Modification of olfactory-related behavior in juvenile Atlantic salmon by changes in pH

The hypothesis that low pH modifies the response of salmonids to certain olfactory stimuli was tested. An interactive video-computer system was used to monitor the behavior of juvenile Atlantic salmon (Salmo salar). At a pH of 7.6, animals were attracted to glycine and avoidedL-alanine. These effects were dose-dependent, with a threshold of 10(-7) M. The response of the fish to both amino acids changed when the pH of the test chamber was gradually lowered from 7.6 to 5.1; they became attracted toL-alanine and indifferent to glycine. These effects were reversible with a return to pH 7.6. Our findings suggest that acid rain may contribute to reductions in salmonid populations in acidified rivers by impairing the recognition of olfactory cues by salmon during their spawning migration.

Behavioral responses by migratory chum salmon to amino acids in natal stream water

We propose that amino acids in natal stream water have Important roles in Pacific salmon homing. This study hypothesized that amino acids found in natal stream water have a role in the ability of mature male chum salmon (Oncorhynchus keta) to home to the Osaru River (OR), Hokkaido, Japan. Behavioral experiments were conducted in a two-choice test tank using various combinations of control water (natural Toya Lake water; NLW and three artificial stream waters using amino acids: 1) artificial OR water (AOR); 2) AOR without L-glutamic acid, the major amino acid in OR water (AOR-E); and 3) artificial water matching another stream (ALS) that had much higher amino acid concentrations than OR. In behavioral tests, the fish did not select between AOR and AOR-E, but still chose AOR over NLW, AOR-E over NLW, and AOR over ALS. These results suggest that migratory male chum salmon respond to amino acid mixtures in their natal stream water and appear to be affected by multiple amino acids.

The sense of scents: olfactory behaviors in the zebrafish

The olfactory sensory system is perhaps the most intriguing of the sensory systems making up the peripheral nervous system. Understanding how olfactory sensory stimuli result in behaviors relevant to the animal is made complicated by the fact that olfactory stimuli are more difficult to quantify than light and sound stimuli. Furthermore, in all vertebrates the olfactory sensory neurons regenerate throughout life, presenting a fascinating problem of how both the functional repertoire of olfactory sensory neurons and fidelity of connections to the central nervous system are maintained. Olfactory behaviors are crucial for feeding and reproduction and the olfactory information essential to these behaviors appears to be processed separately in distinct regions of the central nervous system. Zebrafish represent an excellent model system in which the strength of genetics and development can be combined with neuroethological techniques to unravel the mechanisms underlying olfactory behaviors in vertebrate animals.

Effects of phenoxyethanol on the innate immune system of gilthead seabream (Sparus aurata L.) exposed to crowding stress

Phenoxyethanol is routinely used in seabream aquaculture to minimise fish stress response despite the secondary negative effects which have been observed. In this study, two different doses (60 and 200 microl/l) of phenoxyethanol, sedative and narcotic, were tested for their ability to reduce the stress caused in gilthead seabream (Sparus aurata L.) by crowding. Blood glucose and serum cortisol concentrations were measured as stress indicators. In order to study the effects of the treatment on the innate immune system of crowded specimens, two parameters of the innate immune response, serum complement activity and phagocytosis, were assessed. The results show that anaesthesia itself produced a stress response in the fish and affected the immune system, although the effects were greater with the narcotic dose. When the effects of anaesthesia on crowded fish were analysed, the results pointed to a slight reduction in stress as a result of the sedative dose of phenoxyethanol (lower increase in cortisol and lower reduction in phagocytosis). However, additive negative effects were seen in crowded fish when the narcotic dose of phenoxyethanol was used. Since the use of phenoxyethanol is a common practice in aquaculture, the significance of the results should be considered.

Effects of four anaesthetics on the innate immune response of gilthead seabream (Sparus aurata L.)

Anaesthesia may depress the immune system in mammals, but there is no available information on this topic in fish. In the present work, four anaesthetics that are used in aquaculture, MS222 (0 19 mM), benzocaine (0.21 mM), 2-phenoxyethanol (16 mM) and quinaldine sulphate (0.083 mM), were tested in order to observe their effects on the gilthead seabream (Sparus aurata L.) innate immune system. The results showed that the four anaesthetics produced increased blood glucose levels after an hour. In addition, benzocaine and 2-phenoxyethanol depressed complement activity and phagocytosis, while MS222 and quinaldine sulphate did not. Some anaesthesia is a common practice in aquaculture, the data obtained should be taken into account to avoid possible immunodepression in farmed fish.

Inhibitory effect of anaesthesia with 2-phenoxyethanol as compared to MS222 on glucose release in isolated hepatocytes from rainbow trout (Salmo gairdneri)

1. Glucose production by freshly isolated hepatocytes from rainbow trout was studied after anaesthesia of the animals with 2-phenoxy ethanol (2PE) or tricaine methanesulphonate (MS222). 2. At the end of the procedure, hepatic contents of glycogen, glucose, lactate, ATP, ADP, AMP, were not significantly different between the two treatments. 3. Glucose production was considerably lower for 2PE than for MS222 anaesthetized trouts. This discrepancy results probably from an inhibition of glycogenolysis, suggesting that 2PE anaesthetized animals were less stressed than MS222 anaesthetized ones.

Morphological and physiological development of olfactory receptor cells in rainbow trout (Salmo gairdneri) embryos

The morphological and functional differentiation of the olfactory receptor cells were investigated in developing rainbow trout (Salmo gairdneri) embryos by means of light and electron (transmission and scanning) microscopy and electrophysiology. Ciliated receptor cells first appeared when the olfactory placode was folded to form a groovelike structure rostrad to the eye at stage 24 (day 18; 18 days postfertilization). Ciliated receptor cells predominated until immature microvillar receptor cells developed in stage 28 (day 26) embryos. At stage 29, the day of hatching, the anterior edge of the olfactory epithelium contained only ciliated receptor cells, and the midregion contained both ciliated and microvillar receptor cells. Spontaneous neural firing activity was recorded from the olfactory mucosa as early as stage 25. The neural responses to amino acids were initially recorded from stage 26 embryos, containing sparse ciliated receptor cells with a few short cilia. The D-enantiomers of amino acids were less effective. From these results we concluded that in rainbow trout the olfactory receptor cell has two separate morphological forms, ciliated and microvillar. These are ontogenetically distinct; the ciliated receptor cells preceded the microvillar. The ciliated receptor cells respond to amino acid stimulation.

Homing and Orientation of Cutthroat Trout (Salmo clarki) in Yellowstone Lake, with Special Reference to Olfaction and Vision

In-season homing was exhibited by mature cutthroat trout (Salmo clarki) displaced from spawning tributaries to Yellowstone Lake during late May to early August 1964, 1965, and 1966. Of 1908 trout tagged and displaced from Clear and Cub creeks to three release points in the lake (1.55–7.95 km) and to the mouths of the streams, 614 (32.2%) homed, 119 (6.2%) strayed, and 28 (1.5%) were captured by anglers. Only slight differences in homing performance from various release points occurred, but there were differences among years and between streams. Adjusted mean homing times from the various release points ranged from 16 hr to 155 hr, with an inverse relation between homing times and the distance to the release point apparent in one year. Blockage of the olfactory or visual sense did not affect the per cent of trout homing or straying. However, visual clues did increase the speed of homing, since homing times for blinded trout were much longer than for olfactory-occluded, control (anesthetized only), or non-anesthetized trout. A compass-type orientation occurred which was apparently not in response to visual or olfactory stimuli. A general east-northeastward (Clear and Pelican Creek trout) or northward (Cub Creek trout) orientation was exhibited by blind, anosmic, control, and non-anesthetized trout that were float-tracked from an open-water point. Blind and anosmic trout oriented as well as control trout. The directions of orientation were not in the directions of the home-streams, and orientation was not at a constant angle to the current directions or the sun azimuths.

Electroencephalographic Studies of Homing Salmon

When adult spawning salmon (Oncorhynchus tshawytscha, 0. kisutch) arrive at the "home" pond, most regions of the brain are electrically inactive, but the olfactory bulbs and posterior cerebellum are relatively highly active. Infusion of various natural waters from nearby sources other than the home pond into the olfactory sac produces little or no change in spontaneous electroencephalographic patterns recorded from the olfactory bulbs. Water from the home pond, however, produces a vigorous response of high amplitude. These findings suggest that olfaction is an important factor in guidance during the final phases of homeward migration of salmon, and that olfactory discrimination occurs at the level of either the olfactory bulbs or the olfactory epithelium.

OLFACTORY PERCEPTION IN JUVENILE SALMON: II. CONDITIONED RESPONSE OF JUVENILE SOCKEYE SALMON (ONCORHYNCHUS NERKA) TO LAKE WATERS

Sockeye salmon smolts were conditioned to distinguish between waters from two natural sockeye nursery systems, Great Central Lake (from which the smolts were obtained) and Cultus Lake. The attractant from each water was volatile, but that from Great Central Lake was the more readily volatilized of the two. Volatile material from Great Central Lake water was collected and shown to evoke a response in the group of fish conditioned to whole Great Central Lake water.

2-Phenoxyethanol as a General Anaesthetic for Sockeye Salmon

The dose–response relationship of 2-phenoxyethanol, as a general anaesthetic, in adult sockeye salmon (Oncorhynchus nerka) has been investigated. At 11 °C the effective dose (ED50) and lethal dose (LD50) were approximately 43 and 130 ml/100 Imperial gal, respectively. The therapeutic ratio [Formula: see text] was more than 3, indicating a good margin of safety. At a lowered aquarium temperature of 4 °C the anaesthetic effects of 2-phenoxyethanol were potentiated. ED50 and LD50 at this temperature were approximately 25 and 130 ml/100 gal of water, respectively. The therapeutic ratio was more than 5, indicating that the margin of safety was increased by the decrease in temperature.

Resumption of Feeding by and Survival of Adult Sockeye Salmon (Oncorhynchus nerka) Following Advanced Gonad Development

Adult, migrating, fasting sockeye salmon (Oncorhynchus nerka) were held in captivity in fresh water without spawning well beyond the time when they would normally have done so and died. A few of the fish were then gonadectomized and force feeding was begun. A few unoperated fish were fed similarly while the remainder served as unoperated, unfed controls. The gonads of the operated fish were well developed. After a period of feeding of about four months some fish in each group had survived. The fed fish had regained their green color and much of their weight and vigor, while the surviving unfed fish were extremely emaciated and listless. At this time voluntary feeding by the force-fed fish was observed for the first time, and it was then found that the five surviving unfed controls would also take food voluntarily. While two of these fish died without apparent improvement in their condition, the other three gradually regained green color, weight and vigor.

Alarm Reaction of the Top Smelt, Atherinops affinis (Ayres)

The "alarm" substance of the top smelt, Atherinops affinis (Ayres), has been isolated by extraction with methanol or ether from suffocated top smelt. These concentrated extracts, when introduced into an aquarium containing top smelt, induce a strong alarm reaction in the fish, characterized by rapid swimming, jumping, and often severe seizures. The fact that extracts from white surfperch, Phanerodon furcatus (Girard); surf smelt, Hypomesus pretiosus (Girard); northern anchovy, Engraulis mordox (Girard); or Pacific herring, Clupea pallasi (Valenciennes) caused only mild excitation in the top smelt indicates the species-specificity of the alarm reaction.