Yasunobu Yanagisawa

Filial cannibalism by mouthbrooding males of the cardinal fish, Apogon doederleini, in relation to their physical condition

SynopsisPaternal brood cannibalism was observed in a population ofApogon doederleini in Shikoku Island, Japan. Of 361 egg masses mouthbrooded by males, 47 disappeared within a day of spawning. A stomach check with a syringe ascertained that they had been consumed by the males. The frequency of this cannibalism increased as the breeding season advanced. As males completed 4–7 breeding cycles in a breeding season and spent 80% of the time mouthbrooding without taking ordinary food, their physical condition deteriorated greatly late in the breeding season. We concluded that parental physical condition is an important factor in the occurrence of brood cannibalism.

Parental strategy of the cichlid fish Perissodus microlepis, with particular reference to intraspecific brood ‘farming out’

SynopsisOne parent was experimentally removed from brooding pairs of Perissodus microlepis in the field. The removal elicited drastic behavioural changes in the remaining parent and young. The remaining parent sometimes showed a sequence of peculiar behaviours which were not observed when guarding the young with its mate. Some left the brooding site with young in their mouths and then put the young under the care of another pair of brooding parents.

The Social and Mating System of the Maternal Mouthbrooder Tropheus moorii (Cichlidae) in Lake Tanganyika

Territorial behaviour, reproduction and migration of the epilithic algal eater,Tropheus moorii, were investigated in Lake Tanganyika, Africa. Adults of both sexes had individual feeding territories which adjointed each other. Males, who occupied higher rocks than females, usually stayed at the same sites for more than 5 months. Females left their territories to pair with males in the males’ territories. Paired females actively foraged under the protection of their mates for up to 3 weeks prior to spawning. After spawning, females usually settled in a site unoccupied by territory-holders to mouthbrood the offspring for a month. An examination of the ovaries and a removal experiment of dominant males suggest that females cannot attain fully mature ovaries in their own territories and choose males whose territories can provide enough food to satisfy their nutritive demand. The evolution of a number of local colour morphs in this fish is briefly discussed in relation to social selection.

Active browsing by mouthbrooding females of Tropheus duboisi and Tropheus moorii (Cichlidae) to feed the young and/or themselves

SynopsisFishes usually do not eat while brooding offspring in their mouths. In two epilithic algal eaters Tropheus duboisi and T. moorii in Lake Tanganyika, however, mouthbrooding females exhibited feeding actions. In T. duboisi, the feeding rate of mouthbrooding females was 80 percent of that of males and non brooding females irrespective of the developmental state of their offspring. In T. moori, females brooding early embryos rarely fed but their feeding rate increased with development of offspring. An examination of specimens revealed that such females took food for nourishment of themselves and the young in the former species but for nourishment of only the young in the latter.

Monogamy and sex role reversal in the pipefish Corythoichthys haematopterus

We observed the mating pattern and social behaviour of the pipefish Corythoichthys haematopterus in temperate waters of Japan during three successive breeding seasons. Males cared for a clutch in their brood pouch for 9-19 days until hatching and had several broods in the season with nonbrooding intervals of only 1 or 2 days. The population sex ratio was female biased and some females were always excluded from reproduction. Although males were sometimes courted by unmated females together with their regular partners, they always mated with the latter. The pair bond was maintained until the next season if both members survived. When males lost their partners, they remated with neighbouring unmated females within a few days. In contrast, widowed females remained unmated for a long time. Females had larger home ranges and were more active in courtship displays than males. This pipefish provides the first example of sex role reversal among monogamous syngnathid fish. We suggest that mate guarding by females is a primary proximate factor for maintenance of monogamy in this fish. Copyright 2001 The Association for the Study of Animal Behaviour.

Life-history pathways in relation to gonadal sex differentiation in the anemonefish, Amphiprion clarkii, in temperate waters of Japan

SynopsisThe process of gonadal sex differentiation in Amphiprion clarkii was investigated for 2 years at Murote Beach, Shikoku Island, Japan. Six color phases were discriminated on the basis of the caudal fin coloration, which corresponded well to six gonadal phases. From changes of the color phases with growth, three life history pathways were detected: (1) subadult male → subadult female → adult female, (2) subadult male → adult male → adult female, (3) subadult male → adult male. Different pathways were due to the difference of timing among individuals in the development of ovarian tissues of the hermaphroditic gonads involving the atrophy of testicular tissues. Irreversible differentiation of ovarian tissues of the gonads occurred more frequently among nonbreeders (10 cases) than among breeders (4 cases). The second pathway, which has been thought the norm of tropical anemonefishes, was therefore not primary in this population. This can be attributed to ecological conditions: fish are able to move between host sea anemones and nonbreeders can escape from social suppression by adult pairs because of high population density of hosts.

Parental care in a monogamous mouthbrooding cichlid Xenotilapia flavipinnis in lake Tanganyika

Breeding pairs ofXenotilapia flavipinnis held their territories on the sandy bottom and repeated several breeding cycles. Females mouthbrooded the eggs and early larvae but afterward males took over the mouthbrooding role. When the young became free swimming, they were guarded by both parents and remained in the spawning territory. Males played a leading role in the guarding, while females were more active in foraging during the guarding period. It was concluded that males’ active participation in the parental care could accelerate the gonadal recovery of females and consequently could maximize the fecundity of serially monogamous pairs.

Breeding ecology of an amphidromous goby of the genusRhinogobius

Field observations of markedRhinogobius sp. DA (Dark type) individuals and monthly sampling in the Kashiwa River, Shikoku Island, Japan, indicated the breeding season of the species to be from mid-April to early July, peaking in May. Mark-and-recapture data showed that at least half of the females spawned more than once in one breeding season. Although eggs in male-guarded nests were all at the same developmental stage, their mean number exceeded that of pre-spawning yolk stage oocytes per female, suggesting that at least some guarding males received eggs from more than one female. The physical condition of both sexes deteriorated considerably during the breeding season, the hepatosomatic index of guarding males decreasing concurrently with the development of eggs. The decline in physical condition of guarding males was attributed mainly to their restricted feeding opportunities.

Geographical colour variation in cichlid fishes at the southern end of Lake Tanganyika

SynopsisGeographical colour variation and distribution of 48 common cichlid fish species were studied at 20 sites along an 85 km shoreline at the southern end of Lake Tanganyika, Africa. Sixteen species had two or more colour morphs and 11 species showed a limited distribution in the study area. They were all rock-dwellers. Distributional borders of the color morphs and species with a limited distribution mostly lay in two long sandy beaches, 7 and 13 km long. We suggest that the long sandy beaches can be effective barriers against dispersal of shallow-water rock-dwelling cichlid fishes.

Male–male competition for large nests as a determinant of male mating success in a Japanese stream goby, Rhinogobius sp. DA

Abstract Males of the stream goby Rhinogobius sp. DA (dark type) court females in deep pools and care for the eggs under stones in shallow riffles. We studied male–male competition for access to females and nest sites to understand how male size influences the mating success of this species. In field observations, larger males won in fighting with other males. However, large males did not tend to monopolize courtship opportunities, and the frequency of successful courtships, after which males led the females to the nests, was not related to male body size. The fact that courted females always escaped from the fighting sites once males began fighting likely explains why male size was not positively related to courtship success. Large males occupied large nest stones, and the number of eggs received in the nest was correlated positively with nest size. In aquarium experiments with two tiles of different sizes provided as nesting materials, males always chose the larger nest and, when two males were introduced simultaneously, the larger one occupied the larger nest. These results suggested that male mating success of this goby is determined by male–male competition for large nests rather than for access to females.