Vertebrates

	When being female is better
	Fisheries and fish prices in Hong Kong
	Acrossocheilus parallens (Nichols) (Osteichthyes: Cyprinidae) newly recorded from Hong Kong
	Understanding bat language: The echolocation calls of Hong Kong bats
	New reptile and amphibian records for Kau Sai Chau, Sai Kung
	The naming of rats

When being female is better

by Yvonne Sadovy

The mandarinfish, Synchiropus splendidus, is a particularly attractive dragonet (Family: Callionymidae) which is favoured in the marine aquarium trade in Hong Kong and elsewhere. Little is known of the life history or fishery of this species. Males are particularly heavily sought by aquarists because their extended first dorsal fin, a sexually dimorphic character, (Fig.1) is thought to be especially attractive. Fishing tends to be sexually selective as a result. A study was initiated in 1997, funded by the National Geographic Society, to investigate the reproductive biology and effects of fishing on the mating system of this species, and will be completed this year. The mating system was studied by directly observing natural populations in the field in Palau, Micronesia, and the fishery was observed directly in the Visayas, Philippine Islands. Marine aquarium shops in Hong Kong were periodically inventoried to determine the sizes and sexes of fish available at retail outlets. The work was carried out in collaboration with Dr. Mariella Rasotto of the University of Padova, Italy.

Our results suggest that this species has a rather unusual mating system that involves regular spawning spots on the reef at which males and females assemble, in mini spawning aggregations, each evening. There is a strong, size-based, dominance hierarchy among the males such that larger males mate significantly more frequently than small males, both by excluding smaller males, and, we think, because females prefer to mate with larger males. Each female spawns only once each night but may go several nights without spawning so, on any one night, there is intense competition among males for a few active females. Spawning (mating) occurs after a female and male align themselves and rise slowly to about a metre above the substrate and release sperm and eggs.

The fishery of this species was observed in the Philippines where fishers use a specially designed mini speargun; the spear itself consists of two sewing needles which are fired into the side or tail of the animal. The capture of this species is quite specialized since they are difficult to spot and are only visible briefly during dawn and dusk or when there is heavy cloud cover. The fishers say that they select the bigger fish because the price of the attractive males is about twice that of the females. This selectivity was also suggested when retail outlets of aquarium businesses visited in Hong Kong and most fish observed were male. The Philippine fishery was clearly depleted according to interviews with fishers.

The effects of sex selective fishing, in general, and especially in respect of species involved in the marine aquarium trade, are virtually unknown. Over 1,000 species are traded globally for home aquaria, of which about 340 species have been recorded in Hong Kong where a small component of the global trade is operating (Chan and Sadovy, 1998). In the case of the mandarinfish, we were able to determine, from removal experiments in the field to mimic selective fishing on the largest males present (the males were replaced after the experiment), that selective fishing apparently has two effects. The first, obvious one, was the removal of dominant males producing a female bias to social groupings in the field. The second, unexpected, finding was that females were increasingly reluctant to pair with progressively smaller males. This led to increased numbers of failed pre-spawning rises, a longer time spent in the water column for male/female alignment to take place, and the possibility of increased predation pressure as a result; successful predations are rarely observed in the field, yet in this study we observed several such events following male removals.

This study suggests that to understand the full impacts of selective fishing for the aquarium trade on reef fish populations detailed knowledge is needed, both of the biology of the target species and the manner of operation of the fishery. This growing trade is worth billions of dollars globally (Wood, 2001), and involves an estimated 36 million fish traded annually. Yet it is little monitored, rarely regulated and its impacts virtually unknown. In recognition of some of these problems, the Marine Aquarium Council is developing a certification system to promote good practice (Holthus, 2001). Lady mandarins, beware!

Bibliography

Chan, T.C., & Y. Sadovy. (1998). Profile of the marine aquarium fish trade in Hong Kong. Aquarium Sciences and Conservation 2:197-213.

Holthus, P. (2001). Certification for quality and sustainability in the collection, culture and commerce of marine ornamentals. Marine Aquarium Council NEWS 1^st Quarter 2001.

Wood, E. (2001). Collection of coral reef fish for aquaria: global trade, conservation issues and management strategies. Marine Conservation Society, 80 pp.

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