No abstract

No abstract

Chemical signals (pheromones) have been shown to be involved in schooling, territorial marking, species, sex and individual recognition, courtship, the induction of physiological readiness for mating, and in parent–young interactions. Alarm substances released from damaged skin elicit avoidance behavior. Pheromones may also be involved in homestream recognition in some anadromous species. Most pheromones investigated act as "releasers"; a few "priming" effects have been observed. In most of the chemically mediated interactions surveyed it is not clear that communication in a generally accepted sense is involved, or whether fish are simply responding adaptively to those metabolic products which inevitably "leak" into the environment and only fortuitously provide "information" to conspecifics. In a few cases, specializations in chemical secretions or secretory structures indicate that they have evolved for communication. It is proposed that a combination of factors — the availability of a wide array of soluble biochemical products, the diffuse nature of the sites from which such products might be released, and the lack of strong selection for complex chemical messages — has resulted in the relatively simple "unritualized" systems of chemical communication which appear to be characteristic of fish.Key words: chemical signals, pheromones, reproduction, schooling, homing, parental behavior, fright reaction

No abstract

We examine aspects of the fertilization dynamics of rainbow trout (Oncorhynchus mykiss) that may play a role in determining reproductive success of males of different age and status competing for spawning. There were no differences in the gonadosomatic indices and relative yields of milt of adult (3-year) and precocious (1-year) male rainbow trout collected from a wild population. The concentration of sperm in the milt of precocious males was higher than that of adult males. The duration of sperm motility was similar in the two groups of males and increased over the period of sampling. Interaction of a male with a nesting female caused an increase in milt yield, but did not affect sperm concentration, sperm motility, or fertilization rates. There was a sharp decline in fertilization rate 20 s or more after activation of the sperm or eggs by fresh water. Exposure to milt suspension for as little as 0.5 s resulted in fertilization of <27% of eggs. The short gamete longevity and the speed with which fertilization occurs indicate that the timing and position of sperm release may play a critical role in determining the reproductive success of males in competition for spawning with a single female.