Gunzo Kawamura

Ontogenetic Changes in Behavior and Sense Organ Morphogenesis in Largemouth Bass and Tilapia nilotica

Abstract The development of sensory systems and the coincident acquisition of associated behaviors were examined in two paternal brooders, largemouth bass Micropterus salmoides and Nile tilapia Tilapia nilotica. In newly hatched eleutheroembryos of largemouth bass, the eyes are unpigmented, the nares are closed, and the free neuromasts and taste buds are not developed. Six hours after hatching (when the epithelium of the otic vesicle is ciliated), the eleutheroembryos are able to aggregate by responding to the movements of neighboring siblings. Thereafter, four correlations between sense organ development and initiation of fish behavior were observed: appearance of the first free neuromasts on the head and positive rheotaxis; morphological completion of the larval-type retina and positive phototaxis; formation of twin cones in the retina and optomotor reaction; and appearance of taste buds in the oral cavity and selective feeding. The ontogenetic development of the sense organs of Nile tilapia reflects ad...

A comparative study on morphological differences in the olfactory system of red sea bream (Pagrus major) and black sea bream (Acanthopagrus schlegeli) from wild and cultured stocks

The improving technology in artificial propagation of aquatic animals is having a direct effect on increasing aquaculture fishery production of many aquatic food species throughout the world. High-valued fish species are being produced en masse and released into the wild to augment populations depleted due to over-fishing and habitat degradation. This study was conducted to determine the effect of procedural conditions in mariculture hatcheries on the olfactory systems of fish in Kagoshima Prefecture, Japan, and to compare the results with fish from wild stocks. Red sea bream (Pagrus major) and black sea bream (Acanthopagrus schlegeli) were suitable candidates for this study because of their economic importance and history in mariculture production, especially ongoing restocking of natural populations via stock enhancement programs in Japan. An extensive survey revealed a high percentage of fish with an abnormal single olfactory nasal opening. The single abnormal nasal opening contrasted strongly with a pair of natural nasal openings, an anterior and a posterior nares, in normal fish of both species whereby olfactory water is sampled when the fish swims. Ultrastructural observation of lamellar topography demonstrated not only a substantial variation in sensory epithelial distribution patterns in red sea bream of cultured stock but also showed that the sensory epithelial area in abnormal cultured fish was significantly smaller (P<0.005) than the lamellar area in wild fish. The densities/mm2 of microvillous and ciliated olfactory receptor neurons in both species were not significantly different when normal fish were compared with abnormal fish. Nonetheless, there were some notable irregularities in distribution patterns of the two receptor neurons on the lamellar surface. In abnormal red sea bream, the density of ciliated nonsensory cells was relatively higher than the normal fish. The kinocilia in cultured fish (normal red sea bream with anterior and posterior nares; CNR, 6.45±0.83 and abnormal red sea bream with a single nasal opening; CAR, 8.05±1.39 μm SD) were significantly longer (P<0.05) than the ones observed in wild fish (5.46±1.39 μm SD). Further, ciliary beat cycle and metachrony were evident in normal fish olfactory epithelia but were usually not evident in abnormal fish. The results indicated that gross and micromorphological abnormalities in the olfactory systems of fish are a consequence of certain procedural condition(s) in mariculture facilities. The physiological and behavioral implications of morphological deformities in fish olfactory systems are discussed, especially in the context of ensuring production of healthy, normal fish for marine ranching programs and ecological preservation.

Blue and green fish aggregation devices are more attractive to fish

Abstract To examine the attractiveness of coloured fish aggregation devices (FADs), six sets of four to six FADs of the kite type were deployed in coastal waters and dive observations were carried out for 15 months. The FADs had the same dimensions but different kite colours: white, black, blue, green, yellow and red. Fish abundance and aggregation patterns around the FADs were scored and statistically analysed. Fish tended to be most abundant near the blue and green FADs, least abundant near the black and white FADs, and intermediate near the yellow and red FADs. Aggregations stayed closer to green and blue FADs than to white, yellow, black or red FADs. The more attractive FADs were the less visible ones. Thus, fish were attracted to blue and green FADs on the basis of hue rather than contrast.

Near-ultraviolet radiation guides the emerged hatchlings of loggerhead turtles Caretta caretta (Linnaeus) from a nesting beach to the sea at night

Hatchling sea turtles (Caretta caretta) emerge from their beach nests at night and crawl seaward immediately, even where the sea is not visible to them. This sea-finding ability of hatchlings is one of the outstanding phenomena of animal orientation. The primary sea-finding mechanism is an orientation towards light, and blindfolded hatchlings could not find the sea. Hatchlings of loggerhead turtles avoid yellow and orange light and are strongly attracted to light in the near-ultraviolet to green part of the spectrum. Here we demonstrate in experiments at a nesting beach that (1) loggerhead hatchlings orient to near-ultraviolet radiation, and (2) the intensity of near-ultraviolet radiation is always higher seaward than landward on all nights. These results are consistent with long-term monitoring data that show emergence of loggerhead hatchlings takes place during any phase and position of the moon. To prevent mis-orientation of hatchlings, roads, and human settlements fronting turtle nesting beaches should use lights that do not emit near-ultraviolet radiation.

The eyes of the common carp and Nile tilapia are sensitive to near-infrared

Fish biologists have shown little interest in near-infrared (NIR) sensitivity because water absorbs light in the red and near-infrared and because downward irradiance in clear ocean water is mostly blue light. In recent years, however, Nile tilapia Oreochromis niloticus was shown to be NIR sensitive by behavioral techniques. This study confirmed NIR sensitivity in the common carp Cyprinus carpio and Nile tilapia by using a more sensitive technique than a behavioral one. Cardiac conditioning experiments showed that both fishes are sensitive to 865 nm NIR. The conditioned response to 865 nm NIR was observed in Nile tilapia when the eyes were not covered and the pineal window was covered, but not when the same fish had its eyes covered and the pineal window exposed to the NIR. The eyes are thus, the NIR-sensitive organs in Nile tilapia. To identify the NIR photoreceptor, the retina was examined by histology. The retina exposed to 865 nm NIR showed incomplete dark adaptation with rods exposed from retinal epithelial pigment. Though the reaction to NIR seemed to be mediated mainly by the red cone, the involvement of the rod could not be ruled out.

Effective range of traditional Malaysian FAD as determined by fish-releasing method

Abstract An experiment to determine the effective range of a traditional Malaysian FAD, the unjam, was conducted in waters off the Terengganu coast, South China Sea. Seventy-two fish of different species, with a float and line attached as a marker, were released at a distance of 30 m from the unjam and subsequently increased by every 30 m until no fish were observed heading towards the unjam. It was found that the effective range of the unjam was 180 m. Landmark orientation was hypothesized that, as the released fish were all unjam-associated species and residents in the area, they had been familiar with the surroundings and had learnt the “home” unjam.

Effects of several factors on growth of milkfish (Chanos chanos Forskal) fingerlings reared with artificial diets in aquaria

Abstract This paper presents the effects of feeding level, feeding frequency, salinity of water, kind and particle size of diets, and stocking density on the growth of milkfish (Chanos chanos Forskal) fingerlings which were reared with artificial diets in laboratory tanks. Experimental groups were designed using orthogonal array L8, and the results were evaluated statistically. Growth of the milkfish fingerlings varied markedly with the kind of diets used and feeding level. The feeding frequency and particle size of the diets also affected growth of the fingerlings significantly, but the salinity of the water did not. The weight gain of the fingerlings did not vary with the stocking densities significantly, whereas the increase (%) in body length was greater at a lower stocking density. The milkfish fingerlings showed the best growth in terms of both weight gain and increase in body length when reared on a purified diet containing 35% casein and 15% gelatin as protein sources under the following conditions: feeding level, 30–35% of body weight; feeding frequency, twice a day; particle size of diets, 125–250 μm diameter; and stocking density, 5 fish 5-liter tank. The means and confidence limits of the weight gain (%) and increase (%) in body length of milkfish fingerlings under the best conditions adopted were estimated to be 360 ± 63.7 and 62.1 ± 10.6, respectively.

Morphology of the sense organs of anchovy Engraulis japonicus

The morphology of the lateral line system, the inner ear, the olfactory epithelium and the taste bud of the wild adult anchovy Engraulis japonicus was examined by photo microscopy and scanning electron microscopy. Hematoxylin solution was injected into the lateral line canals to show the arrangement of the lateral line system. The lateral line system has well-developed supraorbital, infraorbital and preoperculomandibular canals on the head, dense canal branches on the operculum, lateral line canals on the trunk, and no free neuromasts. The inner ear comprises three semicircular canals and three otholithic end organs: the sacculus, the lagena and the utriculus. The olfactory organs and taste buds were examined by scanning electron microscopy. The paired olfactory organs on the snout have rosettes of lamellae, whose sensory epithelium consists of receptor cells of both the ciliated and microvillous type. The taste buds are distributed only inside the mouth, and mostly between the teeth of the upper and lower jaws, and between the gill teeth on the gill rakers. Well-developed lateral lines on the head are advantageous for schooling, and the taste buds in the mouth and on the gill rakers are advantageous for filter-feeding on plankton.

Effectiveness of a sugarcane-fish combination as bait in trapping swimming crabs

Abstract Swimming crabs are known to be highly sensitive to saccharides, in response to which they show strong food searching behaviour. This study was done to examine the possibility of using sugarcane as an attractant in basket traps for Portunus pelagicus and Charybdis japonica during their reproductive season. A bait combination of sugarcane and fish was found more effective than fish bait alone, whereas sugarcane alone was ineffective. The use of the sugarcane-fish combination resulted in an extremely male-biased catch of P. pelagicus, one result of which would be the conservation of the population of this crab.

Colour preference of five marine fishes: bias for natural and yellow-dyed krill in laboratory tanks, sea cages and an earthen pond

In this study, the colour preference during feeding was determined in three members of the family Sparidae: girella (Girella punctata Gray), the black porgy (Acanthopagrus schlegeli Bleeker) and the Japanese silver bream (Acanthopagrus latus Houttuyn); and in two members of the family Scombridae: the Japanese horse mackerel (Trachurus japonicus Temminck et Schlegel) and the spotted mackerel (Scomber australasicus Cuvier). The three sparids are omnivorous and are confined to neritic habitats and the two scombrids are schooling planktivores and open-ocean forms. The experiments were conducted under three different holding conditions: grey and white tanks in the laboratory, sea cages and an earthen pond. The prey used in the tests was the Antarctic krill, in its natural colour (control) and in artificial colours of yellow, red, green, blue (produced with food dyes) and black (Chinese ink). These prey were offered in different two-colour pairs to groups of fish, and the colour of the krill attacked first was recorded. The frequencies of first attacks against each colour of the different pairs were analysed by the paired-preference test and Thurstones law of comparative judgment. The data were converted into mean z-scores and significant biases from zero were noted. The five species took without hesitation all the krill of all colours, but preferred blue krill the least, and did not clearly distinguish red from black. The three sparids showed a strong bias for yellow krill under all holding conditions. The two scombrids preferred natural krill and showed poor colour preference. The observed colour preference was probably due to colour per se and may be an innate ability, rather than due to relative brightness (sensitivity of the fish eye), prey conspicuousness (pigmented eyes of the krill), or the associated taste of the dyes.