Murray–Darling Basin Authority Native Fish Strategy Strategies to improve post release survival of hatchery-reared threatened fish species Michael Hutchison, Danielle Stewart, Keith Chilcott, Adam Butcher, Angela Henderson
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Figure 25: Cod from all treatment groups showed a tendency to use cover cells (including the cover cell in the predator compartment) and cells distal from an introduced predator. The image above shows a control group of Murray cod fingerlings. The predator is a golden perch. The movement of increased numbers of cod fingerlings to the far cell after introduction of the predator is clearly seen in Figure 26, but none of the trained groups showed greater use of the far cell compared to control fish. A minor drop in use of the predator cell can be seen across all groups in Figure 27 following introduction of the predatory fish. In Figure 28 it can be seen that use of cover cells changed little before and after introduction of the predator. A minor drop can be seen immediately after introduction of the predator across all groups. This was related to initial startle responses and scattering when the predator was released into the predator cell. 
Figure 26: Mean numbers of Murray cod (control, 24 hr trained, 48 hr trained and 72 hr trained) recorded in the far cell for five minutes before introduction of a predator and for 10 minutes after. The predator was introduced at time 0 denoted by the dashed line. Counts of Murray cod were recorded every 15 seconds. The maximum possible count at any one time is eight fish. Number of replicates for each treatment is eight. Error bars have been excluded for clarity of reading the graph. 
Figure 27: Mean numbers of Murray cod (control, 24 hr trained, 48 hr trained and 72 hr trained) recorded in the predator cell for five minutes before introduction of a predator and for 10 minutes after. The predator was introduced at time 0 denoted by the dashed line. Counts of Murray cod were recorded every 15 seconds. The maximum possible count at any one time is eight fish. Number of replicates for each treatment is eight. Error bars have been excluded for clarity of reading the graph. 
Figure 28: Mean numbers of Murray cod (control, 24 hr trained, 48 hr trained and 72 hr trained) recorded in cover cells for five minutes before introduction of a predator and for 10 minutes after. The predator was introduced at time 0 denoted by the dashed line. Counts of Murray cod were recorded every 15 seconds. The maximum possible count at any one time is eight fish. Number of replicates for each treatment is eight. Error bars have been excluded for clarity of reading the graph. 
Figure 29: Total number of movements recorded for trained (24 hr, 48 hr & 72 h) and untrained control groups of Murray cod for 15 minutes before and after introduction of a predator (golden perch). Movements were recorded every 15 seconds. Number of replicates in each treatment group=eight. Error bars show one standard error of the mean. Before the introduction of a predator, movements were frequent across all treatment groups. Post-introduction of a predator, movements were reduced across all groups (Figure 29). Movements were least in the 72 hour trained fish and were almost half those of control fish exposed to a predator (Figure 29). Variances were homogenous between treatment groups after exposure to a predator and general ANOVA showed a significant difference between the means of treatment groups (p =0.039). The 72 hour trained fish suppressed their territorial behaviours and related movements more than both the control fish and 24 hour trained fish. The other trained groups were not significantly different to the control group (Table 4). Table 4: Pairwise differences in movements of Murray cod fingerlings post introduction of a predator. Means with the same subscript are not significantly different at the P=0.05 level
Freshwater catfish Variances were homogenous between all treatment groups in each of the tank zones (predator, near, centre and far). There was a tendency for increased use of the far zone of the aquarium by 24 hour, 48 hour and 72 hour trained catfish (compared to controls) after introduction of a predator (Murray cod) to the aquarium (Figure 30). ANOVA showed a significant difference between treatments in the far cell (p=0.05). Pairwise tests confirmed that 48 hour trained fish used the far cell significantly more than controls (Table 5) after introduction of a predator. Figure 31 shows typical use of cells by 72 hour trained fish after introduction of a predator. ANOVA also showed significant differences in use of the near cell after introduction of a predator (p=0.028). The trend was for reduced use of the near cell by trained fish compared to control fish. Table 6 shows that 48 hour trained fish used this cell significantly less than control fish after introduction of a predatory fish. 
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