Dale F. Leavitt

An evaluation of gravimetric and inert marker techniques to measure digestibility in the American lobster

Abstract Two markers routinely used in digestibility studies, chromic oxide and the generic moiety of total ash, were tested in feeding experiments with adult American lobsters ( Homarus americanus Milne Edwards) to determine if chromic oxide would deter voluntary intake and if ash would be absorbed in the gastrointestinal tract. Chromic oxide incorporated into a test diet at levels up to 1% did not suppress dry matter intake. Observations of pigment excretion patterns in the feces proved there was a differential passage rate of the chromium pigment. It is not valid to use chromic oxide as an indigestible marker to measure apparent digestibility in the American lobster. Total ash as an indigestible tracer was unsatisfactory as it appeared to be absorbed through the gut wall, as measured gravimetrically by the difference in ash intake compared with fecal ash. This resulted in a significant underestimation of apparent digestibility when comparing an ash-ratio measurement with a gravimetric measurement of digestibility. It was concluded that gravimetric measurement of apparent digestibility is the method of choice.

Studies on the Mineral Requirements of the Adults American Lobster

Abstract In a series of laboratory and field studies, the effects of dietary mineral supplements were tested on adult lobsters (Homants americanus). Both semipurified diets and diets formulated from commercial ingredients were used. Results of these studies indicated that the optimum ratio of calcium and phosphorus (Ca:P) for adult lobsters was about 1:1, which agrees with optimum levels determined previously for juvenile lobsters. Results also indicated that added mineral supplements are of no particular benefit to adult lobsters in diets formulated for commercial use in pounds, as long as the ash present in the commercial ingredients has a Ca: P ratio near 1:1.

A refractometric method of determining serum protein concentration in the American lobster

Abstract A rapid simple method of quantitating serum protein concentration in lobster hemolymph was developed using a Uricon ® specific gravity refractometer. A correlation coefficient of r = 0.985 (n = 21) was observed in calculating serum protein concentration, Y = 5449.417X – 7295.321 ( Y = serum protein concentration (mg/ml), X = refractive index). This procedure provides a nondestructive field method to assess a lobsters physiological state without returning samples for laboratory analysis.

A rapid technique for preparing microorganisms for transmission electron microscopy.

A rapid and efficient method of preparing microorganisms for transmission electron microscopy is reported. In developing the method Salmonella, streptococcal, and protozoal specimens were fixed with glutaraldehyde. After fixation cells are collected on a membrane filter, washed with buffer, postfixed with osmium tetroxide, then washed with distilled water and stained en bloc with uranyl acetate. Specimens are dehydrated using a graded series of acetone and then infiltrated with graded mixtures of acetone and Spurr embedding medium. Finally the membrane filter is cut into small pieces and embedded in fresh embedding medium polymerized in polyethylene capsules. By collecting and processing the specimens on membrane filters, numerous centrifugations are eliminated from standard procedures. The use of a low viscosity embedding medium allows for rapid infiltration and embedding of the specimen. Using this technique microbial specimens can be sectioned after less than 4 hours preparation.

The Effect of Aerococcus viridans (var.) homari on the Oxygen Binding Capacity of Hemocyanin in the American Lobster (Homarus americanus)

Abstract The effect of gaffkemia (Aerococcus viridans) infection on the oxygen binding capacity of the hemocyanin component of the American lobsters hemolymph was examined both in vivo and in vitro. Spectrophotometric and electrophoretic examination of the hemocyanin indicated that accompanying gaffkemia infection was a 50% reduction in the oxygen binding capacity of the hemocyanin. Serum protein levels were unaffected by the infection. In vitro growth of A. viridans in lobster sera resulted in similar findings. Death from gaffkemia may be a result of hypoxia arising from bacterial impairment of the lobsters respiratory exchange system, rather than a result of nutrient depletion as has previously been reported.

A DESCRIPTION OF THE MUSCLE NET SURROUNDING THE DIGESTIVE EPITHELIUM IN THE MIDGUT GLAND OF THE LOBSTER HOMARUS AMERICANUS

The organization of the muscle cell layer surrounding the tubules of the midgut gland in Homarus americanus was examined with transmission and scanning electron microscopy. This layer contains a uniform network of broad circular myofilaments interconnected by smaller longitudinal connectives. The primary means of constriction of the lumen of the tubule appears to be by contraction of the circular muscle fibers. The longitudinal myofilaments may provide both structural support and a means for conducting the contractile impulse along the tubule. The decapod hepatopancreas, or midgut gland, is a multilobed organ comprised of numerous blindly ending tubules, connected by a graduated series of collecting ducts. The collecting ducts coalesce into two main ducts which articulate at the pyloric-intestinal junction. As the primary organ for digestion and absorption of nutrients, both digestive enzymes and the products of digestion are moved through the tubules; the food brei moves from the stomach to the tubules and the enzymes and digestive waste products return from the tubules to the stomach. In a general sense, the midgut gland may be equated to the vertebrate small intestine with associated digestive organs, while the true decapod intestine may be equated with the large bowel. Although Gibson and Barker (1979) have published a thorough review on the hepatopancreas, including the basic cell types, sequence of digestive epithelial cell development, and enzymatic activity of the cells involved in both extracellular and intracellular digestion, the mechanism for moving the enzymatic secretions out and the food solution into the tubules of the hepatopancreas is poorly known and often casually dismissed. For example, Stanier et al. (1968) described only a discontinuous stellate network of contractile fibrils around each tubule of Carcinus maenas, and Young (1959) did not mention muscular activity associated with the hepatopancreas of Penaeus setiferus. The musculature associated with the tubules of the midgut gland in Astacus fluviatilis were reported as a series of parallel circular fibers of striated muscle with smaller longitudinal connectives (Pump, 1914). The striated muscle found in the hepatopancreas of crayfish was described as tonic muscle (Loizzi, 1971). The contractile function of tonic invertebrate striated muscle can be equated to that observed in vertebrate intestinal smooth muscle (Prosser, 1973). Van Weel (1974) speculated that the action of the muscle fibers surrounding each tubule of the midgut gland was similar to the squeezing and releasing of a rubber syringe during filling and emptying. This study examines the musculature around the tubule of the midgut gland in the American lobster Homarus americanus, confirming Pumps (1914) work at the level of scanning electron microscopy and provides indirect evidence for a peristaltic transport mechanism to move materials within the tubules of the hepatopancreas.

A comparison of techniques for the measurement of growth in adult lobsters

Abstract Four non-destructive measures of growth (wet weight in air, wet weight in water, displacement volume and carapace length) were correlated to two destructive measures of growth (dry weight and total body protein level) in adult American lobsters ( Homarus americanus ). All non-destructive parameters were significantly ( P

Photoelectric measurement of lobster (homarus americanus) response to feed attractants

Abstract The apparatus described was designed to measure the speed and direction of lobster response to feed attractants with minimal observer influence on the test animal. Lobster activity was monitored in an 84 × 10 × 10 in (213 × 25 × 25 cm) plexiglas tank based on interruption of photoelectric cells. Impulses from the photocells trigger the pens of a 6-channel event recorder. During its operation the apparatus is covered with an opaque plastic sheet. Lobster behavior was such that the animals always settled in one of the chamber ends and the test material could be injected at the far end. The lobsters responded to a variety of test materials.