William H. Neill

Effects of water temperature and dissolved oxygen on daily feed consumption, feed utilization and growth of channel catfish (Ictalurus punctatus)

Abstract Feed intake (FI), feed efficiency (FE), protein efficiency ratio (PER) and weight gain (WG) of juvenile channel catfish initially weighing 15.0±0.23 g (10–12 cm initial total length) were evaluated under three regimes of time-varying water temperature (mean daily water temperature for Stoneville, MS, USA; mean +3; and, mean −3°C) and three of dissolved oxygen (DO; 100, 70 and 30% air saturation, at each temperature). Two independent experiments lasting 6 and 8 weeks, respectively, simulated spring and fall temperature and photoperiod patterns. Temperature–oxygen regimes were applied to randomly assigned duplicate 110-l aquaria with individual biofilters. Fish were fed once daily, to slight excess, a commercial catfish floating feed. After 45 min, uneaten feed was collected, dried and weighed; then FI was calculated by difference. Fish in each aquarium were weighed collectively, biweekly. In both experiments higher temperatures and higher DO levels produced increased feed consumption. A multivariate regression model was fitted to the data to describe the combined effects of temperature and DO on FI. There was a progressive reduction in FI as DO declined from 100 to 30% air saturation. In both trials weight gain was higher for fish held 3°C above the mean water temperature at 100% air saturation values of DO; whereas, the lowest values of WG were obtained for fish held at 30% air saturation and 3°C below the mean water temperature. Weight gain increased with temperature, with maximum rates reached at 27.1°C with DO equivalent to 100% air saturation. In contrast, when DO was 30% air saturation, growth rates plateaued as ambient temperature exceeded 22.8°C. This model will assist in optimization of feeding practices in channel catfish aquaculture.

Distributional Ecology and Behavioral Thermoregulation of Fishes in Relation to Heated Effluent from a Power Plant at Lake Monona. Wisconsin

Abstract Cooling water for a 220-megawatt power plant is pumped from 5 m beneath Lake Mononas surface, heated about 10 C, and discharged into the littoral zone. Maximum temperatures in the effluent-outfall area approach 35 C in summer and 14 C in winter; unheated parts of the littoral zone rarely exceed 29 C. To assess distributional responses of fishes to operation of the power plant, the outfall area and two reference areas were electrofished on 30 dates between 8 August 1968 and 21 August 1969. Some fishes avoided the outfall area; these were Perca flavescens, Cottus bairdi, subadult Morone mississippiensis, and subadult Ictalurus melas. Others were occasionally or usually concentrated in the outfall area relative to reference areas—Lepisosteus osseus, adult Cyprinus carpio, adult M. mississippiensis, young Lepomis gibbosus, L. macrochirus, and Micropterus salmoides. The tendency for fish of a given species and size to concentrate in or avoid the outfall area generally did not reverse from season to s...

Ecophysiology of marine fish recruitment: A conceptual framework for understanding interannual variability

Abstract Present data and our application of logic do not permit confident rejection of the null hypothesis: Interannual variation in recruitment of marine fishes (typified by certain flatfishes) is independent of ecophysiological factors. Our inability to reject this hypothesis reflects not its likely validity, but rather a lack of conceptual structure and appropriate data for realistic evaluation of alternative hypotheses. Therefore, in this paper, we set aside as presently intractable the problem of understanding in any generalizable way the specific effects of environment on interannual variation in marine fish recruitment. Instead, we return to a conceptual scheme first proposed almost 50 years ago by F.E.J. Fry for considering effects of environmental factors on the physiology of fishes. We first extend this scheme to population-level responses, including recruitment, and then even further, to community/ecosystem-level responses. Fry supposed that all of environment can be resolved into five classes of physiological effects—controlling (which set the pace of metabolism), limiting (which constrain maximum metabolism), lethal (which completely interdict metabolism), masking (which increase obligatory metabolic work), and directive (which release and unload metabolism by guiding enviroregulatory responses). We suggest that corresponding effects can be recognized at the levels both of population and community/ecosystem. The key analogy is that environment operates on individuals through metabolism, on populations through recruitment, and on communities/ecosystems through abiotic and biotic diversification. In the context of marine-fish populations, we propose that scope for population increase is the difference between maximum and maintenance recruitment to the spawning stock. Maintenance recruitment is the product of critical spawner density and spawner mortality rate; this product varies with environment as the resultant of controlling effects on the metabolism of individuals, and is increased by loading due to masking factors— e.g. , predation—that increase one or both multiplicands. Maximum recruitment is limited by deficiencies of resources, primarily food, but also, potentially, by low spawner density. Population-level lethal factors cause extinction, by reducing population scope to sub-zero values for a time exceeding the generation interval. Directive factors distribute the population in space and time, influencing not only habitat use and zoogeographic range, but also providing context for genetic adaptation and speciation. Exploration of this conceptual scheme from the perspective of flatfish life-history strategies and population dynamics, leads to several testable ecophysiological hypotheses about recruitment.

Temperature Preference versus Acclimation in Fishes: Selection for Changing Metabolic Optima

Abstract We present a model that accounts for the variety in observed relationships between temperature preference and acclimation in fishes. The preferred temperature is that temperature at which Frys scope for metabolism is maximized. Thermal acclimation shifts the temperature for maximum scope in such a way that Zahns types of temperature-preference acclimation correspond with Prechts types of metabolic compensation. The model predicts that fishes exhibiting Prechts “partial,” “no,” and “inverse” compensation prefer temperatures that are increasing, independent, and decreasing functions of acclimation temperature, respectively. Experiments with bluegill Lepomis macrochirus and blue tilapia Tilapia aurea, together with information from the literature, provide support for the model.

Magnitude and ecological implications of thermal inertia in skipjack tuna,Katsuwonus pelamis (Linnaeus)

SynopsisHeat exchange experiments with sedated and free-swimming skipjack tuna,Katsuwonus pelamis (Linnaeus), yielded the following results: For fish between 0.4 and 3.5 kg in weight (W), 1)inertial resistance to cooling and warming were virtually equal over the same span of temperature (18° to 30° C);2)thermal inertia of red muscle, white muscle, and brain (in intact, living animals) was proportional to W0.45 (i.e., coefficient of temperature change, k, ∞ W−0.45 for each tissue);3)white muscle, brain, and ventricular blood equilibrated with a changed environmental temperature about 1.1, 3.3, and 20 times as rapidly as red muscle;4)the countercurrent heat exchanger was about 95% efficient as a thermal barrier between gills and red muscle; consequently, only about half (30%–80%, depending on W) the total heat transfer between the red muscle and the environment occurred across the gills;5)under conditions of thermal equilibrium, the red muscle and white muscle of sedated fish were warmer than the environment by amounts independent of environmental temperature but proportional to W0.58 and W0.61, respectively; in contrast, the excess temperature of the brain was independent of fish weight but bore a weak, positive relation to environmental temperature; and,6)in two free-swimming fish stimulated to violent activity by chasing, the red muscle warmed at rates up to 0.3° C min−1, ultimately attaining temperatures 1.5° and 3.4° C above pre-chasing equilibrium levels. Comparison of our results with those of other researchers indicated that skipjack tuna exchange core heat with the environment only about 60% as rapidly as do typical teleosts and even somewhat more slowly than do air-breathing aquatic reptiles. Results 1) and 5) were taken to imply no short-term physiological thermoregulation in skipjack tuna; problematic evidence for physiological thermoregulation in other tunas and in aquatic reptiles is discussed. Calculations based on thermal inertia, excess temperature, and rate of warming indicated that minimum and maximum rates of metabolism in the red muscle of skipjack tuna are about 4 and 25 cal g−1 hr−1, respectively. Similar considerations suggested that large thermal inertia and high rates of metabolism may pose an ecological problem for skipjack tuna as they grow in body mass; excess core temperature may become so large that the muscle of the fish overheats, especially during periods of greatest activity in warm waters; speculative upper temperature limits are offered for skipjack tuna as a function of body size and activity level. Two potential benefits of large thermal inertia are discussed and illustrated with simulation models; these are 1) substantial independence from rapid fluctuations of environmental temperatures as the fish move between the upper mixed layer and the thermocline, and 2) inertial ‘memory’ of thermal history to permit or enhance perception of weak temperature gradients.

Modelling animal movement as a persistent random walk in two dimensions: expected magnitude of net displacement

We present semi-empirical model of persistent random walk for studying animal movements in two-dimensions. The model incorporates an arbitrary distribution for the angles between successive steps in the tracks. Inclusion of a turning angle distribution enables explicit computation of the effect of persistence in the direction of travel on the expected magnitude of net displacement of the animal over time. We employed a form-analogous approach to obtain expressions for the expected net displacement and derived root mean square of the expected displacement of an animal at the end of a multi-step random walk in which turning angles were drawn from the Lemicon of Pascal, the elliptical, the von Mises, and the wrapped Cauchy distributions. The accuracy of these expressions for the expected magnitude of net displacement was tested by comparison with simulated results of persistent random walks where turning angles were drawn form the wrapped Cauchy distribution. Our results should be useful in predicting two-dimensional distribution of moving animals for which frequency distributions of the turning angles can be measured.

Effects of dietary lipid and environmental salinity on growth, body composition, and cold tolerance of juvenile red drum (Sciaenops ocellatus).

Simultaneous, 6-week feeding trials were conducted in which diets containing menhaden, corn, coconut and hydrogenated menhaden oil at 7.0%, plus a diet containing 14% menhaden oil, were fed to triplicate groups of juvenile red drum (Sciaenops ocellatus) at two different salinities (5 and 32%.). Weight gain was significantly (p < 0.05) affected by diet and salinity. Fish fed the diet containing 14% menhaden oil had the greatest weight gain; whereas, fish fed the diet containing coconut oil gained the least weight. Fish in brackish water had significantly greater weight gain than fish in full-strength seawater over the 6-week period, although fish fed coconut and saturated menhaden oil in brackish water had reduced survival. Dietary lipid also significantly affected muscle and liver total lipid, hepatosomatic index (HSI), and intraperitoneal fat (IPF) ratio, as fish fed the diets containing 14% menhaden oil had higher values for all of these body condition indices.After the feeding trial, fish were subjected to a chronic cold tolerance assay. In the chronic trial, where temperature was gradually reduced over a 3-week period, fish fed the diets containing menhaden oil had significantly lower median lethal temperatures (MLT) than those fish fed the diets containing coconut, corn and saturated menhaden oils. No significant effects of cold exposure were observed on muscle and liver total lipid. Cold exposure prompted a modification in lipid metabolism by lowering total saturated fatty acids and raising (n − 3) highly unsaturated fatty acids (HUFA) in the neutral lipid of liver. Fish with the lowest MLT in the chronic assay exhibited signs of conserving (n − 3) HUFA and depleting (n − 6) fatty acids [primarily 18:2 (n − 6)], resulting in higher (n − 3)/(n − 6) ratios in the polar lipid of liver. These data suggest that the lower lethal temperature of juvenile red drum can be reduced through dietary manipulation involving the inclusion of high levels of dietary lipid rich in (n − 3) HUFA.

Behavioral Thermoregulation by Fishes: A New Experimental Approach

Electronic equipment allows fishes, by their spatial movements, to regulate the temperature in experimental tanks. Swimming into warmer water causes the temperature of the entire tank to increase; conversely, swimming into cooler water causes the temperature to decrease. The technique may be adapted for studying simultaneous behavioral regulation of temperature and nonthermal factors.

Effects of dietary sodium chloride on red drum juveniles in waters of various salinities.

Abstract Three 8-week feeding trials were conducted to determine the effects of supplemental dietary salts on growth and osmoregulation of juvenile red drums (Sciaenops ocellatus) at various water salinities. In each experiment, sodium chloride was added to a basal diet composed of semipurified and practical ingredients; the basal diet provided intrinsic levels of 0.80% Cl, 0.84% K, and 0.92% Na on a dry-matter basis. In fresh water, red drums fed the basal diet supplemented with NaCI at 2% had significantly (P < 0.05) greater weight gain and feed efficiency than fish given the basal diet alone. In brackish water (6‰ salinity), fish given the diet supplemented with NaCI at 2% had weight gains that were numerically but not significantly (P = 0.076) greater than gains offish fed the basal diet. In full-strength artificial seawater (35‰), fish fed diets supplemented with NaCI at 2 and 10% had weight gains not significantly (P = 0.23) different from those of fish fed the basal diet, and those fed the diet sup...

The Maximum Power Principle in Behavioral Thermoregulation by Fishes

Abstract The maximum power principle suggests that successful biological systems maximize the flow of useful energy. Using this principle in conjunction with Frys metabolic scope concept, we have developed a model of behavioral thermoregulation for fishes that reasonably predicts frequency distributions and swimming speeds of fish in thermal gradients: fish respond to temperature gradients by swimming at speeds that are proportional to the rate of change of metabolic scope with respect to temperature. As a result, reduced thermoregulatory swimming power occurs at temperatures that give higher levels of metabolic scope; this maximizes both available surplus power and residence time under conditions of high surplus power availability. Within the zone of high residence time (=preferred temperature zone), fish respond to changes in the gradient of metabolic scope with increased turning, thus increasing their frequency of occurrence near the temperature that permits maximum metabolic scope.