Embryonic Development of Landlocked Atlantic Salmon and Brook Trout

David Marancik & G. Russell Danner MS, DVM

Maine Department of Inland Fisheries & Wildlife


DRAFT January 2002

Abstract

Embryonic development of Pacific Salmonid fishes can be divided into thirty visually identifiable stages between fertilization and hatch. An aquaculturist’s ability to readily recognize these stages in landlocked Atlantic salmon (Salmo salar sebago) and Eastern brook trout (Salvelinus fontinalis) could prove to be useful when estimating percentage survival, estimated time to hatch, or for determining a time of death. Past research has been successful at mapping out the embryonic development of Pacific salmon and correlating this development with water temperature. (Velsen, 1980). This article illustrates these specific stages of development in landlocked Atlantic salmon and Eastern brook trout development because they are important aquaculture species in the eastern United States. Their embryos are somewhat smaller than Pacific salmon’s embryos making it more challenging to identify developmental stages. Although exact details of development may vary between landlocked salmon and brook trout, the stages illustrated within this article provide a reasonable depiction of development for the smaller salmonids. This publication provides additional information about fertilization techniques, water hardening, and egg disinfection.

Introduction

The production of salmonid eggs for private and public aquaculture represents a significant capital investment. Salmonid fishes require between two and five years to become sexually mature, they spawn only once per year, they have a relatively low fecundity compared to other teleost fishes, and they have a limited egg production lifespan. Consequently, quality salmonid eggs are of considerable value. Poor egg quality, infertility, and early embryonic death in salmonid eggs can destroy public and private aquaculture, public restoration efforts, and stock enhancement programs. Early and accurate identification of developing embryos in Atlantic salmon and Eastern brook trout (hereafter referred to as brook trout) eggs would allow broodstock producers to more precisely estimate the number of viable salmon embryos expected. Currently many broodstock facilities raise extra broodfish, collect as many eggs as are available in order to have insurances against poor fertilization and early embryonic death losses, and then discard extra embryos if they are not needed. This management strategy is expensive, labor intensive, and wasteful. An accurate, expeditious, and economical means of assessing salmonid egg fertility, and development would allow broodstock producers to better manage their resources.

Salmonid Biology

Landlocked Atlantic salmon and brook trout are poikilotherms animals whose body temperature varies with that of their environment. In temperate environments, daily and seasonal weather changes cause regular variances in the temperature of fish’s environment. Landlocked Atlantic salmon and brook trout are coldwater stenotherms that generally inhabit waters with summer temperatures 21°C or less, and are most active between 10 and 15°C. These temperature changes alter a poikilotherm’s physiological and metabolic activity including feeding, locomotion, growth, spawning timing, and specifically, embryo development.

Feral landlocked salmon and brook trout migrate upstream or downstream from a lake or river into a spawning area through September and August. The spawning fish are triggered by autumn decreases in water temperature and daylight. Males defend and clear a circular area of cobblestone or gravel stream bottom to produce a “redd” in which the male and female spawn, fertilize, and cover their eggs. A redd contains one or more egg nests from a single mating pair. Spawning occurs between October and November, and the eggs incubate unguarded but concealed within redd nests. The time necessary for egg incubation depends primarily upon water temperature. Between December & February, the eggs hatch but the young egg sac fry (called “alevins”) remain hidden within the gravel using their attached yoke-sac as nutrients for continued growth and development. The alevins won’t begin to feed until the yolk sac has been almost completely absorbed. Water temperatures increase in the spring season and the alevins emerge from the gravel stream bottoms and begin to feed on small aquatic organisms.

Under natural water temperature conditions in Maine, landlocked Atlantic salmon and brook trout young remain buried in the streambed gravels for approximately six-months (e.g., October/November–April/May; Warner and Havey 1985, Bonney in production, Danner, 2000). Under natural conditions salmon egg survival is generally greater than 90% to emergence (Warner and Havey 1985; Hobb 1948; Jordan 1976).

For more information or a complete report, please contact:

Russell Danner, MS, DVM
Fish Health Laboratory
RR5 Box 975
Burns Road
Augusta, Maine 04330
Telephone: (207) 287-2813
Email: grdanner@prexar.com