Steven Evans, 21, Levi Evans, 18, and Tom Evans, 22, were all convicted of an offence of destroying or attempting to take or destroy any fish in water which is private property, and an offence of fishing for trout without a licence.
The case relates to an incident on a private stretch of the River Wye, in Monsal Dale, in Derbyshire, on August 24 last year when four defendants were identified.
The case against all three, of Park Hall Caravan Site, Oswestry, was proved in their absence following a hearing at Northern Derbyshire Magistrates Court, in Chesterfield.
Each of them was ordered to pay a fine, costs, compensation for dead fish and victims' surcharge totalling £1,008.
A fourth defendant James Hezekiah Evans, 21, of Yarnfield, Staffordshire, pleaded guilty to the offences and was ordered to pay a total of £434 comprising a fine, costs, compensation for dead fish and victims' surcharge.
The penalty was imposed for the charge of stealing and killing a total of 28 fish. There was no separate penalty imposed for fishing without a licence.
The case was brought by The Environment Agency under the the Salmon and Freshwater Fisheries Act 1976 and the Theft Act 1968, as amended by the Marine and Coastal Access Act 2009.