Satiation,digestive tract evacuation and return of appetite in the European minnow,Phoxinus phoxinus (Cyprinidae) following short periods of pre-prandial starvation

Synopsis In adultPhoxinus phoxinus (Cyprinidae), starvation for 4 or 16 days had no significant effect on the rate of foregut evacuation of the first satiation meal consumed after the starvation period. Starvation for 4 and 16 days had no significant effect on the rate of return of appetite after that first meal. A model based on the rates of foregut evacuation and return of appetite predicted that in the presence of excess food, the foregut contents would represent about 4% of total body weight. This prediction was corroborated experimentally. The effect of the length of starvation on the size of the first meal was not consistent. The results suggest that the hyperphagia noted in minnows starved for 16 days is a consequence of the persistence on succeeding days of the rates of evacuation and return of appetite achieved on the first day of realimentation.     

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.     

Capacity for growth compensation in juvenile three-spined sticklebacks experiencing cycles of food deprivation

The capacity of three‐spined sticklebacks Gasterosteus aculeatus (initial mean mass 0.280 g) to compensate for recurrent periods of food deprivation of 2, 4 or 6 days followed by 2 days of ad libitum feeding on enchytraeid worms over 56 days was assessed by measuring appetite and growth. Control fish were fed daily. The total number of days on which fish were fed ranged from 14 (6‐day cycle) to 56 (controls). Deprived sticklebacks were hyperphagic on the first day of re‐feeding in a cycle and this hyperphagia increased with successive cycles. Mean daily consumption on first day of refeeding was: controls, 62.9 mg; 2 days, 108 mg; 4 days, 98.8 mg; 6 days, 101 mg. The hyperphagia did not increase as the preceding period of deprivation within a cycle increased. Hyperphagia was not maintained on the second day of re‐feeding. The 4 day and 6 day groups initially showed hypophagia on the second day of re‐feeding. Mean daily consumption on second day of re‐feeding was: controls, 62.6 mg; 2 days, 62.2 mg; 4 days, 54.2 mg; 6 days, 50.0 mg. Over the experiment, consumption on the second day of the 4 day and 6‐day groups increased towards the control level, suggesting a developing compensatory response. The highest mean daily consumption per days fed was shown by the 2 day group. The relationship between number of days fed and total food consumption and specific growth rate suggested that the 2 day group almost compensated for the periods of deprivation. Performance declined for the 4 day and 6 day groups, although even at the highest level of deprivation, a positive growth was achieved. Mean specific growth rate in mass (% per day) was: controls, 2.33; 2 days, 1.89; 4 days, 1.21; 6 days, 0.86. Initial mass and total food consumption accounted for most of the variance in specific growth rate. Other indices of performance including lipid concentration, dry matter concentration and the RNA:DNA ratio in white muscle were positively related to quantity of food consumed by each group. Growth efficiency of sticklebacks in terms of wet mass gained and wet mass consumed over the experimental period was 19.4% and did not differ among control and treatment groups. The growth rates of the sticklebacks experiencing cyclical deprivation were comparable to growth rates previously recorded for sticklebacks fed daily, but consuming similar mean daily rations.     

Assessing water quality suitability for shortnose sturgeon in the Roanoke River,North Carolina,USA with an in situ bioassay approach

The aim of this study was to determine the suitability of water quality in the Roanoke River of North Carolina for supporting shortnose sturgeon Acipenser brevirostrum, an endangered species in the United States. Fathead minnows Pimephales promelas were also evaluated alongside the sturgeon as a comparative species to measure potential differences in fish survival, growth, contaminant accumulation, and histopathology in a 28‐day in situ toxicity test. Captively propagated juvenile shortnose sturgeon (total length 49 ± 8 mm, mean ± SD) and fathead minnows (total length 39 ± 3 mm, mean ± SD) were used in the test and their outcomes were compared to simultaneous measurements of water quality (temperature, dissolved oxygen, pH, conductivity, total ammonia nitrogen, hardness, alkalinity, turbidity) and contaminant chemistry (metals, polycyclic aromatic hydrocarbons, organochlorine pesticides, current use pesticides, polychlorinated biphenyls) in river water and sediment. In the in situ test, there were three non‐riverine control sites and eight riverine test sites with three replicate cages (25 × 15‐cm (OD) clear plexiglass with 200‐μm tear‐resistant Nitex^® screen over each end) of 20 shortnose sturgeon per cage at each site. There was a single cage of fathead minnows also deployed at each site alongside the sturgeon cages. Survival of caged shortnose sturgeon among the riverine sites averaged 9% (range 1.7–25%) on day 22 of the 28‐day study, whereas sturgeon survival at the non‐riverine control sites averaged 64% (range 33–98%). In contrast to sturgeon, only one riverine deployed fathead minnow died (average 99.4% survival) over the 28‐day test period and none of the control fathead minnows died. Although chemical analyses revealed the presence of retene (7‐isopropyl‐1‐methylphenanthrene), a pulp and paper mill derived compound with known dioxin‐like toxicity to early life stages of fish, in significant quantities in the water (251–603 ng L^?1) and sediment (up to 5000 ng g^?1 dry weight) at several river sites, no correlation was detected of adverse water quality conditions or measured contaminant concentrations to the poor survival of sturgeon among riverine test sites. Histopathology analysis determined that the mortality of the river deployed shortnose sturgeon was likely due to liver and kidney lesions from an unknown agent(s). Given the poor survival of shortnose sturgeon (9%) and high survival of fathead minnows (99.4%) at the riverine test sites, our study indicates that conditions in the Roanoke River are incongruous with the needs of juvenile shortnose sturgeon and that fathead minnows, commonly used standard toxicity test organisms, do not adequately predict the sensitivity of shortnose sturgeon. Therefore, additional research is needed to help identify specific limiting factors and management actions for the enhancement and recovery of this imperiled fish species.     

Effects of fish size and ration level on the growth and food conversion efficiency of rainbow trout, Salmo gairdneri Richardson

The growth rates of rainbow trout, Salmo gairdneri , which ranged in size from 0.6 to 5.2 g and were provided rations of three different sizes, were measured during a 15-day study. The relative maintenance rations (food/gram of fish at zero growth rate) decreased with increases of fish size. Consequently when fish were kept at low ration levels the growth rates and gross efficiencies of food conversion of 'large' fish were greater than those of 'small' fish. However, as ration level increased, the effects of fish size grew at the same rates or slower than small fish. With increases of ration to the highest levels (9–12%/day) gross efficiency values for large fish began to decline while those for small fish continued to increase.     

Gastric evacuation rates and daily rations of Arctic cod (Boreogadus saida) at low temperatures

Gastric evacuation rates were determined for different sizes of Arctic cod (Boreogadus saida) at sub-zero temperatures (−1.4 and −0.5°C). These temperatures represent ambient conditions for Arctic cod in the Canadian high Arctic. Evacuation half-times, the time required for half of the content of the stomach to be evacuated, were longer (36–70 h; mean=51 h) than those reported in studies carried out on other fish species. Gastric evacuation rates at low temperatures were equal to, or below, those predicted by extrapolation from experiments conducted at higher temperatures. There were no significant differences in evacuation rates among fish size-groups or diets, but evacuation rates were slower for fish that had been starved prior to experiments. Estimated daily rations for Arctic cod in Resolute Bay, N.W.T., were 0.51% body weight for small fish (4.5 g) and 1.13% body weight for large fish (51 g). Slow stomach evacuation rates at low temperatures may limit daily food intake when food is seasonally abundant. This may contribute to slow growth rates and limited maximum size of Arctic cod in Canadian high Arctic waters. Received: 14 July 1997 / Accepted: 15 November 1997     

Diel vertical movements by lotic mayfly nymphs under variable predation risk

1. The diel foraging periodicities of two grazing mayfly (Ephemeroptera) nymphs, Heptagenia dalecarlica and Baetis rhodani, under variable fish (European minnow) predation risk were examined in a series of laboratory experiments. 2. Heptagenia dalecarlica were almost exclusively nocturnal in their use of feeding areas on stone tops. There was a sharp increase in the proportion of nymphs out of refuge at nightfall, both in the control and fish-odour treatments. In a treatment with freely moving fish, H. dalecarlica decreased their activity during both the day and night. In feeding trials with three freely foraging minnows, nymphs were completely safe when they had access to refuges beneath stones, whereas almost half the nymphs were consumed when no refuges were available. 3. Baetis rhodani nymphs reduced their use of stone tops when exposed to four caged minnows or a freely moving fish, but this occurred both day and night. In feeding trials, B. rhodani were captured only while in the water column, and their mortality risk was independent of refuge availability. 4. It is suggested that because H. dalecarlica lack efficient post-encounter defences, they must rely on pre-encounter mechanisms to reduce the threat of fish predation. It appears that in order to dwell sympatrically with fish, H. dalecarlica have evolved a coexistence by hiding strategy. In contrast, Baetis are vulnerable to fish attacks only if they enter drift in daylight, and are thus able to remain on stone tops both during the day and at night.     

The effects of feed restriction during organogenesis on embryo-fetal development in the rat

BACKGROUND: Given the role of nutrition and body weight gain in normal development, pharmaceuticals intended to reduce appetite and promote weight loss will generate safety data that may be challenging to interpret. To aid with this, the effects of feed restriction and subsequent body weight reductions on embryo-fetal development were investigated in the rat. METHODS: Groups of 20 timed pregnant female Sprague-Dawley rats were offered Certified Rodent Diet 5002 either ad libitum or in restricted amounts of 20, 15, 10, and 7.5 g/day from Gestation Day (GD) 6-17. Clinical signs, body weights, and food consumption were recorded. Cesarean sections were performed on GD 21 and fetuses were sexed, weighed, and examined for external, visceral, and skeletal development. RESULTS: Mean maternal body weights at the end of the feed restriction period, GD 18, were reduced 0.87 x, 0.80 x, 0.69 x, and 0.63 x control mean in the 20, 15, 10, and 7.5 g/day groups, respectively. Mean body weight gains for the restriction period inclusive, GD 6-18, were 0.49 x and 0.24 x control at 10 and 7.5 g/day, respectively, and a mean body weight loss occurred at 10 and 7.5 g/day (0.95 x and 0.85 x mean GD 6 body weight, respectively). Fetal body weights were reduced 0.95 x, 0.93 x, 0.90 x, and 0.76 x control at 20, 15, 10, and 7.5 g/day, respectively. This resulted in a reduction in gravid uterine weight at 10 and 7.5 g/day. There were no external, visceral, or skeletal malformations attributed to feed restriction. There was an increase in the skeletal variation of wavy ribs and a decrease in ossification at 7.5 g/day. CONCLUSIONS: These data demonstrate that feed restriction-induced reductions in maternal gestational body weight gain of approximately 50% compared to ab lib fed rats only caused a reduction in fetal body weight. Even up to a 15% maternal gestational body weight loss had no effect on embryo viability in rats, but retarded fetal growth significantly enough to induce minor changes in skeletal development. There were no external, visceral, or skeletal malformations associated with any of the levels of maternal body weight reduction or loss.     

The application of radiography to the study of fish nutrition

The measurement of individual food consumption rates of fish held in groups using radiography has enabled the development of a new approach to fish nutrition trials. In order to compare diets, groups of individually numbered fish are fed different experimental diets over extended periods of time (similar to standard nutrition trials) and food consumption rates are measured regularly over the course of the experiment. Analysis of covariance is then used to compare regression coefficients, obtained from mean consumption-growth relationships, from each diet. The advantages of the approach are several: (1) differences in appetite between fish fed different diets are monitored; (2) fewer fish are needed to establish consumption-growth curves over a large range of consumption rates; (3) measured food consumption rates, not ration levels, are used to calculate 'true' growth efficiencies; and (4) other factors, such as absorption efficiency, trypsin activity, the concentration of free amino acids in tissues and protein turnover can be measured for individual fish and related to differences in food consumption between fish in the same group. The approach has been used successfully with a variety of species to compare the growth response of groups fed two or more diets.     

Effects of different food restrictions on somatic and otolith growth in Nile tilapia reared under controlled conditions

.Nile tilapia Oreochromis niloticus , initial age 12 days, were given an unrestricted (NR) or restricted (R) ration over 93 days which resulted in fish of very different sizes although the body condition factor ( K ) and the viscero-somatic index ( I _V) remained almost unchanged. In a second stage (64 days) each group (NR & R) was divided into three subgroups that were subjected to 0 (NR0, R0), 15 (NR15, R15) and 30 (NR30, R30) days of food restriction, respectively. The impact of the different treatments on the somatic growth during the second stage of the experiment had an effect, with a highly significant difference between the mean ± S.D. masses ( M _T) in the different subgroups (NR0= 115.0 ± 26.6 g; NR15 = 94.8 ± 24.9 g; NR30 = 56.3 ± 28 g; R0 = 76.4 ± 20.1 g; R15 = 72.l ± 17.6 g; R30 = 43.6 ± 17.2 g). Similarly, K and I _V decreased. Irrespective of the initial feeding condition, the width of the otolith microincrements started to decrease at the end of the first or second day of restricted feeding. In the subgroups given a restricted food ration for 30 days (NR30 and R30), this decrease reached a plateau at about day 30, which was maintained even when the restriction had ended. This slowed growth did not lead to any marked halt in microincrement formation, since there were no significant differences (ANOVA; P >0.05) in the numbers of increments counted in the various subgroups. The results show that in 153 day old fish, a period of severe food restriction, even if prolonged (15 to 30 days), had no influence on the timing of the laying down of microincrements but only affected their growth.     

Effect of population density and feeding rate on the fathead minnow (Pimephales promelas)

Juvenile fathead minnows ( Pimephales promelas ) were stocked in tanks at different densities and different ration levels, in two experiments, to determine effects on final population density, growth and fecundity. Length and weight of fish increased with increased food availability. Egg size was exponentially related to growth and perhaps directly to ration level. High population density appeared to limit growth and gamete development regardless of food abundance. Additionally, water volume appeared to limit numbers (tolerance density) of fish which can be supported in a specific volume of water.     

Effects of increased suspended sediment on growth rate and gill condition of two southern Appalachian minnows

Despite the recognition that increased suspended sediment concentration (SSC) is a correlate of imperilment for native riverine fishes, research is limited on the effects of SSC on small non-game species. This study quantifies the impact of suspended sediment on fish growth and gill condition of two stream-dwelling minnows. Specific growth rate (i.e., percent change in mass per day) and gill condition (i.e., lamellar thickness and interlamellar area) were measured in young-of-year whitetail shiners, Cyprinella galactura, and federally threatened spotfin chubs, Erimonax monachus, exposed for 21 days to increased SSC (0, 25, 50, 100, and 500 mg L⁻¹). Exposure to elevated SSC caused a significant decrease in specific growth rate in both species and at all life stages tested. The effect of increased SSC was greatest in spotfin chubs, which exhibited a 15-fold decrease in specific growth rate at the highest treatment (500 mg L⁻¹). Effects of increased SSC were least for 8–9-month-old whitetail shiners, which had growth rates similar to controls for 25, 50, and 100 mg L⁻¹ treatments. These minnows exhibited a greater response to increasing SSC than salmonids at low to moderate SSC, and a lesser response at higher sediment levels. Gill damage was minimal at the three lowest treatment levels, moderate at 100 mg L⁻¹ and severe at 500 mg L⁻¹, indicating that respiratory surfaces of upland minnows may be much more sensitive than other species. Specific growth rate decreased significantly with increasing gill lamellar thickness, suggesting that respiratory impairment is one mechanism responsible for negative impacts of excessive sediment on small riverine fishes.     

Contamination of food by crude oil affects food selection and growth performance,but not appetite,in an Arctic fish,the polar cod (Boreogadus saida)

The polar cod (Boreogadus saida) is recognized as a key species in Arctic marine food webs and it may, therefore, be important for the transfer of xenobiotics from lower trophic levels to its main predators, birds and sea mammals. The present work examines the effects of foods contaminated with 200 or 400 ppm crude oil on food selection patterns and appetite-growth relationships in polar cod using X-radiography. It is shown that sexually mature polar cod consumed mixtures of uncontaminated and oil-contaminated foods, and did not show a reduced overall appetite as compared with fish provided with uncontaminated food only. Food selection was, however, influenced by both sex and individual appetite. Male fish selected uncontaminated food when appetite was low, whereas females ingested contaminated and uncontaminated foods equally, irrespective of appetite level. The ingestion of oil-contaminated food led to a significant depression in growth performance in both male and female fish. Food contaminated with oil at a concentration of 500 ppm was completely rejected by both sexes.     

Disentangling effects of growth and nutritional status on seabird stable isotope ratios

A growing number of studies suggest that an individual’s physiology affects its carbon and nitrogen stable isotope signatures, obscuring a signal often assumed to be only a reflection of diet and foraging location. We examined effects of growth and moderate food restriction on red blood cell (RBC) and feather δ¹⁵N and δ¹³C in rhinoceros auklet chicks (Cerorhinca monocerata), a piscivorous seabird. Chicks were reared in captivity and fed either control (75 g/day; n = 7) or ~40% restricted (40 g/day; n = 6) amounts of high quality forage fish. We quantified effects of growth on isotopic fractionation by comparing δ¹⁵N and δ¹³C in control chicks to those of captive, non-growing subadult auklets (n = 11) fed the same diet. To estimate natural levels of isotopic variation, we also collected blood from a random sample of free-living rhinoceros auklet adults and chicks in the Gulf of Alaska (n = 15 for each), as well as adult feather samples (n = 13). In the captive experiment, moderate food restriction caused significant depletion in δ¹⁵N of both RBCs and feathers in treatment chicks compared to control chicks. Growth also induced depletion in RBC δ¹⁵N, with chicks exhibiting lower δ¹⁵N when they were growing the fastest. As growth slowed, δ¹⁵N increased, resulting in an overall pattern of enrichment over the course of the nestling period. Combined effects of growth and restriction depleted δ¹⁵N in chick RBCs by 0.92‰. We propose that increased nitrogen-use efficiency is responsible for ¹⁵N depletion in both growing and food-restricted chicks. δ¹⁵N values in RBCs of free-ranging auklets fell within a range of only 1.03‰, while feather δ¹⁵N varied widely. Together, our captive and field results suggest that both growth and moderate food restriction can affect stable isotope ratios in an ecologically meaningful way in RBCs although not feathers due to greater natural variability in this tissue.     

Effects of food deprivation on expression of growth hormone receptor and proximate composition in liver of black seabream Acanthopagrus schlegeli

The effects of food deprivation on the hepatic level growth hormone receptor (GHR) were investigated in black seabream (Acanthopagrus schlegeli) both at the protein level (by radioreceptor assay) and at the mRNA level (by ribonuclease protection assay). Serum levels of growth hormone (GH) and triiodothyronine (T₃) were also measured. Condition factor and hepatic proximate composition of the fish were also assessed. Significant decrease in hepatic GHR binding was recorded as early as on day 2 of starvation. On day 30 this decrease was even more pronounced, with the level in the starved fish reaching less than 20% the fed control level. A concomitant decrease in the hepatic GHR mRNA content was also noted during this period, with a progressive decrease from day 2 to day 30 of starvation. The extent of decrease in the mRNA content was less pronounced than the decrease in receptor binding, with the hepatic GHR mRNA content in the day 30 starved fish representing approximately 30% of the level in the fed control. In large contrast, serum GH level increased progressively during starvation. After 30 days of starvation, serum GH levels in the starved fish were more than three times the concentration found in the fed control. Serum T₃ levels, on the other hand, decreased during starvation, with the difference reaching significance on day 15 and day 30. After 30 days of starvation, serum T₃ levels in the starved fish were only approximately 40% the concentration found in the fed control. The hepatic lipid content exhibited an increasing trend during starvation. On day 30 the hepatic lipid content of the starved fish had doubled the level found in the fed control. However, the hepatic protein content did not exhibit much change during starvation. There was also a minor decrease in the moisture content of the liver during starvation, but the condition factor of the fish as a whole registered a gradual decrease during the course of food deprivation.     

High ambient ammonia promotes growth in a ureogenic goby, <Emphasis Type="Italic">Mugilogobius abei</Emphasis>

Mugilogobius abei has the ability to produce large amounts of urea when exposed to high ambient ammonia. Despite this metabolically costly approach, and reports of growth inhibition effects of ammonia on fish, M. abei exposed to ammonia shows no adverse effects on growth. To investigate this observation the growth of M. abei was measured at room temperatures for 8 weeks at a constant ration level under solitary and grouped conditions, in 20% SW with or without (control) 2 mM NH₄Cl. Furthermore, pituitary mRNA levels of growth hormone, oxygen consumption, incorporation of external ¹⁵N-ammonia into amino acid and protein fractions as well as behavioral activities were also examined. The specific growth rates of ammonia-exposed fish under grouped condition over the 8 weeks were significantly higher than those of control, while those rates under solitary condition were not significantly different between the treatments. The pituitary of ammonia-exposed fish had higher growth hormone mRNA than in control fish. The use of ¹⁵N isotope revealed that M. abei can actively use external ammonia as a supplementary nitrogen source. Oxygen consumption of ammonia-exposed fish was significantly lower than that of control fish. Locomotor activity and aggressive behavior under grouped condition were significantly reduced in ammonia-exposed fish as compared to those of control. These combined alterations in the ammonia-exposed fish may result in the higher growth rates.     

The cost of living for freshwater fish in a warmer, more polluted world

Little of the vast literature on the temperature physiology of freshwater fish is useful in predicting the effects of global warming. In the present review a series of laboratory experiments is reviewed in which rainbow trout (Oncorhynchus mykiss) were exposed to simulated global warming, a 2 °C increment superimposed upon the natural thermal regime, in the presence and absence of two common freshwater pollutants, ammonia and acidity (low pH). Simulated global warming had little effect on the growth and physiology of trout fed to satiation over much of the summer. However, in late summer, when ambient water temperature was at its highest, the addition of 2 °C caused a marked inhibition of appetite and growth, although this impact was not exacerbated by a reduction in food availability. In winter, + 2 °C stimulated metabolism, appetite and growth by approximately 30–60%. Exposure of satiation‐fed trout to low levels of pollutants produced unexpected results. Ammonia (NH₃ + NH₄⁺ = 70 μm) stimulated summer growth and energy conversion efficiency, whilst acidification (pH 5.2) increased appetite and growth but caused no disturbance of electrolyte balance. These pollutant effects were additive upon, but not synergistic with, the effects of + 2 °C. The ability of the fish to acclimate to the experimental conditions was tested with acute lethal temperature and/or toxicant challenges. Fish exposed to + 2 °C had a slightly (0.2–1.0 °C) but significantly higher lethal temperature than those exposed to ambient temperature when fed to satiation. However, there was no evidence of acclimation to either ammonia or low pH. It is concluded that the impact of global warming on freshwater fish will vary seasonally. The additional temperature may provide growth benefits in winter, but may threaten fish populations living towards the upper end of their thermal tolerance zone in (late) summer.     

Utilization of grass carp faeces by the IsopodAsellus aquaticus (L.) in the laboratory

Grass carp (Ctenopharyngodon idella Val) faecal pellets derived fromElodea nutallii consumption were efficiently utilized by the detritivoreAsellus. Immature and adult individuals of 2.1–3.2 mm and 4.9–6.0 mm respectively, exhibited a high mean specific growth (9.03%/day and 3.33%/day) when offered faecal pellets as food during two weeks experimental trials. Individuals of the same groups, when fed onElodea which had been mechanically fragmented to simulate the macerating action of the grass carp pharyngeal teeth, grew at rates (9.57%/day and 4.06%/day) not significantly different from those fed on faecal pellets. However, the growth rates of animals fed on freshElodea (6.40%/day and 2.23%/day) were significantly lower than in the above trials, indicating that the morphological destruction of the plant tissue could be responsible for the higher observed growth. The control trials, including unfed animals, showed negative growth (– 0.49%/day and – 0.48%/day).Grass carp herbivory makes a new food resource available to benthic invertebrates by converting fresh plant material to small plant fragments.     

A Test for Male Parental Care in a Fundulid, the Bluefin Killifish, Lucania goodei

Under field conditions, breeding male bluefin killifish, Lucania goodei, have been observed aggressively defending territories from other breeding males, non-breeding females, and minnows (mainly Notropis harperi). We performed an aquarium experiment to test whether male aggression serves to protect newly deposited eggs from predation. We allowed a male and a female to spawn in a yarn mop, removed the female, and exposed the eggs to one of four treatments (spawning male present, two minnows present, spawning mal+two minnows present, no adult fish present). Mops were censused daily for seven days. Egg predation rates were highest in the male+minnows and male only treatments. Egg predation rates in the male+minnows treatment did not differ from the predicted predation rate (sum of male only and minnows only treatments). Hence, there is no evidence for male parental care in L. goodei. In addition, we compared the egg predation rates (filial cannibalism) between males of 3 different color morphs and found no evidence for differential egg cannibalism.     

Effects of qualitative and quantitative food restriction treatments on feeding motivational state and general activity level of growing broiler breeders

Growing broiler breeder chickens are fed restricted rations to limit body weight at sexual maturity. This experiment tested a proposal (Brouns, F., Edwards, S.A., English, P.R., 1994. Effect of dietary fibre and feeding system on activity and oral behaviour of group housed gilts. Appl. Anim. Behav. Sci. 39, 215-223.) that feeding motivation is reduced by using qualitative rather than quantitative food restriction, and it examined relationships among suppression of growth rate, feeding motivational state and general activity level. From 2 to 15 weeks of age, female broiler breeders were reared in six groups of 20, each with a different feeding treatment. The six treatments were: high and low levels of diet dilution (600-700 g/kg and 300-350 g/kg oat feed, ad libitum), appetite suppression (50-60 g/kg and 25-30 g/kg calcium propionate, ad libitum) and quantitative restriction (recommended daily ration and twice that amount). Birds were conditioned to an operant (PR1 schedule) feeding procedure with their respective treatment diets from 3 to 7 weeks, and this was used to measure feeding motivation in 12-min tests at three times of day (1000, 1300 and 1600 h) at 8, 10, 12 and 14 weeks. Proportions of time spent sitting were measured as an index of general inactivity in systematic observations at 9, 11, 13 and 15 weeks. Although the diet dilution and appetite suppression (qualitative) treatments did not limit growth rates as intended, they and the quantitative treatments produced a range of mean body weights to compare with feeding motivation whenever birds were tested. With body weight as a covariate, there were significant effects on numbers of operant responses in 12 min (the measure of feeding motivation) of weight, age, time of day and treatmentxtime interaction, but not treatment. Feeding motivation was positively correlated with suppression of growth rate, regardless of how that suppression was achieved. However, the experimental procedure required all test birds to be without food from 0900 or 0915 h, and motivation was lowest in the earliest (1000 h) test with qualitative but not quantitative treatments. Hence, there was some evidence that feeding motivation may be partially suppressed with qualitative food restriction; distinction can be made between short-term and longer-term feeding motivation. General activity level (inversely reflected by time spent sitting) was closely correlated positively with both suppression of growth rate and feeding motivation. As a fundamental relationship between feeding motivation and reduction of growth rate was not altered by using qualitative rather than quantitative food restriction, these results support an earlier conclusion (Savory, C.J., Hocking, P.M., Mann, J.S., Maxwell, M.H., 1996. Is broiler breeder welfare improved by using qualitative rather than quantitative food restriction to limit growth rate? Anim. Welfare 5, 105-127.) that broiler breeder welfare is not improved with qualitative restriction methods.