The Analysis Species and Life Stages


It is required to select an "Analysis Fish" that represents the abilities of the fish population that will be modeled in the fish passage analysis. It is important to consider whether you are modeling the strongest swimmers or weakest individuals of a fish species.

The swim speeds and leaping abilities that are reported in the Performance Database represent a range of abilities if available, and FishXing will use the average as a default for model inputs. Similarly Hydraulic Criteria is generally based on the average abilities of a singular species of interest.

Before beginning the passage analysis, it is necessary to identify the species and life stage you will be analyzing. To provide a comprehensive assessment of fish passage at the culvert, it may be necessary to assess the passage capability  of several species and life stages.    FishXing uses two different approaches for evaluating fish passage conditions:

1. Biological modeling approach: Models the progress of an individual fish as it leaps into and swims through a culvert.

2. Hydraulic Criteria approach:  Compares the hydraulic conditions in the culvert with  criteria that must be satisfied to ensure adequate passage conditions exist.

Both methods require that a species and life stage be identified, because the analysis is based on physical (e.g., swimming speed) and behavioral (e.g., seasonal movement) attributes of specific species and life stages.

Approaches for defining the Analysis Species

Factors Affecting
Fish Passage

Biological Modeling Approach

Hydraulic Criteria Approach

Outlet Pool Depth

  •  Required Depth for Leaping

  •  Required Depth for Leaping

Entering Culvert Outlet

  • Capable of Leaping?

  • Leaping Speed

  • Body Length

  • Maximum Outlet Drop

Swimming Capabilities

  • Swim Categories

  • Swim Speeds

  •  Times to Exhaustion

  • Occupied Velocities

  • Maximum Water Velocity

  • Occupied Velocities

Water Depth for Swimming

  • Body Height

  • Adequate Submergence

  • Minimum Required Depth

Timing of Movement

  • Low and High Fish Passage Flows

  • Low and High Fish Passage Flows


Considerations when Choosing a Species and Life Stage for Analysis

Different species and life stages of fish have different swimming capabilities and movement needs which will determine a fishes’ ability to pass through a culvert crossing.

 It is possible that regulation or policy will dictate which fish species you will use in the analysis.. If, on the other hand, you need to choose which species and life stages to analyze, then there are two primary factors to consider.

1)  The swimming capabilities of the species and life stages present in the stream; and

2) The time of year when passage is needed.

The Literature Swim Speed spreadsheet may be helpful in comparing the swimming capabilities of different species and life stages.  The Fish Movement section discusses some factors to consider when estimating the timing of fish movements.

The range of flows analyzed in FishXing are defined by the Low Passage Flow (QLP) and High Passage Flow (QHP).When looking at a population of fish species, generally the weakest swimming fish and lifestage will determine passage at high flows while the largest fish will determine passage limitations at the lowest flows.

As stated in the Fish Movement section, adult and juvenile fish may be more active during certain time periods (such as late spring movement of juvenile coho salmon or during spawning runs of adults) or there may be certain periods when adult or juvenile fish are absent from a particular stream reach. In addition, most river systems have variable flow regimes due to seasonally variable precipitation (e.g., winter rains, spring snow melt, or summer drought).  When choosing the species and life stage to analyze it is important to consider the intersection of seasonal flows with the fish’s seasonal movement to determine when high flows or low flows may be limiting to fish passage through the culvert.      

See Fish Passage Flows,  Fish Movement, Other Factors Affecting Swimming Speed and Leaping Capability, Flow Guidelines for Fish Passage Flows