Hybridization: creating new strains of trout

Hybridization creating new strains of trout

Over the years scientists and fish farmers have produced various trout hybrids. The motivation behind this has been to diversify trout fisheries and to find out if hybrids were in some way better than their parent species. trout and the North American brook char (which is often referred to as the brook trout). The result of the cross is the very beautiful tiger trout (sometimes also called the zebra or leopard trout).

Other experiments included crosses between rainbow trout and brown trout to

In the 1970s various hybrids were created in fish hatcheries and then stocked in stillwaters for anglers to catch. Most of the hybridization attempts were only interesting experiments. This wasn’t a new thing. Two pioneers of salmonid rearing, Francis Day and Sir James Maitland, produced many hybrids in the 1870s and 1880s.

Modern experiments

Modern experiments have been mostly concerned with hybrids between the brown

The second apparent advantage in producing hybrid trout is what is called ‘hybrid vigour’, which was seen in first generation fish. This means that the hybrid can be a ‘better’ fish (stronger and more robust) than either of its parents, having more of the ‘good’ points than the ‘bad’. Although this ‘advantage’ is widely believed and much discussed among both zoologists and anglers, there is very little scientific evidence for its existence in animals, and virtually none among higher animals.

The tiger trout is not notably larger, faster-growing or stronger than its two parent species. In the case of sterile hybrids, the energy normally used in producing eggs or milt goes into body bulk, either more fat and muscle or just faster growth. But in the 1990s trout farming has made such huge strides in producing both massive brown and rainbow trout that the hybrids are no longer seen as having any real advantages. create the brownbow hybrid. And then as an extension of this, the sunbeam trout was produced by crossing a brownbow hybrid with a brown trout.

Occasionally tiger trout are found in the wild. For example, a number were caught in small tarns in the Lake District. The population resulted from the introduction of American brook char to a water in which native brown trout were living. Since the trout occupied the most suitable breeding places, the brook char had either to breed in unsuitable areas (which is unlikely) or join the trout when spawning. When they spawn alongside the trout, hybrids are often the result.

As a general rule hybrids among different species of salmonids occur only when man has altered the habitat in some way or another. In most fish there are barriers against cross-breeding. For example, different species spawn at different times of the year. Other species spawn in different places, and still others have distinct behavioural displays before or during spawning which act to ensure that only members of the same species get together.

Naturally occurring tiger trout hybrids which followed the introduction of the brook char to the water are another aspect of human interference with nature.

Why experiment?

There were two main reasons for experimenting with hybrids for fishery purposes. One was that since hybrids are infertile (although not all are), they could be introduced into a fishery with no fear of creating a population of inter-related hybrids or back-crosses with established stocks. In practice this didn’t prove an important advantage because trout farmers manage their stocks efficiently.