Light is much like the Force, “Its energy surrounds us, binds us.”, and although most life on our planet requires its presence to survive, light is not a topic the average person spends a great deal of time thinking about (Kershner, 1980). Light impacts all creatures on our planet, defining how they perceive the world around them, shaping how life functions and triggering evolutionary processes. Because of the significance light has on all life, understanding its effects on the life cycles, patterns and development of salmon is essential for salmon fisheries to be able to create environments that produce healthy salmon of the highest quality, reduce the risks associated with early maturation of salmon stocks and improve their overall profits.

Research into the effects of light on fish is nothing new, in fact light has been long used as a tool in fishing, historically being purposed to lure fish to it so they could be captured more easily. Over many years this research discovered that, “(a)tlantic salmon is very sensitive to light, both for smoltification during the freshwater stage and during the on-growing stage in sea water.”. Further studies showed that the use of high intensity artificial lighting in salmon pens can be used “to suppress early maturation during the on-growing stage”, leading many salmon fisheries to implement artificial lighting in their salmon pens (Orrego, 2018.). The impacts of light on salmon development is due to the fact that, much like human beings, fish require a hormone called melatonin to properly sync their biological rhythms, allowing them to determine night from day, the current season and time of day. This process takes place in the pineal gland of fish which works as a mini computer, that absorbs the light signals taken in by the fish and translates them to “rhythmic hormonal signals” that flow through the blood stream providing information that is vital to many species as it often dictates when they rest, mate, hunt, or perform other functions needed for their health and survival (Bruning, 2016). Most melatonin production occurs at night signalling the change in the time of day to the salmon, and triggering a change in their swimming behaviours as their feeding, mating and migration are mainly done during the night where the dark waters can help conceal salmon from predators. This light dependant biological clock that we share with fish is what signals their bodies to develop, grow and reach sexual maturity and allows for the effects of artificial lighting to trick these processes to promote growth while delaying maturity in the salmon. Knowing that the biological process of salmon can be altered using light has promoted further studies into exactly how light impacts salmon stocks, to try and achieve the perfect lighting formula.

Fisheries and Oceans Canada examined two southwestern New Brunswick salmon fishery sites in 2001, and observed that “more than 30% of the fish in some sea cages…” matured earlier than their wild counterparts with speculation that this is due to a lack of light exposure within the pens (cages) (Aquaculture Science Branch, 2012). This early maturation, called ‘grilsing’, results in the quality of the salmon dropping significantly increasing the risk of the grilsing salmon developing health issues, contracting diseases and impacting their market price, if they make it to market at all. These complications result in a domino effect triggered by the removal of stock that is impacted by any disease or health issues, causing additional stress to the healthy salmon in the pen, which negatively impacts their health, perpetuating an infuriating cycle that can be difficult to remedy and can greatly impact the finances of the fishery.

In the 2012 report on the 2001 study from Fisheries and Oceans Canada, analyzed the effects of photomanipulation on salmon in the Bay of Fundy within the two sites in southwestern New Brunswick. This study demonstrated that the time of year in which photomanipulation was implemented could be another major factor in discovering the perfect formula for lighting in salmon fisheries. Site #1 placed two artificial lights in six pens, lighting three on November 21, 2001 and the other three on February 15, 2002 and keeping them lit until May 31, 2002 and allowed for six other pens to be naturally lit as a control. Site #2 had two pens that were lit for 24 hours a day from October 31, 2001 to May 31,2002 and two that were naturally lit as control. Throughout this process the salmon in these pens were constantly filmed and samples were taken from each pen periodically to record their “Sex, round weight, fork length, girth, dressed weight, mean fat content, and gonad weight…” as well as their “length, weight, sex, maturity, and total muscle fat content (leanness)” to compare the lit pens to each other as well as the control pens (Aquaculture Science Branch, 2012).

Their findings showed that while the growth rate of salmon in the artificially lit pens was slower at first, it became “consistently greater than in the control cages”, with the pens that were lit in November producing salmon that were growing “at a rate of 0.32% body mass per day, compared to the control pens at 0.29% per day” [Figure 1]

(Aquaculture Science Branch, 2012). In addition, the rate that the salmon matured was considerably slower in the artificially lit environment than within the naturally lit control pens, with 22% and 17.5% of all the fish in control pens at Site #1 and Site #2 respectively, reaching maturity while the results of maturity in the artificially lit pens produced fascinating results. The pens that were initially lit in February had an average 11% maturity rate in its salmon, while the pens lit in October at Site #2 saw “…8.5% of the males and 1% of the females were mature.” [Figure 2],

but those pens initially lit in “…November showed consistently that only 2% of the males sexually matured and none of the females matured by May 2003.” [Figure 3],

with later experiments showing that lighting pens even as late as December will still yield similar results (Aquaculture Science Branch, 2012). Across all lit and unlit pens the total lipid (fat) levels showed “no detectable difference” in the samples taken in the initial harvest indicating that increasing the salmon’s exposure to constant light does not negatively impact its nutritional value, but does increase its size and delays sexual maturity at a considerable level, especially when this period of increased light exposure runs from late fall/early winter until the end of May. Discovering the optimal time of year and duration of constant light exposure for salmon stocks allows for fisheries to manage the costs associated with operating and maintain artificially lit pens. For each 70m sea pen the estimated “cost of purchasing, wiring, and operating the lights was less than $5,000 per cage (2002 dollars).”, when adjusted for inflation that equates to approximately $7,200 today. While that may not be a small amount of money, “the potential net financial gain from maintaining high production rates and flesh quality, (and) the result of delaying sexual maturity, would be greater than $100,000 per farm.” ($148,000 today) making implementing artificial lighting in salmon pens a worthwhile investment.

Another important piece in the quest to achieve the perfect lighting formula is the type of lighting being used in these processes. While other types of lighting have been used in the past, white metal halide and light emitting diode (LED) lights are now more commonly used in todays fisheries. These two lighting types both share benefits to salmon faming such as an “increased abundance of larval, juvenile and adult fish, and zooplankton in the vicinity of lights, when compared to unlit controls.”, but which is the best?!

White metal halide and LED lights both perform in the same capacity in their ability to draw in other marine life, which drew concerns as to what impact these lights have on the salmon’s diet and other marine animals. Hay et al. (2004) studied whether or not salmon stocks in British Columbia were ingesting wild organisms that had been attracted by artificial light, but found no evidence that proved this was occurring, while “DFO researchers have [recently] examined the stomach contents of harvested farmed salmon and found they were almost all empty. This shows that even when farmed salmon are at their hungriest, right before harvest, they still do not try and eat wild fish.” (Cermaq Canada, 2017). These facts partnered with regulation surrounding incidental catches, greatly lessen the impacts this lighting may have on other marine life.

In a 2012 trial organized by the company Leroy and conducted at Gildeskål  Research Station used the then, “newly designed LED lighting system from Philips” to try and determine what would set these two lighting types apart and determine which was better (Orrego, 2018). Starting the trial in December 2012, LED lighting was placed in two 90 m circumference pens, with two other 90 m pens being fitted with white metal halide lighting. Maintaining a very controlled environment and consistently monitoring the salon and their development, it was found that the LED lights had superior quality when compared to the salmon that had developed in the pens lit by white metal halide lights. Even more impressive was the dramatic difference between the sexual maturity rates between the pens lit by LED lights and those lit by white metal halide lights, with only an average of 0.13% of salmon in the LED pens reaching sexual maturity while an average of 2.58% of those salmon exposed to white metal halide reached their sexual maturity [Table 1].

In regards to the importance of this difference the manager of research and development of the Gildeskål Research Station, Johan Johansen said, “We have used lights during winter and so far assumed that the proportion matured fish is unavoidable background noise, but the solution from Philips close to eliminated all maturation. With good salmon prices the return on investment is very short” (Orrego, 2018). This near elimination of maturity by Philips LED lighting system translates into greatly reduced health risks, an overall higher quality of salmon and larger salmon at time of harvest with the salmon exposed to LED lights producing “3.4% better results for the LED lighting based on harvesting data.” [Table 2] (Orrego, 2018). Impressed with the results of this trial, the Director of Research at the Institute of Aquaculture at the University of Stirling, Professor Herve Migaud stated that “these results clearly showed an increased biological efficiency including suppression of maturation and enhancement of growth as compared to metal halogen…The use of these new systems commercially could contribute to boost productivity while improving fish welfare at sea.” validating LED lighting as the superior lighting choice in salmon fisheries (Orrego, 2018).

The scope of the impact and effect of light on salmon is still being fully examined in hope of creating that ‘perfect’ lighting formula. While the formula for lighting in salmon fisheries has yet to be ‘perfected’, “[t]his is not the end of the journey of improving lighting regimes for the benefit of Salmon farming. Recently the impact of light is further investigated in other applications such as environmental manipulation of salmon swimming depth in order to reduce sea lice infection in Atlantic salmon farms, biomass density control, (and) fish brain development.”, that will all work in tandem to someday achieve that perfect lighting formula for salmon fisheries (Orrego, 2018). But until that formula is discovered implementing the correct type of lighting at the right time of year can greatly improve the quality and health of salmon stocks through drastically reducing their maturity rates and increasing their growth, while reducing the overall production costs and increasing returns for fisheries.

*For more information on the impacts of lighting on salmon fisheries please visit the sources below*


Aquaculture Science Branch. (2012, May). The Effect of Photoperiod on Growth and Maturation of Atlantic Salmon (Salmo salar) in the Bay of Fundy. Retrieved from Fisheries and Oceans Canada:

Bruning, A. (2016, October 25). Disruptive light: when night becomes day for fish. Retrieved from IGB:

Cermaq Canada. (2017, December 12). Learning about underwater lights at our salmon farms. Retrieved from CERMAQ Canada:

Hay, D. E., Bravender, B. A., Gillis, D. J., & Black, E. A. (2004). An investigation into the consumption of wild food organisms, and the possible effects of lights on predation, by caged Atlantic salmon in British Columbia. Canadian Manuscript Report of Fisheries and Aquatic Sciences 2662: 35 p.

Kershner, I. (Director). (1980). Star Wars: Episode V The Empire Strikes Back [Motion Picture].

Morais, P., Dias, E., Cerveira, I., Carlson, S. M., Johnson, M. C., & Sturrock, A. M. (2018, December 18). How Scientist Reveal The Secret Migrations of Fish. Retrieved from Frontiers for Young Minds:,being%20seen%20by%20hungry%20predators.

Orrego, R. (2018, February 24). Effect of LED lighting on growth and development of Atlantic Salmon. Retrieved from Fish Farming Expert:

Stewart, H. L., Nomura, M., Piercey, G. E., Dunham, A., & Lelliott, T. L. (2013). Ecological Effects of Blue LED Lights Used in Aquaculture. Retrieved from Fisheries and Oceans Canada:

The Fish Report. (2018, June 4). Some Like It Dark: Light Pollution And Salmon Survival. Retrieved from FishBio:,a%20lantern%20(USFWS%202015).&text=In%20a%20study%20of%20predation,2012).