Broodstock are like all other animals; crowd them and they get excited; excite them and they become stressed; stress them and they will get sick. The key is to maximize yield by minimizing stress.

Broodstock are an orchestration of hormones all fighting to get their jobs due before the inevitable. There are the obvious hormones racing about; gonadotropins to mature the gonad and steroids to mature th gametes and cause the secondary sex characteristics. However, behind the scenes all sorts of other hormones are looking after the physiological transition from seawater to freshwater; the exact opposite of becoming a smolt. Digestive hormones also change as the fish stop eating and releases nutrients from stored reserves. In a netfull, broodstock have a lot of endocrinology happening without having to deal with stress.

Cortisol and some other stress hormones called glucocorticoids serve to liberate energy reserves and increase the availability of high energy sugars. This is for the "flight or fight" mechanism everyone has heard about. Cortisol has another effect that is a little more dramatic: it can effect a shutdown of the reproductive process. It can also serve to repress the immune system if the stress persists. Here's the point: If broostock are stressed at critical times, they'll never spawn or will yield poor quality gametes. With rough handling, brood can die or bug numbers increase to the point where BKD or other diseases can occur in the offspring.

Nice concept to leave the fish alone and enjoy the autumn of their lives, but reality dictates that fish are handled several times before they can be spawned. Thankfully, there are sedatives and anesthetics.

There are many ways to knock fish out. Some are better than others and some are near to voodoo. Duty and responsibility dictate that only approved products be discussed. Be aware Tat some unapproved products do not have to live up to claims. Currently, metomidate for non-food fish and tricaine methanesulfonate (TMS in Canada; MS-222, Tricaine-S and Finquil in USA) for food fish, are the only approved products for use in North America.

Metomidate is a sedative. It works from the inside out. That is, at lower doses it affects the central nervous system by acting as a blocker of sensory input processing. However, it does not block the processing of pain. This is accomplished by an anesthetic such as TMS, which dulls the peripheral nervous system and the perception of pain, but doesn't block the processing from the other senses; sort of like being paralyzed feeling no pain but being aware. Ideally, the preferred method is to use a sedative prior to anesthesia. This two step treatment is good at keeping cortisol levels down when compared to no treatment or TMS alone (Kreiberg and Powell, 1991). However, from a practical level, expense and time are considerations. Like metomidate, TMS at high doses is also thought to act centrally, so this may serve the purpose in a practical sense. Dr. George lwama at the University of British Columbia has published in this area and the reader is directed to his articles for further in depth information.

When TMS is used as described on the label, it can serve to lessen the impact of handling stress on fish in part by reducing the cortisol response. It is then safe to handle your fish, provided all care and respect are given to the fish and the gametes they are growing. A few cautionary notes: 1) cover anesthetic baths; sunlight can degrade tricaine in solution, 2) Tricaine is acidic so freshwater anesthetic baths must be buffered with balkng soda or salt water, 3) aerate the bath and change the bath often because skin, slime (and whatever) will clog the fishes' gills, and 4) never use any tricaine product in the presence of metal. The latter only a chemist would understand.