Muscle fiber number, cross-sectional area, and composition were studied in response to enlargement produced by synergistic ablation in the mouse soleus muscle. The effect of the location of a histological section on the number of fibers that appear in the section was also studied using the mouse soleus muscle. Enlargement was produced in the soleus muscle of 15 male and 15 female mice by ablation of the ipsilateral gastrocnemius muscle. Fiber counts, using the nitric acid digestion method, revealed no difference between control and enlarged muscles in male and female mice. Mean fiber area, determined by planimetry, was 49.1 and 34.5% greater following enlargement in male and female mice, respectively. Increase in muscle weight could be totally accounted for by the increase in fiber area following enlargement. A transformation of type II to type I fibers occurred following enlargement for both sexes. Counts of fibers from histological sections revealed that there was a progressive decrease in the fiber number as the section was moved from the belly to the distal end of the muscle. The results of these studies indicate that muscle enlargement in the mouse soleus muscle is due to hypertrophy of the existing muscle fibers.

Chronic reduction of gravitational load in the rear limbs of rats to simulate the influence of near-zero gravity in skeletal muscles has been shown previously to elicit atrophy in the soleus muscle. Use of this model by the present investigation indicates that soleus atrophy was characterized by a decline in the number of fibers in groups that contained the slow isoenzyme of myosin and which were classified as type I from intensity of staining to myofibrillar actomyosin adenosinetriphosphatase (ATPase) and to NADH tetrazolium reductase. Furthermore total fiber number was not changed, whereas fibers containing the intermediate isoenzyme and those classified as type IIa increased. There results could be explained by either a change in the composition within existing fibers or a simultaneous loss of slow fibers and de novo synthesis of intermediate and fast fibers. Evidence for transformation included an absence of embryonic or neonatal myosin in muscles from suspended rats and the constant fiber number that was unchanged by 4 wk of suspension. Furthermore although fiber areas of both groups of type I and IIa fibers declined during suspension, variability of the fiber areas within each group did not increase.

Four experiments with feed‐trained crappies Pomoxis spp. were conducted to enhance the knowledge of growing crappies as food fish. Two experiments compared growth performance of juvenile Black Crappies P. nigromaculatus and White Crappies P. annularis (1) between fish that were fed two locally available commercial feeds or (2) among fish reared at densities of 0.81, 1.62, 3.25, and 6.50 g/L. No significant difference in growth performance between species was detected. Performance was significantly affected by commercial feed, but survival and feed conversion ratio (FCR) were not. An inverse relationship existed between density and growth variables except final biomass, which had a direct relationship with density; survival rate was not different among density levels. For the third experiment, Black Crappie growth in light‐blue control tanks was compared with growth in environmentally enhanced tanks (150 L) that had top cover structure (TCS), bottom dark coloring (BDC), or a combination of both. Fish growth was not different between control and enhanced tank treatments but significantly differed between the TCS and BDC treatments. In the fourth experiment, growth was compared between hybrid crappies that were fed using 12‐ and 24‐h belt feeders. Fish that were fed by use of the 12‐h belt feeders had improved FCR relative to continuous 24‐h feeding. These experiments demonstrated that crappies can be cultured successfully indoors, with no difference in early growth between species. Additionally, crappie growth could be affected by tank environment and by feeding regimen.

Sunfishes Lepomis spp. are cultivated as sport fish, and recently interest has been shown in culturing them as a food fish based on commercially available feeds that vary in composition according to the life stage of the fish. We evaluated seven commercial larval starter feeds with northern bluegill L. macrochirus macrochirus and redear sunfish L. microlophus in the effort to relate growth performance to diet nutrient composition. The dependent variables were production weight, survival rate, feed conversion ratio, and mean individual weight and length. The proximate composition and fatty acid and amino acid compositions of feeds were related to the dependent variables. Survival rate ranged from 84% to 96% for bluegills and from 15% to 35% for redear sunfish, and individual mean weights ranged from 67 to 238 mg and from 31 to 78 mg for these two species. Relating the compositional analysis of feeds to the dependent variables indicated that isoleucine influenced mean individual weight for both species. Northern bluegill growth performance suggested a negative correlation with carbohydrates, while redear sunfish growth indicated a positive relationship with energy. This study shows that commercial starter feeds can vary greatly in how they influence sunfish growth performance. Further study is needed to determine what dietary variables, including factors other than nutrient profiles, are most important.