowl of ova. Instead split the eggs into two bowls and use a single male per bowl. That way one male's sperm will not be fertilizing most of the eggs, as is usually the case when more than one male per bowl is used.

Richard Eager

E-mail: dreager@awod.com

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COMMENTS 2 :

I mean Alosa sapidissima.

You need to know that I am not personally involved in the drift net egg-take operation for the shad eggs. That is contracted out to companies with years of experience stripping shad eggs. I have participated in that operation on both the Delaware River and the Connecticut River and I am aware of the techniques used. I strongly believe that present egg viability is greatly dependent on WHO is stripping the adult shad and the particular batch of shad in the run on any one night. The egg-take crews are capable of delivering 80% to 90% viable batches of eggs so their artistry is not in question. I can tell when new personnel take part in a night's egg-gathering by the quality of the eggs received at the hatchery the next morning. Our egg-take effort on the Connecticut River extends over a 12-14 day period and includes the beginning and the end of the run. After two seasons of looking at egg size and viability I feel that most of the smaller eggs, less than 2 mm, can be removed by sieving. Those eggs less than 2 mm are either the immature eggs from the too aggressive stripping you mention or are just smaller fertilized eggs that will not hatch.

We are presently considering the effect of various ionic concentrations and the timing of their use on egg viability. After I spent a lot of time shotgunning journals for viability related articles I eventually found some that seem to connect good early cell development to the timing of the presence of ionic concentrations in the early fertilization process. Nothing to do with shad but all relevant information that might prove beneficial.