The Difference Between Fish Cages and Survey Gill Nets

Fish cages and survey gill nets are fisheries management tools used for different tasks, yet they are often confused. Yet, understanding the differences between them matters for fisheries managers, researchers, and operators who need to: 

• Protect fish welfare and containment
• Maintain data quality
• Comply with regulatory frameworks

Fish cages are designed for containment and controlled handling during grading, health checks, transport preparation, and short-term stock management. Survey gill nets are scientific fish sampling nets used to capture defined size ranges for stock assessment, biodiversity monitoring, and environmental programmes.

This guide explains how each system is used, how fish cage mesh size and choice influence outcomes, and what to consider when selecting equipment for fisheries or research.

What Fish Cages Are Used For

Fish cages are used to contain and manage fish during handling, including grading, health checks, transport preparation, and short-term stock management. In fisheries and aquaculture settings, cages allow fish to be securely held while maintaining water exchange, supporting fish welfare and containment during routine operations.

Cage specification should be based on the job at hand. Fish cage mesh size and mesh aperture must suit the species and size class, with flow and fouling risk considered for the site and holding duration. Fine mesh is commonly used where juvenile containment is required. Larger apertures can improve circulation during longer deployments, provided escape risk remains controlled.

We supply fish cages and tank covers professionally manufactured to specification for fisheries and aquaculture operations.

In the UK, fish holding and movement activities can fall under the aquatic animal health and movements requirements published by Defra delivery bodies, including Cefas and the Environment Agency [1].

The GOV.UK guidance set includes detailed requirements for:

• Moving live fish and shellfish

• Farm authorisation

• Permissions for introducing fish

Where fish are introduced to a fishery, the Environment Agency states that a site permit is required and that introducing fish without consent can lead to prosecution and fines up to £50,000. Consent usually takes up to 10 working days and may take up to 20, depending on checks and site conditions [2].

What Survey Gill Nets Are Used For

Survey gill nets are used as scientific sampling nets to assess wild fish populations under controlled, repeatable conditions.

They support fisheries monitoring, stock assessment, and environmental surveys by capturing defined size ranges and enabling:

• Consistent measurement of population
• Species composition
• Size distribution over time

In the UK, survey data contribute to the evidence regulators use when setting catch limits, closures, and management measures. Mesh size is central to the selectivity of survey gill nets. Fish are retained when the mesh aperture corresponds to the body size being sampled, which is why survey programmes specify exact mesh sizes, panel layouts, and deployment durations. These controls help protect data quality and limit avoidable stress or mortality during sampling.

We manufacture survey gill nets for fish sampling that are rigged to order for research and monitoring work. The use of fixed nets, including gill nets, can be restricted by catch limits and closed fishing areas managed by the Marine Management Organisation. GOV.UK guidance confirms that it is illegal to use restricted fishing gear in a closed area for the specified period, and breaches of licence conditions are a criminal offence [3]. Catch limits are measured in kilograms or tonnes of live weight, and real-time or seasonal closures may be applied to protect spawning fish or juvenile stocks.

Choosing the Right Mesh for Fisheries Work

Mesh selection affects containment, fish welfare, and sampling accuracy. For both fish cages and survey gill nets, the mesh aperture should be chosen based on species, size range, and operational purpose.

For fish cages, mesh is selected to balance secure containment with water flow. Fine mesh is commonly used where juvenile fish are held, or escape prevention is critical. Larger mesh sizes may be suitable for adult fish or longer holding periods, as they improve circulation and reduce fouling. Material choice and knot type also affect durability and handling.

For survey gill nets, mesh size controls selectivity and determines which fish are sampled. Survey specifications often define precise mesh sizes and panel layouts to ensure results remain comparable across locations and time periods. Deployment duration is usually limited to reduce stress and mortality.

To Recap, Fisheries Professionals Should Consider

• Target species and size class

• Purpose of use, such as holding, grading, or population sampling

• Deployment duration and retrieval frequency

• Water flow, fouling risk, and site conditions

• Survey protocols or regulatory requirements

Practical Use in Fisheries Management

Fish cages are suited to situations where fish must be held securely with minimal handling. Typical uses include grading, inspection, health checks, and short-term stock management. Cages support observation and handling while reducing repeated capture and associated stress.

Survey gill nets are suited to monitoring tasks that require structured sampling. They are used in stock assessments, environmental impact studies, and biodiversity surveys where selectivity and repeatability are essential. Deployment is planned around defined timeframes and sampling protocols to support consistent data collection.

Many fisheries and research programmes use both systems as part of wider management strategies. Selecting the appropriate tool for each task supports welfare, reliable sampling, and efficient operation. 

Choosing the Right Netting with Collins Nets

Collins Nets are a family-owned and run company with over 35 years of experience supplying netting to the fisheries and aquaculture sectors. Fish cages and survey gill nets are manufactured and rigged to order, allowing mesh size, depth, panel configuration, and materials to be matched to specific operational or research requirements.

This specification-led approach supports consistency in survey work and welfare-focused containment where fish are held for handling or management. For practical guidance on applications, materials, and best practices, please turn to our Blog. For additional answers on specifications, ordering, and use, click on our FAQs.

Call 01308 485422 or use our contact form to discuss fish cages, survey gill nets, and mesh specifications.

External Sources

1. GOV.UK, “aquatic animal health and movements requirements”: https://www.gov.uk/government/collections/aquatic-animal-health-and-movements-guides
2. GOV.UK, “”Environment Agency”: https://www.gov.uk/guidance/permission-to-move-live-fish-to-or-from-a-fishery
3. GOV.UK, “illegal to use restricted fishing gear”: https://www.gov.uk/guidance/understand-fisheries-catch-limits-and-closed-fishing-areas