Egg Incubation, Alevins & Early Fry Rearing

By G. R. Danner MS, DVM

Volume 2, Issue 12
December 2000
Updated November 2002

four-cell brook trout embryo
Fig. 1. Four-cell brook trout embryo.

eight-cell salmon embryo

Fig. 2 Eight-cell salmon embryo.

All eggs fertilized and unfertilized, undergo water hardening.

The embryonic development that follows in fertilized eggs can be divided into three phases-cleavage, gastrulation and organogenesis. In salmonids, there are at least 27 distinguishable stages of development (Vernier, 1969). Different development stages can be viewed through the egg shell with the aid of Stockard solution and a hand lens or dissecting microscope. Egg quality begins with broodstock health and care.


Brook trout embryos
Fig. 3. Brook trout embryos completing epiboly.

Eggs, alevins, and fry are affected by water quality parameters.

Hatchery water quality should be measured and adjusted to maximize egg, alevin, and fry growth.

Stockard Solution (1 liter):

50 ml formaldehyde, 40 ml glacial acetic acid, 60 ml glycerin, and 850 ml distilled water.


salmonid embryo
Fig. 4. Salmonid embryo with caudal bud

Sources of information about trout and salmon incubation and early rearing:

Marancik, D. & G.R. Danner. 2001 Embryonic Development of Landlocked Atlantic Salmon and Brook Trout. Maine Dept. of Inland Fisheries and Wildlife, Augusta.

Pennell, W. & B. Barton. 1996. Principles of Salmonid Culture. Developments in Aquaculture and Fisheries Science, 29. Elsevier, New York.

hatching alevins

Fig. 5. Hatching alevins.

Vernier, J-M. 1969. Chronological table of the embryonic development of rainbow trout, Salmo gardneri Rich. 1836. Ann. Embryol. Morphog. 2:495-520. (Trans. From French by Fish. Mar. Serv. Transl. Ser. 3913, 1976)


pigmented eyes
Fig. 6. Pigmented eyes

Images from Velsen, F. P.J. 1980. Embryonic development in eggs of sockeye salmon, Oncorhynchus nerka. Can. Spec. Publ. Fish. Aquat. Sci. 49:19p.

Special points of interest:

Fertilization rates can be determined after approximately 24 hrs of incubation.

Stockard solution makes it possible to see internal egg development stages.

Evaluating dead eggs can help determine the cause of death.