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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.

Ontogenetic development of the sense organs of the flounder, from newly hatched larvae to 72-day old juveniles was examined by light- and scanning electron-microscopy and correlation with changes in behaviour was made. The larvae are capable of horizontal orientation when the otic epithelium is ciliated at 6 hours from hatching. Newly hatched larvae have at least two types of olfactory receptor cells and a pair of free neuromasts with well developed cupula. At 9 hours from hatching, the larvae avoid obstacles by mechanoreception. At 3 days from hatching, eyes are deeply pigmented, the visual system is morphologically complete, and the larvae initiate feeding and are positively phototactic. Differentiation of the taste buds occurs 9 days from the onset of feeding, at this time, food preference is exhibited by the larvae in the sea. Retinal rod cells differentiate at 25 days and twin cones form at 29 days from hatching. Positive phototaxis disappears at 30 days and the larvae become nocturnally active at 33 days from hatching. The shif from pelagic to benthic habit occurs at this stage.

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...

Horizontal eyes and head movements made by a crucian carp swimming in an experimental channel set in the circulating tank were recorded cinematographically and analyzed frame-by-frame. And the width of a cone of the animal used was measured histologically and an angular extension of a cone against a lens was calculated. Though the eyes sometimes moved with the head, the approximate stable orientations of eyes, making slight fluctuations within one or two degrees, were observed in the traces of eye movements. Depending on an angular extension of a cone in temporal retinal region against a lens (0.7 degree), it was confirmed that these slight fluctuations do not interfere with vision but sharpen the edge of a retinal image, and so the compensation was substantially perfect. And it was concluded that the carp is capable of keeping retinal image stable for 200-800 ms while swimming even at relatively high speed.

The retina of two teleosts, S. tapeinocephalus and H. poecilopterus, having comparatively different behaviours, were compared morphologically, and the following results were obtained. 1. Both twin and single cones were found in the retina of S. tapeinocephalus, while only single cones were obscrved in the retina of H. poecilopterus. 2. The topographical specialization of the retina was higher in H. poecilopterus than in and S. tapeinocephalus, havingcomparatively, and a well-developed area centralis was found not only in the dorsotemporal retinal region but also at the bottom. It is believed that the retina of S. tapeino-cephalus is more advantageous for the movement perception than that of H. poecilopterus. for which visual acuity is more important than movement perception. 3. Numerical relationship of various cells, such as bipolar, amacrine, horizontal and ganglion cells, to the cones was studied in each region of the retina, and it was found that such cells were most numerous in the region of hgih cone density. 4. The functional significance of the retinal elements and of the cone mosaic are discussed.

To clarify the axis of horizontal eye rotation of fish, a 35mm camera filmed the optomotor reaction of the animal from above, and the axis of horizontal eye rotation was estimated mechanically. Moreover, the muscles and the space between the eye and the orbit were studied anatomically. The axis of the horizontal eye rotation is not a single point. The axes measured geometrically seem to lie around an optic center of an eye, and the axis tended to shift a little bit nasalward when the eye rotated nasalward.

The ability of teleosts to respond to the place of polarized light was determined by theri heart beat rate. When the plane of polarized light was changed, apparent cardiac deceleration was observed in tilapia, rainbow trout, and yellowtail, but there was no response in common carp and crimson sea-bream. To determine which organ perceives polarized light, the eye or the pineal organ, one or both were covered in some tests on tilapia and rainbow trout. The response disappeared when their eyes were covered. The fishes that respond posses polarized light vision, and polarized light is perceived by the eye.

The accuracy of the compensation of the horizontal eye movements must be discussed in rela-tion to head movements. To clarify the head movements of swimming fish, it was observed by the use of strain gage imbedded in fish body. The results were compared with the cinematographical measurements. From the records of strain-changes, the horizontal flexing movements of tail, trunk and head could be clearly detected. It is apparent that, though there is specific variation, tail and trunk show the regular wave-form movements, while the head of carp and crucian carp shows rather irregular wave-form movements, which is similar to the movement measured cinematographically. Hence it was concluded that a cinematographical angular measurement of head was accurate and reliable.

This study examined the eye development of ayu fish. Visual threshoild improved with fish growth.