What is the difference between underwater and surface aquaculture lighting?

Underwater aquaculture lighting and surface aquaculture lighting differ primarily in where the light source is positioned relative to the water: underwater systems submerge LED fixtures directly into the water column to stimulate fish behaviour and biological responses, while surface systems mount lanterns above the waterline to illuminate the surrounding area for safety, navigation, and operational visibility. The choice between them is not simply a matter of preference — it depends on the species being farmed, the biological outcome required, and the operational environment of the installation. Both approaches serve distinct purposes, and many offshore fish farms deploy them together.

How does underwater aquaculture lighting actually work?

Underwater aquaculture lighting works by submerging waterproof LED fixtures directly into the water column, typically within or around fish cages, where light penetrates the surrounding water to influence fish behaviour, feeding patterns, and biological cycles. The light source operates below the surface, delivering photonic energy directly into the environment where the fish live, without the attenuation and scattering losses that occur when light must travel through the air-water interface first.

The physics of underwater light transmission are central to how these systems function. Water absorbs and scatters light differently depending on wavelength: blue and green light penetrate to greater depths, while red and orange wavelengths are absorbed more rapidly. Well-designed LED aquaculture lighting accounts for this by selecting spectral outputs that match the biological requirements of the target species and the depth at which the fish are held. In salmon farming, for example, fixtures are typically positioned at depths that ensure consistent light exposure across the full vertical extent of the cage, preventing the formation of dark zones where fish might seek refuge from the photoperiod treatment.

The fixtures themselves must be engineered to withstand continuous immersion in seawater, biofouling pressure, and the mechanical stresses of offshore environments. Robust housing, corrosion-resistant materials, and high ingress protection ratings are not optional features in this context — they are operational requirements. A fixture that fails mid-treatment cycle disrupts the biological programme and may require a costly maintenance dive to replace.

How does surface aquaculture lighting differ in its delivery method?

Surface aquaculture lighting delivers illumination from above the waterline, mounting marine lanterns on cage structures, walkways, mooring lines, or support frames to light the surrounding area rather than the water column itself. Unlike underwater systems, surface lights do not interact directly with the fish’s immediate environment — they serve the operational and navigational needs of the installation above the surface.

The primary function of surface aquaculture lighting is marking and visibility. Offshore fish farms present a genuine collision risk to vessels operating in the area, particularly in poor visibility, at night, or in adverse weather. Surface-mounted marine lanterns define the perimeter of the installation, mark cage positions, and illuminate working areas for crew safety during night operations. In this respect, surface aquaculture lighting performs a role closely analogous to aids-to-navigation infrastructure — ensuring that the installation is visible and its boundaries clearly defined to approaching vessels.

The delivery method also differs in terms of coverage. A surface lantern with omnidirectional output can mark a structure across a wide arc, providing visibility to vessels from multiple approaches simultaneously. Underwater fixtures, by contrast, direct their output into a defined volume of water and are not intended to be seen from the surface at navigational distances. This distinction in delivery method reflects a fundamental difference in purpose: surface lighting protects the installation and the people around it, while underwater lighting is a production tool operating within the biological environment of the fish.

What are the biological effects of each lighting type on fish behaviour?

Underwater aquaculture lighting produces direct biological effects on fish by manipulating the photoperiod — the daily cycle of light and dark — that governs key physiological processes. Surface lighting, positioned above the waterline, has minimal direct biological effect on fish held in submerged cages because the light intensity reaching the fish is insufficient and inconsistent to reliably drive photoperiod responses.

Biological effects of underwater lighting

The most significant application of underwater LED aquaculture lighting is photoperiod manipulation to suppress or advance sexual maturation in salmonids. Atlantic salmon, for example, are highly sensitive to changes in day length: as natural day length shortens in autumn, the fish begin to mature sexually, diverting energy from growth into reproductive development. By maintaining artificial long-day conditions through continuous or extended underwater illumination, farmers can suppress this maturation response, keeping fish in a growth phase for longer and improving the uniformity and quality of the harvest.

Beyond maturation control, light intensity and spectral composition influence feeding behaviour, schooling patterns, and stress responses. Fish exposed to appropriate light levels tend to distribute more evenly through the water column, reducing competition for feed and improving feed conversion ratios. The specific biological response depends on the species, the light intensity at the fish’s depth, the spectral output of the fixture, and the duration of the photoperiod treatment — all parameters that require careful calibration for each farming operation.

Biological effects of surface lighting

Surface lighting contributes indirectly to fish welfare by enabling safer, more efficient night-time operations. Crew working in well-lit conditions around cages can monitor fish behaviour, manage feeding equipment, and respond to issues more effectively than in darkness. However, surface lights positioned directly above open net pens can, in some circumstances, attract zooplankton and other organisms to the surface, which may draw fish upward and alter their distribution within the cage — an effect that should be considered when planning surface lighting layouts around open-top pen systems.

Which aquaculture species benefit most from underwater lighting?

Atlantic salmon is the species most extensively studied and most directly benefiting from underwater aquaculture lighting, primarily because of the well-documented relationship between photoperiod and sexual maturation in this species. However, other salmonids, including rainbow trout and sea trout, respond similarly to photoperiod manipulation, and underwater lighting is increasingly applied across a broader range of farmed species as the technology matures.

The key criterion for whether a species benefits from underwater lighting is photoperiodism — the degree to which the species uses day length as a biological cue for seasonal processes such as maturation, smoltification, or spawning. Species with strong photoperiodic responses are the most responsive to light-based management interventions. Salmon aquaculture has driven the majority of commercial development in underwater fish farm lighting because the economic impact of premature maturation is substantial and well-quantified.

Cod and halibut farming operations have also explored underwater lighting for maturation control and growth optimisation, with results that vary by species and production system. In warm-water aquaculture, some operators use underwater lighting to attract prey organisms or to manage the distribution of fish within enclosures, though the applications differ significantly from the photoperiod management approach used in cold-water salmonid farming. As research continues, the range of species for which underwater marine aquaculture lights deliver measurable production benefits is expected to expand.

When should surface lighting be chosen over underwater lighting?

Surface aquaculture lighting should be chosen when the primary requirement is safety, navigation marking, or operational visibility rather than biological manipulation of the fish. Any offshore fish farm installation requires surface lighting to meet maritime safety obligations — marking the perimeter of the installation for approaching vessels and ensuring crew can work safely at night. This is a non-negotiable operational requirement, not an optional enhancement.

Specific situations where surface lighting is the appropriate choice include:

• Marking cage perimeters, mooring lines, and structural elements to prevent vessel collisions in all visibility conditions
• Illuminating walkways, feed systems, and work platforms for crew safety during night operations and in adverse weather
• Providing navigational reference points for service vessels approaching the installation in darkness or reduced visibility
• Installations where the farmed species does not exhibit a significant photoperiodic response to artificial light
• Hatchery or onshore recirculating aquaculture systems where overhead or ambient lighting is sufficient for fish management

Surface and underwater systems are not mutually exclusive. Most serious offshore aquaculture operations deploy both: surface marine lanterns to fulfil safety and navigation marking obligations, and underwater fixtures to manage the biological environment of the fish. Sabik’s aquaculture lighting solutions address both requirements, providing purpose-built marine lanterns engineered to perform reliably in the offshore environments where fish farms operate — from the North Sea to the open ocean.

What are the key technical differences between underwater and surface aquaculture lights?

The key technical differences between underwater and surface aquaculture lights reflect their fundamentally different operating environments and purposes. Underwater fixtures must withstand continuous immersion, biofouling, and hydrostatic pressure at depth, while surface marine lanterns must resist wave impact, salt spray, UV exposure, and the mechanical stresses of offshore structural mounting — without the requirement for pressure-rated housings.

Ingress protection and pressure ratings

Underwater aquaculture lights require IP68 ratings as a minimum, confirming protection against continuous immersion at specified depths. The pressure rating of the housing is a critical specification — fixtures deployed at 10 to 30 metres of depth must maintain integrity against the hydrostatic pressure at those depths across a service life measured in years. Surface lanterns require high IP ratings for weather resistance and wave splash, but do not face the same hydrostatic pressure demands. The structural and sealing requirements of the two product categories are therefore distinct, and a surface lantern is not a substitute for a rated underwater fixture regardless of its IP rating.

Spectral output and photometric design

Underwater LED aquaculture lighting is typically designed with specific spectral outputs calibrated to biological effect — blue-green wavelengths that penetrate water effectively and match the photoreceptor sensitivity of the target species. Photometric design focuses on delivering consistent intensity throughout the water column at the operating depth, accounting for the absorption and scattering properties of seawater. Surface marine lanterns, by contrast, are designed for maximum visibility at distance across the air medium, with photometric outputs calibrated to IALA visibility requirements rather than biological effect. The two product categories are engineered to entirely different photometric standards and serve different purposes in the aquaculture lighting system.

Power supply and cable management also differ significantly. Underwater fixtures require submersible cabling, watertight connectors, and cable management systems that can tolerate continuous immersion and the movement of cage structures in open water. Surface lanterns may be solar-powered, eliminating the need for a cabled power supply entirely — a significant operational advantage in remote offshore installations where running power cables to every surface marker is impractical. Solar-powered surface lanterns for aquaculture marking deliver autonomous operation without grid dependency, reducing both installation complexity and ongoing maintenance requirements in environments where service access is costly.

To discuss surface or underwater aquaculture lighting requirements for your installation, contact Sabik’s technical team for specification support tailored to your operating environment.