- Lydia Roush
Three crayfish of varying size and color were captured and examined in a fish tank for 10 hours. Aggressive, subordinate, feeding, and cleaning behaviors were recorded for each crayfish. Crayfish 1 was found to be the largest and most aggressive individual. Crayfish 2 attempted aggressive behaviors with Crayfish 1 and Crayfish 3, and ate the most food. Crayfish 3, the smallest crayfish, had the most recorded behaviors due to its need to avoid the aggressive behaviors of Crayfish 1 and Crayfish 2.
Crayfish are small crustaceans that reside in freshwater habitats (Olden 2009). Their anatomy is strikingly similar to marine lobsters’, their closely related cousins. Crayfish breath using gills, and are good ecological indicators of water quality. Most crayfish are rather delicate, and cannot survive polluted, dry, or saline situations. However, the red swap crayfish is incredibly robust for its species, and has the capacity to tolerate undesirable habitats and environments. This species can easily be found in calm, fresh waters including ponds, slow streams, and rasacas.
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The red swamp crayfish is easily identifiable (Olden 2009). Its long, slender claws, bright red color, and knobby carapace separate it from other common freshwater crustaceans. The Turkish crayfish is almost anatomically identical to the red swamp crayfish, however the Turkish crayfish remains a deep brown, while the red swamp crayfish is colored a brilliant red (HarlioÄŸlu 2004). While invasive to many European countries, the Turkish crayfish has not been introduced to the United States, and therefore should not be found in any of her freshwater systems.
Native to the Gulf Coast, the red swamp crayfish is an edible delicacy for residents of this area (McClain and Romaire 2004). Louisiana, famous for their exquisite creole cuisine, realized the economic potential of this species and began farming red swamp crayfish for human consumption. Other states followed in suit, and the red swamp crayfish was introduced to freshwater systems across the United States. While ecologically benign in Gulf States, the red swamp crayfish has become a detrimental problem in states like Washington and Ohio.
Red swamp crayfish are sensory organisms that use their bodies to feel and taste their surroundings (Turner et al. 1999, Zulandt et al. 1999). Every movement is coordinated; and legs, antennae, claws, eyes, and tail are all directed in a way that optimizes survival (Hughes and Wiersma 1960). These crayfish can expend little energy perched on a rock filter-feeding, their slender legs and v-shaped feet pick through small stones in search of food, their large claws act as both a balancing mechanism and superior weapons. Both sets of antennae are constantly searching for food, and instantly recognize when food has entered the water (Zulandt et al. 1999).
Juvenile crayfish establish hierarchies amongst themselves, and adult crayfish are able to recognize individuals who have acted aggressively towards them in previous encounters (Bergman and Moore 2003, Issa et al. 1999, Keller and Moore 2000, Zucker 1971, Daws et al. 2001). There is a highly social and ranked culture among crayfish, whose establishment is founded on strength and gusto.
The following hypotheses were derived from the available literature: 1.) Crayfish will possess different aggressive/retreating behaviors based on relative size/color. 2.) Crayfish will exhibit a “pecking order.” 3.) Regardless of size, crayfish will eat and clean the same amount. These hypotheses will be tested using the following methods.
Materials and Methods
Aggressive, subordinate, feeding, and cleaning behaviors were examined for three crayfish of varying size and color. Crayfish were obtained from a rasaca and placed in an aquarium. The aquarium was equally lit on both sides by two lamps (Figure 1). Crayfish were allowed to adjust to the aquarium for a week, and allowed to adjust to the light for a minimum of two hours before observations began. Crayfish were viewed for a total of ten hours. Behaviors were analyzed continuously for 1-2 hour periods at a time.
Aggressive behavior was initiated when a crayfish’s body would become erect, raise its claws above its head, and move them in a sweeping motion. Culmination of aggressive behavior occurred when one crayfish would attack an opposing crayfish. Attacks consisted of pinching, ramming, and climbing on the foe. Subordinate behavior occurred when an aggressor approached and foe, and the foe retreated. Two types of retreat were counted: walking or running away, or swimming backwards in a projectile fashion. Crayfish were fed chicken or turkey in excess once a day. Each return to the feed was counted as a new feeding behavior. Cleaning consisted of the crayfish rubbing their legs and claws across their carapace, legs, claws, eyes, and antennae. Behaviors were considered stopped when the crayfish ceased preforming them. Behaviors were considered new and tallied when crayfish started them after previously exhibiting a different behavior (usually sitting).
Crayfish 1, the largest, more opaque crayfish, spent 38.5% of the observation time attacking Crayfish 2 or Crayfish 3, 14% of the observation time eating, and 47.5% of the observation time cleaning (Figure 2). Crayfish 1 never exhibited any avoidance behaviors.
Crayfish 2, the medium sized, most brightly colored crayfish, spent 21% of its time attacking Crayfish 1 and Crayfish 3, 7% of time avoiding conflict by walking, 9% of its time avoiding conflict by swimming backwards, 33% of its time feeding, and 30% of its time cleaning (Figure 3).
Crayfish 3, the smallest, blue crayfish, didn’t attack either Crayfish 1 or Crayfish 2, spent 59% of observation time avoiding conflict by walking, 27% of observation time avoiding conflict by swimming backwards, 10% of observation time feeding, and 4% of observation time cleaning. Crayfish 3 also displayed the most behaviors, and was the most active crayfish in the tank, mainly due to avoiding the other two crayfish (Figure 4).
Crayfish did exhibit a pecking order that appeared to be based on size. The largest crayfish, Crayfish 1, had the highest rate of attack. The smallest crayfish, Crayfish 3, had the highest rate of avoidance, causing him to have the highest number of documented behaviors in the tank. Crayfish, however, did not eat and clean the same amount. Crayfish 1 spent the most time cleaning, while Crayfish 2 spent the most time eating. Crayfish 3 did very little of these activities. These results hint that size may be a key component to crawdad behavior. Hormones, body mass, or experience may regulate behaviors at different stages of development, and more precise measurement and implementation may help distinguish any potential influences. It may also be valuable to attempt to mate and raise crayfish in isolation to decipher which behaviors may be learned and which are innate. Cross-fostering experiments between crayfish species may also help identify species-specific behaviors.
A more detailed study of individual behaviors is necessary for this species. Each behavior is so complex and multi-faceted that careful examination of only leg use, feeding, antennae, etc. should be conducted. The initial behavioral examinations of this study were far too broad, and although this study showed potential trends in crayfish behavior, a more detailed study will help tease these out.
During this study, crayfish also presented scototaxis-like behaviors. When both lamps were turned on, illuminating the fish tank, crayfish became tense and attempted to avoid the light and retreat into darker areas. Examination of this species in the terror tanks would be interesting, and may help to explain additional behavioral tendencies.
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Figure 1. Diagram of experimental design. Three red swamp crayfish of varying color and size were place in an aquarium with two lamps on either side, providing equal lighting within the aquarium.
Figure 2. Pie chart of prominent behaviors exhibited by Crayfish 1 during the 10-hour observation period.
Figure 3. Pie chart of prominent behaviors exhibited by Crayfish 2 during the 10-hour observation period.
Figure 4. Pie chart of prominent behaviors exhibited by Crayfish 3 during the 10-hour observation period.
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