Protein, lipid, water and caloric contents of immature rainbow trout, Salmo gairdneri Richardson, growing at different rates

Protein, lipid, water and caloric contents of immature rainbow trout, relative to size of whole fish, growing at different rates were examined by use of allometric analysis (y = ax^b, Huxley, 1932). Fish grew at different rates as a result of differences in ration size (satiation, or 4–5% of dry body weight), temperature (7 and 12°C) and bGH (bovine growth hormone) administration. In fingerlings, protein, lipid and caloric contents tended to increase (v. body weight) as a percentage of body composition, whereas above fingerling size, protein decreased while lipid and caloric contents still increased. These trends occurred regardless of growth rate differences. The correlations between protein, lipid, caloric contents and body weight were high so reliable estimates of body components can be made from body weight for all experimental treatments. At satiation rations (7 and 12°C), there were no significant differences in protein content, but lipid and caloric contents were significantly higher in control fish. At low rations, protein and caloric contents were lower than those at satiation rations and lipid was lower than in the control group. On a dry weight basis, in uninjected fish at 12°C, ration size did not influence the percentage composition (protein and lipid) but the low ration group had lower energy values per unit of body dry weight. At low temperature (7°C satiation), fish had lower lipid and higher protein content (dry weight basis) than their controls (12°C satiation), thereby resembling bGH injected fish at satiation rations. Values of caloric content estimated from protein and lipid values by use of standard conversion factors differed sufficiently from caloric values directly determined by bomb calorimetry to suggest that caloric values of lipids may change during growth. The increase in body caloric content during growth apparently results mainly from an increase in the percentage of lipid. The similarity of body composition between different growth rate groups implied a tendency for conservation of relative proportions of components such that body composition can be approximated from body weight. Equations were also given to describe the relationship between water content and body constituents, and the relationship between condition factor (K) and both the body dry weight and lipid content.     

The combined effect of feeding time and ration on growth performance and nitrogen metabolism of greenback flounder

Greenback flounder Rhombosolea tapirina ( c. 2 g) fed to satiation had significantly ( P <0·01) higher feed consumption in the evening than in the morning whereas there was no difference between feeding times for flounder fed restricted rations (1 or 2% body weight per day) because they consumed all of the ration. Differences in growth performance were due to feeding time and ration. Carcass moisture, lipid and energy content were significantly ( P <0·001) different between rations; length gain was significantly affected by feeding time ( P <0·05) and ration ( P <0·001); weight gain showed a significant ( P <0·001) interaction between feeding time and ration. The relationship between feed consumption and specific growth rate showed that the exponential gradient was significantly higher ( P <0·01) for the evening fed fish and indicated feed efficiency for evening fed fish increased as feed consumption increased. Urea excretion increased from 12–20 to 58–63% of total nitrogen excretion at the 1 and 3% rations, respectively. Ammonia and urea excretion were significantly affected by ration ( P <0·001) and feeding time ( P <0·05). Fish fed the 2% ration in the evening had higher growth efficiency and significantly ( P <0·01) lower rates of urea excretion than fish fed 2 or 3% ration in the morning. It is suggested that the higher energetic costs associated with differences in ammonia and urea excretion contributed to differences in growth efficiency.     

Food consumption and growth of larvae and juveniles of three cyprinid species at different food levels

Synopsis The relationships between food availability, consumption and growth were analyzed from the onset of feeding to an age of 90 days in three cyprinid species. Fish were held at 20 ± 0.5° C and given two (three) constant rations of approximately 30, (40) or 100% dry body weight (dbw) ind^-1 day^-1. Food consisted of living zooplankton, the size of which correlated with fish size. At high food densities consumption rates decreased rapidly with fish size in all three species. At reduced rations, fish consumed most of the food offered until they were larger than 10 mg dbw. In all species and at each feeding level daily rations consumed increased allometrically with body size. Respiration rate, expressed as routine metabolic rate differed insignificantly between the three species. At high ration levels, growth rates of small bleak, Alburnus alburnus, were distinctly lower than those of roach, Rutilus rutilus, and blue bream, Abramis ballerus. At low food supply all three species grew at similar rates. Assimilation efficiency at low food conditions was approximately twice that of the well-fed groups. If the caloric equivalents of oxygen consumption as measured in well-fed fish are applied to fish fed at low rations their energy budgets do not balance. This indicates the limitations of fish larvae in the partitioning of energy for growth or activity at such conditions.     

Effects of temperature and ration level on the growth and food conversion efficiency of Salmo gairdneri, Richardson

The effects of temperature and ration size on the growth rate and gross efficiency of food conversion of juvenile rainbow trout Salmo gairdneri were evaluated during 25-day seasonal experiments. Rations ranged from near-starvation to repletion levels. Test temperatures were 3 and 6°C higher than the controls which fluctuated dielly and seasonally. At rations near maintenance, elevated temperatures decreased trout growth. As the feeding rate increased the detrimental effect of temperature on growth was ameliorated. At repletion feeding levels, elevated temperature up to 17°C improved trout growth by increasing the maximum food consumption rate. With a temperature increase from 6.9 to 22.5°C maintenance rations increased from 2.2 to 7.5 % body weight per day. Gross efficiency was dependent upon ration level and temperature. As the food consumption rate increased, efficiency increased to a maximum, then generally declined at repletion levels. Elevated temperatures resulted in reduced efficiencies at low consumption rates but temperatures had little effect at high ration levels. A field study provided estimates of the food consumption relationships established in the laboratory, suggested any substantial increase of stream temperature without a concomitant increase of food abundance would result in decreased trout production.     

Feeding and growth of juvenile sea bass: the effect of ration and temperature on growth rate and efficiency

The effect of ration on the growth of pairs of juvenile sea bass Dicentrarchus labrax fed squid mantle was recorded at four temperatures: 6, 10, 14 and 18) C, covering the range typical of Welsh coastal waters. Initial weight of the fish ranged from 2.8 to 15.9 g. A predictive model for the maximum meal size (M_max) at temperatures between 10 and 18) C, accounted for 95% of the variance in lnM_max. Even when offered excess food, bass at 6) C had a low rate of food consumption [0.19% body weight (BW) day^?1] and lost weight (G=?0.04% day^?1). Predictive regression models for specific growth rate (G) accounted for 86% of the variance at reduced rations and 70% at maximum meals. The relationship between G (calculated for total biomass per tank) and ration was a decelerating curve. G at maximum meals increased with temperature, at lower rations G decreased with temperature. For a pair of bass with a combined weight of 15 g, predicted maintenance ration ranged between 0.7 and 2.3% BW day^?1 and increased with temperature. Maximum meal size was more sensitive to temperature than maintenance ration. At 18) C optimum ration was 7.4% BW day^?1. At lower temperatures, the optimum ration was the maximum meal. The maximum gross growth efficiency was 17.4% at 18) C. Mean absorption efficiency was 94.8%. Ration level had no significant effect on absorption efficiency, which was lowest at 6) C. Condition indices (Fulton condition factor, wet and dry liver—somatic indices and body depth index) increased with meal size at all temperatures except 6) C. An increase in temperature between 10 and 18) C generally resulted in a decrease in condition indices at a given ration. When comparisons were made at a given standard length, gut and carcass weight increased with ration. Visceral fat and gut weight decreased with increased temperature.     

Bioenergetics of growth of a cyprinid, Phoxinus phoxinus (L.): the effect of ration and temperature on growth rate and efficiency

Growth of minnows, Phoxinus phoxinus , weighing 1-5.5 g was studied experimentally at five ration levels from starvation to ad libitum and four temperatures ranging from 5 to 15°C. The relationship between specific growth rate (SGR) and ration was a decelerating curve. SGR at maximum rations increased with increased temperature, but at restricted rations it decreased with increased temperature. Predictive models for the specific growth rates were developed using multiple regression. Maintenance rations and optimum rations both increased with increased temperature. Maintenance rations were less sensitive to temperature than optimum rations and mostly lay between 1 and 2% of body weight per day. Conversion efficiencies increased with increased ration from zero value at the maintenance ration to a peak at the optimum ration, then decreased with further increases in ration. At a given restricted ration level, conversion efficiencies generally decreased with increased temperature. At maximum rations, conversion efficiencies were relatively insensitive to temperature. Growth in wet weight, dry weight and energy content showed similar responses to ration, temperature and body weight.     

饲料蛋白质水平与投喂频率对大黄鱼生长、体组成及蛋白质代谢的影响

以初始体重为(13.640.18)g的大黄鱼( Pseudosciaena crocea R.) 幼鱼为实验对象, 采用32双因子实验, 研究饲料蛋白质水平(40%、45%、50%)和投喂频率(2次/d、1次/d)及其交互作用对其生长、体组成和蛋白质代谢的影响。养殖实验在海水浮式网箱中进行, 养殖周期为8周。结果表明: 饲料蛋白质水平和投喂频率对大黄鱼幼鱼的增重率(WGR)、特定生长率(SGR)和饲料转化率(FCR)均影响显著(P0.05)。在40%和45%蛋白质组, 1次/d投喂的大黄鱼幼鱼的WGR和SGR均显著低于2次/d投喂组, 而FCR则相反。在2次/d投喂时, 45%蛋白质组的大黄鱼幼鱼SGR显著高于40%蛋白质组, 但与50%蛋白质组差异不显著(P0.05)。而在1次/d投喂时, 50%蛋白质组的大黄鱼幼鱼SGR显著高于40%和45%蛋白质组。在两种投喂频率下, 随着饲料蛋白质水平提高, 鱼体水分含量均有升高趋势, 蛋白质含量显著升高而脂肪含量显著下降(P0.05)。饲料的蛋白质水平和投喂频率分别对大黄鱼幼鱼的肝脏指数(HSI)、内脏指数(VSI)和血清中的谷丙转氨酶(ALT)及谷草转氨酶(AST)均影响不显著(P0.05)。投喂频率对肝脏的ALT和AST的影响不显著(P0.05)。在同一投喂频率下, 肝脏ALT和AST均随着饲料蛋白质水平的增加而显著提高(P0.05)。饲料中的蛋白质水平和投喂频率对大黄鱼幼鱼的生长和FCR的影响存在显著的交互作用(P0.05), 而对血清和肝脏中的ALT和AST、HSI、VSI、肥满度(CF)以及体组成的影响均无交互作用。       

Do random fluctuations in daily ration affect the growth rate of juvenile three-spined sticklebacks?

The effect of random fluctuations in daily ration on the growth performance of individual juvenile three-spined sticklebacks Gasterosteus aculeatus was studied in experiments lasting 21 days at 14°C and a photoperiod of 10L:14D. Two mean ration levels were used: a maintenance ration of 2%, and a high ration of 6% of initial body weight per day. For experimental fish, the daily ration varied randomly about the required mean value with a coefficient of variation of 33%. The controls received a constant daily ration. The experiment was replicated in winter (Dec.-Jan.) and spring (Mar.-Apr.). At a given ration, there was no significant difference between the specific growth rates of fish receiving constant or varying ration. Neither the final dry weight, final body water content nor final lipid content (% dry weight) differed significantly. As expected, ration had a significant effect on growth rate, final dry weight and body lipid and water content. There was a significant difference in mean growth rate between the winter and spring replicates. The growth rates observed in these experiments were compared with those predicted from a previously described empirical growth model developed for sticklebacks fed constant rations. The model underestimated mean growth rates.     

Growth and feed utilization in two strains of gibel carp, Carassius auratus gibelio: paternal effects in a gynogenetic fish

Gibel carp ( Carassius auratus gibelio Bloch) is a natural gynogenetic fish which requires sperm of the same or related species to activate egg development. The eggs of one gibel carp were divided into two batches. One batch was 'fertilized' with sperm from gibel carp (strain DD), and the other 'fertilized' with sperm from red common carp ( Cyprinus carpio red variety) (strain DR). The juveniles were transferred to the laboratory 36 days post-hatch. Triplicate groups of each strain were fed a formulated diet at either 3% or satiation ration for 8 weeks. At both the restricted and satiation rations, specific growth rate was significantly higher in strain DR than in strain DD. At the 3% ration, there was no significant difference in feeding rate or feed conversion efficiency between the two strains. At the satiation ration, strain DR had a significantly lower feeding rate but higher feed conversion efficiency than strain DD. At the satiation ration, strain DR had a significantly lower intake protein, but higher recovered protein than strain DD. There was no significant difference in faecal protein loss between the two strains. At the 3% ration, strain had no significant effects on intake protein, faecal protein or recovered protein. Neither faecal energy loss nor recovered energy was affected by strain or ration. At both the 3% and satiation ration, final body contents of dry matter and lipid were significantly lower in strain DR than strain DD, while there was no significant difference in protein and energy content between the two strains at either ration level. The results suggested that gibel carp 'fertilized' with sperm of common carp grew faster than those 'fertilized' with sperm of gibel carp through increased feed conversion efficiency and protein retention.     

Aspects of energetics of adult walleye pollock, Theragra chalcogramma (Pallas), from Alaska

Body energy partitioning was examined for field-caught, adult walleye pollock; additional laboratory studies were conducted on fish held under controlled temperature conditions at Seward, Alaska.
Average consumption for pollock feeding daily was 0.5% of body weight (3100 cal) at 5°C, resulting in an average growth of 0.12% body weight day⁻¹. These results suggest that large pollock grow at similar rates and have similar food conversion efficiencies to those of Atlantic cod held at similar temperatures.
Resting metabolic rates measured on adult fish were combined with similar data from juveniles to calculate a regression of specific metabolic rate against wet weight: y = 173x⁻⁰²⁶. Maintenance rations amounted to 4.8 cal g⁻¹ day⁻¹ at 5°C, very close to the 0.28% value for juveniles. Estimation of metabolic rate using maintenance ration data resulted in values that were 55% higher than those obtained from oxygen consumption data for unfed fish. Weight loss during starvation was 0.18% of body weight day⁻¹ at 5°C, corresponding roughly to a starvation metabolic rate 50% lower than the resting metabolic rate we report.
We estimate that an adult pollock will lose about 37% of its prespawning body weight and about 46% of its body energy during spawning. These losses result, primarily, from changes in the weight of gonad, liver and somatic tissues as opposed to changes in specific energy content of those tissues.     

Effect of water temperature,feeding frequency,and protein percent in the diet on water quality,growth and behavior of Nile tilapia Oreochromis niloticus (Linnaeus, 1758)

This study evaluated how water temperature (26, 28, and 30°C), number of meals per day (one or two meals), and protein percent in diet (20, 25 and 30%) impact growth performance, biometric indices, and feeding behavior of Nile tilapia, Oreochromis niloticus. Fish were randomly allocated into 18 equal replicate groups. Higher final body weight was observed in fish reared at 30°C and fed one meal per day containing 30% crude protein. Better weight gain, weight gain %, feed conversion ratio, specific growth rate, and condition factor were recorded in fish reared at 26°C and fed one meal per day containing 30% protein. The best length weight relationship was obtained in fish reared at 26°C and fed one meal per day containing 30% crude protein. Shorter feeding duration and duration of appetite inhibition latency were recorded in fish reared at 30°C, fed one meal per day, and given a diet containing 30% protein. The highest proactivity was recorded in fish reared at 30°C, received one meal per day, and with 25% crude protein in their diet. Conclusively, rearing Nile tilapia at 26–30°C with a lower feeding frequency (one meal/day) and a 30% crude protein diet achieved better performance and feeding behavior.     

Effect of protein synthesis inhibitor cycloheximide on starvation,fasting and feeding oxygen consumption in juvenile spiny lobster Sagmariasus verreauxi

Metabolism in aquatic ectotherms evaluated by oxygen consumption rates reflects energetic costs including those associated with protein synthesis. Metabolism is influenced by nutritional status governed by feeding, nutrient intake and quality, and time without food. However, little is understood about contribution of protein synthesis to crustacean energy metabolism. This study is the first using a protein synthesis inhibitor cycloheximide to research contribution of cycloheximide-sensitive protein synthesis to decapod crustacean metabolism. Juvenile Sagmariasus verreauxi were subject to five treatments: 2-day fasted lobsters sham injected with saline; 2-day fasted lobsters injected with cycloheximide; 10-day starved lobsters injected with cycloheximide; post-prandial lobsters fed with squid Nototodarus sloanii with no further treatment; and post-prandial lobsters injected with cycloheximide. Standard and routine metabolic rates in starved lobsters were reduced by 32% and 41%, respectively, compared to fasted lobsters, demonstrating metabolic downregulation with starvation. Oxygen consumption rates of fasted and starved lobsters following cycloheximide injection were reduced by 29% and 13%, respectively, demonstrating protein synthesis represents only a minor component of energy metabolism in unfed lobsters. Oxygen consumption rate of fed lobsters was reduced by 96% following cycloheximide injection, demonstrating protein synthesis in decapods contributes a major proportion of specific dynamic action (SDA). SDA in decapods is predominantly a post-absorptive process likely related to somatic growth. This work extends previously limited knowledge on contribution of protein synthesis to crustacean metabolism, which is crucial to explore the relationship between nutritional status and diet quality and how this will affect growth potential in aquaculture species.

     

Intestinal protein synthesis in guinea pigs infected with Trichostrongylus colubriformis

The fractional synthesis rate (FSR) and daily synthesis of protein were measured in the small and large intestines of infected guinea pigs and uninfected animals fed ad libitum or quantitatively reduced rations. The FSR of the infected and parasite-free parts of the small intestine was unchanged but was increased by about 40% in the large intestine. Daily protein synthesis (mg/g body wt.) by infected guinea pig was greater by about 24% in the entire small intestine and by over 70% in the large intestine. These increases were not due to anorexia since the FSR and daily protein synthesis by the small and large intestines of the reduced ration animals were less than those of the infected group. Greater weight of the small intestine may explain increases in daily protein synthesis in the small, but not in the large intestine where weight was unchanged. Responses which may affect protein synthesis in the infected and parasite-free intestines are discussed.     

Growth and protein synthesis of barramundi, Lates calcarifer, fed lupin as a partial protein replacement

Protein synthesis is an essential growth process in all animals. Little information is available on post-prandial protein synthesis and even less where different protein sources are compared. Protein synthesis was measured at 4 and 24 h after feeding juvenile barramundi in order to determine the effect of using lupin as a partial protein replacement for fish meal on the post-prandial protein metabolism. Juvenile barramundi (4.3 ±0.6 g) were held in a recirculation system (27 °C, salinity 10‰ and 24 h light) for 15 days. Fish were fed one of two isonitrogenous isoenergetic diets (40% crude protein, 16% lipid and 18.5 GE MJ kg^− 1). One diet was formulated with 100% fish meal as the protein source while the other had 45% of the protein replaced with lupin ingredients (lupin kernel meal (Lupinus angustifolius) and lupin protein concentrate). All fish were fed a ration of 6%·d^− 1 and feed intake was not significantly different between the two diets. Specific growth rate (SGR) and growth efficiency (in relation to protein (PPV) and energy (PEV)) were 6.5 ± 0.14%·d^− 1, 43.8 ± 2.72% and 38.31 ± 1.56%, respectively, and were not significantly different between the two diets. There was no significant difference in protein synthesis between the two diets at 4 and 24 h after feeding, however protein synthesis was significantly higher 4 h after feeding than at 24 h (p = 0.02). Neither growth performance nor protein metabolism was altered by replacing 45% of the protein with lupin protein and indicated this to be a suitable protein source for barramundi feeds.     

The effect of feeding hierarchy on individual variability in daily feeding of rainbow trout, Oncorhynchus mykiss (Walbaum)

Three groups of rainbow trout, Oncorhynchus mykiss , (initial weight 40 g) were fed one of three rations (low, medium or high) for 73 days. Consumption by individual fish within the three ration groups was measured on four occasions (days 27, 55, 64 and 72) using radiography. Food intake by individual fish varied between days and this variability was expressed using the coefficient of variation (CV). Dominant fish within each ration group were defined as individuals with the greater share of the group meal and these fish had low CVs for food intake indicating relatively little variation in daily consumption. By contrast, the fish which had consumed a low mean proportion of the group meal displayed high CVs for food intake, indicating considerable variability in the sizes of individual meals consumed by these fish. As group ration increased, the range of meal sizes and individual CVs in daily feeding decreased, suggesting that the strength of the feeding hierarchy and the variability in individual consumption decreased as food availability increased. It is suggested that radiography can be used to assess social relationships within groups of fish allowing the assessment of feeding hierarchies in larger groups of fish than would be possible by observational techniques.     

Growth and tissue composition as a function of feeding history in juvenile cephalopods

We present the results of a series of experiments that examined the effect of feeding history on the growth and tissue composition of juveniles of two tropical cephalopods; the squid Sepioteuthis lessoniana and the cuttlefish Sepia elliptica. Juveniles were reared in individual containers for between 35 and 42 days at different ration levels, three ration levels for the squid and two levels for the cuttlefish. Although differences in ration were sufficient to cause different growth rates, both in body length and mass, the effects on tissue composition were less definitive. Sepioteuthis juveniles on the highest rations had higher concentrations of water, but no difference in lipid, carbohydrate or protein when compared with their lower ration siblings. In the case of juvenile cuttlefish no difference in tissue composition was detected between the two ration levels. RNA:protein ratios were also determined for the juveniles to provide an estimate of instantaneous growth. A significant correlation was found between body size and RNA:protein ratio in the squid; those juveniles that ate more had higher RNA:protein ratios than lower ration individuals. Significantly, the juvenile cuttlefish showed no relationship between growth rate and RNA:protein ratios, which means that we are unable to use this measure to estimate the growth rates of wild individuals. In conclusion, ration level did affect growth rates and food availability is an important factor in modifying growth rates of wild individuals. However, we could not find, at the individual level, an index or measure that could be used to explain the variability of observed differences in growth rates as a function of nutritional history.     

Influence of body size and food ration on the energy budget of rainbow trout Salmo gairdneri Richardson

Three size classes (3 g, 200 g, 1–3 kg) of rainbow trout, Salmo gairdneri Richardson, were each fed five rations ranging from zero to a 'maximum' ration and the relationships among body size, food ration, metabolism and growth examined. Water temperature was constant at 11–4°C. The gross growth efficiency in wet weight, K , increased asymptotically with increasing ration but decreased with increasing body size. Changes in fat and moisture content of the body, however, were such that Kin terms of energy utilization was independent of body size when the fish were feeding at the same level. This result was not apparent when wet weight values only were considered and use of a constant to convert wet weight offish to calorific values can lead to errors in interpretation of results. Assimilation efficiency averaged 71 -7 % over all feeding groups and was independent of body size and food ration. Total metabolic expenditure, however, increased with increasing body size and feeding level, but at any given feeding level a similar proportion of the energy of the assimilated ration was used for metabolism. At a single feeding level, therefore, the percentage utilization of energy in each category of the energy budget remained similar over all body sizes. Such a result can only be expected under laboratory conditions but it provides a base-line for comparison with the performance of other more complicated systems.     

海水和淡化水养殖凡纳滨对虾饲料蛋白需求量的比较研究

本研究从生长、饲料利用和体成分等指标综合评价饲料蛋白质含量对凡纳滨对虾的影响。研究发现,在海水养殖环境下,饲料蛋白水平对凡纳滨对虾的存活率、增重率、特定生长率、饵料系数、蛋白效率和虾体粗蛋白含量均有显著性影响(p<0.05)。摄食饲料蛋白含量38%的海养凡纳滨对虾有较高的存活率、增重率以及最高的特定生长率。饵料系数随蛋白含量的增加而减小,虾体粗蛋白含量随饲料蛋白水平升高而增加,而蛋白含量38%和41%实验组饵料系数和虾体粗蛋白含量均没有显著性差异(p>0.05)。淡化水养殖条件下,凡纳滨对虾的存活率随饲料蛋白水平的增加而提高,而增重率和特定生长率均在饲料蛋白含量35%实验组最高,饵料系数随蛋白含量的增加先减小后增大,蛋白含量35%实验组饵料系数显著小于其他实验组。海水养殖条件下,凡纳滨对虾的存活率、末体重、增重率、特定生长率和蛋白质效率均高于淡水养殖的对虾。对虾虾体粗蛋白、粗脂肪和粗灰分含量均随盐度升高而升高,而虾体水分随着盐度的升高而降低。     

Growth depensation and aggression in laboratory reared coho salmon: the effect of food distribution and ration size

Groups of recently emerged coho salmon fry Oncorhynchus kisutch were reared for 3 months on food that appeared either asynchronously at a single location (localized) or synchronously and spatially dispersed (dispersed). Groups were further subdivided into those receiving low (1%) or high (3% body weight per day) rations, with five replicate groups for each treatment combination. At low ration there was greater growth depensation, i.e. growth variation, in groups receiving localized as compared to dispersed food. At high ration there was no difference. There was no effect of food distribution upon mean fish weight, but groups receiving high rations had greater mean fish weights than groups receiving low rations. There was no overall difference in the frequency of chasing between any of the treatment combinations. However, in localized food groups, dominants defended positions close to where food entered the tank, giving them greater access than subordinates. In dispersed food groups, while dominants also defended particular areas, this did not result in greater access to food. These results demonstrate that although feeding methodology may not directly influence the frequency of aggressive interactions, feeding methods which facilitate food monopolization by dominants can accelerate the growth of these individuals at the expense of subordinates. In aquacultural applications where greater size is desirable, or otherwise selected for, this may result in the unintentional selection for increased aggressiveness.     

Nahrungsaufnahme,Stoffumsatz und Energiehaushalt des marinen HydroidpolypenClava multicornis

Clava multicornis Forskål (Cnidaria, Hydrozoa) from the North Sea was cultured under a variety of environmental conditions, and quantitative aspects of the following processes examined: food intake, growth, oxygen consumption, losses of material, and food conversion. The experiments were conducted in sea water (salinity 32 ‰) at different constant temperature levels (6°, 11° and 16° C) and different daily food rations. The polyps were fed living larvae of the brine shrimpArtemia salina. Daily rations ranged from 2.3 % (6° C) to 19.0 % (16° C) of the dry weight of the polyp colonies. The food ration essential for minimum growth increased with the test temperature. The calorific value of theArtemia larvae was 5854 cal per g organic dry substance. The calorific values of the colonies ofClava multicornis increased at all 3 test temperatures with ascending daily food rations; they ranged from 5367 to 6003 cal per g organic dry substance. Colony growth was determined in 3 different ways: by measuring the increase in polyp number, the length increase of all polyps of a given colony, and the increase of the dry weight of the organic substance of a given colony. Growth was exponential in all 3 cases. The lowest test temperature, or small daily rations, caused slow growth; the highest temperature, or large daily rations, resulted in rapid growth. Oxygen consumption of individual colonies was measured at 16° C and 3 different daily rations; the colonies showed the same intensity of respiration at all 3 daily rations. A colony of 1.5 mg organic dry substance respired 0.107 ml oxygen per 24 hours, a colony of 5.0 mg, 0.269 ml oxygen. At 11° and 16° C gonophores developed well and were counted; at 6° C no gonophores were observed. The amount of the excrement discharged byC. multicornis at 16° C increased from 26.0 % of the food eaten (minimum daily ration) to 39.3% (maximum daily ration). Gross efficiency increased with falling temperature and rising daily ration. At 16° C, net efficiency increased with rising daily ration. On the basis of the data obtained for gross efficiency, oxygen consumption and excrementation, an energy budget was made up.