Large Rainbow Research Articles

Cause for the Decline of Large Rainbow Trout in a Tailwater Fishery: Too Much Putting or Too Much Taking?

We studied causes for the decline of large (>40 cm total length, TL) rainbow trout Oncorhynchus mykiss and the transition from put–grow–take to put-and-take conditions in Lake Taneycomo, a popular tailwater in Missouri. In this fishery, rainbow trout densities have been sustained against increasing fishing pressure over the last 30 years mainly by increasing stocking rates of catchable-size fish (23–33 cm TL). Short residence times of rainbow trout resulting from heavy fishing pressure and high vulnerability to angling are generally considered the main reason for this speciesˈ limited growth after stocking in cold tailwaters. However, we found that increasing stocking rates in Lake Taneycomo have been paralleled by food base degradation, leading to submaintenance consumption rates for rainbow trout (i.e., poor growth conditions). A less prominent role of residence times was evident in the decline of poststocking growth and fewer large fish. In contrast to resident brown trout Salmo trutta, high diet similarity was observed across all sizes of rainbow trout collected during the 3-year study, hinting that this species may have a relatively limited capacity to partition food resources intraspecifically in some cold tailwaters. This limitation may contribute to the tendency of rainbow trout to fail to reach large sizes in these environments. Our findings indicate that when poststocking growth of rainbow trout is desired in cold tailwaters, greater attention to energetic conditions is warranted.

Comparison of Creel Returns from Rainbow Trout Stocked at Two Sizes

Creel returns of stocked rainbow trout Oncorhynchus mykiss are often below management objectives. In the Hoover Dam tailwater, Colorado River, predation by striped bass Morone saxatilis limits creel returns of stocked rainbow trout. On two occasions, we stocked large (33-em) and small (21–25-cm) rainbow trout into the tailwater to compare returns to the creel. Angler return rates for the two stockings were 47% and 22% for the large fish and 1 % and 2% for the small fish. Costs of large fish returned to the creel were US$6.02 and $12.86 per fish for the two stockings. Costs of small fish returned to the creel were $59.00 and $29.50 per fish for the two stockings. Annual survival of large rainbow trout did not increase compared with small fish. Stocking large rainbow trout is a cost-effective option for the Hoover Dam tailwater and may improve creel returns in other waters where predation limits survival of stocked fish.

Gradual transfer to sea water of rainbow trout: effects on liver carbohydrate metabolism

The levels of glycogen and glucose, as well as of the activities of several key enzymes of glycogenolysis, glycolysis, gluconeogenesis and the pentose phosphate shunt were assessed in livers of small (97 g) and large (166 g) rainbow trout Oncorhynchus mykiss during gradual transfer to sea water (salinities of 0, 9, 18 and 28%). Plasma glucose and protein levels were also evaluated. Liver carbohydrate metabolism changed during gradual adaptation of rainbow trout to sea water. Glucose increased with salinity in livers of both sizes of animals, as did glycogenolysis and gluconeogenesis, but this latter only in large animals, and glycolytic rates in small animals. The different responses in metabolic parameters between sizes of animals may reflect a higher stress of the small animals and/or a better adaptation of large animals to increased salinities, in a way similar to that previously suggested by other authors after evaluation of non‐metabolic parameters. The changes observed at 28% can also be the result of reduced food consumption.

RETINOIC ACID MODULATES RETINAL DEVELOPMENT IN THE JUVENILES OF A TELEOST FISH

Small (<30 g) juvenile rainbow trout (Oncorhynchus mykiss) possess retinal photoreceptor mechanisms sensitive to light in the near ultraviolet, short (blue), middle (green) and long (red) wavelengths. During normal development, the ultraviolet cone mechanism gradually disappears until, by approximately 60&shy;80 g, individuals are no longer sensitive in the ultraviolet. This shift in spectral sensitivity is associated with the loss of a single class of photoreceptor cells &shy; small accessory corner cones &shy; from the retinal photoreceptor cell mosaic. Treating small (<15 g) rainbow trout with 10(-6) mol l-1 all-trans retinoic acid (20 min exposure by immersion) induced a precocial loss of ultraviolet photosensitivity and an associated change in the retinal photoreceptor cell mosaic only 2 weeks after treatment. These changes were indistinguishable from the events that occur during normal development. Six weeks after exposure to retinoic acid, large (>90 g) rainbow trout, which had lost their ultraviolet cones during normal development, were once again ultraviolet-photosensitive and small accessory corner cones were found in their retinas. These results imply that the ultraviolet-sensitive cones, although lost at one point during development, can reappear at another time during the life history of the same individual. Retinoic acid is involved in these morphogenetic processes.

Effect of temperature and feed ration on energy utilization in large rainbow trout, Oncorhynchus mykiss (Walbaum)

Abstract In one experiment, temperature and feed ration were varied for rainbow trout, Oncorhynchus mykiss (Walbaum), with an initial size of about 1200g. In two experiments the feed ration was varied between parallel tanks, with naturally fluctuating ambient temperatures, and containing rainbow trout with an initial size of about 1000g and 400–550g, respectively. Growth and feed efficiency were measured in all experiments. An ad libitum feed ration without wastage produced the most effective energy utilization in most experimental groups. At best an average of 50% of the gross energy was utilized for growth. The relation between growth rate and feed ration was linear, and there was no optimum point for feeding below this level. The observed intake of energy is compared with growth, measurements of digestibility, feeding and starving metabolism. It is also linked to earlier observations of intake by rainbow trout fingerlings to give equations expressing the energy needs of rainbow trout of different sizes (30–1500g). These are intended to be used for efficient rearing at different temperatures (10–22°C).

Habitat selection by rainbow trout Oncorhynchus mykiss in a California stream: implications for the Instream Flow Incremental Methodology

AbstractWe quantified microhabitat selection of rainbow trout (Oncorhynchus mykiss) at 2 flows (low= 1.13 m3. s−1 and high =4.95 m3. s−1) in the Pit River, California. Flows were controlled by an upstream dam and habitat availability was similar during 4 sampling periods at low flow and 2 periods at high flow. A principal components analysis reduced 6 microhabitat variables to 3 new variables that explained 80% of the observed variance. The 3 components loaded heavily on velocity variables, depth variables and substrate. Microhabitat selection generally differed among macrohabitats (i. e., pools, runs, and riffles). Rainbow trout selected different microhabitats at high flow relative to low flow in response to the availability of deeper, faster water. At low flow, depth and velocity selection were positively correlated with seasonal temperature change for adults but not juveniles. Rainbow trout apparently sought shelter in interstitial spaces in the substrate of runs and riffles during the day in early winter. Generally, large rainbow trout were observed in pools, intermediate‐sized fish in runs, and small trout in riffles. The largest fish occurred in slow, deep areas of pools, where they moved slowly without orientation to flow and were not observed feeding, whereas small fish generally faced upstream and fed in all habitat types. Foraging forays were directed up in the water column at velocities similar to the mean water column velocities at holding positions. Rainbow trout were the most abundant species in 76% of the population survey stations. Other species that might have influenced microhabitat selection by rainbow trout were uncommon.

Optic nerve response and retinal structure in rainbow trout of different sizes

This study presents evidence of ultraviolet (UV) sensitive, ON center ganglion cells in the fish retina. We determined the spectral sensitivity of ON and OFF responses from the optic nerve mass potential in small (18.0–28.5 g) and large (59.5–835 g) rainbow trout, with special reference to UV sensitivity. Under a mid + long-wavelength adapting background, the ON response of small fish revealed the presence of a UV cone mechanism (λ max 390 nm) which was absent in large specimens. Under similar background conditions, the OFF response of both small and large fish showed one sensitivity peak, dominated by inputs from an M-cone mechanism. An almost complete absence of the accessory corner cones from the retinal mosaic was correlated with the loss of UV sensitivity.

The effect of time-restricted demand feeding on feeding activity growth and feed conversion in rainbow trout ( Oncorhynchus mykiss)

The effect of restricted access to a demand feeding system was evaluated for cage-reared rainbow trout with an initial weight of 0.46 – 0.61 kg during 4 summer months. The purpose was to find the access time that produced optimal levels of food supply, as assessed by measurements of growth rate and feed conversion. Following a period during which fish had 24 h access to food per day, feeding regimes were reduced to 3, 5 or 7 h of access to the feeder per day for treatment groups. The time available for feeding within each restricted regime was divided into two feeding periods during each day. Fish held under the control feeding regime were given unrestricted access to the demand feeder (24 h/day). Restricted access time to the demand feeders resulted in a significantly reduced number of feeder actuations and thus lowered food supply compared with the unrestricted regime. Restricted access to the feeder also resulted in a decreased growth rate during the first 28 days after the transition from unrestricted feeding. This was particularly obvious for the trout allowed to feed for only 3 h per day. Following the initial period of low growth rate, specific growth rates increased in the restricted groups and became similar under all the feeding regimes, at about 1.1% per day. The feed conversion (FC) varied with food access time. The self demand food supply was used most efficiently by fish fed for 3 h per day (FC = 1.0) and least efficiently by fish fed on the unrestricted regime (FC = 1.6). Trout on the other two regimes, with 5 and 7 h feeding, showed intermediate conversion of 1.1 and 1.2, respectively. The results suggest that two feeding periods per day, each of about 2 h duration, are sufficient for optimal growth of large (0.5 – 2 kg) rainbow trout adapted to demand feeders. The number of bites per day was correlated with the water temperature. Biting activity peaked at 16 °C. After 2–3 h of feeding, trout on the time-restricted feeding regimes exhibited a significantly lower bite activity, probably due to the fish becoming satiated.

A model for exchange of organic chemicals at fish gills: flow and diffusion limitations

A mathematical model for the exchange of neutral organic chemicals at fish gills was formulated based on limitations imposed by flows of water and blood to the gills, diffusion barriers defined by gill morphology, and chemical binding relationships within water and blood. This model was parameterized independently of exchange measurements and validated against datasets on the relationship of chemical uptake rates for large rainbow trout and small guppies to chemical hydrophobicity. This model was found to closely predict the magnitude and trends of observed gill uptake rates in these datasets, predictions deviating from observed values by no more than a factor of two over a range of octanol:water partition coefficients from 2 to > 10 6. Elimination rates for small guppies were also predicted. This analysis suggests that gill exchange can be understood and predicted on the basis of fundamental physiological and morphological variables.

A simple flow-limited model for exchange of organic chemicals at fish gills

A mathematical model for the exchange of organic chemicals by fish gills was formulated based solely on the limitations imposed by the flows of water and blood into the gills. For large rainbow trout, this model was found to closely follow the magnitude and trends of observed gill uptake rates over a range of octanol/water partition coefficient from 1 to 106. Observations averaged only about 30% less than model predictions. This modest lack-of-fit is presumably due to the effects of diffusional barriers and ionization which would further limit uptake, although uncertainties in model parameters and data are likely also partly responsible. This analysis suggests that these basic physiological parameters are of major importance in the regulation of exchange at fish gills and should be accounted for in more detailed toxicokinetic models. Also, this simple model could by itself be useful for approximate assessments of accumulation of organic chemicals by fish.

A comparison of oxygen debt in small and large rainbow trout, Salmo gairdneri Richardson

The potential for anaerobic metabolism in fish white muscle appears to increase with body size. Larger fish have higher white muscle glycolytic potential (Somero & Childress, 1980) and display both higher rates of lactate production and higher maximum concentrations of lactate following exhaustive exercise (Goolish, in press). The post-exercise elevation in oxygen consumption by fish (' oxygen debt ') is considered to be the result of processes involved in the recovery from anaerobic metabolism (Gaesser & Brooks, 1984; Milligan & McDonald, 1988) and therefore may also be influenced by body size. The present study compares the oxygen debt of small and large rainbow trout following exhaustive exercise. The respirometer consisted of flow-through tubular chambers (75 and 4200 ml) immersed in a constant water bath (15 C). Oxygen consumption rates were calculated from the flow rate and the change in dissolved oxygen as measured with a Camlab $8543 oxygen meter (Cambridge, U.K.). Mean sizes (*s.E.) of the large and small fish were 32.7cmf3.1 (n = 4) and 7.8 cm 0.6 (n = 3), respectively. Individual post-absorptive fish were placed in the respirometer and monitored until stable control levels of oxygen consumption were observed. The fish were then removed, exercised for 6 min, and returned to the respirometer. Maximal burst activity was induced using a net in tanks of approximately the same relative size (3 by 4 body lengths). Rates of oxygen consumption were determined after 1.2,3,4,5,6 and 8 h, and expressed as a percentage of the mean pre-exercise level. The relative increase in oxygen consumption following exhaustive swimming was higher for the larger fish at each sampling time (Fig. I). The duration of the response was also longer for the large fish (8 h) than for the small fish (5 h). The relative increase in oxygen consumption was significantly higher for the larger fish when the data were combined for the duration of the response (P < 0.02), but individual sampling times were not significantly different. The higher relative increase for large fish was partly due to their lower standard metabolic rate; 58.6 and 96.1 mg 0, kg-' h-' for large and small fish, respectively. The area under each curve was used to calculate the total amount of oxygen consumed above pre-exercise levels. Averaged over the duration of the response, the absolute increases in respiration rates following exercise were similar for the large and small fish; 40.4 and 49.5 mg O2 kg- h-', respectively. Post-exercise oxygen consumption expressed per gramme of white muscle was also similar for large (0.69 mg 0, g-') and small fish (0.65 mg Having white muscle lactate production (Goolish, in press) and post-exercise oxygen consumption data from the same group of fish also provides an opportunity to examine the relationship between these variables and the cost of glycogen restoration. The oxygen debt data from the group of large fish (33 cm) are used here because of their lower variability. Lactate production for fish of the length, subtracting the resting level, is 34.7 pmol g-l (Goolish, in press). This is equivalent to energy production of 1.94 J g-l of white muscle tissue, assuming a 2 : 1 ratio between lactate and each glucosyl unit (Stevens & Black, 1966; Wardle, 1978) and that 558 J are obtained per gramme of glycogen (Wardle, 1975). The

Influence of Rainbow Trout (Oncothynchus mykiss) on Density and Feeding Behaviour of a Perlid Stonefly

Stonefly (Paragnetina media) density was reduced in a rainbow trout (Oncorhynchus mykiss) enclosure by approximately 35%, whereas in a trout exclosure no significant changes in density occurred. Of the 35% reduction, approximately two-fifths and three-fifths were attributable, respectively to direct consumption of stoneflies by trout, and emigration by stoneflies from the predator-stressed section of stream. With trout present in laboratory aquaria, predator avoidance behaviour resulted in stoneflies remaining significantly more on dark substrate on which they were less vulnerable to trout predators. Stoneflies consumed significantly fewer prey (enchytraeid whiteworms) over 24 h, in the presence of both small (2.0–4.0 cm) and large (10.0–12.0 cm) rainbow trout in aquaria, compared with stoneflies feeding in trout-free aquaria. Feeding rate and substrate selection did not differ between well-fed and starved (5 d) nymphs.

Electrofishing Injury to Large Rainbow Trout

Electrofishing Injury to Large Rainbow Trout

Influence of Electrofishing Pulse Shape on Spinal Injuries in Adult Rainbow Trout

Abstract Adult rainbow trout Salmo gairdneri captured by electrofishing were analyzed for spinal injury by X-ray photography and autopsies. The effects of three electrical pulse shapes were compared. Of 209 fish captured, 50% suffered spinal injuries involving an average of eight vertebrae that were dislocated, splintered, or both. One-quarter-sine wave pulses injured a significantly higher proportion of fish (67%) than either exponential pulses (44%) or square wave pulses (44%; P < 0.05). Quarter-sine waves also damaged significantly more vertebrae per fish (average, 9.5) than did exponential pulses (6.6); the average number damaged by square waves (8.2) did not differ significantly from either of the other means. Electrofishing could bias mark–recapture studies of large rainbow trout. Electrofishing in waters containing endangered or threatened species should be considered with great caution.

Beam expander for making large rainbow holograms

Beam expander for making large rainbow holograms

Blood, ensiled or frozen, as feed for salmonids

Blood from the slaughtering of cattle was tested as a protein source in moist diets for large rainbow trout ( Salmo gairdneri Richardson) and salmon ( Salmo salar L.). The blood was used in its natural form. In the first experiment the blood was preserved by acid, and in the second experiment it was preserved by freezing or by acid. The control diet contained fish or fish offal and binder meal. In the test diets blood replaced half the amount of raw fish or fish offal which represented nearly 20% of the protein in the feed. Unlike frozen blood, blood silage did not cause pellet consistency problems. No negative effects with respect to weight increase, health, body composition or organoleptic properties of the fish were observed when blood was used in the diet or when formic acid was used as preservative instead of freezing the fresh commodity. The apparent digestibility of blood protein exceeded 97% and was not significantly affected by the various methods of preservation.

Protein sparing effects in large rainbow trout, Salmo gairdneri

Large rainbow trout (250–550 g) were fed to satiation or 0.5% live weight/day, one of six balanced diets varying in protein (30%, 43%, 52%) and lipid levels (12%, 24%). Growth and changes in body composition were measured over a 60-day feeding period. Mean appetite varied inversely with dietary digestible energy. Total weight gain over the 60-day period was not significantly different ( P = 0.05) for fish fed to satiation on diets containing 43 or 52% protein at the 24% lipid level. Weight gain was significantly lower among fish fed to satiation on the 30% protein, 12% lipid diet than those fed diets containing 43 and 52% protein, at either lipid level. When feeding level was limited to 0.5% of live body weight/day, weight gain was significantly higher for those fish fed diets containing 43 or 52% protein and 24% lipid, than fish fed all other diets. An increase in dietary lipid from 12 to 24% resulted in a significant increase in gross conversion efficiency of both dietary energy and protein, at all three dietary protein levels when fish were fed to satiation. A similar trend resulted when feeding level was reduced to 0.5% live weight/day. Dietary protein concentration did not significantly affect gross conversion efficiency of protein within either feeding rate. Increasing dietary protein tended to result in an increase in gross conversion efficiency of lipid at both dietary lipid levels within each feeding rate.

Comparative Analysis of lonoregulation in Rainbow Trout (Salmo gairdneri) of Different Sizes Following Rapid and Slow Salinity Adaptation

Plasma ionic values and gill (Na+,K+)-ATPase activity were compared for rainbow trout (Salmo gairdneri) of three different fork lengths (&lt; 11, 11–15, and &gt; 15 cm) following transference (1) from freshwater directly into seawater of 28–29‰ (DTT), (2) from freshwater directly into an estuarine environment at Fortune Bay where salinity fluctuated primarily between 17 and 29‰ (DTF), (3) from freshwater into a salinity that slowly increased to 28‰ in 22 d (SAT), and (4) from freshwater into freshwater (FC). Trout of all sizes displayed better growth, lower mortality, and better ionoregulatory capacity as judged by plasma Na+, K+, and Cl−concentrations and (Na+,K+)-ATPase activity in sea cages in Fortune Bay (DTF). The poorest ionoregulatory capacity and growth was in the direct transfer from freshwater to salinity of 28–29‰ (DTT). Failure of small trout to adapt to constantly high salinity of 28–29‰ was due to a slower development of (Na+,K+)-ATPase activity, excessively high plasma Na+and Cl−concentrations, hemoconcentration, and tissue dehydration. Except for trout severely stressed by high salinity, growth in seawater was more favorable than in freshwater. Prince Edward Island estuaries are very favorable as adaptation and rearing areas for small and large rainbow trout.

Two remarks on rainbow scattering

Two neglected aspects of rainbow scattering are discussed: (i) monotonously decreasing (repulsive) potentials can sometimes show rainbow effects; (ii) relatively deep potential minima do not necessarily lead to larger rainbow angles mod theta R mod than slightly shallower ones. Thus there exist potentials with one minimum and a repulsive core for which the relationship V1(r) 0 (i.e. mod V1min mod > mod V2min mod ) but which produce rainbow angles with mod theta 1R mod < mod theta 2R mod .

Ionic and respiratory regulation in rainbow trout during rapid transfer to seawater

Ionic and respiratory parameters of large rainbow trout were measured during freshwater to seawater transfer. Branchial Cl− efflux increased immediately on transfer and urine excretion of Cl− increased after 14 h. Branchial Na+ efflux however did not start to build up until 4–5 h after transfer and there was no increase in urinary Na+ excretion. These differences are discussed.