Maximize Performance

We are continually researching methods and techniques to improve the growth, survival and quality of the freshwater fish stocked into BC rivers and lakes.  This work provides provincial fisheries managers and fish culturists with tools for improving recreational fishing and for protecting and conserving wild fish populations and biodiversity.  FFSBC strives to improve fish performance by researching Non-Reproductive Technologies and Size at Stocking.

Non-Reproductive Technologies

Triploid (3n) Technology

The use of non-reproductive technology in hatchery production has direct benefits to the fishery and protects wild fish populations. This technology involves a sterilization process that is unique to each species of fish. Such treatments increase the cost on a per-fish basis but the fishing benefits can be substantial. Currently, the majority of lakes in BC are stocked with diploid (2N) rainbow trout. However, a treatment or combination of treatments has been conducted for trout releases into almost 40% of lakes to improve the fishery. Similar techniques have and are being developed for eastern brook trout, cutthroat and kokanee.

Currently, the FFSBC induces triploidy through the application of hydrostatic pressure or heated water to the eggs shortly after fertilization. This technique results in the retention of the second polar body normally extruded shortly after fertilization creating three sets of chromosomes instead of the usual two sets. The result is sterility in both males and females. This triploidy method can achieve 100% sterility if the technique has been optimized for the species.

The benefits of sterility include: potential increase in longevity, growth, flesh quality, and the conservation of wild fish.  Triploid fish can potentially live longer and attain a larger size-at-age than diploid fish due to the fact that energy usually diverted into reproductive development can go to somatic (body) growth and natural post-spawning mortality is reduced. Stocking sterile fish into lakes can result in a higher number of larger “bright” fish being available to the fishery.  It also has the advantage of reducing the risk of potential genetic interactions between hatchery and wild fish and/or preventing the establishment of hatchery populations in areas of conservation or biodiversity concerns.

Also, in lakes where there is no spawning habitat, mature females become egg-bound when they cannot find a suitable place to lay their eggs.  It is more difficult and takes longer for a female to recover from a spawning cycle when eggs have to be reabsorbed.  The fish is therefore less attractive to the angler for a longer period of time.

All-female Non-Reproductive (AF3n) Technology

The production of AF3n fish for stocking derives the benefits of both the processes of feminization and triploidization (AF and 3n). Sterilization manifests itself differently depending on the sex of the fish. Female triploids are hormonally and functionally sterile (i.e. no development of functional oocytes (eggs), and no behaviour changes). Male triploids are sterile but still produce hormones that cause changes associated with maturation including deterioration of flesh quality, early mortality and the development of testes and other secondary sex characteristics. In addition, they demonstrate "false" spawning behaviour, including migration and interactions with other fish on the spawning beds regardless of their inability to reproduce.  This behavior can potentially displace wild functionally reproductive males, possibly reducing the fitness of the wild population.

The double treatment (AF3n) for stocking programs further reduces the risk to wild fish since the females will not display “false spawning” and it ensures that if there is a small percent of individuals for which the tripoidy process did not result in sterility, the stocked population would be functionally unable to spawn by virtue of the fact that all progeny are females.

Eastern brook trout are not native to BC in watersheds east of the Rockies.  All eastern brook trout that are produced and stocked in the province of BC are all-female triploid (AF3n) to prevent any interbreeding with the closely related native char species (including bull trout, Dolly Varden and lake trout) or the establishment of naturalized populations.  Although this is done mainly for conservation reasons, the quality of the fish in the fishery is also improved.   The photo below compares brook trout of the same age from the same lake.  The AF3n fish (top) is bright and has firm flesh.  The diploid fish (bottom) has put more of its energy into the production of secondary sex characteristics and less into growth, making it less desirable to the angler.

All-Female (AF) Technology

The creation of an all-female population of fish is labour-intensive. The FFSBC produces all-female populations of fish by crossing sex-reversed females with normal females. To create sex reversed females, normal fry are exposed to testosterone derivatives to halt ovary development and produce normal testes. These "masculinized" females remain genetically female (XX) but functionally male although the sperm must be extracted by hand as these fish generally do not develop a sperm duct. Once mature they are crossed with normal XX females to create all-female progeny for release.

An all-female stock has benefits over a mixed sex (male and female) stock in that it takes advantage of the slower maturation in females compared to males which means more time available to the fishery. Over 80% of males in some stocks exhibit precocious maturation (or “jacking”). These males mature during their first season in the fishery, and with this, comes a high post-maturation mortality, lower flesh quality and an overall smaller fish size. In addition, the stocking of all-female progeny in the absence of males effectively creates a functionally non-reproductive population.

Stocking Sizes

Fisheries managers can improve small lake fisheries by matching specific lake characteristics with the appropriate strain and stock selection, stocking rates, regulations and even stocking the appropriate size of fish.  Although limited somewhat by geographic, economic and individual hatchery facility constrains, the size of fish to be stocked into a lake is an important factor to consider depending on the lake.  In monoculture lakes, survival of even small fish is very good and recruitment into the fishery is likely.  In lakes mixed species lakes, lakes that contain non-salmonid competitor or predatory fish species, size-at-release of trout is more important.  In a study comparing growth and survival of fish stocked at different, survival of large fish (stocked at >20g) was two to three times better that of small fish (stocked at <10g) in mixed species lakes.  More details on this study can be found in the following report.