Site availability and density-dependent constraints on the acanthocephalan Pomphorhynchus laevis in rainbow trout, Oncorhynchus mykiss (Walbaum)

Parasitology ◽  
1991 ◽  
Vol 102 (3) ◽  
pp. 405-410 ◽  
Author(s):  
R. M. Bates ◽  
C. R. Kennedy
Keyword(s):  
Rainbow Trout ◽  
Oncorhynchus Mykiss ◽  
Alimentary Tract ◽  
Experimental Investigations ◽  
Small Fish ◽  
Threshold Density ◽  
Pomphorhynchus Laevis ◽  
Rainbow Trout Oncorhynchus Mykiss ◽  
Intestinal Length ◽  
The Mean

Threshold density levels were investigated experimentally in rainbow trout, Oncorhynchus mykiss, for the acanthocephalan Pomphorhynchus laevis. Fifty small fish 120–150 mm long were infected with 50 cystacanths each every 4 weeks for 16 weeks, and samples of up to 10 fish examined at 1, 5, 9, 13 and 17 weeks after the original infection. The mean intestinal length was found to have increased significantly over this period, from a mean of 125 to 173 mm and the mean number of parasites recovered increased after each interval of 4 weeks, and significantly from 19·30 to 86·40 per fish over the 17 weeks. The distribution of the parasites in the alimentary tract of O. mykiss was unaltered, indicating that the favourable region for establishment had remained unchanged. The failure to detect any manifestations of competition is discussed, and the relevance of conventional approaches to experimental investigations of both intra- and interspecific competition in fish was queried, and contrasted to the situation in birds and mammals.

Assessing the effects of positive buoyancy on rainbow trout (Oncorhynchus mykiss) held in gas supersaturated water

1990 ◽  
Vol 68 (5) ◽  
pp. 969-973 ◽  
Author(s):  
J. M. Shrimpton ◽  
D. J. Randall ◽  
L. E. Fidler
Keyword(s):  
Rainbow Trout ◽  
Oncorhynchus Mykiss ◽  
Ambient Pressure ◽  
Large Change ◽  
Bladder Volume ◽  
Bladder Pressure ◽  
Small Fish ◽  
Swim Bladder ◽  
Rainbow Trout Oncorhynchus Mykiss ◽  
The Impact

We examined the effects of swim bladder overinflation associated with dissolved gas supersaturation on rainbow trout (Oncorhynchus mykiss). The change in swim bladder volume with increased swim bladder pressure was measured in fish subjected to a decrease in ambient pressure. An expansion of swim bladder volume occurs that is related to the excess swim bladder pressure. The volume change results in a decrease in density and positive buoyancy in the fish. Small fish are adversely affected when exposed to gas supersaturated water because of the high swim bladder pressure required to force gas out the pneumatic duct. Changes in behaviour and depth distribution of fish held in gas supersaturated water were measured in a 2 m deep observation column. A large change in density caused small fish to increase depth and compensate for the swim bladder expansion. Although swim bladder inflation occurs for all sizes of trout held in gas supersaturated water, the impact is greatest for small fish and they must compensate by seeking depth. However, adequate depth to compensate for positive buoyancy may not always exist. In such a case, fish must swim continuously in a head down position to overcome excess buoyancy. The power necessary for a fish to swim with an overinflated swim bladder is greatest for small fish that show the largest change in density.

The relation between age-0 rainbow trout (Oncorhynchus mykiss) abundance and winter discharge in a regulated river

2003 ◽  
Vol 60 (2) ◽  
pp. 135-139 ◽  
Author(s):  
Matthew G Mitro ◽  
Alexander V Zale ◽  
Bruce A Rich
Keyword(s):  
Rainbow Trout ◽  
Oncorhynchus Mykiss ◽  
Prediction Interval ◽  
Critical Time ◽  
Regulated River ◽  
Test Model ◽  
High Discharge ◽  
Rainbow Trout Oncorhynchus Mykiss ◽  
Model Predictions ◽  
The Mean

We identified and experimentally tested a discharge–abundance relation that predicted, based on the mean river discharge in the second half of winter (15 January – 31 March), the spring abundance of age-0 rainbow trout (Oncorhynchus mykiss) in a section of the Henrys Fork of the Snake River, Idaho, with complex bank habitat. We also considered a competing hypothesis in which autumn abundance determined spring abundance. We established that large abundances of age-0 trout were present in autumn (34 000 – 81 000) and lower abundances remained in spring (8000 – 15 000). Winter loss of age-0 trout was initiated in January. Spring abundance in 1996–1998 was related to autumn abundance (r2 > 0.99) and mean discharge in the second half of winter (17.1–22.8 m3·s–1; r2 > 0.99) but not mean discharge in the first half of winter (15.1–21.1 m3·s–1; r2 = 0.11). We experimentally maintained a high discharge (20–21 m3·s–1) in the second half of winter in 1999 to test model predictions. Autumn abundance failed to predict spring abundance (observed = 11 109; predicted = 6822; 95% prediction interval = 4669–8975). However, the discharge–abundance model accurately predicted spring abundance (predicted = 11 980; 95% prediction interval = 10 728 – 13 231). Higher discharge in the second half of winter may have provided more bank habitat at a critical time for survival.

The effect of handling and blood removal on plasma levels and hepatic deiodination of thyroid hormones in adult male and female rainbow trout, Oncorhynchus mykiss

2002 ◽  
Vol 80 (2) ◽  
pp. 372-375 ◽  
Author(s):  
Keith J Todd ◽  
J Geoffrey Eales
Keyword(s):  
Rainbow Trout ◽  
Thyroid Hormones ◽  
Oncorhynchus Mykiss ◽  
Adult Male ◽  
Plasma Levels ◽  
Temporary Increase ◽  
Male And Female ◽  
Rainbow Trout Oncorhynchus Mykiss ◽  
Adult Females ◽  
The Mean

We studied the effects of handling and blood removal (0.4% of body mass) on the thyroid system of fasted ~1000-g adult male and female rainbow trout, Oncorhynchus mykiss, over a 3-day period. Relative to undisturbed controls, bleeding lowered the mean hematocrit (HCT) by 19% and on day 1 increased the hepatic inner-ring deiodination of 3,5,3'-triiodothyronine (T3) (T3IRD), but did not alter thyroxine (T4) outer-ring deiodination (T4ORD) or inner-ring deiodination (T4IRD) activity or plasma T4 or T3 levels. Regardless of treatment, hepatic T4ORD activity and HCT were lower in females than in males, and over the 3 days following bleeding, the plasma T3 level increased and the plasma T4 level decreased progressively for both sexes. We conclude that handling and bleeding induce a temporary increase in hepatic T3 conversion to 3,3'-diiodothyronine with no change in T4 conversion to reverse T3. This is consistent with independent control of T3IRD and T4IRD activities. Furthermore, HCT and hepatic T4ORD activity are lower in adult females, and 10 days after transfer of trout to smaller tanks, plasma T4 and T3 levels may still be adjusting.

Factors affecting swim bladder volume in rainbow trout (Oncorhynchus mykiss) held in gas supersaturated water

1990 ◽  
Vol 68 (5) ◽  
pp. 962-968 ◽  
Author(s):  
J. M. Shrimpton ◽  
D. J. Randall ◽  
L. E. Fidler
Keyword(s):  
Rainbow Trout ◽  
Oncorhynchus Mykiss ◽  
Partial Pressure ◽  
Strong Dependence ◽  
Arterial System ◽  
Bladder Pressure ◽  
Small Fish ◽  
Swim Bladder ◽  
Factors Affecting ◽  
Rainbow Trout Oncorhynchus Mykiss

We examined the response of the rainbow trout (Oncorhynchus mykiss) swim bladder to gas supersaturated water. Cannulas positioned in the swim bladder of fish were connected to a pressure transducer, allowing direct measurement of swim bladder pressure. When denied access to the surface, fish held in supersaurated water showed an increase in swim bladder pressure. This response showed a strong dependence on the total gas pressure and the oxygen partial pressure of the water. The minimum level of gas supersaturation observed to cause this response corresponds to a ΔP of 27 mmHg [Formula: see text]; 1 mmHg = 133.3 Pa). The threshold ΔP for swim bladder inflation increased as the partial pressure of dissolved oxygen increased. Movement of supersaturated gases from the arterial system into the swim bladder is passive and causes a rise in swim bladder pressure until the diffusion gradient is nil or the gas is expelled through the pneumatic duct. The threshold for release of gas out the pneumatic duct is dependent on the size of the fish. Small fish have higher duct release pressures and are subject to a higher degree of pressure buildup within the swim bladder than larger fish.

Over-winter lipid depletion and mortality of age-0 rainbow trout (Oncorhynchus mykiss)

2004 ◽  
Vol 61 (8) ◽  
pp. 1513-1519 ◽  
Author(s):  
Peter A Biro ◽  
Ashley E Morton ◽  
John R Post ◽  
Eric A Parkinson
Keyword(s):  
Rainbow Trout ◽  
Oncorhynchus Mykiss ◽  
Lipid Content ◽  
Risk Taking ◽  
Selective Pressure ◽  
Small Fish ◽  
Laboratory Findings ◽  
Size Dependent ◽  
Rainbow Trout Oncorhynchus Mykiss ◽  
Lipid Contents

In this study we identify the size-dependent risk of winter starvation mortality as a strong selective pressure on age-0 rainbow trout (Oncorhynchus mykiss) that could promote the risk-taking behaviour and allocation of energy to lipids previously observed in young trout cohorts. Age-0 trout subjected to simulated winter starvation conditions gradually depleted lipid reserves to a critical minimum lipid content below which death occurred. Small fish with lower lipid content exhausted lipid reserves earlier, and experienced high mortality rates sooner, than larger fish with greater lipid content. Consequently, winter starvation endurance was dependent upon size-dependent lipid reserves and winter duration. To validate the laboratory findings in the field, we stocked several size classes of hatchery-raised trout with known lipid content at the start of winter into two experimental lakes, and estimated survival and lipid depletion at winter's end. Larger age-0 trout had greater initial lipid reserves than smaller trout. Individuals depleted most of their lipid reserves over the winter, and experienced mortality that ranged from just under 60% for the largest individuals to just over 90% of the smallest individuals. Many survivors had lipid contents near, but none were below, the minimum lipid content determined in the laboratory.

Sign in / Sign up

Export Citation Format

Share Document