Fish Hatchery Management - fisheries & aquaculture

t70FISH HATCHERY MANAGEMENTequilibrium they become inactive. opercular movement decreases. whenthe fish can no longer make swimming movements, the respiration becomesquite rapid, and opercular movements are difficult to detect. At this point,the fish may be removed from the water and spawned. If gasping and muscularspasms develop while a fish is being spawned, it should be returnedto fresh water immediately. If the fish has been overexposed to the drug,respiratory movements will cease. Rainbow trout placed in a 2(j4 parts permillion solution of M5-222 require 30 to 45 seconds to become relaxed.concentrations of 0.23 gram of benzocaine per gallon of water or 0.45gram of MS-222 per gallon of water are commonly used to anesthetizedfingerling Pacific salmon.Use of MS-222 as an anesthetic for spawning operations is widespread.However, concentrations as low as ltl.9 parts per million have reducedsperm motility. Therefore, the anesthetizing solution should not come rncontact with the reproductive products. Adult Pacific salmon have beenanesthesized with a mixture of 40 parts per million MS 222 and l0 partsper million quinaldine. carbon dioxide at concentrations of 200 400 partsper million, is used in some instances for calming adult pacific salmon. Itcan be dispersed into the tank from a pressurized cylinder through a carborundumstone.Both ether and urethane have been used in the past, but both should bediscontinued due to the high flammability of ether and the possible carcinogenicproperties of urethane.Artificial Control of Spawning TimeManagement requirements and availability of hatchery facilities often makeit desirable to spawn fish at times different from the natural spawning date.Several methods have been used with success.PHOTOPERIODcontrolledlight periods have been used with several species of fish tomanipulate spawning time. The Fish and wildlife Service's Salmon culturalLaboratory, Entiat, washington, conducted a 13-year study to determinethe effect of light control on sockeye salmon spawning. The study showedthat salmon exposed to shortened periods of light spawn appreciably earlier.Egg mortalities can be significantly higher, however. Light, not temperature,is apparently the prime factor in accelerating or retarding sexualmaturation in this species; although temperatures varied from year to year,salmon receiving no light control spawned at essentially the same timeeach year.