By: Chris Davis

Rainbow trout were introduced into the UK from the US in the early 1900’s.

This introduction coincided with the need to build extra water supplies for the growing industrial cities such as Bristol and Birmingham.

For a fish that is unable to breed naturally in all but a few British rivers the Rainbow trout has been an incredible success. This is due to its eagerness to feed compared with the native brown trout and its habit of shoaling.

Both of these soon made it a firm favourite with the fishermen and because of the Rainbow trout’s faster growth rate it was a favourite with the fish farmer as well.

The only fly in the ointment was that two different strains of rainbow trout were used – the Kamloops and the Shasta strain. Unfortunately these strains became sexually mature at different times of the year.

This resulted in fishermen catching ‘coloured’ fish in both late and early season.

The development of egg treatment solved this problem by producing Diploid rainbow trout which were all sterile females. This resulted in ‘clean’ fish all year round. As a bonus these trout also grew faster.

The introduction of these ‘sexless’ rainbow trout had another benefit for the angler. It opened the door for the abolition of the closed season for rainbow trout. Pressure from both fishery owners and fishermen forced the abolition of the closed season.

The fishery owners benefited from this move and the faster growth rate of these diploid rainbow trout soon resulted in a new national record fish.

As a result a race began between fish farmers to grow bigger and bigger rainbow trout to meet the demands of the anglers.

Another race began between fishery owners to stock these ‘jumbo’ rainbow trout to attract fishermen to their fisheries.

Selective breeding has since pushed up the growth rate of both rainbow trout and brown trout even more.

Coupled with intensive feeding programs and egg treatment this has produced today’s Jumbo rainbows.

This has led to a totally confusing situation in the record fish list where separate records now exist for all trout species. There are now separate records for fish which have been recently stocked against fish that have been in the water for a period of time or fish that are ‘wild’.

Note. The current British record for rainbow trout stands at 33Lb. 4oz.