Swim Categories


Fish swimming performance has been classified into three distinct categories:

FishXing models the latter two categories, Prolonged and Burst.

Swimming categories are based on limitations imposed by time and on biochemical processes which supply the fuel to the muscles (Beamish 1978). The proper differentiation among swimming categories can be clearly seen when examining the relationship between time to exhaustion and swimming velocity for a particular fish. For some species, the distinction between burst and prolonged swimming and between prolonged and sustained swimming can be seen as slope changes on a graph of swimming time vs swimming velocity. For a thorough discussion of this topic that uses sockeye salmon as an example, see Brett  (1964).    For other species, the relationship between swimming time and swimming velocity does not include slope changes between all swimming categories (Peake et al. 1997).

Unfortunately, the literature contains inconsistent usage of terms to describe swimming categories.  Before interpreting study results, it is important to clearly understand the actual definition of the swimming category used by the authors. 

Sustained Swim Speed

Sustained performances are those speeds that fish can maintain for long periods (>200 minutes) without muscular fatigue (Beamish 1978). At sustained speeds, energy is supplied to slow oxidative (red) muscle fibers through aerobic processes. These fibers do not fatigue and do not have high power output (Webb 1994). Metabolic demand is matched by its supply and waste production is matched by its removal (Jones 1982). A subcategory of sustained performance is cruising speed; these speeds are used by migrating fish or fish that are negatively buoyant and must swim to maintain their place in the water column (e.g., tuna). The maximum sustained speed is the highest velocity that a fish can maintain without eventually fatiguing. Swim speeds above sustained speed fall into the prolonged or burst swimming categories.  

Prolonged Swim Speed

Prolonged performances are those speeds that fish can maintain for 20 seconds to 200 minutes and ends in fatigue (Beamish 1978). The prolonged category spans the swimming speeds between sustained and burst. At prolonged speeds, energy is supplied to slow (red) and/ or fast oxidative glycolytic (pink), and /or fast glycolytic (white) fibers through aerobic and anaerobic processes, respectively. As speed increases so does anaerobic metabolism. White muscle fibers have high power output but low energy reserve which results in eventual fatigue (Webb 1994).

Since swimming at prolonged speeds can be maintained for relatively extended periods and appears to not impose undue physical stress on the fish, these speeds are commonly  used in assessment and design  of culverts. Many regulatory agencies guidelines recommend using prolonged swim speeds to design or assess fish passage through culverts.  

Critical Swim Speed

A sub-category within prolonged performance is the critical swimming speed, which is the maximum velocity that can be maintained by a fish for a specific period of time (Brett 1964) . This type of swimming performance is often reported in the literature and the Literature Swim Speed Table includes data derived from critical swimming speed tests. When the time between velocity increases in the critical swimming test is about one hour, the critical swimming speed approximates the speed that delineates the change from sustained to prolonged swimming, i.e., maximum sustain swimming speed  (Brett 1964).  More information about critical swimming speed test is provided in the Swim Speed Test section.

Burst Swim Speeds

Burst performances are the highest speeds attainable by fish and can be maintained for only short periods of time (<20 seconds) (Beamish 1978). At burst speeds, energy is primarily supplied to myotomal (body) white muscle through anaerobic processes (Webb 1994). The conclusion of short periods of burst swimming occurs as a result of the exhaustion of extracellular energy supplies or accumulation of waste products (Colvavecchia et al. 1998). Fish often use burst speeds to pass through short high velocity areas, such as the inlet or outlet of a culvert.  Median and paired fins tend to power slow swimming which is supplemented and then replaced with body and caudal (tail) fin undulation swimming at higher speeds and for acceleration (Webb 1994). At burst speeds the caudal (tail) fin is expanded and made as rigid as possible (Nursall 1962).  When fish swim at low speed they modulate the frequency and amplitude of their body and caudal fin undulation and at high speed they only modulate frequency (Bainbridge 1958, Webb 1971).  

Recovery Time and Burst Swimming

If fish must swim in burst mode to pass through high velocity areas it is important to consider their ability to recover and perform multiple bouts of exhaustive swimming.   

A fish’s ability swim in  burst mode may be limited in the short term (a few hours to a day) because some fish species require relatively long periods to recover from exhaustive exercise (Black et al, 1962). Additionally, some fish die after performing exhaustive exercise. For example, trout subjected to intensive exercise for six minutes had a mortality rate of 40 percent with the majority of death occurring four to eight hours post-exercise (Wood et al. 1983). Reviews of recovery from exhaustive exercise have revealed that species differences span several orders of magnitude (Milligan and Wood 1987, Nelson 1990, Boutilier et al. 1993, Keiffer 2001).  For example, salmonids have high burst speeds but appear to recover relatively slowly.  Paulik et al. (1957) found that coho salmon recovery from exhaustive exercise was 67 percent after three hours and full recovery occurred only after 18 to 24 hours. These fish were forced to swim until they could no longer maintain their position upstream of an electrical shock. Steelhead were able to re-perform their baseline swim speed after six hours (Paulik and DeLacy 1957).  On the other hand, juvenile Atlantic sturgeon (Acipenser oxyrhynchus) and shortnose sturgeon (A. brevirostrum) have relatively low burst speeds but recover more quickly than salmonids.  Juvenile sturgeon recovered their baseline oxygen consumption rates in 30 minutes, muscle energy metabolite levels in one hour and muscle lactate levels in six hours (Kieffer 2001).  It is thought that species differences in recovery rates reflect differences in ecological requirements, morphology, and behavior (Keiffer 2000).  

Migrational Delays and Multiple Crossings

Anadormous fish migrating upstream to spawn do not consume food.  Therefore, they have a limited energy supply with which to complete their journey to their natal stream and to spawn.  Migrational delays can reduce an individual’s fitness  and ability to reproduce.  High velocities through culverts related to seasonal high flows should be evaluated to ensure they do not exceed acceptable levels and cause migrational delays. .  Migrational delays can also result from the cumulative effect of many culverts in series. The energy demands and recovery time required to pass through multiple crossings should be considered when evaluating fish passage. If fish must cross through several culverts during their upstream movements, it is important to consider their ability to perform multiple bouts of exhaustive swimming.  

See Fish Swimming and Swim Speed Tests, Fish Calculations Overview