Peter B. Johnsen

Chemical enhancement of feeding for the herbivorous fish Tilapia zillii

Abstract Chemical enhancers of feeding for a herbivorous fish, Tilapia zillii , have been determined by bioassay of substances derived from a model food plant. Feeding enhancement was produced by glutamic acid, aspartic acid, lysine, citric acid and malic acid. Alanine and serine, which were found in previous work to be feeding stimulants for T. zillii , were ineffective as feeding enhancers. Citric acid, when added to a non-preferred diet, will cause an increase in consumption to a level equivalent to that of a most-preferred food. In addition, adding citric acid causes increases in bite size and rate of feeding. T. zillii show a general feeding response to acidic substances; the effectiveness of an enhancer increases as the PH of the substance decreases.

Spatial gradient detection of chemical cues by catfish

Summary1.Unrestrained brown bullhead catfish (Ictalurus nebulosus) were trained to turn toward the higher concentration when two concentrations of a mixture of amino acids were simultaneously flowed over the cutaneous taste epithelium on the right and left maxillary barbels.2.The minimum detectable Weber fraction was dependent upon the stimulus solution concentration with smaller Weber fractions being detected at weaker concentrations. Brown bullheads were capable of detecting a concentration difference of 0.3 Weber fractions at the highest stimulus solution concentration and 0.1 Weber fractions at the lowest.3.Variations in the time-of-arrival of the stimuli at the two barbels, greater than those occurring during normal testing, did not alter the values of the minimum discernable Weber fraction. This indicates that spatial rather than temporal differences in concentration were the basis of these responses.4.Anosmic bullheads were as sensitive to concentration differences as intact fish, indicating that discrimination was made using the taste receptors on the barbels.5.These experiments show that bullheads can compare the intensity of a taste stimulus at two distinct receptor fields and thus define a gustatory chemical space. This ability is a requirement for tropotactic orientation to chemical gradients and suggests that such a mechanism may be important in nature.

Chemical feeding stimulants for the herbivorous fish Tilapia zillii.

Abstract 1. 1. Chemical feeding stimulants for an herbivorous fish, Tilapia zillii have been determined by fractionation and bioassay of substances derived from a model food plant. 2. 2. Stimulation was produced by amino acids; glutamic acid, aspartic acid, serine, lysine and alanine produced the bulk of stimulatory activity. 3. 3. These amino acids are among the most abundant in the test plant, and are markedly different from the amino acids found to stimulate feeding in carnivorous fish. 4. 4. On the basis of these results, a chemically-mediated mechanism of feeding niche separation is postulated.

Behavioral responses of bonnethead sharks (Sphyrna tiburo) to controlled olfactory stimulation

Swimming behaviors of bonnethead sharks (Sphyrna tiburo) were observed in response to chemical stimulation. Large volume (10 ml) samples were introduced into the path of swimming sharks. In still water, tight turning and circling were observed while samples introduced in the presence of a water current elicited a swimming pattern of connected loops moving downcurrent. A headmount attached to the shark allowed small volume (0.5 ml) samples to be directed into the olfactory capsules. Stimulation in still water produced the turning and circling behaviors as observed for the large volume samples and stimulation in moving waters produced the same connected loops pattern. Other experiments confirmed that the small volume samples quickly dilute below threshold and therefore the behaviors observed in response to the 0.5 ml samples are swimming patterns released by the chemical signal but are presumed to be modulated by factors other than chemical cues. Additionally, it was demonstrated that bonnethead sharks can ...

Sex pheromones of the sea lamprey (Petromyzon marinus): Steroid studies.

Pheromone-containing and pheromone-devoid samples of male sea lamprey (Petromyzon marinus) urine were analyzed for the concentrations of nine steroids [dehydroepiandrosterone (DHEA), testosterone (T), dihydrotestosterone (DHT), progesterone (P), androstenedione (A), estrone (E1), estradiol (E2), corticosterone (B), and cortisol (F)] by radioimmunoassay (RIA). Samples analyzed included native urine that had been enzymatically hydrolyzed with mixed β-glucuronidase/sulfatase. Values of the analyses were used to prepare solutions of the individual steroids for bioassay at concentrations which bracketed the urinary concentrations. Results show that only testosterone elicited a preference response in spawning-run female sea lampreys, and in concentrations three to four orders of magnitude greater than those found in active, unhydrolyzed male urine. The possibility that testosterone acts as a pheromone in this species is discussed.

A Solid Matrix Bioassay for Determining Chemical Feeding Stimulants

Abstract Attempts to manipulate the chemical composition of fish feeds and baits to increase their efficacy have required experimental studies to determine feeding preferences for species of interest. This article describes a generally useful assay method in which test stimuli are incorporated into a solid agar matrix. Agar disks are then presented to fish in a two-choice feeding assay. The agar disk assay is simple and inexpensive, requires only small quantities of test materials, and gives direct information about consumption and preference.

Chemosensory Orientation Mechanisms of Fish

In the aquatic environment, solubility rather than volatility is the limiting factor for chemical dispersion, and thus, compounds of wide variety become potential information messengers. Because most bodies of water are in motion, these stimuli and their information can be carried over considerable distances, and animals such as fish, which are very sensitive to chemical stimulation, may exploit this information for many important functions in their life histories. Chemical signals are known to play significant roles in reproduction, homing, feeding, schooling, defense and parent/young interactions of fish.

Molecular Strategies for Improving the Quality of Muscle Food Products

The flavor quality of muscle foods is dependent upon several key premortem factors such as an animal’s age, breed, sex, and nutritional status. While these factors are all involved in the development of the final flavor of a food, additional textural and flavor changes develop both during the period of postmortem aging (Koohmaraie et al. 1988; Ouali 1990) and during cooking and storage of the food (Etherington, Taylor, and Dansfield 1987; Kato and Nishimura 1987; Ouali et al. 1987; Spanier, Edwards, and Dupuy 1988; St. Angelo et al. 1987, 1988).