Douglas B. Noltie

Use of Compensatory Growth to Double Hybrid Sunfish Growth Rates

Abstract We studied the use of compensatory growth (CG) to grow fish larger than control fish that were fed every day without restriction. Five treatment groups of 10 juvenile hybrid sunfish (F1 hybrid of female green sunfish Lepomis cyanellus × male bluegill L. niacrochirus) received repeating cycles of no feeding and refeeding; fixed no-feed periods of either 2, 4, 6, 10, or 14 d distinguished the treatment groups. No-feed periods elicited the CG state and were immediately followed by days of ad libitum refeeding. Refeeding periods within each treatment group (D2, D4, D6, D 10, or D14) were continued until mean daily food consumption by fish no longer exceeded that of controls fed ad libitum every day (i.e., ad libitum refeeding was continued for as long as hyperphagia persisted, then another no-feed period began). Fish in two groups, D2 and D 14, consumed more food and significantly outgrew controls by 2 and 1.4 times, respectively, in 105-d experiments. Gross growth efficiency (GGE, fish weight gained...

Effect of feeding frequency on food consumption, growth, size variation, and feeding pattern of age-0 hybrid sunfish.

Four treatment groups of age-0 hybrid sunfish (female green sunfish Lepomis cyanellus×male bluegill L. macrochirus) were fed to satiation at one of four frequencies (one, two, three or four meals per day) for 30 days. Fish fed three and four times daily showed the greatest consumption and growth rates; food conversion ratios did not differ among the four treatments (P>0.05). Because growth and food conversion were not enhanced when feeding was increased from three to four times daily, the optimal feeding frequency for growth was considered to be three times per day. However, the extent of inter-individual size variation (% change in CV) declined with increasing number of daily feedings (P<0.05), suggesting that more frequent feeding may produce fish of more uniform sizes. Daily feeding patterns also changed in response to feeding frequency, indicating that when fish are fed at a particular frequency, knowledge of feeding pattern is necessary so that appropriate food amounts can be supplied at each provisioning. Our results suggest that an optimal feeding frequency should be determined not only on the basis of growth and food conversion efficiency, but also according to influences of daily feeding pattern and the desire to achieve size uniformity.

An in vivo model fish system to test chemical effects on sexual differentiation and development : exposure to ethinyl estradiol

Abstract A model system was characterized which may be used as an in vivo screen for effects of chemicals or environmental mixtures on sexual differentiation and development of reproductive organs and gametes. We evaluated the effects of a model environmental estrogen, ethinyl estradiol (EE 2 ), on the d-rR strain of medaka, Oryzias latipes , using a nano-injection exposure. Gonad histopathology indicated that a single injection of 0.5–2.5 ng EE 2 /egg can cause phenotypic sex-reversal of genetic males to females. Sex-reversals could be detected as early as 7 days post-hatch. Sex-reversed males had female-typical duct development and the secondary sex characteristics we measured were generally consistent with phenotype, with the exception of a few EE 2 -exposed XX and XY females which possessed ambiguous anal fins. Using discriminant analysis, we determined that the presence or absence of the secondary sex characteristic, a dorsal fin notch, was a very reliable indicator of gonadal sex. No instances of gonadal intersexes were observed. Ethinyl estradiol also appeared to reduce growth but not condition (weight-at-length) and exposed XX females appeared to have a higher incidence of atretic follicles relative to controls. Our results suggest that estrogenic chemicals may influence sexual differentiation and development and that the medaka model is well suited to assessing these effects.

Group holding impedes compensatory growth of hybrid sunfish.

An earlier study with a repeating no-feed/refeed schedule (D2 schedule) elicited compensatory growth (CG) in age-0 hybrid sunfish (F1: female green sunfish, Lepomis cyanellus×male bluegill L. macrochirus) held individually and fed ad libitum on feeding days. Weight gain under these conditions exceeded that of daily-fed controls. The present study sought to determine whether similar growth improvement would result when hybrid sunfish were held in groups and fed to satiation on the D2 schedule. In Experiment 1, age-0 hybrid sunfish were held in groups of 10 fish per 25-l chamber at 24°C and fed four times daily to apparent satiation on feeding days. Under this regime, fish fed according to the D2 schedule gained less weight than the controls (P<0.10). Experiment 2 was run in an effort to duplicate the results of the previous study. When age-0 fish were held individually at 24°C and fed ad libitum on feeding days, those fed on the D2 schedule gained significantly more weight (P<0.10) than the controls. These results indicate that group holding in combination with satiation feeding impedes the full expression of the CG capacity of hybrid sunfish. The major impediment under group holding may be the negative effects of social interactions on food consumption and growth efficiency.

Variation in food consumption, growth, and growth efficiency among juvenile hybrid sunfish held individually

Abstract Daily food consumption, growth, and gross growth efficiency (GGE) were studied in juvenile hybrid sunfish (female green sunfish, Lepomis cyanellus×male bluegill, Lepomis macrochirus) fed ad libitum and held individually for 112 days. There were substantial inter-individual differences in food consumption; mean specific daily ration differed significantly (P

Testing Bioenergetics Models under Feeding Regimes That Elicit Compensatory Growth

Abstract We tested bioenergetics model predictions of fish growth and food consumption under feeding regimes that elicited compensatory growth (CG) responses and for control fish fed ad libitum daily. Three treatment groups of seven juvenile hybrid sunfish (F1 hybrid of female green sunfish Lepomis cyanellus × male bluegill L. macrochirus) received repeating cycles of no feeding and refeeding; fixed no-feed periods of either 2, 4, or 14 d distinguished the treatment groups. The no-feed periods induced CG and were immediately followed by days of ad libitum refeeding. The refeeding periods for each treatment group were continued until the groups mean daily consumption no longer exceeded that of the controls, after which another no-feed period began. Bioenergetics model predictions of cumulative consumption and fish weight in 105-d experiments were not significantly different from observed values in the control group (2–3% model error). However, the model underestimated cumulative consumption (18–25%) and o...

Effects of methyl testosterone exposure on sexual differentiation in medaka, Oryzias latipes

Studies were conducted to characterize effects of a known androgen on sexual differentiation and development of medaka, Oryzias latipes (d-rR strain), at two life stages. Embryos were injected with graded doses of methyl testosterone (MT) prior to epiboly. The occurrence of sex-reversal, and the gonadosomatic index (GSI) were evaluated in adults. Primary germ cells were counted and gonad volumes calculated for larvae to determine if sex-reversal could be detected at an early life stage. Sex-reversal of genetic females to phenotypic males was observed at both life stages. The GSI for phenotypic females was greater than for phenotypic males, while the GSI in XX males was similar to XY males. MT appeared to reduce the GSI of XX females exposed to MT but not sex-reversed. Our results indicate that embryonic exposure to androgens influences sexual development in medaka. Utilizing the d-rR strain of medaka allows detection of an effect as early as 2 weeks after chemical exposure making this a useful tool to screen chemicals for effects on sexual differentiation.

Effects of Social Interaction on Growth of Juvenile Hybrid Sunfish Held at Two Densities

Abstract The effects of competitive social interaction on cumulative food consumption (CC), absolute growth rate (AGR), gross growth efficiency (GGE), and development of interindividual weight variation were quantified for juvenile hybrid sunfish (F1: Female green sunfish Lepomis cyanellus × male bluegill L. macrochirus) held in low-density (5 fish in 25 L) and high-density (20 fish in 25 L) groups for 50 d. Individually held hybrid sunfish without social interaction were used as controls. All groups were fed a commercial diet to apparent satiation three times daily. Mean CC, AGR, and GGE declined 7% and 24%, 21% and 34%, and 14% and 15%, in the low- and high-density groups, respectively, relative to controls. Patterns of declining CC and GGE with increasing fish density indicated that elevated activity and stress from social interaction caused much of the growth decline at the low density, while reduced food consumption caused the additional growth loss at the high density. Coefficients of weight variati...

Demography, Growth, and Reproductive Allocation in Stream-Spawning Longnose Gar

Abstract The demography of breeding populations of the longnose gar Lepisosteus osseus has heretofore remained unstudied. During the summer of 1992, longnose gars were captured en route to spawning sites in Weaubleau Creek, a tributary of Missouris Harry S. Truman Reservoir. To characterize the spawners, individual age, growth, and morphometric data were obtained. The spawning population consisted of smaller, younger males and somewhat fewer older, larger females. As expected, Weaubleau Creek spawners exhibited heightened condition values relative to other longnose gar populations assessed outside the breeding season. Females displayed greater backcalculated total lengths at age and higher growth rates than males, with these differences being manifested early in life. Examination of individual yearly growth increments suggested that most longnose gars in Weaubleau Creek were annual spawners. Females made substantial investments of time and biomass in reproduction, as their gonad weight–body weight relati...

Examining Neosho Madtom Reproductive Biology Using Ultrasound and Artificial Photothermal Cycles

Abstract We examined whether extended laboratory simulation of natural photothermal conditions could stimulate reproduction in the Neosho madtom Noturus placidus, a federally threatened species. For 3 years, a captive population of Neosho madtoms was maintained under simulated natural conditions and monitored routinely with ultrasound for reproductive condition. Female Neosho madtoms cycled in and out of spawning condition, producing and absorbing oocytes annually. Internal measurements made by means of ultrasound indicated the summer mean oocyte size remained consistent over the years, although estimated fecundity increased with increasing fish length. In the summer of 2001, after 3 years in the simulated natural environment, 13 out of 41 fish participated in 10 spawnings. Simulation of the natural photothermal environment, coupled with within-day temperature fluctuations during the spring rise, seemed important for the spawning of captive Neosho madtoms. The use of ultrasound to assess the reproductive ...