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Spring spawning seasonPosted Wednesday, January 12, 2011, at 12:17 PM
Spawning is a fairly complicated process at Roaring River. We start by separating the males and female brooders into different raceways. It is fairly easy to distinguish the sexes because the mature males have a hooked lower jaw and usually a thinner or narrower head and body. Females, on the other hand, lack the hooked jaw and have a more rounded head and body.
Once separated, the females are checked for eggs. They are dipped from the raceway into a tub of spring water, picked up by hand, and, when relaxed, a light pressure is put on the fish's belly. If she is ready to spawn, the eggs are readily released. Those "ripe" with eggs are put into another holding area while the rest are returned to the raceway to be rechecked in five to ten days.
Females ready to spawn are then dipped into a tub of water containing an anesthetic to relax them so the eggs can be taken without injuring the fish or the eggs. At Roaring River hatchery, eggs are taken by the air-spawning method. A hypodermic needle is inserted into the body cavity near the pelvic fin of the anesthetized fish. A pressure of two and a half to three pounds of pure oxygen is then injected into the body cavity. The gentle gas pressure forces the eggs out with no harm to the fish.
Besides being faster, the benefits of this technique include cleaner eggs, fewer eggs left in the fish, and less damage to the eggs or the fish because handling is reduced.
The first eggs taken from a fish are inspected visually to see if they are good. A good egg is one that is ready for fertilization and will have a uniform yellow-orange appearance. Overripe or "bad" eggs have matured beyond the point where they can be fertilized and will have a "bull's-eye" look -- clear glassy edge with solid, opaque middle.
Eggs can be fertilized only within a very limited time period and a few days on either side of that period decreases the percentage of eggs that can be successfully fertilized. That is why the broodstock are checked every 5 to 10 days.
Females with overripe eggs have their eggs stripped and discarded to avoid the stress of having to reabsorb them. Good eggs are collected in a pan which is placed in water to keep the eggs cool. Each female will yield up to 5,000 eggs, depending on her size and age.
The anesthetized male is stripped of its milt, the solution containing sperm, by the hand-spawning method. The milt is added to the eggs and gently stirred with a finger to promote complete fertilization.
A sample of the eggs is counted which gives us an idea of how many eggs there are per ounce and the eggs are then put into jar incubators. The number of ounces of eggs in the jars is measured and the total number of eggs is calculated.
Once the collecting pan is full, the eggs are poured into a bucket of water and taken inside the hatchery to water harden, a process where the egg absorbs water and becomes round and firm. After about 45 minutes, the hardening process is complete.
Water temperature determines how soon the eggs will hatch. At Roaring River the normal water temperature is 57°F and it takes about 21 days for the eggs to hatch. After all the eggs hatch the incubator jars are poured onto wire mesh screens suspended in troughs of flowing water.
The sac fry, newly hatched fish which rely on food stored in a pouch on their belly called a yolk sac, will fall through the screens and sink to the bottom of the trough. Dead eggs and other debris will remain on the screen and be discarded. The percentage of eggs that hatch varies from 50 to 70 percent at Roaring River.
The sac fry receive nutrition from the yolk sac for the first two weeks after hatching. When the sac is completely absorbed, the fry are fed a fine-grained commercial feed made of fish meal, vegetable meal and vitamins. Initially, the fry are fed 12 times a day, but as they grow the number of feedings decreases while the size and amount of the feed increases.
During this time, the troughs are frequently cleaned and a disease watch is kept. If any sign of a parasite or disease problem is detected, medication is dripped into the tanks. Once the fry reach three to four inches they are transferred outside to complete the growing process
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Paul Spurgeon serves as the hatchery manager at Roaring River State Park.
Hot topicsSpring spawning season
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