Stunting is widespread among brook trout Salvelinus fontinalis populations in high alpine lakes in the eastern Sierra Nevada, California. Due to their small size and poor condition, stunted brook trout are undesirable as sport fish. In the same area, a few lakes contain large brook trout. Population density was the primary difference between lakes with different sized fish. I hypothesized that in lakes with large fish the food ration per individual was sufficient and that in lakes with stunted fish the food ration was the limiting factor. I carried out removal experiments on eight brook trout populations to test the hypothesis (1) that fish size is inversely related to population density, and by that evaluate density reduction as a means of improving growth in stunted brook trout. I considered seven additional hypotheses regarding the relationships between brook trout population density and growth, fecundity, and recruitment: (2) growth response is proportional to density reduction; (3) growth response is inversely proportional to pre-reduction density; (4) growth responses of juvenile and senescent fish are less affected by density reductions than mature, reproductively active fish; (5) growth response to density reduction is inversely proportional to lake elevation; (6) fish size is proportional to angling pressure; (7) fecundity response is proportional to the reduction in population density; and (8) recruitment response is inversely related to density. I used gillnets to simultaneously remove part of the population and estimate population size through catch depletion methods that allow variable catchability. Catchability varied with lake size and with abundance, increasing as population abundance declined. Increased catchability can be explained by behavioral responses. I measured and aged 16000+ brook trout from 71 lakes, 9800+ from the eight experimental lakes. I validated annual structures on otoliths using a fluorochrome mark. For the experimental lakes, I back-calculated previous population sizes using estimates of number at age in 1989, catch at age in 1987-1988, and survival rates at age estimated from catch data collected in 1987-1989. I converted population estimates into density estimates of fish and biomass per lake surface area and volume. I tested hypothesis 1 by using survey data from 61 populations and by experimentally manipulating density in eight populations. The survey data suggested that size differences between populations of brook trout are a function of population density. Results from the eight removal experiments showed that fish size was inversely related to population density, though the increases in fish size were minor. The relationship between change in length and weight was roughly proportional to the change in density (hypothesis 2). Hypothesis 3 suggested differences in the severity of stunting in alpine lakes, and that the growth response of severely stunted populations would be more pronounced than the response of less stunted fish in lower density populations. The result was opposite; the growth response in lower density populations was greater than the response in higher density populations, suggesting that the growth response may have been proportional to the pre-reduction density. Hypothesis 4 suggested that the growth response for juvenile brook trout would be less than that for the pre-senescent adult population. The results refuted the juvenile portion of hypothesis 4: response for juveniles was greater than the response of the adults, perhaps because of greater recuperative abilities in young fish. The data supported the hypothesis that the growth response would be diminished in older fish. There was no relationship between elevation and growth response (hypothesis 5). Sport fishing had little effect on the growth of brook trout populations (hypothesis 6). Heavily fished populations were also stunted. Stunted brook trout had fecundities similar to non-stunted brook trout of the same size (hypothesis 7). Individual fecundity did increase in response to density reduction, but no more than would be expected from the increase in size. In several populations mean absolute fecundity decreased with age. Ovary weight was maintained by an apparent increase in mean egg size in older fish. The recruitment response varied between lakes (hypothesis 8). Recruitment did increase, likely in response to reduced cannibalism or competition, but I also found recruitment failure at the highest levels of density reduction. Strong cohorts were produced by increased juvenile survival rather than increased population fecundity, since population fecundity had decreased due to removal of most of the adult population. In one lake with almost no recruitment, densities remained low and fish weight doubled. For density reduction to be an effective means of increasing fish size, recruitment must be inhibited. / Science, Faculty of / Zoology, Department of / Graduate

by Chow Cheuk Yi. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1989. / Bibliography: leaves 179-192.

No description available.

I assessed the relationship between growth of fish in situ, food consumption, prey type and fish community descriptors in 12 perch (Perca flavescens) populations exhibiting a 1.8 to 10-fold range in growth rates. / Perch growth rates consistently decreased as fish numerical density increased (r$ sp2$ = 0.60) and increased as feeding levels increased (r$ sp2$ = 0.30). I found no significant relationship between the quantity of food consumed by perch and fish numerical density. Prey quality explained from 50 to 95% of the observed variability in growth but was related to fish numerical density in only one of the 3 perch age classes studied. / I conclude that non-exploitative interactions (operating through increased activity costs) is a more viable explanation for the among-population variability in fish growth rates than is exploitative competition (yielding decreases in the total quantities of food consumed and/or prey quality).

In aquaculture, a thorough knowledge of the specific environmental requirements of a species is needed in order to maximize growth rate and survival. There is a paucity of data regarding the fundamental environmental requirements for the ongrowing phase of clownfish juveniles. This prompted the design of three experiments to determine the best feeding regimen, temperature and stocking density that maximize growth and survival of Amphiprion percula. Ration size and feeding frequency are important factors for optimizing fish growth during the juvenile grow-out phase. A factorial growth trial was conducted to determine the effect of feeding frequency and ration size on the growth of juvenile clownfish (Amphiprion percula).Three feeding frequencies (1, 2 and 3 times daily) and six rations (2,4,6,8, 10 and 12 % body weight per day (BW.day⁻¹)) were used to test the growth response over a twelve week period. Non-linear regression analysis on the effect of ration, independent of feeding frequency, on growth resulted in a significant (n = 36; r² = 68.7) parabolic model: In y = -0.0302x² + 0.5159x + -4.4377. Maximum growth corresponded to a ration of 8.5% BW.day⁻¹. Survival as a function of ration was significantly lower at 2% BW.day⁻¹. Data were further examined with Analysis of CoVariance (ANCOVA) to determine the effect of ration on growth at each feeding frequency. The combination revealed a maximum growth rate when the fish were fed a ration of 10% BW.day⁻¹ divided into two equal meals. The required ration per meal to maintain maximum growth was also found to decrease as feeding frequency increased. The determination of the best temperature for growth is of great importance due to the direct relationship between fish metabolism and temperature. The thermal preferendum of A. percula has already been estimated at 26 ± 0.7°C but it is not known whether this closely approximates the temperature for maximum growth. Sixteen tanks were set to different temperatures ranging between 21.5 and 30.2 °C. Ten juvenile A. percula were placed in each tank and growth was measured fortnightly over the course of the 10 week experiment. Non-linear regression analysis resulted in significant models for fish length (y = -0.0005x² + 0.00267x - 0.0338; r² = 56.7, n = 11) and weight (y= -0.00016x² + 0.0084x - 0.1073; r² = 61.6, n = 11). These models predict that maximum growth would be at 27.7 and 27.1 °C for length and weight, respectively. Temperature, over the range tested, had no apparent effect on survival. There was no significant difference between the temperatures for maximum growth and the preferred temperature. The effect of stocking densities ranging from 0.2 fish.L¹ to 4.0 fish.L⁻¹ on growth were used in the third experiment. The fish were fed to satiation twice daily and growth was measured fortnightly throughout the 8 week experiment. No effects on growth, survival or coefficient of variation were found within the range of stocking densities tested.

No description available.

Highly unsaturated marine lipids are common ingredients in salmon diets, and they are prone to oxidative change. The present study was undertaken to examine the growth and health of coho salmon (Oncorhynchus kisutch) fed diets containing herring oil autoxidized to different degrees. The efficacy of dietary vitamin E in ameliorating any adverse effect on performance was investigated. Herring oil was oxidized to one of two levels (relative to a control) by aeration and mild heating (40 °C). Peroxide values and iodine numbers were recorded to monitor the extent of autoxidation. Depletion of dietary linolenic acid series fatty acids (n3FA), and the labile vitamins A, C, and E, provided further evidence of the progress of lipid oxidation. The mean initial body weight was 5.1 g/fish, and growth (weight and length) was measured at 3 or 6 week intervals for 28 weeks. Experimental diets contained 16.8% lipid, primarily as herring oil. One diet was made with corn oil replacing herring oil, and another contained a combination of low and highly oxidized oil. Vitamin E (as dl-ɑ-tocopheryl acetate) was added at either 30 IU/kg dry diet or 1000 IU/kg dry diet. At 23 weeks, 1/3 of the fish were vaccinated against vibriosis. At 28 weeks the fish were twice challenged with live Vibrio sp. Immunocompetence was estimated by mortality and by plasma agglutination. The inclusion of autoxidized herring oil reduced the nutritive value of the diets. The poorer growth and feed efficiency of fish fed diets containing oxidized oils appears to have resulted from a combination of appetite suppression and nutrient deficiency. The relative importance of these factors in influencing growth and feed efficiency depended upon the extent of the oxidation, with appetite suppression being most apparent in fish fed diets containing moderately oxidized oil. Dietary supplementation with a high level of vitamin E had no ameliorating effect on growth or feed efficiency. Health and immunocompetence were not impaired by the presence of oxidized dietary lipid, or improved by the addition of vitamin E. / Land and Food Systems, Faculty of / Graduate

A feeding experiment was designed to examine how fish growth rates are affected by the size abundance of pelagic zooplankton. Juvenile chinook salmon, Oncorhynchus tshawytscha , were raised in 90 m³ mesh enclosures in Saanich Inlet, B.C. The enclosures permitted ample water and zooplankton circulation while retaining 5-6 gram juvenile salmon. The enclosed fish grew at an average rate of 1.8% wet body weight/day for a six week experimental period. Weekly growth rates ranged from 3.9%/day while food was abundant, to -0.5%/day when food was scarce. Several analytical methods were used to establish a relationship between fish gr.owth and the size and abundance of zooplankton in the enclosures. There is a strong relationship between the fish growth rates and the abundance of 1.4-4.5mm prey. Rates of successful search vary directly with the size and inherent contrast of a prey item. A minimum rate of successful search of 2.0m³/hour was estimated from a functional response curve for salmon feeding on 1.4-4.5mm zooplankton. This value is discussed in relation to a salmonids physical capabilities and results from previous field studies and tank experiments. Daily growth increments on the otoliths of the enclosed fish were examined with respect to daily variations in water temperature and zooplankton abundance. Extremes in food abundance appear to have a significant and consistent effect on the spacing of the growth rings. However, water temperatures would have to be kept constant in order to establish any closer relationship between food abundance and otolith growth rings. / Science, Faculty of / Zoology, Department of / Graduate

A series of five experiments were carried out to determine the effect of supplementary enzymes on growth performance and feed utilisation of juvenile gilthead sea bream, Sparus aurata, fed diets in which soybean meal (S8M) partially replaced fish meal (FM). In the first of these experiments the addition of cocktails containing 1 g/kg low pH active protease and 1 glkg a-galactosidase or 1 glkg high pH active protease and ] glkg a.-galactosidase to a 320 glkg SBM, 260 glkg FM pressed diet were both found to significantly (P<0.05) improve performance of fish fed these diets compared to fish fed the unsupplemented diet and a 320 glkg FM, 220 glkg SBM diet. This improvement in performance was not obtained when fish were fed 440 glkg SBM, 230 glkg FM diets with the same enzyme combinations. In some parameters performance of fish decreased as the SBM level in the diets was increased. The significant improvements observed in Experiment 1, with addition of enzyme cocktails to the 320 glkg S8M diet, were not repeated in any of the subsequent experiments. The second experiment was aborted due to ahnormal feeding hehaviour of the fish. In the third experiment, in which the enzymes employed in Experiment 1 were used individually at 1 glkg in 320 glkg SBM diets, no significant differences in specific growth rate (SGR), food conversion ratio (FeR) or protein efficiency ratio (PER) were noted in comparison to fish fed the unsupplemented diet. This was also the case with fish fed diets to which the two enzyme cocktails had been added at enzyme inclusion levels of 0.5 glkg each. Although no significant differences were found, feeding the diet with low pH protease alone appeared to increase performance compared to fish fed the unsupplemented diet, and the results of fish fed diets with high pH protease alone or with a.-galactosidase alone indicated that there was a decrease in performance compared to fish fed the unsupplemented diet. In Experiment 4 fish fed 320 g/kg SBM diets with 0.5, 1.0 and 1.5 g/kg low pH protease showed similar SGRs, FCRs and PERs which appeared to show an improved performance (although not significantly so) compared to fish fed diets with 1.0 glkg agalactosidase used together with either 0.5 or 1.0 glkg low pH protease. In the fmal experiment fish were fed 320 g/kg SBM extruded diets to which 0, 0.33, 0.66, 1.00 and 1.33 glkg of low pH protease had been added. Although no significant differences in SGR, FCR or PER were obtained, fish fed the diets containing 0.66 and 1.33 glkg protease appeared to improve performance compared to fish fed any of the other diets or a diet containing 320 glkg FM and 220 glkg SBM. Fish fed the other 320 glkg SBM supplemented dietc; gave similar results. A histological study of the position of nuclei in hepatocytes and the presence of fat globules around hepatopancreatic tissue in liver samples taken from fish fed the various experimental diets failed to show any relationships with either SBM level or enzyme inclusion in the diet. A series of analyses on the distribution of activities of six enzymes in the digestive tract of sea bream indicated that relative activities differed from one enzyme to another and from one region to another. In an investigation into the variation of pH in various parts of the digestive tract after one or two feeds, it was observed that within the first 24 hours after feeding the pH in the stomach decreased to a minimum value of 2.5 and the pH in the rest of the intestine varied between 6.5 and 7.7. vi From a series of gastric evacuation trials which were performed, it was found that the time of day sea bream were fed a meal influenced the gastric evacuation rate, with fish fed in the afternoon taking longer to evacuate the meal than fish fed a similar meal in the morning. Doubling the size of a meal did not double the gastric evacuation time. Instead, the time to evacuate a given percentage of the larger meal only increased by 1.4 and 1.6 times in fish fed the pressed and extruded feeds respectively compared to fish fed the smaller meal. When the sea bream were fed multiple meals it was found that the evacuation rate of an earlier meal was increased by a subsequent meal. A series of trials investigating the distribution in consumption of a population of sea bream fed a single meal indicated that there was a wide variation in the amount of food consumed by each fish in the population and it was observed that even fish of the same size consumed very different quantities of food. Before any definite conclusions can be drawn regarding the use of the three enzymes tested in these experiments to improve growth and feed utilisation in FM-substituted diets, further investigations need to be carried out in an attempt to obtain more significant results. This thesis has shown that additional research into the mode of action of these enzymes is required as well as studies into how the digestive physiology of the sea bream may affect the use of these (and other) supplementary enzymes.

Relative weight (Wr) of yellow perch (Perca flavescens) was evaluated for fish collected from the Indiana waters of Lake Michigan in June, July and August of 1976 and 1984-1991. Computation of Wr was completed for individual fish in 20 mm intervals over the size range from 100-219 mm using Wr = (W/Ws) 100 where W=weight of a fish in grams and Ws=standard weight for a fish of the same length. Length was highly correlated with weight in all years for males, females and sexes combined (r=0.97-0.99). Distributions of predicted weights for fish at 130 mm and 250 mm were at or near modes of the populations used to construct the Ws equation for yellow perch. Relative weights consistently decreased with increasing size in all years for males, females and sexes combined. Using 1976 length-weight data when the yellow perch population was sparse and fast growing as a standard (100%) for comparison, relative condition factors (Q) increased with increasing size in some years and decreased with increasing size in others for males females and sexes combined and it did not appear to be length dependent. When comparing Wr at 100 mm and 200 mm by sex and month, f hales had higher Wr than males at 100 mm in seven of nine years in June, six of nine years in July and only four of nine years in August. Female fish also had higher Wr than males at 200 mm in eight of nine years in June and July and six of nine years in August. There appeared to be no consistent pattern or trend of Wr increasing or decreasing by month for males, females or sexes combined. When Kn was evaluated for 100 mm and 200 mm fish by sex and year, male fish had higher Kn than females at 100 mm in all eight years. Male and female fish at 200 mm were more similar; male fish had higher Kn in three years, lower Kn in three years and equal Kn in two years. No relationships were found at 200 mm comparing Wr or Kn and CPE (quality/ h) for males (r=0.43; r=0.42), females (r=0.12; r=0.13) or sexes combined (r=0.28; r=0.22). Simple linear correlations of proportional stock density (PSD) with Wr and Kn revealed relative weights increased with PSD for 100 mm (r=0.51) and 200 mm (r=0.72) fish. Relative condition factors also increased with PSD for 100 mm fish, however the relationship was weak (r=0.30) but a strong correlation was found between Kn and PSD (r=0.81) for 200 mm fish. Based on these results, it appears that either Kn or Wr may be used inassessing the condition of yellow perch from the Indiana waters of Lake Michigan. / Department of Biology