Epidermal characteristics of reproductive subsets in an inshore population of winter flounder, Pseudopleuronectes americanus

The winter flounder, Pseudopleuronectes americanus (Walbaum), population off Newfoundland can include a 'non-reproductive post-mature' subset at any time together with 'reproductive' and 'immature' subsets. Skin samples were taken from male and female specimens from each subset in the winter, after reproductive flounder have normally undergone a pre-winter phase of gonadal recrudescence, and also during the spring prespawning period and in the summer following spawning. Results for immature flounder demonstrate that fish size influences epidermal thickness in this species. The epidermis of reproductive flounders is thick, representing a secondary sexual characteristic, during gonadal recrudescence. A thick epidermis is most pronounced on the blind-side, particularly in prespawning males. Although the epidermis of non-reproductive post-mature fish was thinner than in prespawning males and females, it was thicker than in immature flounders. Also, the epidermal thickness of non-reproductive post-mature individuals can still display some seasonal change although gonadal recrudescence has not been sustained. There is also a relationship between condition factor and epidermal thickness which is manifested particularly clearly in immature and non-reproductive post-mature flounder.     

A critical period for nutritional control of early gametogenesis in female winter flounder, Pleuronectes americanus (Pisces: Teleostei)

When female winter flounder ( Pleuronectes americanus ) were subjected to periods of satiation feeding alternating with starvation it was found that the first part of their normal six-month feeding period could be associated with subsequent gametogenesis, whereas feeding in the later part of the normal feeding period was not necessary. Conversely if females were not fed during the first part of the normal feeding season they were likely to become non-reproductive, although high condition fish or a non-spawner could become gametogenic in spite of starvation at this time. Feeding restricted to the later part of the normal feeding season was therefore not generally associated with successful gametogenesis for the following year's spawn. When the first part of the feeding period was further subdivided with satiation feeding limited to one or more months within it, most fish became non-reproductive. The exceptions which became reproductive were females which had high post-spawn condition maintained in the month following the immediate spawning period for the individual fish. A nutritionally sensitive period for early gametogenesis in female winter flounder therefore appears to occur in the early part of the normal feeding season, close to the normal spawning period. The experimentally produced non-reproductive females were generally halted in a previtellogenic stage of development for the most advanced oocytes which is consistent with a nutritionally related inhibition of gametogenesis close to the previous spawning period.     

The effects of feeding regime on proximate body composition and patterns of energy deposition in juvenile Arctic charr, Salvelinus alpinus

Juvenile Arctic charr, Salvelinus alpinus , subjected to either food deprivation or restricted feeding showed reductions in relative sizes of both liver and viscera. With food deprivation, percentage lipid decreased and percentage water increased in the eviscerated carcass, which is in agreement with findings for several other fish species. Following transfer from a restricted to a satiation feeding regime, the relative sizes of both liver and viscera increased to levels exceeding those of fish fed continuously to satiation. At the end of the experiment the percentage liver lipid content of restricted-satiation fed fish was higher than in fish fed to satiation. These differences in energy deposition patterns were, however, not sufficiently large to produce marked differences at the whole animal level, since whole body lipid energy: protein energy ratios and energy utilization efficiencies were similar for restricted-satiation and satiation fed fish.     

Effects of feeding regime on food consumption, growth rates and tissue nucleic acids in juvenile Arctic charr, Salvelinm alpinus, with particular respect to compensatory growth

Juvenile Arctic charr responded to a change from restricted to satiation feeding by showing a growth spurt (compensatory growth). During this period of rapid growth the fish became hyper-phagic and in the days immediately following transfer from restricted to satiation feeding showed improved food conversion efficiency compared to their counterparts raised on a liberal feeding regime. Tissue (liver and muscle) nucleic acid concentrations were influenced by feeding regime, and RNA : DNA ratios were low in both starved fish and those fed restricted rations. Following transfer from restricted to satiation feeding, tissue RNA : DNA ratios were rapidly restored to initial levels. The uses of tissue RNA: DNA ratios both in evaluating nutritional status and as growth indices are discussed.     

The effects of chronic plasma cortisol elevation on the feeding behaviour, growth, competitive ability, and swimming performance of juvenile rainbow trout

Plasma cortisol elevation, a common consequence of stress, occurs in salmonids of subordinate rank; these fish acquire a smaller share of available food and grow more slowly. This study examined the role of cortisol itself in these phenomena. Cortisol implants, with parallel sham and control treatments, were used to create a chronic threefold elevation in plasma cortisol levels in juvenile rainbow trout, and the individual feeding patterns of the fish were evaluated using X-ray radiography. The three treatment groups were (1) held alone and fed to satiation, thereby providing a measure of voluntary appetite, or mixed together in equal proportions and fed to either (2) satiation or (3) half-satiation, thereby allowing assessment of the additional effects of competitive interaction and food limitation. Chronic plasma cortisol elevation had significant negative effects on individual appetite, growth rate, condition factor, and food conversion efficiency, independent of whether the fish were held under unmixed or mixed conditions. Under the latter, mean share of meal was reduced and fin damage increased in cortisol-treated fish; negative growth effects were more severe with food limitation, but the response patterns were otherwise unchanged. Even in the absence of other groups, cortisol-treated fish showed more variable feeding patterns. When compared at the same individual ration levels, cortisol-treated fish had lower growth rates, reflecting a higher "cost of living." Cortisol treatment had no effect on aerobic swimming performance. These results suggest that the structure of the feeding hierarchy may not be determined solely by competitive ability but may also be greatly influenced by differences in the feeding behaviour of unstressed fish versus stressed fish caused by cortisol elevation in the latter.     

不同饵料对稀有鲫生长和繁殖的影响

饵料对鱼类生长发育和繁殖具有重要影响。为了筛选稀有鲫(Gobiocypris rarus)幼鱼和成鱼阶段最适投喂方式, 实验将出膜5周末(日龄为35 day after hatching)的幼鱼随机分为5个组: A组投喂丰年虫; B组每周前6d (days)投喂丰年虫, 后1d投喂商业化微颗粒S3饲料; C组每周前3.5d投喂丰年虫, 后3.5d投喂饲料; D组每周前1d投喂丰年虫, 后6d投喂饲料; E组一直投喂饲料; 各组均采用饱食投喂策略。每2周统计生长、存活指标, 直至第21周(147 dah), 在17周(119 dah)取材用于观察性腺发育程度。在产卵后统计各组产卵量、孵化率和子代畸形率。结果显示: (1)E组存活率和特定生长率显著低于其他组(P<0.05); (2)从产卵量、孵化率和子代畸形率上看, B组产卵量显著高于其他组(P<0.05); (3)从性腺组织学上看, 不同投喂方法对精巢的成熟度无显著影响, 但投喂过丰年虫的稀有鲫卵巢发育成熟度显著优于E组。研究结果提示:适量加入丰年虫比单一投喂活饵或饲料更有利于稀有鲫的生长和繁殖。建议在标准化养殖过程中, 幼鱼和成鱼期的稀有鲫采取丰年虫与饲料投喂频次比值为6﹕1的方式最佳。     

Effect of starvation and refeeding on digestive enzyme activities in juvenile roach, Rutilus rutilus caspicus

We evaluated the effects of starvation and refeeding on digestive enzyme activities in juvenile roach, Rutilus rutilus caspicus. Fish were divided into four feeding groups (mean mass 1.68 ± 0.12 g). The control group was fed to satiation twice a day throughout the experiment with formulated diet (SFK). The other three groups were deprived of feed for 1(S1), 2(S2), and 3(S3) weeks, respectively, and then fed to satiation during the refeeding period. The results showed that trypsin specific activity was not affected significantly either by starvation or refeeding, in all experimental groups. Chymotrypsin specific activity did not change significantly in S1 fish during the experimental period. In S2 and S3 fish no significant changes were observed during the starvation period. Upon refeeding, the activity increased in S2 fish, while it decreased in S3 fish. Amylase specific activity decreased significantly during the starvation period in all experimental groups. Upon refeeding, the activity increased. Alkaline phosphatase specific activity did not change significantly during the experiment period in S3 fish, while it showed significant changes during the starvation and refeeding period in the S1 and S2 fish. Starvation also had a significant effect on the structure of the intestine.     

Laboratory studies on food intake, growth and food conversion of young herring, Clupea harengus (L.)

Food intake, growth and food conversion of young, O-group herring were studied at two temperatures and feeding regimes over a period of 19 weeks. The food intake of fish fed to satiation twice daily showed considerable variation. Food intake per fish at 14.5° C was about three times that at 6.5° C, and was generally much higher than in most other species of fish studied. The mean increase in wet weight over the 19-week period was 0.581 g/week at 14.5° C and 0.236 g/week at 6.5° C in fish fed to satiation and 0.094 g/week at 6.2° C and a ration of 1.3% of the body weight. Growth depensation was found to occur even in fish fed to satiation. The changes in specific growth rate, that is the percentage increase in weight/day, showed similar trends at different temperatures and food regimes. The mean conversion efficiency of fish on a ration of 1.3% at 6.2° C was higher than that of fish fed until satiation, at 14.5 and 6.5° C. The conversion efficiency of fish fed to satiation at 14.5° C showed a distinct decrease with increasing weight while at 6.5° C such a clear trend was not observed. In general, the conversion efficiency of young herring were found to be much lower than that of most other species studied. The weight exponent of the quantitative relationship between food intake and body weight at 14.5° C was 0.744. The total metabolic expenditure at 14.5° C, calculated using Winberg's (1956) 'utilization coefficient, gave a weight exponent of 0.773.     

Annual cycles of growth and reproduction in hatchery–reared Florida largemouth bass, Micropterus salmoides floridanus, raised on forage or pelleted diets

Annual cycles of growth and reproduction of hatchery–reared Florida largemouth bass, Micropterus salmoides floridanus , were investigated. Animals were raised on either forage (goldfish, Carassius auratus ) or a pelleted salmon feed. Male and female year–class 1 largemouth bass were sampled throughout one complete yearly cycle (January–December). A biphasic growth cycle was observed in both forage–fed and pellet–fed fish. No increase in body length or weight was observed until approximately midway through the spawning period (May), after which fish grew at a consistent rate for the remainder of the study. The reproductive cycle of forage–fed fish was characterized by a rapid increase in gonadosomatic index (GS1) between January and April, followed by a prolonged spawning period (April–July) during which GSI progressively declined. Fully regressed gonads were observed in September and October, and a resumption of gonadal recrudescence was observed between October and December. Visceral adipose deposits (expressed as mesenteric fat index; MFI) were resorbed during gonadal growth and the initial stages of the spawning period, and restored during the post–spawning phase. Fish raised on pelleted feed had growth and reproductive cycles that parallelled those of forage–fed fish, but several significant differences were observed between the two diet groups. During the growth phase of the cycle, pellet–fed largemouth bass grew significantly faster than forage–fed largemouth bass, and had significantly larger MFIs than forage–fed largemouth bass at all times of the year. Pellet–fed fish also had significantly larger GSIs than forage–fed fish. These data indicate that diet composition may be an important determinant of growth and reproductive function in this species.     

Effects of 17α-methyl-testosterone on spermatogenesis and spermiation in the grey mullet, Mugil cephalus L.

Diets containing 17α-Methyl-testosterone were given to grey mullet, Mugil cephalus , during the refractory period in its reproductive cycle at the dosage of 25 mg or 12.5mgkg⁻¹ fish. Fish in experiment I were fed the diet containing methyl-testosterone every day for 55 weeks, and fish in Experiment II were fed the same diet daily for the first 10 weeks, and three times per week for the next 42 weeks. Fish were checked for the presence of sperm weekly or bi-weekly and tested for fertility during the spawning season. Terminal gonad weights and histology were compared with control groups. This study demonstrated that male mullet will mature 3 weeks or less by oral administration of 12.5 mg methyl-testosterone kg⁻¹ fish daily. Fish can then be maintained in mature condition by feeding them methyl-testosterone at 12.5 mg kg⁻¹ three times per week.     

Anovulation in non-reproductive female Damaraland mole-rats (Cryptomys damarensis)

Within colonies of Damaraland mole-rats (Cryptomys damarensis), anovulation in non-reproductive females is thought to play an important role in maintaining reproductive skew. Pituitary sensitivity and ovarian structure were examined in three groups of females that differed with respect to their social environment and breeding status to determine whether anovulation is due to inhibitory social cues or is merely the result of a lack of copulatory stimulation. The contribution of gonadal steroid negative feedback to neuroendocrine differences in the reproductive systems of the respective groups was also investigated. LH secretion after a 0.5 micrograms GnRH challenge in females that had been removed from the presence of the breeding individuals for at least 6 months (removed non-reproductive females) was significantly higher than in non-reproductive females in the colony, but significantly lower than in reproductive females. In both removed non-reproductive females and reproductive females, corpora lutea were observed in ovaries of seven of eight females, indicating that ovulation occurs spontaneously in subordinate females on removal from the breeding pair. Circulating progesterone concentrations in removed non-reproductive females were significantly higher than in non-reproductive females, indicating that circulating progesterone is not responsible for infertility in non-reproductive females. Indeed, after hystero-ovariectomy, reproductive females continued to show significantly greater GnRH-stimulated LH secretion than non-reproductive females. Thus, differential inhibition of gonadotrophin secretion in breeding and non-breeding females occurs independently of gonadal steroids. It is concluded that female Damaraland mole-rats are spontaneous ovulators and that anovulation results from inhibitory social cues within the colony, not a lack of copulatory stimulation. Since non-reproductive females are infertile, inhibition of the hypothalamo-pituitary-gonadal axis has the potential to play a causal role in maintaining reproductive skew in colonies of C. damarensis.     

Differential behavioral responses by reproductive and non-reproductive male round gobies (Neogobius melanostomus) to the putative pheromone estrone

Previous studies have shown that the frequency of gill ventilation during exposure to estrone and gonadal extracts in the round goby (Neogobius melanostomus) is linked to olfactory sensory input. Control over gill ventilation may be a regulatory mechanism used for odorant sampling during reproductive periods. In this study, we examined changes in gill ventilation in osmic and anosmic (nasal occluded), reproductive and non-reproductive male round gobies to a putative steroidal pheromone estrone (1,3,5(10)-estratrien-3-ol-17-one). We tested 5 different concentrations of estrone (10(-12) to 10(-8) M) and showed that the response threshold for estrone varied with the male's reproductive status; it was 10(-11) M in reproductive males, and rose to 10(-9) M in non-reproductive males. However, anosmic reproductive and non-reproductive males did not respond to estrone. These findings suggest that olfactory responses to putative pheromones may change depending on the reproductive status of the fish.     

Effects of dietary beta-1, 3 glucan on innate immune response of large yellow croaker, Pseudosciaena crocea

The present study was conducted to investigate the effects of dietary beta-1, 3 glucan on the innate immune response and protection against Vibrio harveyi infection in large yellow croaker, Pseudosciaena crocea. A basal diet was supplemented with 0% (control), 0.09% (low) and 0.18% (high) beta-1, 3 glucan to formulate three experimental diets. Each diet was randomly allocated to triplicate groups of fish in floating sea cages (1.5 x 1.5 x 2.0m), and each cage was stocked with 100 fish (initial average weight 9.75+/-0.35 g). Fish were fed twice daily (05:00 and 17:00) to apparent satiation for 8 weeks. The results of 8 weeks feeding trial showed that low glucan supplementation (0.09%) significantly enhanced fish growth, whereas high supplementation (0.18%) did not. The serum lysozyme activity was significantly increased with the increase of dietary glucan (P < 0.05), and fish fed the diet with high glucan had significantly higher lysozyme activity compared with low glucan. There were no significant differences in alternative complement pathway (ACP) activity between fish fed diets with and without supplementation of glucan. The phagocytosis percentage (PP) and respiratory burst activity in fish fed the diet with 0.09% glucan were significantly higher than those in fish fed with the control diet (P < 0.05), but both immunological parameters significantly decreased in fish fed the diet with high supplementation compared with low supplementation and no significant difference was observed between the control and high supplementation groups. The challenge experiment showed that fish fed the diet with low glucan had significantly lower cumulative mortality compared with the control and high glucan groups (P < 0.05), but no significant difference was observed between the control and high supplementation groups. These results suggested that low glucan could enhance growth and innate immunity of large yellow croaker with an 8-week oral administration, but higher supplementation did not influence growth, or further improve immunity of large yellow croaker.     

Influence of temperature and reproductive state upon the jamming avoidance response in the pulse-type electric fish <Emphasis Type="Italic">Brachyhypopomus pinnicaudatus</Emphasis>

The electric organ discharge (EOD) in Brachyhypopomus pinnicaudatus is modified by temperature and reproductive state. We studied the influence of these variables upon a complex behavior, the jamming avoidance response (JAR). Experiments were performed in non-reproductive fish and in two groups of fish after the induction of reproductive state (by nature or by acclimation at 28°C). JARs were elicited at 20 and 30°C by free-run electric stimuli with different Ls (interval difference between stimulus and EOD). In non-reproductive fish, JARs induced by stimuli with +Ls showed temperature sensitivity, with smaller responses at 30°C. Conversely, similar JARs were obtained at both temperatures in reproductive fish. These observations were replicated in curarized preparations. Stimuli with –Ls were almost ineffective in non-reproductive fish at 30°C, whereas adequate JARs were shown by reproductive fish. Phase-locked stimuli were used to evaluate the duration of the low-threshold electrosensory periods preceding and following the EOD. In non-reproductive fish, the temperature step induced a shortening of these periods. The opposite effect was observed in reproductive fish, probably explaining the differences in JAR capability. A prolongation of the low-threshold periods would favor the perception of electrocommunication signals during courtship. JAR changes would be a consequence of this adaptation.     

Effect of winter feeding and starvation on the growth performance of young‐of‐year (YOY) great sturgeon,Huso huso

The objective of this study was to evaluate the feeding rate of the great sturgeon (Huso huso) young of the year (YOY) and to investigate the effects of different feeding rates in maintaining the weight of fish during short periods of winter starvation. Six feeding rates of 0.2, 0.4, 0.6, 0.8, 1.0% body weight (BW) day^?1 and feeding to satiation were considered for the first experiment. Each feeding rate was randomly assigned to three replicate tanks, with continuous feeding throughout a 5‐week winter period of water temperatures below 10°C. Fifteen fish were held in each of 18 tanks with an average initial body weight of 219.6 ± 6.9 g. After 5 weeks of feeding, the best performance was observed in fish fed 1% BW day^?1, but negative growth was observed in fish fed 0.2% BW day^?1. In the second experiment, fish were deprived of feed for 3 weeks at winter temperatures. Weights and condition factors of all fish decreased during starvation, while the differences in mean weight before and after the starvation period were not significant in fish fed a level of 0.2% BW day^?1 and those fish fed to satiation. No mortality was recorded in either experiment. Results of this study indicate that a feeding rate of 1% BW day^?1 would be sufficient for commercial fish farming of YOY of this species to maintain them over winter. Also, to maintain fish weights and prevent weight loss in overwintering ponds, a feeding rate of around 0.3% BW day^?1 seems appropriate for hatcheries.     

Evidence of differences in growth and food intake regulation in different genetic strains of channel catfish

Norris and USDA-103 strains of channel catfish Ictalurus punctatus were compared for growth rate and food conversion ratio under satiation feeding and restricted feeding (1% body weight day⁻¹) regimes. At the start of the experiment Norris fish weighed 2·8 g, USDA-103 fish weighed 14·0 g. Therefore, a regression of the loge of specific growth rate against the log_e of mean body size with an empirically derived fixed slope of -0·37 was used to compare growth rates. Under both feeding regimes the USDA-103 strain had faster specific growth rates and more efficient food conversion. In subsequent studies, voluntary food intake of size matched fish (60 g average) from these two strains was compared using a radiographic method. Fish were acclimatized to tank conditions for 3 weeks prior to voluntary food intake measurement. Half of the groups were deprived of food for 2 days prior to food intake measurement, while the remaining groups were fed 1% body weight day⁻¹. The USDA-103 strain fish ate significantly more food and grew faster than the Norris strain fish. Previously fasted Norris fish subsequently ate more than their fed counterparts, whereas the fed USDA-103 fish consumed more food than the fasted USDA-103 group. When the USDA-103 strain fish were deprived of food for 4 , 2 or 0 days, all groups subsequently consumed between 4·5 and 5·0% of body weight in one meal. The USDA-103 fish, unlike the Norris fish were not stimulated to consume more after short-duration fasting. Taken together, these results suggest that there are genetic differences in growth, food conversion ratio and regulation of food intake between Norris and USDA-103 strains.     

Growth performance and body composition in response to dietary protein and lipid levels in Nile tilapia (Oreochromis niloticus Linnaeus, 1758) subjected to normal and temporally restricted feeding regimes

A factorial experiment was designed to examine the effect on compensatory growth (CG) of Nile tilapia Oreochromis niloticus fed diets containing different protein and lipid levels under normal and temporally restricted feeding regimes. Four diets were formulated to contain either 30% or 36% crude protein, and 5% or 11% crude lipid. Triplicate replicates of each treatment were assigned to 24 150‐L tanks (20 fish/tank density). Fish (mean initial weight ± SD = 8.79 ± 0.34 g) were then fed either the normal feeding regime (thrice daily to apparent satiation) or the restricted regime (1 day feed deprivation followed by 3 days of feeding to apparent satiation) over a 44‐days study period. Fish receiving a diet under the restricted regime achieved weight gains (WG) comparable to fish consuming the diet containing 30% protein and 5% lipids under the normal feeding regime. Fish maintained on the restricted feeding regime exhibited reduced feed intake (FI), WG, feed efficiency ratio (FE), protein efficiency rate (PER) and hepatosomatic index versus fish on the normal feeding regime, except WG in fish fed the diet with 30% protein and 5% lipids. However, the resultant FI (85%~94%) was higher than the excepted 75% intake when fish were subjected to the restricted regime. Feeding 11% lipid diets led to improved FI, WG, FE, and PER compared to feeding the 5% lipid diets. Increased FI, WG, and FE, but reduced PER were observed in fish fed with 36% protein versus fish fed 30% protein. Fish receiving the 36% protein diets had lower whole‐body moisture and ash contents, but elevated whole‐body protein and lipid contents compared to those receiving the 30% protein diets. Whole‐body moisture contents were lower, but whole‐body protein, lipid and ash contents were higher in fish fed 11% lipid diets than in fish fed 5% lipid diets. There was an increase in whole‐body moisture content, but a decrease in protein and lipid content in response to the restricted feeding regime. Ash content was not affected by the feeding regime. The present study shows that Nile tilapia fed diets subjected to a restricted feeding regime exhibited growth comparable to those fed the diet at 30% protein and 5% lipid levels under a normal feeding regime. This positive effect was more pronounced in diets at a high protein level or in a combination of high protein and lipid levels.     

The effect of feeding strategies and body weight on growth performance and hematological parameters of Siberian sturgeon (Acipenser baerii,Brandt 1869): Preliminary results

The purpose of present study was to investigate the growth performance and hematological parameters of Siberian sturgeon Acipenser baerii in three feeding strategies (satiation feeding, restricted feeding and starvation). We considered two body weights 465.75 ± 11.18 g and 250.40 ± 12 g for large fish and small fish, respectively. In a 45‐day experiment, eighteen fiberglass tanks were used for six triplicate treatments. In restricted feeding strategy, the fish were fed to 50% of satiation and starved treatments were an absolute feed deprivation throughout the experiment. At the end of 45‐day period, the hematological parameters were measured. The reduction of weight, condition factor and daily growth rate in the smaller fish was dramatically higher than the larger fish. Feed deprivation increased the rate of weight loss. Specific growth rate were negative in the large and small fish of starved treatments. The hematological results revealed no significant differences in except for the number of monocytes in larger fish. Large satiated fish showed the highest number of monocytes. In general, these strategies (restriction and deprivation) did not have any negative impacts on the hematological parameter in both sizes but respect to fish body weight, difference in total feed input between satiated and restricted treatments changed growth performance. It seems that restricted feeding (50% of satiation) in large fish was enough to achieve optimal growth while the amount of feed provided for small fish was not enough. Therefore; we can conclude that the restricted feeding is an effective strategy in rearing sturgeon at higher weight when the rearing condition is unsuitable.     

Oxygen uptake of growth hormone transgenic coho salmon during starvation and feeding

Oxygen uptake of growth hormone transgenic coho salmon Oncorhynchus kisutch was measured in individual fish with a closed-system respirometer and was compared with that of similar-sized non-transgenic control coho salmon during starvation and when fed a fixed ration or to satiation. Transgenic and control fish did not differ in their standard oxygen uptake after 4 days of starvation, although control fish had a higher routine oxygen uptake, scope for spontaneous activity and initial acclimation oxygen uptake. During feeding, transgenic fish ate significantly more than control fish, and had an overall oxygen uptake that was 1·7 times greater than control fish. When fish that had eaten the same per cent body mass were compared, transgenic fish had an oxygen uptake that was 1·4 times greater than control fish. Differences in oxygen uptake in growth hormone transgenic coho salmon and non-transgenic fish appear to be due to the effects of feeding, acclimation and activity level, and not to a difference in basal metabolism.     

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.