How can artificial light enhance welfare and growth for farmed fish?

Posted by Guttorm Lange on 7/6/20 12:28 PM
Guttorm Lange

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Artificial light sources can significantly increase farmed salmon growth when used correctly, and in some instances, by up to 15%. However, it takes a bit more than a corrosion-resistant and waterproof lamp. We need to understand fish’ biology to provide precisely the light it needs.

25 to 30 years ago, fish farmers discovered that the fish gathered at strips of light from the footbridge on the cage. Fish with access to light showed significantly better growth rates. So it was by coincidence fish farmers became aware of light’s impact on fish’ cycle.

Thorough research has folowed, and at AKVA group, we spend a lot of time investigating how correct use of light impacts fish physiology. Several factors determine this, and you need a solid understanding of fish biology to utilize the effect of artificial lighting. Here’s a crash course in light and fish biology.

How do salmon relate to light?

The fish have hormonal (endocrine) processes that are affected by light. Sexual maturation is such a process. And as most have learned when studying aquaculture, a sexually mature fish has far lower meat quality than a prepubetal one. The fish become lazy. So the basic idea around light control is to keep fish from reaching puberty.

Not all light is created equal

Throughout evolution, fish have developed sensitivity for light at specific wavelengths, and in practice, this means that they are sensitive to specific colors. Some wavelengths (colors) penetrate water further than others, and green and blue light has the most extended range. Salmon are susceptible to this light. White light contains all of the colors of the rainbow. But salmon relate to blue and green light. The remainder of the color spectrum has little impact and is perceived as “noise” to the fish. In a traditional metal halogen lamp, 80% of the light will be completely irrelevant. Such lamps are not optimal for use in the cage.

How the light is presented makes a difference

Salmon is a fish that is easily stressed, and we all take measures to reduce stress levels. Good fish welfare means good fish health and better earnings for the fish farmer. Sharp contrasts are a typical cause of increased stress levels, so we should light the cage to reduce contrasts.

We need to return to fish biology to see the whole picture:

One of the essential passages for light is at the salmon’s front head. It’s called the pineal window and allows light to the pineal gland. As we know, the salmon do have eyes, and the eyes’ retinas also transmit light information to the brain’s photoreceptors. When lamps concentrate light and direct it vertically down the cage, two unwanted side effects occur:

  1. There is a sharp separation between dark and light, and the fish become more stressed by moving in such contrasts
  2. We don’t target the eyes very well, and the fish miss out on valuable light information. Consequently, we get less impact from our light management.

Better light management provides better returns

We agree that the we use light to prevent sexual maturation of the fish because prepubertal salmon have a far superior food quality than sexually mature fish. Overall, we are doing quite well with regard to this KPI. Only 1-2% of fish delivered to harvesting plants are sexually mature. Thus, this is not the area to benefit from excellent light management. You must leverage light management to increase fish growth, not only to control sexual maturation, and then you can significantly increase profit.

The modern lamp for cages

For years, AKVA group, has worked on developing light technology based on fish biology. However, without considering the extraordinary challenges that arise from subsiding electronics in water, we wouldn’t benefit from what we have discovered.

Our newest lamp, AKVA Aurora SubLED Combi, provides the fish with the appropriate light in a reliable and efficient manner.

The lamp’s design and technical construction is an answer to nature’s wear and tear. A PE and acrylic surface replace any metal, and this has several positive effects. For a start, we avoid corrosion. Nor is a metal-free lamp exposed to stray current. Consequently, the sacrificial anode, a part that needs regular replacement and would have increased the lamp's weight, is redundant.

The lamp is built around a core of aluminum bronze with stripes of LED lights glued to this core in an octant. It creates a dome-shaped light that strikes the fish’s various light sensors and reduces stressing contrasts.

The core also lay the basis for a heat exchange that reduces plankton growth. The metal conducts heat from the lights, which encounters the cold environment in the cage and create circulation. The heat exchange provides sufficient cooling so that we avoid using environmentally harmful silicone oil.

We have removed the control section from the actual lamp and placed it in a cabinet at the edge of the cage, reducing the weight significantly; a 1200 Watt lamp weighs no more than 6.5 kilograms. Removing electronics from the water is also beneficial for HSE, supported by the operating voltage being 48V DC rather than the standard 240V AC.

Better lamps provide a better light environment

In other words, it is not irrelevant which type of light the fish is exposed to, and reliability and efficiency are about a lot more than resistance to rust. Naturally, a modern lamp that can contribute to increased fish growth represent a more significant investment than a standard lamp that only control sexual maturation. A fish farmer with a sound commercial approach will instantly try to calculate the investment to see whether it can provide a better result. When doing so, please factor in these added values:

  • A light proven to enhance welfare in salmon will pay for itself in reduced mortality, less stress, better control of physiological processes and finally better growth
  • Reduced time in the cage reduces operating expenses and improves liquidity
  • Also, AKVA group has dedicated staff who can assist in finding the optimum light solution for each individual location

 

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Topics: light management

Guttorm Lange

Written by Guttorm Lange

Guttorm Lange is Product Manager PLP, Lights, Sensors at Akva group

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