Burrows usually contain a single female, or sometimes a male and female together, but occasionally they may contain additional crawfish. Successful survival and reproduction within the burrow depends on many factors, such as the severity and length of the dry period, characteristics of the burrow such as depth, soil type and moisture and health of the animal.
Immature crawfish and crawfish forced to burrow by rapidly dropping water levels may construct shallow burrows that will not have sufficient moisture for survival during lengthy dry periods or drought.
Soil types with limited clay content or soil with very high clay content that cracks when dry also may limit crawfish survival while in burrows. Once sealed in, crawfish are confined to the burrow until the hard plug that seals the entrance is sufficiently softened by external moisture from flooding or rainfall. Pond flooding, especially when associated with heavy rainfall, facilitates and encourages the emergence of crawfish from burrows. Pond crawfish populations usually include 1 holdover adults from the preceding production season or stocking, 2 holdover juveniles from the preceding season and 3 the current young-of-the-year YOY recruits.
The number of age classes and numbers within age classes comprise the overall crawfish density. Crawfish density and population structure have a great impact on overall pond yields and size of crawfish at harvest. The highest densities and most complex population structures usually occur where crawfish have been grown in the same location for several consecutive seasons.
In new ponds and ponds held out of production for a year or longer, crawfish density is often lower and the number of age classes is fewer. In these situations, crawfish are often larger and more uniform in size; however, overall yields may be considerably lower. Unlike most aquaculture ventures, where known numbers and sizes of juveniles are stocked, crawfish aquaculture in Louisiana relies on natural recruitment reproduction from mature animals either stocked or already present to populate the pond.
Population density depends largely on broodstock survival, successful reproduction and survival of offspring. Density is mainly influenced by environmental conditions over which producers may have little or no control. Additionally, improper management after autumn flood-up, including low oxygen levels, abundance of predators or pesticide exposure can negatively impact crawfish populations and subsequent production even when broodstock survival and reproduction are high.
Because of this lack of influence and control over population levels, population density and structure is probably the most elusive aspect of crawfish production. Extended reproduction periods and the presence of carryover crawfish from previous season often result in several size or age groups of crawfish being present in a pond at any given time. These methods are highly variable and subject to many sources of bias or error. Producers generally do not have a good assessment of their populations until harvesting is well underway in late spring, after pond temperatures have increased substantially.
Approximately 11 molts are necessary for young crawfish to reach maturity. A molt cycle is recognised as having five major stages, but it should be understood that the process is actually continuous.
The inter-molt phase is the period in which the exoskeleton is fully formed and hardened. During this phase, crawfish feed actively and increase their tissue and energy reserves. Preparation for molting takes place in the pre-molt stage. This includes the formation of the new, underlying soft exoskeleton while a re-absorption of the calcium from the old shell occurs.
During the late pre-molt period, crawfish cease feeding and seek shelter or cover. Molting is usually accomplished in minutes. The brittle exoskeleton splits between the carapace head and abdomen tail on the back side, and the crawfish usually withdraws by tail flipping.
Hardening calcification of the new exoskeleton takes place during the post-molt period, which can be divided into two phases. Initial hardening occurs when calcium stores within the body are transported to the new exoskeleton. These stones disappear during the initial hardening period after molting.
The second phase of hardening is by absorption of calcium from the water. As crawfish resume feeding, further hardening of the new shell occurs. Molting is hormonally controlled, occurring more frequently in younger, actively growing animals than in older ones. The increase in crawfish size during molting, and the length of time between molts, can vary greatly and are affected by factors such as water temperature, water quality, food quality and quantity, population density, oxygen levels and to a lesser extent by genetic influences.
Under optimum conditions, crawfish can increase up to 15 per cent in length and 40 per cent in weight in a single molt.
In culture ponds, frequent molting and rapid growth occur during spring because of warming waters and adequate food sources. The appearance of mature crawfish increases as the season progresses. Rapid increases in temperature above 80 F may stimulate onset of maturity at smaller sizes, especially under conditions of overcrowding and food shortages.
Crawfish have been known to ingest living and decomposing plant matter, seeds, algae, epiphytic organisms, microorganisms and an assortment of larger invertebrates such as insects and snails. They also will feed on small fish when possible. These food sources vary considerably in the quantity and quality in which they are found in the aquatic habitat.
Living plants, often the most abundant food resource in crawfish ponds and natural habitats, are thought to contribute little to the direct nourishment of crawfish. Starchy seeds are sometimes consumed and may provide needed energy, but intact fibrous plant matter is mostly consumed when other food sources are in short supply. Aside from furnishing a few essential nutrients, living plant matter provides limited energy and nutrition to growing crawfish.
Decomposing plant material, with its associated microorganisms collectively referred to as detritus is consumed to a much greater degree and has a higher food value. The physiology of crayfish changes dramatically during molting ecdysis , which in turn may change both the chemical content and concentrations of the chemical cues released into the water. We hypothesized that conspecifics are sensitive to chemicals released during molting.
A Y-maze experimental design was used to test for differential responses to various molt-related chemical stimuli presented to intermolt male crayfish Orconectes rusticus. The sources of chemical stimuli were recently molted male crayfish, intermolt male crayfish, control aged tank water , and food fish. Behavioral indices of response included initial arm choice, time spent in each arm, time spent at each nozzle, number of arm changes, and meral spread at each nozzle.
Experiments were also conducted where crayfish were presented the same chemical stimuli in each arm to obtain measures of locomotor activity in the different stimuli. In addition, orientation parameters such as walking speed, walking speed to source, and distance to source were analyzed. Intermolt individuals spent more time in the presence of molt signals, although the food stimulus was more attractive than any other stimuli tested.
Crayfish showed a significant initial arm choice when molt stimulus was paired with control. During the identical presentation of chemical stimuli, crayfish showed an increase in locomotor activity in the molt and food chemical stimuli than in the intermolt and control chemical stimuli. There were no significant differences in orientation parameters between chemical stimuli.
These results show that crayfish can discriminate molted male conspecifics from the other chemical stimuli tested. Chemical signals mediate many behaviors in Crustacea.
Crustaceans can use chemoreception to identify and localize food Derby and Atema, ; Moore et al. Crustaceans appear to release alarm signals through urine secretion Zulandt Schneider and Moore, In addition, crustaceans are sensitive to chemicals such as crushed conspecific cues Hazlett, ; Rittschof, ; Hazlett, ; Pijanowska, Physiological and physical changes occur during ecdysis, or molting.
During ecdysis, crustaceans have increased concentrations of hormones, including ecdysone and hydroxyecdysone, in the hemolymph Chang, These hormones initiate many physiological responses such as the reuptake and sequestering of inorganic chemicals and ions, loosening of the old exoskeleton, and the generation of chemicals that form the new exoskeleton underneath the old one Waddy et al.
During and after ecdysis, chemical compounds lost to the aquatic environment may be at altered concentration and composition. The soft exoskeleton following ecdysis is more permeable than a hard exoskeleton to water and perhaps other compounds Aiken, ; Chang et al.
Compounds that would not diffuse across an intermolt exoskeleton may be able to pass after ecdysis before the new exoskeleton has completely hardened. This would alter the composition of the chemicals entering the water. Also, because the soft exoskeleton is not an efficient barrier, higher concentrations of chemicals could pass into the water.
Because many ecological interactions are influenced by chemical signals, the chemical changes associated with molting may bring about differences in those interactions. The purposes of this study were to determine whether male crayfish, Orconectes rusticus Girard, , could distinguish between the chemical signals from recently molted versus intermolt male crayfish. To answer this question, crayfish were presented chemical molt signals paired with control, intermolt or food signals.
This study will elucidate whether crayfish respond to the chemical changes that accompany molting in conspecifics. All crayfish were fed approximately 0. Crayfish used in experiments were housed in ventilated pots Crayfish were 3. Crayfish were starved for 48 h prior to the experiments.
Male crayfish chosen for stimulus collection were mechanically, visually, and chemically isolated in pots Water in the stimulus pots was changed every other day approximately 3 h after feeding. Two reservoir tanks plastic gallon jugs; 3. Chemical stimuli flowed from reservoir tanks through 1. Water exited the tank at the opposite end through four outflow pipes that were controlled by valves. The temperature of both tank and stimulus water were the same to ensure that the vertical position of the odor plume was conserved along the entire arm of the tank.
The outflow pipes were 5 cm above the bottom of the maze. Dye trials were also used to determine the time for the odor plume to travel to the end of the arm. Y-maze setup for attraction experiments. Tank is divided into three sections A, B, C. Flow is regulated by an in-line flow meter. The odors then enter either arm B or C of the tank. Outvalves on the opposite side of the tank draw the odors through the arms in a straight path. Water with intermolt cues and control stimuli aged tank water were collected and frozen 24 h after the water had been changed.
Preliminary behavioral experiments confirmed that there is no difference in crayfish response to frozen versus fresh chemical stimuli used in this study. Stimulus was collected from a single crayfish only once.
Three stock solutions were prepared for each chemical stimulus molt: 31, 33, and 35 individuals; intermolt: 40, 48, and 50 individuals; control: 31, 31, and 40 individuals. These stocks were used to eliminate the possibility that attraction was attributable to the chemical stimulus of particular individuals as opposed to a general population-wide molt status.
Food stimulus was prepared from frozen haddock. The solution was then strained to remove any solid matter. Food stimulus was chosen to elicit a baseline chemosensory response.
Experimental conditions consisted of either two different stimuli or two identical stimuli introduced into the arms of the Y-maze. Within the different-stimuli treatment, each trial was comprised of pair-wise combinations: molt vs. In the identical-stimuli treatment, the same chemical stimulus was presented in each arm of the Y-maze. These latter experiments help to explain differences in activity patterns within a stimulus without the confounding factor of other stimuli present in the tank.
Chemical stimuli were assigned randomly to each reservoir chamber by flipping a coin. The maze was filled with aged tank water, and the bottom was lined with gravel that had been rinsed for 10 min with hot, then distilled water.
Crayfish were acclimated in a gated shelter for 10 min before flow was initiated. The shelter consisted of a bisected 2-inch PVC pipe with a gate of egg-crate and a mesh rear to ensure that the crayfish were exposed to the flow from the arms. Flow was then initiated and crayfish were further acclimated for 8 min dye trials showed that the odor plume arrived at the end of the arm 7 min after flow initiation.
The Y-maze and gravel were rinsed for 10 min with hot, then distilled water between trials. The rostrum position was digitized once every second for the total length of the trial. A crayfish was considered in or out of an arm when its rostrum passed a line separating the two arms from the back of the tank see Fig. From X, Y coordinates, behavioral parameters, including initial arm choice, proportion of time spent in each arm, proportion of time spent at each nozzle within 10 cm of the inflow nozzle , and number of arm changes were calculated.
Initial arm choice was defined as the first arm the crayfish entered. The number of arm changes after initial arm choice were counted for each trial and analyzed for differences between treatments with a one-way ANOVA. This parameter will give a measure of the amount of exploration of the entire tank during trials. The proportion of time spent in each arm is the total time spent in one arm divided by the total time spent in either arm.
The proportion of time at the nozzle was defined as the total amount of time a crayfish spent within 10 cm of the nozzle, provided that it was directly touching with at least one chela or facing the nozzle, divided by the total amount of time spent in either arm.
Meral spread is the distance between the tip of the right and left chelae and has been used as a measure of aggressiveness Thorpe and Ammerman, ; Bruski and Dunham, ; Zulandt Schneider et al.
Walking speed, time spent in either arm, time spent at either nozzle, time spent moving, and walking speed while moving in the arms was measured for the identical chemical stimulus presentation. Time spent in either arm or at either nozzle was calculated for each treatment. Crayfish, while chemically stimulated, travel in a pattern consisting of periods of movement and periods of no movement.
Therefore, the proportion of time spent moving and the walking speed while moving in the arms were measured. Walking speed while moving in the arms was calculated by analyzing whether the crayfish was both in an arm and was moving. From these data points, average walking speeds were calculated and analyzed with a one-way ANOVA across chemical stimuli.
Odor sources often induce changes in locomotion patterns of chemosensory animals Kleerekoper, ; Teyke et al. Behavioral analysis that looks at changes in those patterns provides insight into ecologically important responses to chemical stimuli. Orientation parameters calculated from the digitized videos were average walking speed, average distance to source, and average walking speed to the source.
These parameters have been used in the past to characterize orientation behavior to a food source in crayfish Moore et al. Because the experimental conditions for each treatment were different different paired stimuli present , parameters cannot be compared across treatments and only within a treatment. Therefore, paired tests were chosen instead of multivariate statistics. In the molt vs.
Percentage of initial arm choice for control A and experimental B treatments. Stimuli are molt odor black , control white , intermolt hatched , and food gray. Crayfish spent significantly more time in the arms with the molt and food stimuli when paired with control chemical stimuli see Fig. Crayfish spent significantly more time in the molt arm over the intermolt arm in the molt vs. There were no significant differences in time at the nozzle for the intermolt vs.
All tests resulted in at least three arm changes between the paired stimuli. Animals did not choose one arm and stay within that arm. There was a statistical difference between stimuli for the parameters of the proportion of time spent moving see Fig.
There were no differences in the overall walking speed, time spent in either arm, or time spent at either nozzle between chemical stimuli. Parameters measured during identical odor presentation of stimuli. They can be aggressive and may attempt to eat fish. However, crayfish are actually fairly shy and may often attempt to hide under leaves or rocks. If you are going to keep a crayfish as a pet, remember to give it some hiding space. At night, some fish become less energetic and settle to the bottom.
The crayfish might see it as a danger and hurt or kill it with its claws. Crayfish are great escape artists and may try to climb out of the tank so any holes in the hood should be covered. In nations where imported alien crayfish are a danger to rivers, such as England, catching and keeping crayfish as pets is one of the main means of the spread of destructive species - since they are often flung back into a different river.
Crustacean Quiz. Invertebrate Home.
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