For assessment of hindgut content weight, five mature and five immature crawfish were collected prior to depuration and then from designated replicates at each 12-h
sample period. Equal numbers of males and females were collected when possible. Ž
. Crawfish were immediately and individually frozen y18
8C and at a latter date thawed, weighed, and dissected. The intestine, or hindgut, was separated at its junction to the
midgut and left attached to the anus. The telson, with intact anus and attached hindgut, was removed from the abdomen and centered over a pre-weighed aluminum pan.
Contents of the hindgut were collected in the pan by flushing the gut with 3 ml of distilled water dispensed from a small syringe through the anus. Gut contents from each
of the five mature and five immature crawfish were pooled, and dry weight was recorded after drying overnight at 75
8C. Dry gut content weight was computed as a percent of whole wet crawfish weight, wet abdominal muscle weight, and dry abdominal
muscle weight. Gut evacuation rate was determined as the mean percentage loss for each 12-h duration, and net incremental loss was defined as the percent of the mean total loss
Ž .
after 48 h that occurred at each 12-h increment. Mortality that occurred during purging was determined by closely examining every animal after removal from designated
containers in each purge system. Sexual maturity of dead and surviving crawfish was Ž
. also determined as described by McClain 1994 .
The experimental approach consisted of a randomized incomplete block design with test date as the blocking factor. Data were analyzed with the General Linear Model
Ž .
procedure in a factorial arrangement of treatments system and time interval using the Ž
Micro SAS Statistical Software System Statistical Analysis Systems version 6.10, SAS .
Institute, Cary, NC . Main effects were tested for interactions and analyzed indepen- Ž
. dently if no significant interaction P F 0.05 occurred. For the independent analyses, if
significant differences were present, Duncan’s multiple range test was used to separate treatment means at P F 0.05. The relationship between water temperature and gut
Ž .
evacuation rate or crawfish mortality was determined by simple linear correlation analysis.
3. Results
Ž .
About 950 kg of crawfish 35,000 individuals were examined for purge-related mortality over the 2-year period of investigation. The percentage of crawfish dying
during purging for each year, and the proportion of immature crawfish in the catch and those that died during purging are depicted in Table 1. The maturity status of a
substantial portion of dead crawfish could not be identified in 1998 as a result of cannibalism. Minimal unidentifiable remains were found in 1997. The data indicate that
mortality increased with an increase in duration of purging, with a greater incidence of death among immature crawfish. Mortality was highly variable with respect to test
Ž .
period Table 2 , and no trend relative to harvest period or temperature was observed. Mortality after 24 and 48 h of purging averaged 9 and 12, respectively. Although
results were highly variable, no significant differences due to purge system type were Ž
observed for mortality or composition regarding identifiable or unidentifiable maturity .
Ž .
status of the dead crawfish Table 3 .
Table 1 Ž
. Mean percent maturity and mortality for crawfish ns 35,264 subjected to purging
Hour Percent
Percent Percent
Percent immature of catch
mortality immature of total dead
unidentifiable of total dead 1997
37.8 –
– –
48 –
8.0 70.5
– 1998
68.2 –
– –
24 –
8.7 71.6
10.6 48
– 14.2
84.0 19.3
About 1500 crawfish were dissected for determination of hindgut content. The Ž
. average amount of hindgut contents dry weight basis voided during purging, based on
Ž .
percentage of whole crawfish weight, generally declined with time Table 2 . The maximum net evacuation efficiency was - 90, and crawfish averaged 57, 63, 78, and
81 evacuation of the hindgut after 12, 24, 36, and 48 h of purging, respectively. Of the 11 evaluation period averages, only one mean net evacuation peak occurred within the
Ž .
first 12 h of purging 26 May 1998 ; no peaks occurred at 24 h, four occurred at 36 h, and six occurred after 48 h of purging. Mean percent evacuation for each 12-h increment
was generally positively correlated with water temperature at harvest and during purging Ž
. minimum, maximum, and median for separate correlations; temperature at harvest had
Ž .
the higher correlations, which were only significant at the 12-h r s 0.705; P s 0.016
Table 2 Ž
. Ž
. Water temperature
8C at harvest and during purging, mean SD percent net evacuation of hindgut contents, and percent mortality for each test period
Date Temperature
Percent gut evacuation Percent mortality
a
Harvest Purge
12 h 24 h
36 h 48 h
24 h 48 h
ŽMin– .
Max Ž
. Ž .
Ž . Ž .
10 April 1997 19
19–21 57 13
60 8 87 2
82 5 14
a
Ž .
Ž .
Ž .
Ž . 24 April 1997
18 18–21
57 21 49 17
84 11 89 5
8
a
Ž .
Ž .
Ž . Ž .
8 May 1997 23
20–25 48 28
68 10 80 8
85 5 7
a
Ž .
Ž . Ž .
Ž . 4 June 1997
25 24–26
63 16 84 4
85 3 79 3
3 Ž
. Ž .
Ž .
Ž . 26 February 1998
16 19–20
39 27 66 8
75 13 80 6
5 11
Ž .
Ž .
Ž .
Ž . 4 March 1998
12 19–20
49 25 34 22
63 13 82 8
4 10
Ž .
Ž .
Ž . Ž .
25 Mar ch 1998 17
17–23 53 17
62 16 79 6
76 4 4
11 Ž
. Ž
. Ž .
Ž . 14 April 1998
20 19–22
56 20 67 12
78 8 81 6
7 8
Ž .
Ž .
Ž .
Ž . 28 April 1998
21 23–25
50 13 60 19
71 27 85 5
3 6
Ž .
Ž .
Ž . Ž
. 12 May 1998
25 20–22
69 12 74 10
82 3 65 14
9 18
Ž . Ž .
Ž .
Ž . 26 May 1998
26 19–20
79 9 75 7
68 26 72 6
28 34
Average 20
20–22 57
63 78
81 8
12
a
Not determined.
Table 3 Response values for crawfish purged in either spray and submerged systems for 12-, 24-, 36-, or 48-h
durations during 1998. Means followed by superscripts were significantly different, and other mean compar- Ž
. isons within category by duration were not significantly different P 0.05
12 h 24 h
36 h 48 h
Percent mortality
a a
Spray 9
13
a a
Immersion 9
18 Percent immature of dead
a a
Spray 67
85
a a
Immersion 86
81 Percent unidentifiable of dead
a a
Spray 8
19
a a
Immersion 18
19 Percent gut eÕacuation
B
Spray 58
64 68
76
A
Immersion 54
62 79
79
a
Not determined.
Ž .
Ž . and 24-h r s 0.870; P s 0.0005 durations. The correlation coefficients r for the 36-
Ž .
Ž .
and 48-h periods were 0.282 P s 0.401 and y0.433 P s 0.1835 , respectively. Ž
. Net gut evacuation rate was slightly affected by purge system type Table 3 . Only at
Ž .
the 36-h period was there a significant difference P s 0.03 , with crawfish in the
immersion system having the higher rate. The most notable difference between the two systems is that the mean peak in net gut evacuation occurred at 36 h in the immersion
system and at 48 h in the spray system. Because there was a general lack of differences due to purge system type and with no
significant interaction between system and purge duration, data were pooled with regard Ž
. to computations and analyses of hindgut content as a percent of tissue weights Table 4 .
Overall, the purging process resulted in a significant reduction in the percentage of contents of the hindgut, although the reductions at each 12-h increment were not always
Ž .
significant P 0.05 . There were small differences and no obvious trend due to
maturity. Approximately 70 of the net total excrement loss occurred during the first 12 h, about 77 occurred within 24 h of purging, and 97 occurred within 36 h of purging
Ž .
Table 4 .
4. Discussion
