Chloe, Eternity, Chanel No 5, Obsession, Old Spice, Boss and for those more mature and discerning among us, Hai Karate and Brut 33. All these scents are worn for one reason: to attract a mate. Alternate reasons for some people to wear excessive amounts of scent while on aircraft are to cause severe irritation and discomfort to fellow passengers. The amount applied is inversely proportional to the cost.

Hidden under the perfumes, notes and tones of the scent is a constituent chemical or two that has a more subtle effect – or so the makers of scent hope. This chemical, usually musk, is designed to induce attention, interest, or passion. Indeed, the idea of wearing scent is to draw attention to oneself in the interest of an encounter.

It is commonly held that more overt environmental stimuli will induce ‘the mood’. In humans, ambiance has much to do with romance and that which follows. So does time of day, or appetite. The sense of smell or perception of scent without an odour is not the foremost of what is normally considered in assisting arousal. However, mammals communicate by smell more than is given due regard. Consider when a bitch is in heat in a household: she never leaves the house, yet the yard is full of fighting dogs.

As with mammals, other vertebrates including fish, use chemical messengers called pheromones. Pheromones have multiple functions: they communicate reproductive status, coordinate reproductive behaviour among members of a group and stimulate maturation and mating.

Pheromones can be distinct chemicals, but are usually chemicals or hormones used in the final maturation of the gonads. By using hormones or the degradation products of hormones used in final maturation, the animal makes use of ‘waste’ chemicals that are directly indicative of reproductive status. These waste chemicals are released with the gametes or in urine to signal an occurring or imminent event, namely ovulation or spermiation.

In cats, the chemical signaling of reproductive status is widely known. Tomcats love to spray to display availability. Deer in a rut will think of little else and as hunters will attest, can be detected by scent alone. There is little need to mention ferrets in heat.

Fish too use chemical signals to indicate maturative status. Communal spawners such as herring are a prime example. A constituent of herring milt evokes spawning behaviour in the population and the seashore becomes white with their activity. In roe-on-kelp operations, herring are impounded in cages that contain kelp suspended from ropes. At an appropriate time, isolates of herring testis are added to the cage and the frothing begins. In solitary species, the female fish will release pheromones to indicate to prospective males that she is ready to mate. The male fish detects the pheromone, becomes sexually active and seeks the said female. This is important in territorial species where the only way to enter a territory of a competitor is to be invited in for a little loving.

Perhaps the best documented effect of pheromone effects are described for goldfish by the Albertan endocrinologist Norm Stacey (reviewed in Stacey et al., 1994). Take two goldfish (one male, one female), put them in a 20l tank at 20^oC with a little bit of floating green material and keep them under a photoperiod of 14L:10D. In 10 days, the fish will have gonads that are all but mature. The male will start to show interest in the female and ‘bunt’ or bump her sides. He will then ‘nose’ her vent. By then male is literally overflowing with milt. Spawning ensues.

Key here is the synchronization of maturative status by physiology and behaviour. All the environmental conditions are perfect for growing the gonads (recrudescence); all that is needed is a mate. By bunting the female, the male stimulates final oocyte maturation. She releases a pheromone in this case, hydroxy-progesterone (OHP) or one of the many derivatives. This stimulates the male to undergo final maturation of the testis and release another chemical messenger. When the female ovulates, she releases prostaglandins and once that happens, there is no turning back. So, chemical signaling is present from both the male and the female, which then cue final maturation of the gonads and spawning behaviour.

Salmon too use pheromones. The main pheromone is 17,19 dihydroxy progesterone (DOHP) which is important to final maturation of both ova and sperm. Therefore, if this hormone is released to the environment, it indicates maturative status in individual fish. DOPH and derivatives, metabolites and residues both signal reproductive status and induce maturation in fellow spawners.

Salmon pheromones are located in urine as conjugated steroids (joined to water-soluble bits) and directly in ovarian fluid. In males pheromones are in the urine and milt. The chemical message here is to coordinate spawning times in a population.

The anecdotal example of this is when male and female spawners are placed in separate tanks. It seems that the females are ripe before the males. This may be true as the males have missed out on important cues that the females have been broadcasting. Sort of like a 10 day shift out on the farm.

The practice of mixing a few members of the opposite sex in a pen or tank is a good one. This way, both genders will produce pheromones that will synchronize maturation with the rest of the normal population . Another cure is to induce maturation with a spawning agent like Ovaplant or Ovaprim. This brings final maturation into full swing and gets all the juices running on demand.

So the next time a fully-scented person takes the seat next to you on a crowded aircraft, think of the message behind the action. A little ovarian fluid behind the ears may work wonders.

Literature cited

Stacey N.E. et al., 1994. Hormones as sex pheromones in fish. Pp 438-448 in: K.G. Davey, R.E. Peter and S.S. Tobe, eds. Perspectives in comparative endocrinology. National Research Council of Canada, Ottawa.