40 to 140 in 4 Rule. Question

I think you're ok, What did you use for rub/cure? How are you planning to smoke them?

The important question is whether or not you're using CURE in your brine. Salt will in some cases slow down the growth of pathogens, but it's not guaranteed. If you're cold smoking, you really should use cure #1 or tenderquick unless you're well versed and experienced in old world smoking practices. AGAIN, tell us what you used in your brine, and times and temps of your smoking process and someone on here can help you. By giving partial or no information, you're making it impossible to answer your question. As for when the 4 hours starts, it's when the temperature of the food rises higher than 40˚f.

Salt and nitrite will slow or even stop the growth of pathogens if the right concentrations and / or conditions are met.... When smoking fish, the brine / cure mix is considered adequate for several hours of 60-70 deg temp while the fish is in front of a fan to form the pellicle... Once in the smoker, fish is regularly smoked for up to 30 days with a light smoke for several hours a day then no smoke then repeat.... The smoke has a preserving effect also and salmon is usually cold smoked under 70 ish degrees.... There are many methods that use different temp guidelines...
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Copied from the article below....

http://www.douglasbaldwin.com/sous-vide.html

My goal is to maximizing taste and minimizing the risk from food pathogens. While pathogenic microorganisms can be controlled with acids, salts, and some spices, sous vide cooking relies heavily on temperature control (Rybka-Rodgers, 2001).

You were probably taught that there’s a “danger zone” between 40°F and 140°F (4.4°C and 60°C). These temperatures aren’t quite right: it’s well known that food pathogens can only multiply between 29.7°F (-1.3°C) and 126.1°F (52.3°C), while spoilage bacteria begin multiplying at 23°F (-5°C) (Snyder, 2006; Juneja et al., 1999; FDA, 2011). Moreover, contrary to popular belief, food pathogens and toxins cannot be seen, smelt, or tasted.

So why were you taught that food pathogens stop multiplying at 40°F (4.4°C) and grow all the way up to 140°F (60°C)? Because it takes days for food pathogens to grow to a dangerous level at 40°F (4.4°C) (FDA, 2011) and it takes many hours for food to be made safe at just above 126.1°F (52.3°C) – compared with only about 12 minutes (for meat) and 35 minutes (for poultry) to be made safe when the coldest part is 140°F (60°C) (FSIS, 2005; FDA, 2009, 3-401.11.B.2). Indeed, the food pathogens that can multiply down to 29.7°F (-1.3°C) – Yersinia enterocolitica and Listeria monocytogenes – can only multiply about once per day at 40°F (4.4°C) and so you can hold food below 40°F (4.4°C) for five to seven days (FDA, 2011). At 126.1°F (52.3°C), when the common food pathogen Clostridium perfringens stops multiplying, it takes a very long time to reduce the food pathogens we’re worried about – namely the Salmonella species, Listeria monocytogenes, and the pathogenic strains of Escherichia coli – to a safe level; in a 130°F (54.4°C) water bath (the lowest temperature I recommend for cooking sous vide) it’ll take you about 2½ hours to reduce E. coli to a safe level in a 1 inch (25 mm) thick hamburger patty and holding a hamburger patty at 130°F (54.4°C) for 2½ hours is inconceivable with traditional cooking methods – which is why the “danger zone” conceived for traditional cooking methods doesn’t start at 130°F (54.4°C). [Note that Johnson et al. (1983) reported that Bacillus cereus could multiply at 131°F/55°C, but no one else has demonstrated growth at this temperature and so Clostridium perfringens is used instead.]

The 40 to 140 rule only applies to items that have not been treated with a Nitrite Cure...AND..Has had the surface of the meat broken or punctured in some way. See info below from the Food Safety introduction...Additionally, from what you describe you are smoking the fish to 140° which will eliminate bacteria as well. This fish must still be refrigerated...JJ

 Some Guidelines are Standard on SMF...It is important for your Safety, that any Meats that have been Punctured, Probed, Injected or Ground be cooked or smoked at a temperature, typically 225*F or greater, that gets the Internal Temperature of the meat from 40*F to 140*F in 4 Hours or less...Frequently called the 40 to 140 in 4 Rule. (This does not include meats containing Cure #1, Cure #2 and Morton's Tender Quick.)