I would like to point to the difference between the "straw method" and the positive identification method using a catheter that extracts gametes. The latter is the method one would use to know for certain the sex of an LMB. To do this safely requires sedation of the LMB so it isn't injured by the glass tube which is inserted into the oviduct to retrieve eggs for positive identification. If the fish flops around it can break the tube while inserted and even if the tube doesn't break the oviduct could be damaged, be a point of infection, that could later kill the fish. One could consider such a procedure a minor veterinary operation that uses mild anesthesia as part of the procedure. I hope from this description that people can understand the value of what Snipe is doing for his clients. The procedure is involved and requires expertise.
The straw method to which I referred is different. This method instead uses a plastic broom straw for probing the oviduct. The plastic broom straw is polished on the end, is flexible, and is less likely to injure fish. It doesn't require anesthesia and was developed as quick and dirty field technique by wildlife biologists to identify the sex of field samples with higher degree of accuracy than earlier methods of field sexing. The technique yields a high degree of accuracy (> 94%). It can fail in one of two ways. It can fail to identify a female when the straw is not easily inserted into oviduct and it can fail to identify a male when the straw can be inserted into sperm duct to a sufficient depth. There are probably ways to improve the technique with different sized straw for different lengths of LMB. But it is what it is, a simple field technique that isn't 100% perfect but provides highly practical information.
So practical ways to employ the method are:
1. Identifying females in the field in less than a minute for selection of Trophy Path recruits in a mixed sex pond. For example, consider the plan above where the selected recruits are subset of a mixed sex culture of fish. Each year 8 female recruits are selected in the neighborhood of 12" length. If using the straw method to identify sex, then there is only around a 40% chance that 1 of the selection is male. After 2 years there is an 80% chance that 1 of the 16 selected over past 2 years is male. Although not perfect, this is sufficient skewing to get good results.
2. Culling males from a population of mixed sex fish. This includes fish purchased for later selection or positive identification. Above I talk about using the method so as to not have to overwinter fall purchased males in the forage pond. In the practical sense this will lessen the cost of forage over winter and reduce competition allowing for more growth of the females than if all fish overwintered.
For any interested in the broom straw method for field sex identification you can
find a paper describing the method here.
