Maximum Ration Research Articles

Growth, condition, reproductive potential, and mortality of bay scallops, Argopecten irradians, in response to eutrophic-driven changes in food resources

Anthropogenic nutrient enrichment of coastal waters is changing the habitat and food resources of bay scallops, Argopecten irradians. As land-derived nitrogen (N) enters estuaries, phytoplankton abundance, particulate organic matter, and nitrogen content of seston may increase, providing a higher quantity and quality of food. Understanding these changes is important for monitoring declining populations or developing field aquaculture systems. To examine if changes in food resources due to nutrient enrichment will affect growth, condition, reproductive potential, and mortality, we conducted a field experiment in seven estuaries each having a different land-derived N load. We placed juvenile bay scallops within these estuaries for approximately 12 weeks while monitoring food quantity and quality. Stable isotopic signatures suggested that scallops assimilated food from the specific estuaries in which we placed them. Growth rates were relatively high and did not increase with higher phytoplankton concentrations, suggesting that at the densities we deployed, ambient phytoplankton concentrations were in excess of consumption ability. Growth rates decreased at sites with lower salinities, and where high densities of competitors (barnacles and slipper shells) fortuitously settled on the scallops. Condition index significantly increased with higher growth rates. Gonad index and mortality were not related to food resources, but mortality increased with lower salinities. Land-derived N load seems unlikely to directly alter condition, reproductive potential, or mortality. These results suggest that estuaries undergoing anthropogenic nutrient additions may provide food concentrations above the maximum ration assimilable, resulting in high bay scallop growth rates.

Salmonine Consumption and Competition for Endemic Prey Fishes in Bear Lake, Utah–Idaho

Two principal sport fish—the indigenous Bonneville cutthroat trout Oncorhynchus clarki utah and the introduced lake trout Salvelinus namaycush—are the dominant piscivores in Bear Lake, a 282-km2 oligotrophic system. These piscivores rely predominantly on four endemic prey fish species that make up a major portion of the unique Bear Lake fish assemblage. We estimated the annual biomass of pelagic and benthic prey fish by using hydroacoustic and trawling techniques. We also estimated the lakewide abundance of piscivores with a multiple mark–recapture survey and used a bioenergetics model to compare the population-level consumption of prey fish with prey fish production. Prey fish biomass declined to a minimum during 1991 and 1992 but subsequently recovered to reach maximum levels during 1994 and 1995. The proportion of maximum ration estimates from model simulations indicated that the piscivores were consuming well below maximum rations during a period when predation exceeded prey fish production, thereby providing the potential for a predator–prey imbalance. Predation impacts by lake trout cohorts were prolonged because of high survivorship and long life expectancy. Although cutthroat trout outnumbered lake trout, the larger, more piscivorous size-classes of cutthroat trout accounted for only 12.5% of their population. This information, combined with overlapping diets and declining condition factors at increased piscivore biomass, also indicates that lake trout may be competing with cutthroat trout during periods of low prey fish resources. Lake trout predation on juvenile cutthroat trout, combined with competition with other age-classes, also contributes to the poor survival of cutthroat trout. Although prey fish abundance appears to be largely influenced by bottom-up factors related to water elevation, lake trout exert a decoupled predatory threat to the endemic prey fish populations and have the potential to suppress endemic fishes during unpredictable periods of poor prey fish production.

Basic growth relations in experimental rearing of early juvenile cuttlefish Sepia officinalis L. (Mollusca: Cephalopoda)

Basic growth relations were studied in experimental rearing of juvenile cuttlefish during 40 days. Eleven different rations of food were offered in order to establish the maintenance, optimum, and maximum rations during the early life of these animals. The maintenance ration, 2–3.5% of body weight, decreased with age. The optimum rations were, respectively, 16.2%, 14% and 9% during 10, 20 and 40 days of rearing. The maximum rations were, respectively, 40%, 31% and 10% of body weight after 10, 20 and 40 days of rearing. The correlation between conversion rate and growth rate was low, but increased after 20 days of rearing. These data allow determination of the exact quantity and the period of food adjustment during the early life of juvenile cuttlefish and, hence, wasting of food can be avoided. These observations are essential in the development of aquaculture and in experimental rearing of early juvenile cuttlefish.

Effects of temperature and food ration on gonad growth and oogenesis of the green sea urchin, Strongylocentrotus droebachiensis

To assess the effects of both temperature and food ration on gonad growth and oogenesis of the green sea urchin, Strongylocentrotus droebachiensis (O.F. Muller), individuals collected December 1996 (winter experiment) and June 1997 (summer experiment) were maintained for 3 months in one of four experimental treatments: (1) 3 °C and fed ad libitum (high ration), (2) 3 °C and fed one-seventh of the maximum ration (low ration), and (3) 12 °C and fed the high ration; (4) 12 °C and fed the low ration. All individuals were fed an artificial diet and exposed to only 1 h of light every day. At the end of both experiments, mean gonad indices of sea urchins fed the high ration had increased significantly (11–24% and 6–19% in the winter and summer experiments, respectively), while the gonad indices of individuals fed the low ration did not change. At the high ration (both experiments), the increase in gonad index of sea urchins occurred primarily as the result of a significant increase in the mass of nutritive phagocytes, as revealed by histological analyses. Primary oocytes were significantly larger in individuals held at 3 °C than at 12 °C throughout the winter experiment, regardless of food ration; during the summer experiment, primary oocytes were significantly larger in individuals receiving the high ration, regardless of the temperature at which they were held. These results suggest that: (1) food availability is the most important factor regulating energy storage and the relative size of gonads throughout the year, (2) temperature affects the rate of growth and maturation of primary oocytes during the later stages of oogenesis, and (3) once gametogenesis has been initiated, mature ova will be produced, even under conditions of low food availability. Conditions of high food availability in summer and low temperature in winter would thus favor reproductive output in sea urchin populations.

Physiological Ecology Meets the Ideal-free Distribution: Predicting the Distribution of Size-structured Fish Populations Across Temperature Gradients

We describe a habitat selection model that predicts the distribution of size-structured groups of fish in a habitat where food availability and water temperature vary spatially. This model is formed by combining a physiological model of fish growth with the logic of ideal free distribution (IFD) theory. In this model we assume that individuals scramble compete for resources, that relative competitive abilities of fish vary with body size, and that individuals select patches that maximize their growth rate. This model overcomes limitations in currently existing physiological and IFD-based models of habitat selection. This is because existing physiological models do not take into account the fact that the amount of food consumed by a fish in a patch will depend on the number of competitors there (something that IFD theory addresses), while traditional IFD models do not take into account the fact that fish are likely to choose patches based on potential growth rate rather than gross food intake (something that physiological models address). Our model takes advantage of the complementary strengths of these two approaches to overcome these weaknesses. Reassuringly, our model reproduces the predictions of its two constituent models under the simple conditions where they apply. When there is no competition for resources it mimics the physiological model of habitat selection, and when there is competition but no temperature variation between patches it mimics either the simple IFD model or the IFD model for unequal competitors. However, when there are both competition and temperature differences between patches our model makes different predictions. It predicts that input-matching between the resource renewal rate and the number of fish (or competitive units) in a patch, the hallmark of IFD models, will be the exception rather than the rule. It also makes the novel prediction that temperature based size-segregation will be common, and that the strength and direction of this segregation will depend on per capita resource renewal rates and the manner in which competitive weight scales with body size. Size-segregation should become more pronounced as per capita resource abundance falls. A larger fish/cooler water pattern is predicted when competitive ability increases more slowly than maximum ration with body size, and a smaller fish/cooler water pattern is predicted when competitive ability increases more rapidly than maximum ration with body size.

Influence of different rations and water temperatures on the growth rates of shortfinned eels and longfinned eels

Juvenile (12–152 g) shortfinned eels Anguilla australis and longfinned eels A. dieffenbachia caught in New Zealand streams were fed squid mantle Nototodarus spp. 4 days per week in laboratory experiments. A linear multiple regression equation showed the amount of food eaten (0–2·7% w day−1) explained 77·7% of the variation in specific growth rates (–0·60 to +1·07% w day−1) among individual eels, while previous growth rates, water temperature (10·0–20·6°C), and eel weight (12–152 g) explained a further 5·6, 1·4 and 0·8%, respectively. Growth in length ranged from –0·3 to +0·9 mm day−1. Eels which were starved and then given high rations grew substantially faster than expected. Once growth rates were adjusted for differences in ration and other factors, there were no significant differences in growth rates between species or individual fish. Growth of shortfinned eels fed maximum rations of commercial eel food depended on fish size and water temperatures and ceased below 9·0°C. Growth rates in the wild were substantially less than the maximum possible, after seasonal changes in water temperatures were taken into account, indicating that food supplies and not low water temperatures were controlling growth rates in the wild.

Influence of different rations and water temperatures on the growth rates of shortfinned eels and longfinned eels

Juvenile (12–152 g) shortfinned eelsAnguilla australisand longfinned eelsA. dieffenbachiacaught in New Zealand streams were fed squid mantleNototodarusspp. 4 days per week in laboratory experiments. A linear multiple regression equation showed the amount of food eaten (0–2·7% w day−1) explained 77·7% of the variation in specific growth rates (–0·60 to +1·07% w day−1) among individual eels, while previous growth rates, water temperature (10·0–20·6°C), and eel weight (12–152 g) explained a further 5·6, 1·4 and 0·8%, respectively. Growth in length ranged from –0·3 to +0·9 mm day−1. Eels which were starved and then given high rations grew substantially faster than expected. Once growth rates were adjusted for differences in ration and other factors, there were no significant differences in growth rates between species or individual fish. Growth of shortfinned eels fed maximum rations of commercial eel food depended on fish size and water temperatures and ceased below 9·0°C. Growth rates in the wild were substantially less than the maximum possible, after seasonal changes in water temperatures were taken into account, indicating that food supplies and not low water temperatures were controlling growth rates in the wild.

Size-related feeding and gastric evacuation measurements for the Southern brown shrimp Penaeus subtilis

Studies attempting to optimise feeding methods in penaeid aquaculture have often relied on results of growth, survival performance and food conversion ratios. At present, data relating to maximum ration, ingestion rates (IRs), faecal production rates (FPs), foregut evacuation and appetite revival are lacking for Penaeus spp. despite their relevance to the development of models aimed at maximising food use in shrimp culture systems. Size-related feeding and gastric evacuation (GE) measurements were determined for Penaeus subtilis by conducting laboratory-based feeding trials on individual animals. A total of 3482 samples of feed and (or) faeces were collected for quantitative analysis derived from 307 shrimp. Food ingestion was a function of shrimp body weight (BW). Feeding intensity increased progressively with shrimp size, but inversely in percentage terms, resulting in a larger faecal production per BW for smaller shrimp. On average, P. subtilis food ingestion was equivalent to 2.3% of its BW per hour, but consumption in shrimp with empty stomachs reached 4.9% BW/h. Foregut clearance rates (13%) peaked 3 h after food recovery, with the bulk of faeces being produced within 1 h. Food load occurred progressively as more feed was given and evacuated from shrimp stomachs, while feeding continued at reduced levels. Data indicated that control of feeding intensity and resumption of food intake by P. subtilis were not markedly affected by the level of their stomach fullness or by longer food administration intervals. The daily administration of food in shorter feeding intervals, although at continually reduced amounts, may be advantageous in the culture of P. subtilis.

Development and Test of a Whole-Lifetime Foraging and Bioenergetics Growth Model for Drift-Feeding Brown Trout

We developed and tested a combined foraging and bioenergetics model for predicting growth over the lifetime of drift-feeding brown trout. The foraging component estimates gross energy intake within a fish- and prey size-dependent semicircular foraging area that is perpendicular to the flow, with options for fish feeding across velocity differentials. The bioenergetics component predicts how energy is allocated to growth, reproduction, foraging costs, and basal metabolism. The model can reveal the degree to which growth is limited by the density and size structure of invertebrate drift within the physiological constraints set by water temperature. We tested the model by predicting growth based on water temperature and on drift density and size structure data from postemergence to age 12, and we compared the predictions with observed size at age as determined from otoliths and scales for a New Zealand river brown trout population. The model produced realistically shaped growth curves in relation to the observed data, accurately predicting mean size at age over the lifetime of the trout, assuming 24-h maximum rations and including diurnal drift-foraging costs (predicted versus observed weight r2 = 0.94; length r2 = 0.97). The model predicted that, within a given water-temperature regime, growth is limited primarily by reproduction costs but also by increasing foraging costs as trout grow (a phenomenon that is associated with the increasing foraging time that is required in order to feed to satiation on small invertebrate drift prey). Invertebrate drift size structure significantly influenced predicted growth, especially maximum size, through its effect on foraging time. The model has potential in terms of the exploration of growth-limiting factors and has associated use as an environmental-impact tool and as an aid for hypothesis generation in studies of salmonid growth processes.

Biochemical indices for instantaneous growth estimation in young cephalopod Sepia officinalisL.

Aspartate transcarbamylase (ATCase) activity was used to estimate instantaneous growth in young cuttlefish (Sepia officinalis) reared under different diet conditions, and compared with estimation obtained by RNA concentration. During the first month of life, the changes in ATCase activity and RNA content of muscle are related to growth. ATCase appears to be a good index of growth during the first stage of intense cell multiplication. ATCase activity is correlated to food intake up to a maximum ration, but decreases when animals are more than 40 days old. The approach of using ATCase activity as a biochemical index for estimating short-term change in growth rates of young cuttlefish in experimental rearing could be extended to young cephalopods collected in the field, and used to predict the effect of biotic factors in recruitment.

Influence of the European Union Traffic Policy on Traffic Development in Croatia

Joining the European Union is the strategic priority for theRepublic of Croatia. Croatia has always been part of the Europeaneconomic region. The success of adaptability of the Croatianindust1y, particularly of Croatian traffic, to the EuropeanUnion, will greatly depend on the possibility of establishing contractualrelations of the economic and traffic branches with theEU. Therefore, this paper considers in more detail the traffic aspectsof integration.It is a fact that the EU traffic policy is contained in the RomanAgreement (1957) whose aim was elimination of the barriersfor the flows of goods, se1vices and capital, and the integrationof the European region. Thus, it requires equal treatmentof all the traffic branches and all the carriers, freedom forthe activities of transport companies, as welT as freedom for these1vice users to choose the transport means and carriers. Thisnaturally requires maximum rationality in fi·eight flows reflectedon the financial and commercial business activities of acompany.To converge maximally with the European Union is thestrategic priority of the Republic of Croatia, and within the Croatianindus fly this will especially require the adaptation of theCroatian traffic. The basic precondition for the functioning ofthe traffic ~ystem on the European transport market is the compliancewith the rules and standards determined by the internationalconventions.

Effect of ration, temperature and body weight on growth of black porgy,Sparus macrocephalus (B.)

Growth of black porgy,Sparus macrocephalus, was studied experimentally at four ration levels from starvation to satiation and four temperatures ranging from 14.8 to 26.8°C. At maximum rations, the specific growth rate (SGR) increased with temperature and was a negative linear function of body weight. The relationship between SGR and ration levels was a decelerating curve. Stepwise regression was used to develop the predictive models for the specific growth rates. Maintenance rations and optimum rations both increased with increased temperature. The relationship between maintenance, optimum rations and body weight was influenced by temperature. Conversion efficiencies increased with ration from zero at maintenance ration to a peak at the optimum ration, then declined with further increased ration.

A bioenergetic approach on food consumption of roach (Rutilus rutilus (L.)) in a eutrophic lake

A bioenergetics model was fitted for roach to estimate their food consumption in L. Vesijarvi, southern Finland. When tested with independent data the consumption estimates by the bioenergetics model differed less than 10 % from those obtained with other methods. Sensitivity analysis showed that the model estimates are most sensitive to changes in the respiration parameters, the relative change in the consumption estimate being of the same magnitude as that in the value of the parameter. In L. Vesijarvi the bioenergetics model underestimated the seasonal growth of roach age groups 3 and 5 in July and overestimated the growth of older roach, which was due to differences in food availability. The decline in the proportion of maximum ration consumed (the P-values of the model) in late summer was steepest in the age groups 3 and 5 due to the the collapse of the cladoceran density, while older roach were able to complement their diets with plants and detritus. The daily consumption rates were highest in July-August reaching 1.2-2.5g ww in the different age groups. It is suggested that the growth rate of roach is at present limited by the long capture and handling times of the small-sized cladocerans dominant in the lake. Older age groups can complement their diets with other food items but they are also forced to carry out energy-consuming migrations and their growth rate remains low.

Effect of ration and body size on the energy budget of juvenile white sturgeon

Growth and energy budget were measured for three sizes (2.4, 11.1 and 22.5 g) of juvenile white sturgeon Acipenser transmontanus held at 18.5° C and fed tubificid worms at different levels ranging from starvation to ad libitum. For each size‐class, specific growth rate increased linearly with increasing ration, and conversion efficiency was highest at the maximum ration. Growth rate decreased with increasing fish size at the maximum ration, but increased with size at each restricted ration. Conversion efficiency increased with increasing ration for each size‐class and was usually highest at the maximum ration. Faecal production accounted for 3.2–5.2% of food energy. The proportion of food energy lost in nitrogenous excretion decreased with increasing ration. With increases in ration, the allocation of metabolizable energy to metabolism decreased, while that to growth increased. Fish size had no significant effect on the allocation of metabolizable energy to metabolism or growth. At the maximum ration, on average 64.9% of metabolizable energy was spent on metabolism, and 35.1% on growth.

A Bioenergetic Exploration of Piscivory and Planktivory During the early Life History of Two Species of Freshwater Fishes.

In order to explore the trophic relationships of two different feeding strategies during the nursery period a bioenergetic model is applied to the early life history stages of a piscivore, the muskellunge (Esox masquinongy, Esocidae: Salmoniformes) and a planktivore, the bluegill (Lepomis macrochirus, Centrarchidae:Perciformes). The model uses a balanced energy equation to predict consumption based on observed growth and calculated losses to metabolism, excretion and egestion. Estimates are temperature- and weight-dependent and are calculated on a daily basis over the duration of the nursery period. Ambient temperatures and the diet composition as determined from stomach content analysis were used in the model. Comparisons of consumption and metabolic rates between a piscivore and a planktivore suggest that the planktivore has a much higher metabolic rate resulting in greater weight-specific consumption and a larger maximum ration (g g-1 day-1 day-1) than the piscivore. The consumption of prey organisms in relation to prey standing crop by the planktivore ranged up to 2.5% of the standing crop per day, whereas in the piscivore population it approached 18% of standing crop per day; this suggests that consumption by the planktivore on the zooplankton population in eutrophic Crane Lake would likely have less of an effect on the prey population than that of the piscivore in bays of the St Lawrence River.

Influence of Sustained Exercise at Two Ration Levels on Growth and Thyroid Function of All-Female Chinook Salmon (Oncorhynchus tshawytscha) in Seawater

Duplicate groups of seawater-adapted 70-g all-female chinook salmon (Oncorhynchus tshawytscha) were held in flowing seawater (24–29‰; 8–12 °C) corresponding to swimming speeds (SS) of 0.5, 1.0, or 1.5 body lengths (bl)/s for 212 d. Fish were fed either a maximum satiating ration of 75% of maximum ration at each SS. Fish grew four- to fivefold during the study, but neither mean body weight, fork length, specific growth rate, condition factor, nor muscle morphometry was influenced by average SS. However, the SS of individually marked fish were negatively correlated with specific growth rate. At both rations, higher SS increased the internal tissue-carcass ratio, hepatosomatic index, and total body protein. More food was ingested at higher SS resulting in reduced feed efficiency. SS did not alter the plasma L-thyroxine (T4) concentration, but increased the plasma 3,5,3′-triiodo-L-thyronine (T3) concentration and T3/T4ratio. In part, this may reflect the greater food intake at higher SS. The reduced ration depressed all aspects of growth and at 212 d tended to depress both plasma T4and T3, but did not alter feed efficiency. We conclude that exercise over the range of 0.5–1.5 bl/s does not enhance growth, but reduces feed efficiency in seawater-adapted chinook salmon.

Effect of ration size on the growth and energy budget of the grass carp, Ctenopharyngodon idella Val.

Young grass carp (12–13 g) were kept at five ration levels ranging from starvation to ad libitum feeding at 30°C. They were fed duckweed. Food consumption, absorption efficiency and growth were determined directly, and metabolism and nitrogenous excretion calculated indirectly from energy and nitrogen budgets, respectively. The relationship between specific growth rate and ration size was linear. Absorption efficiency for energy was not affected by ration size and averaged 50.6±0.57% (mean±s.e.). Depending on ration size, energy lost in excretion accounted for 4.5–5.9% of the food energy, energy channelled to metabolism accounted for 34.4–48.3% of the food energy, and energy retained as growth accounted for 6.7–11.9% of the food energy. Regardless of ration, a constant proportion of food energy (30.7%) was accounted for by feeding metabolism (total metabolism minus fasting metabolism). The energy budget at the maximum ration was: 100 C=49.1 F+4.5 U+3.6 R fa+30.9 R fe+11.9 G, where C, F, U, R fa, R fe and G represent food consumption, faecal production, excretion, fasting metabolism, feeding metabolism and growth, respectively.

The Growth and Food Ration of Piscivorous Brown Trout (Salmo trutta)

1. In this study we examined how temperature, a major determinant of energy budgets and thus the biological success of ectothermal animals, affects growth and feeding rate of a teleost fish species. 2. Feeding experiments with piscivorous brown trout from the Norwegian River Laerdalselva were performed in the laboratory at water temperatures from 8 to 18°C, to estimate the optimal temperature for growth fed at maximum rations. 3. Optimal temperature for growth was found to be approximately 16°C, which is 2-4 °C higher than reported previously. 4. In contrast to earlier studies, the optimal temperature for growth was similar to the temperature at which maximum feeding rates occurred. 5. Growth increased more rapidly with increasing temperature for small and young fish than for large and old fish

Influence of food concentration on the physiological energetics and growth ofOstrea edulis larvae

Feeding, respiration and growth rates of oyster (Ostrea edulis L.) larvae reared at five food levels were measured throughout the entire larval period. Energy budgets were derived as a function of alga (Isochrysis galbana Parke) food concentration. Ingestion rate (IR, cells h-1) and oxygen consumption rate (\(V_{O_2 } \), nl h-1) were almost isometric functions of larval size [ash-free dry weight, (AFDW, μg)], characterized by the equations: IR=803.9 AFDW1.13 and\(V_{O_2 } \)=4.85 AFDW1.09. Ingested ration was directly correlated to cell concentration up to a maximum at 200 cells μl-1, with further increases failing to support higher ingestion rates. Likewise, growth rate linearly increased with food ration up to 100 cells μl-1 (max. growth efficiency,K1=25%) and reached a maximum at 200 cells μl-1 (growth rate=5.6 μm d-1), with further increases in food not supporting significantly faster growth. Maintenance ration was 2 to 3% daily dry weight (DW); optimum ration increased during larval development from 5 to 20% DW; maximum ration was 20% DW. During larval rearing, an increasing feeding schedule of 50, 100 and 200 cells μl-1 from Days 0, 5 and 10, respectively, is recommended.

Pattern of energy allocation in the southern catfish (Silurus meridionalis)

Energy budgets were compiled for the southern catfish (Silurus meridionalis) under laboratory conditions at different ration size, body weights and temperatures. Though the food energy allocated among the components of the energy budget varied with changing conditions, for the fish fed maximum rations the pattern of energy allocation was independent of body weight and temperature. At the maximum ration about 60% of assimilated energy was deposited in growth and 40% spent in metabolism, indicating a higher proportion allocated to growth and a lower proportion to metabolism than is generally found in fish. This pattern of energy allocation is an energetic strategy adapted to the piscivorous lifestyle of this species.