Yasuhiko Taki

Why is grouper larval rearing difficult?: an approach from the development of the feeding apparatus in early stage larvae of the grouper,Epinephelus coioides

The osteological development of elements forming the oral cavity was examined in early stage larvae of the grouper,Epinephelus coioides, from hatching to 242.5 hours after hatching. By the time of initial mouth opening, at 54 hours after hatching, the fundamental elements, composed of the trabecula, some components of the lower branchial and hyoid arches, the quadrate and symplectic-hyomandibular cartilages, maxilla and Meckels cartilage, had appeared. No further elements were observed until 165 hours after initial mouth opening, except some components in the lower branchial arch and head region. The appearance of new elements and initial ossification of existing cartilage occurred thereafter, but all elements related to feeding either had not appeared or had not started ossifying until 188.5 hours after initial mouth opening. Based on the morphology and developmental modes of these elements, the feeding mode of grouper larvae was considered to be “sucking/grasping.” However, the appearance and ossification of elements occurred slowly, with no transitional phase from sucking to grasping modes of feeding being observed during the study; such delayed development of the feeding-related bony elements was considered to be a cause of the difficulty in rearing early stage grouper larvae.

Year-round spawning and seed production of the rabbitfish, Siganus guttatus

Abstract A series of experiments on the spawning and larval rearing of Siganus guttatus was conducted during a 14-month period in 1984–1985. Spawning occurred every month throughout the year, without hormonal treatment, between the first quarter and the full moon. Fertilization rates and hatching rates were high, with means of 84.2% (n=38) and 89.6% (n=34), respectively. Females that had been fed diets rich in cod liver oil or in a cod liver oil/soybean oil/soybean lecithin mixture spawned repeatedly for at least 4 consecutive months. Larvae reared in 20, 26, and 32‰ salinities showed no significant differences in survival rates at day 21. Survival was higher for larvae fed during days 2–4 with rotifers strained through an 80-μm-mesh plankton net than for those fed unstrained rotifers. Larvae readily accepted Artemia nauplii and artificial diets when these were first introduced on day 15 and day 23, respectively. Higher larval survival was obtained in large tanks (≥5 m3) than in small tanks (500 l). Survival rates of 3.5–16.6% ( x =7.5% ) at day 45 were obtained in six trials of mass larval rearing and 5500–50100 ( x =27 700 ) juveniles per female were produced at day 45, ready for stocking in grow-out farms.

Osteological development of the feeding apparatus in early stage larvae of the seabass,Lates calcarifer

The osteological development of the feeding apparatus was examined in early stage larvae of laboratory-reared seabass,Lates calcarifer. At initial mouth openings 40 hours after hatching, the larvae were equipped with the fundamental elements forming the oral cavity, such as the trabecular roof, the lower branchial and hyoid arches forming the floor, the quadrate and symplectic-hyomandibular cartilages making up the sides, and the maxilla and Meckels cartilage bordering the jaws. The cleithrum appeared almost simultaneously. The mechanics of creating a negative pressure in the oral cavity, which results in a “sucking” mode of feeding, were elucidated from these elements. During a period from 50–60 to 100–110 hours after initial mouth opening (HAMO), new elements such as the premaxilla and jaw teeth appeared, and the ossification of existing elements started. The new elements apparently enabled the larvae to “grasp” food organisms, in addition to the already existing and increasing sucking ability, from 100–110 HAMO.

Lates Calcarifer (アカメ科)仔魚の初期発達

The early growth, yolk and oil globule resorption, early morphological and behavioral development, and initial feeding of hatchery-raised Lates calcarifer were studied. Based on the developmental events and the energy the reby utilized, the early life history of this species can be broken down into the following five phases: 1) rapid early growth due to rapid yolk resorption (from hatching to about 15 hr after hatching (TAH); 2) morphological differentiation and slow growth based on energy from yolk (to about 50 h TAH when the yolk is exhausted); 3) slow growth with initiation ffeeding and swimming activities, based on energy from oil globule and from exogenous food (to about 110 h TAH); 4) accelerated growth and effective feeding and swimming based on the same two sources of energy as in the preceding stage (up to about 120140 h TAH when the oil globule is exhausted); and 5) accelerated growth, effective feeding and swimming and further development based solely on exogenous energy (beyond 140 h TAIT).

Dynamics of exploited populations of the calanoid copepod, Acartia tsuensis

Abstract Cultures of the marine calanoid copepod, Acartia tsuensis , grown in 24-m 3 outdoor tanks and 25-l containers in the laboratory, were harvested at exploitation rates of 0 to 50% of the total population per day. The results showed that when chlorophyll a concentration is maintained at about 10 μg/l, the copepod can withstand an exploitation rate of up to 30%/day, forming cohorts and repeating its life cycle to yield a daily harvest of about 30 μg (dry)/l. The ability of A. tsuensis to resist a declining population under high rates of exploitation is considered to be related to some or all of the following mechanisms which will be at work under low population densities: (1) decrease of mortality; (2) decline of predation on nauplii by copepodids; (3) accelerated recruitment to spawning age owing to accelerated growth; (4) increase of fecundity not associated with increase in body size of adult females; (5) increase of fecundity due to increase in body size of adult females. The present study seems to verify the suitability of A. tsuensis as an organism for mass culturing as a food of marine fish larvae and juveniles.

Morphological aspects of feeding and improvement in feeding ability in early stage larvae of the milkfish,Chanos chanos

The osteological development of elements comprising the oral cavity and fins was examined in early stage larvae of laboratory-reared milkfish,Chanos chanos, from hatching to 200 hours after hatching. Fundamental elements of the oral cavity had developed by the time of initial mouth opening, 54 hours after hatching. The oral cavity was long and cylindrical, with a short, robust Meckels cartilage, and robust quadrate and symplectic-hyomandibular cartilages. The initial ossification of existing elements and addition of new elements occurred between 120–146 hours after initial mouth opening (HAMO), whereas the cartilaginous basihyal and caudal fin-supports appeared at 37.5 and 61.5 HAMO, respectively. Based on the morphology and developmental patterns of characters examined in this study, the feeding mode of early stage larval milkfish was considered to be “straining,” with an improvement in feeding ability occurring between 120–146 HAMO.

Morphological aspects of the development of swimming and feeding functions in the milkfish Chanos chanos.

Development of swimming and feeding abilities based on morphological development of larval and early juvenileChanos chanos was investigated. In larvae smaller than about 6.5 mm SL, mechanical supports of fins and branchial arches were in a primordial stage of development. Supports and rays of the vertical fins and branchial arches rapidly developed from 6.5 mm SL, and all components appeared by about 10.5 mm SL. Thereafter body depth proportion changed and the supports and rays of the paired fins and gill-rakers developed. These developmental events were nearly or totally completed by about 17 mm SL, and we concluded that the larvae transformed to juveniles at this size. By this time, the mode of swimming of the fish shifted from undulating locomotion to caudal propulsion and that of feeding from swallowing paniculate food to filtering and concentrating substrate food matters using gill-rakers and the epibranchial organ. One of the most characteristic, and well-known, phenomena in the life history ofChanos chanos is the mass occurrence in the surf zone of postlarvae of a limited size range. In view of the scheme of the development of mechanical supports of the body and fins, they may acquire a swimming ability strong enough to move against the current only upon reaching about 10.5 mm SL, and if active shoreward migration of the larvae occurs, it is only during the late period of their journey from the spawning grounds to the shore. The sudden disappearance from the surf zone of larvae larger than 15–16 mm SL is obviously related to a change in food habit.

Spawning behavior and early life history of the rabbitfish, siganus guttatus, in the laboratory

Abstract The spawning behavior and embryonic and larval development of Siganus guttatus are described from laboratory observations. Characteristic prespawning behavior began 4 h before actual spawning: the female touched the anal region of the abdomen on the bottom of the tank; the male displayed short, jerky, rushing movements towards the female, often with rapid circling around her. The male and the female separately released small amounts of milt and eggs several times during the pre-spawning ritual. The color of both sexes changed, the male becoming lighter and the female darker in ground color. Spawning took place at 02.30 h on the third day after the first quarter of the moon. During actual spawning, the pair swam side by side, with the female slightly ahead of the male. Fertilized eggs were small (0.56±0.008 mm), demersal and adhesive, with many oil globules. Larvae measured 1.74±0.043 mm total length at hatching, and possessed eight pairs of free neuromasts with long cupulae (60–180 μm) from 6 h to 39 h after hatching. The adult complement of fin ray counts was attained on day 16 when larvae (=juveniles) measured 8.34 mm total length on the average.

Iron in the Enameloid of Perciform Fish

It is known that a high concentration of iron is deposited in the enameloid of some teleostean fish. Previously, Suga et al. (1989) pointed out that the iron concentration in the enameloid is related to the phylogeny of fish rather than to the feeding habits, according to the results of quantitative iron analyses on the teeth of marine teleost fish of the Tetraodontiformes. In the present study, in order for the previous idea to be verified, quantitative iron analysis was made with an electron microprobe on the enameloid offish belonging to the Perciformes, which is the largest group of teleostean fish in the world and consists of both marine and freshwater species. The enameloid of all the fish examined (57 species) contained high iron concentrations ranging from 0.2% to 10.2% at the surface or middle layer, whereas that of an advanced suborder, Tetraodontoidei, of the Tetraodontiformes was very low in iron, at a level which could not be discriminated from the background value of the emission intensity. The distribution pattern of iron in the enameloid was classified into at least two types, namely, type A, in which a high iron concentration was observed mainly in the surface layer, and type B, in which iron was deposited throughout the entire layer, although there were differences in concentration. There were some differences in the concentration and distribution of iron in the enameloid for the families; for example, those of the Scaridae had a type A distribution, with about 0.2% iron only at the surface layer, whereas those of the Cichlidae, Centrarchidae, and Acanthuridae, which showed a type B distribution, contained iron ranging from 2.9% to 10.5% at the surface or middle layer of enameloid. Such differences seemed to be associated with the difference in timing of the commencement of the iron deposition into the developing enameloid, which is probably related to the phylogeny of fish. There was no evidence to support the idea that the iron concentration in the enameloid is associated with the feeding habits offish, as proposed by previous investigators.

Channa siamensis (Günther, 1861), a junior synonym of Channa lucius (Cuvier in Cuvier and Valenciennes, 1831)

Abstract The holotype of Channa siamensis (Günther, 1861) was examined and compared with specimens of all other channid species currently considered to be valid (2 genera, 27 species). As all of the examined morphological characters (meristics, morphometrics, coloration, a patch of gular scales, and cephalic sensory pores) of the small-sized hototype (74.2 mm SL) agree with those for C. lucius except for slight gaps in predorsal length and interorbital width (subject to allometric changes), the authors concluded that C. siamensis is a junior synonym of C. lucius (Cuvier in Cuvier and Valenciennes, 1831).