Embryonic and larval development of a Japanese spinous loach,Cobitis takatsuensis

The embryonic and larval development ofCobitis takatsuensis, a mountain stream spinous loach, was surveyed by incubating artificially inseminated eggs. The mean diameter of the inflated eggs and mean total length of newly-hatched larvae were 2.7 mm and 5.7 mm, respectively. The eggs were spherical, transparent and unpigmented, with a pale yellow yolk and no oil globule. The daily cumulative temperature to hatching was estimated to be 70–110°C. day. Hatched larvae were unpigmented with outer gill filaments on their cheeks, as in otherCobitis species, but the melanophores were comparatively less obvious at each developmental stage. The larvae started feeding eleven days after hatching yolk absorption being completed sixteen days after hatching. All the fin rays were fully developed and the juvenile stage reached at 16 mm TL, 38 days after hatching. Embryonic and larval developmental traits ofC. takatsuensis, such as egg size, clutch size and larval pigmentation, were similar to the Korean species,Niwaella multifasciata, that lives in the upper reaches of the Nak-tong river, andN. delicata, which inhabits Japanese mountain streams, rather than to its congeners. Among cobitine fishes, the spawning of a small number of larger eggs yielding larger larvae without pigmentation, characteristics shared byC. takatsuensis, N. multifasciata andN. delicata, is attributable to adaptation to cold mountain streams.     

Development of eggs,larvae and juveniles of the labrid fish,Halichoeres poecilopterus,reared in the laboratory

Embryonic, larval and juvenile development of the labrid fish,Halichoeres poecilopterus, is described using a laboratory-reared series. The eggs, measuring 0.60–0.72 mm in diameter, were pelagic and spherical with a single oil globule (0.12–0.16 mm in diameter). Hatching occurred 18 h 48 min after spawning. The newly-hatched larvae, measuring 1.46–1.70 mm TL, had 8–114 + 16–18 myomeres. A conspicuous melanophore appeared on the dorsal finfold 8 h after hatching, at ca. 2 mm TL. The yolk was completely absorbed 3 days after hatching, at 2.52–2.72 mm TL. Flexion of the notochord started at ca. 6 mm TL and was finished at ca. 8 mm TL. Aggregate numbers of all fin rays were completed at ca. 14 mm TL. Squamation was almost completed at ca. 20 mm TL.     

Influence of egg size on embryos and larvae of Fundulus heteroclitus (L.)

Egg size for Fundulus heteroclitus (L.) populations is concordant with the distribution of the two F . heteroclitus subspecies, i.e. F. h. heteroclitus eggs are considerably larger than F. h. macrolepidotus eggs. The influence of egg size on survival of embryos during incubation and survival and growth of newly-hatched larvae was estimated for four populations representing both subspecies along the Atlantic coast of the United States and in Delaware Bay. Survival of embryos was determined for incubation periods of 14, 21 and 28 days. Greatest differences in survival were detected following the longest incubation period where less than 50 per cent of the smaller F. h. macrolepidotus eggs survived while little or no mortality was detected among the larger F. h. heteroclitus eggs . Influence of egg size on larval survival was also greatest among those larvae hatched after 28 days where F. h. macrolepidotus larvae survived without food, for an average of 6 days, while F. h. heteroclitus larvae survived 11–12 days. F. h. heteroclitus larvae were significantly larger at hatching than F. h. macrolepidotus larvae. Larval growth rates were the same (0.4 mm day⁻¹) in both subspecies. As a result, size differences at hatching were still maintained after 42 days of growth. The differences in egg size along with other morphological and reproductive characteristics of F. heteroclitus populations probably represent genetically based adaptations to environmental conditions, of which the length of the spawning season is one of the major components stimulating the coevolution of these traits.     

Embryonic, larval and juvenile development of the roughskin sculpin,Trachidermus fasciatus (Scorpaeniformes: Cottidae)

Embryonic, larval and juvenile development of the catadromous roughskin sculpin,Trachidermus fasciatus, were described using eggs spawned in an aquarium. The eggs, measuring 1.98–2.21 mm in diameter, were light reddish-yellow and had many oil globules, 0.05–0.18 mm in diameter. Hatching occurred 30 days after spawning at 2.3–11.3°C. The newly-hatched larvae, measuring 6.9–7.3 mm BL, had a single oil globule, 9–10+25–26=34–36 myomeres and 6 or 7 large stellate melanophores dorsally along the gut. The yolk was almost resorbed, number of pectoral-fin rays attained 16–17, and two parietal, one nuchal and four preopercular spines were formed, 5 days after hatching, at 8.2–8.4 mm BL. The oil globule disappeared, and one supracleithral spine was formed, 11 days after hatching, at 8.9–9.5 mm BL. Notochord flexion began 15 days after hatching, at 9.7–10.3 mm BL. A posttemporal spine was formed 20 days after hatching, at 10.7–10.9 mm BL. The first dorsal fin spines (VII–VIII), second dorsal fin and anal fin rays (18–19, 16–18, respectively) appeared 23 days after hatching, at 12.0–13.7 mm BL. The pelvic fin spine and rays (I, 4) were formed and black bands on the head and sides of the body began to develop 27 days after hatching, at 13.8–15.8 mm BL. Newly-hatched larvae swam just below the surface in the aquaria. Preflexion larvae (8.9–9.5 mm BL), in which the oil globule had disappeared, swam in the middle layer, while juveniles (13.8–15.8 mm BL) began swimming on the bottom of the aquaria. Swimming behavior observed in the aquaria suggested that the fish started to change to a demersal existence at the juvenile stage.     

Characteristics of egg and larval production in captive bluespotted gobies

Spawning of the Hawaiian coral-reef goby Asterropteryx semipunctata was diurnal, occurring at various times throughout the day. Mean length of eggs deposited in nests was 0·76 mm (range 0·67–0·84); mean egg width was 0·47 mm (range 0·41–0·52). Clutch size varied from 296 to 1552 eggs (mean=886±309), and was independent of standard length, total body weight, and body condition. Mean relative clutch size was 1·59 eggs mg^-1 total body weight (range 0·84–2·43). Clutches hatched 4–5 nights after being deposited in a nest. Mean notochord length of newly-hatched larvae was 1·88 mm (range 1·60–2·04). The minimum period of time that elapsed between egg deposition and subsequent growth of a new batch of oocytes to spawning size was 5–6 days, providing a reasonable estimate of minimum spawning interval. Compared with other gobiids, tropical species tend to have shorter incubation periods, smaller eggs and smaller larvae at hatching.     

The life-history strategy of deepwater sculpin, Myoxocephalus thompsoni (Girard), in Lake Michigan: dispersal and settlement patterns during the first year of life

Deepwater sculpin, Myoxocephalus thompsoni (Girard), were sampled from six stations from the 15–100 m depth contours in Lake Michigan between April 1983 and July 1984. In south-eastern Lake Michigan M. thompsoni lay benthic eggs in offshore waters, which hatch between November and August, with peak hatching in March. Abundance of larvae in pelagic samples was higher offshore than inshore, but larval size was greater and development more advanced at inshore stations, indicating an inshore movement after hatching. Larvae reached metamorphosis at 20 mm and settled to the bottom beginning in July. Pelagic larvae 20–40 mm were found in the lower water column at all stations, but newly settled individuals were only captured with bottom trawls at inshore locations (≤60 m depth). Data from ichthyoplankton and bottom trawl samples in 1983 and 1984 indicated that locations for successful settlement of larvae to the bottom extended only as deep as the shallowest fringe of the adult population (> 50 m in 1983). In 1983, maximum density of larvae reached 0.4 individuals m⁻³ by June. Survival from the pelagic larval stage to the demersal young-of-year stage in 1983/1984 was c . 0.1–0.4%. The specific mechanism of mortality at the time of transition to a demersal habit has not been determined.     

Reproductive behaviour and early development of the Drysdale hardyhead, Craterocephalus sp. nov. (Pisces: Atherinidae), from the Alligator Rivers System, Northern Territory, Australia

Craterocephalus sp. nov. showed sexual dimorphism in body shape during the breeding season. Pairing occurred during daylight with a single release of eggs amongst submerged vegetation between sunrise and the early afternoon on the same day. The eggs were demersal, adhesive, spherical (0.87–0.96 mm diameter) and had 12 adhesive filaments (0.5–1.5 mm long) at the animal pole. Approximately 24 oil droplets (0.02–0.08 mm diameter) persisted throughout egg and larval development. Hatching occurred 155–160 h after spawning at 25–27° C.
The yolk-sac larvae were 3.85–3.95 mm notochord length at hatching and began feeding at the surface after absorption of the yolk (3–12 h after hatching). All fin rays were developed in 9.4 mm standard length fry, which moved from midwater to feed on the substrate. Aquarium reared fish first spawned at 30 mm s.L. when 165 days of age.
Features of Craterocephalus reproduction, as they relate to a specific survival strategy, are briefly discussed.     

Determining the optimum temperature and salinity for larval culture,and describing a culture protocol for the conservation aquaculture for European smelt Osmerus eperlanus (L.)

Populations of anadromous European smelt Osmerus eperlanus (L.) are declining across its geographical range in northern Europe, but no practical culture techniques exist to develop stock enhancement programmes for this species. In this study, a culture protocol is described to rear fish from fertilised eggs to mature adults in 2 years involving the use of ‘green water’, live feed and artificial diets. The sequence of embryonic development for eggs incubated at 10°C/0 ppt was described and photographed. To determine the optimum conditions for larval culture, fertilised eggs were reared at a range of salinities (0–20 ppt) and temperatures (5–18°C) until first feeding. Best hatching success (ca. 97%), size at hatch (ca. 0.8 mm) and survival to first feeding (ca. 96%) of larvae were achieved under combined conditions of low salinity (0–0 ppt) and temperature (5–10°C). No larvae survived a salinity of 20 ppt. The time taken from fertilisation to hatch (FtH) and hatching duration (HD) were temperature-dependent ranging from 42 days FtH and 10 days HD at 5ºC, to 10 days FtH and 2 days HD at 18°C irrespective of salinity. The results indicate that conservation programmes could utilise existing salmonid hatchery facilities (i.e. freshwater, ≤10°C water temperature) for stock enhancement. Since on-growing of smelt involves the logistical and technical problems of live feed production, it is recommended that smelt enhancement programme utilise freshwater hatchery facilities to rear fish until hatching, and then stock out onto known spawning grounds in rivers allowing hatched larvae to drift into estuaries to complete the larval and juvenile phases. This approach would minimise the time spent in the hatchery post-hatching, eliminate the need for live food production, prevent the development of predator-naïve fish, and hence would mimic the natural life cycle of the species as closely as possible.     

Growth and morphological development of larval and juvenileepinephelus bruneus (perciformes: Serranidae)

The growth and morphological development of larval and juvenileEpinephelus bruneus were examined in a hatchery-reared series. Average body length (BL) of newly-hatched larvae was 1.99 mm, the larvae growing to an average of 3.96 mm by day 10, 6.97 mm by day 20, 12.8 mm by day 30, 22.1 mm by day 40 and 24.7 mm by day 45 after hatching. Newly-hatched larvae had many mucous cells in the entire body epidermis. By about 4 mm BL, the larvae had developed pigment patterns peculiar to epinepheline fishes, including melanophores on the dorsal part of the gut, on the tips of the second dorsal and pelvic fin spines, and in a cluster on the ventral surface of the tail. Spinelets on the second dorsal and pelvic fin spines, the preopercular angle spine and the supraocular spine, had started to develop by about 6 mm BL. The notochord tip was in the process of flexion in larvae of 6–8 mm BL, by which time major spines, pigments and jaw teeth had started to appear. Fin ray counts had attained the adult complement at 10 mm BL. After larvae reached 17 mm BL, elements of juvenile coloration in the form of more or less densely-pigmented patches started to appear on the body. Squamation started at 20 mm BL. Major head spines had disappeared or became relatively smaller and lost their serrations by 20–25 mm BL.     

Development of eggs, larvae and juveniles of laboratory-reared blue whiting,Sillago parvisquamis (Percoidei: Sillaginidae)

The embryonic, larval and juvenile development of blue whiting,Sillago parvisquamis Gill, are described from a series of laboratory-reared specimens. Mean egg diameter and mean total length (TL) of newly-hatched larvae were 0.71 mm and 1.58 mm, respectively. The eggs were non-adhesive, buoyant and spherical with an oil globule (mean diameter 0.18 mm). Hatching occurred about 20 hours after fertilization at a temperature of 24.0–25.0°C, newly-hatched larvae having 38–40 myomeres. The yolk and oil globule were completely absorbed 3 days after hatching at 2.8–3.2 (mean 3.0) mm TL. Notochord flexion was completed by 7.2–8.2 (7.7) mm TL, and pectoral and caudal fin rays fully developed by approximately 10 mm and 8.5 mm TL, respectively. Completion of fin development occurred in the following sequence: caudal, pectoral, anal and second dorsal, first dorsal and pelvic, the last-mentioned by approximately 11 mm TL. The larvae ofS. parvisquamis andS. japonica, which closely resemble each other in general morphology and pigmentation, could be distinguished as follows. Newly-hatchedS. parvisquamis larvae had more myomeres thanS. japonica (38–40 vs. 32–34) and more melanophores on the dorsal surface of the body (19–28 vs. about 40).Sillago japonica had a vertical band of melanophores on the caudal peduncle, which was lacking in postflexionS. parvisquamis larvae. In addition, juveniles ofS. parvisquamis (larger than 23 mm TL) had melanophores on the body extending anteriorly to below the lateral line to form a midlateral band, whereas no obvious band occurred on similarly-sizedS. japonica juveniles.     

Morphological development and allometric growth patterns in hatchery-reared California halibut larvae

Morphological development, allometric growth and behaviour of hatchery-reared California halibut Paralichthys californicus were studied from hatching to metamorphosis (42 days post hatch, dph) at 187° C. Mean standard length ( L _S) of larvae and juveniles increased from 2.1 mm at hatching to 10.5 mm at metamorphosis with the increase in length being approximately linear. Stages of morphological development were described using the alphabetic staging (A–I) used for other flatfish species. Organogenesis and differentiation were more rapid and complex in yolk-sac (hatching, stage A–3 dph, stage B), preflexion (3–19 dph, stages B–C), and flexion larvae (from 20 to 23 dph, stages D–E), as larvae developed most of their sensory, feeding, respiratory and swimming systems. After notochord flexion at 24–25 dph (stage F), most morphological changes were related to the progressive transformation from a bilateral symmetrical larva to an asymmetrical benthic juvenile (42 dph, stages G–I).     

Early life characteristics of pike, Esox lucius, in rearing ponds: temporal survival pattern and ontogenetic diet shifts

Survival, biomass and diet of pike, Esox lucius , larvae and juveniles were studied over 3 years by stocking free embryos at a density of six fish m⁻² in 12 drainable outdoor ponds. The ponds were sequentially drained at six larval/juvenile developmental stages, up to a total length (T.L.) of 139 mm. The mean rate of survival at harvest decreased irregularly over time and the highest mortality rates were recorded during the early larval period (13 to 27 mm t.l .) and two intervals of the juvenile period (46 to 99 mm T.L. and 121 to 139 mm t.l .). Mean biomass increased dramatically between 46 mm T.L. (19.8 kg ha⁻¹) and 121 mm T.L. (181.8 kg ha⁻¹) and stabilized between 121 and 139 mm t.l . Sharp increases in the mean weight coefficient of variation were recorded during the early larval period (13 to 27 mm t.l .) and between 74 and 121 mm t.l . (development of cannibalism). Diet breadths were relatively narrow in pike larvae and reached maximum levels in 99 mm t.l . juveniles. Average-sized pike exhibited a sequence of size-dependent shifts from a diet composed primarily (in terms of weight) of micro-crustaceans (at 13 mm t.l .), to chironomid larvae (at 74 to 99 mm t.l .), and finally macrocrustaceans (at 121 to 139 mm t.l .). Cannibalism was detected first among the largest fish at the 74 mm t.l . stage. Between-year diet similarity at various developmental stages was consistently high. In 70 mm t.l . fish harvested from different ponds, we found significant among-pond differences in diet composition; however, similar trends of diet changes in relation to fish size were observed from pond to pond. Our results are discussed in light of existing knowledge of young pike trophic ecology and current aquaculture practices.     

Muscle growth in yolk-sac larvae of the Atlantic halibut as influenced by temperature in the egg and yolk-sac stage

Atlantic halibut eggs and yolk-sac larvae were incubated at 1, 5 and 8° C. Eggs incubated at 8° C gave slightly shorter larvae at hatching with a significantly smaller total cross-sectional area of white muscle fibres than eggs incubated at 5° C. Transport of eggs 2 days prior to hatching gave significantly longer larvae at hatching with a significantly larger red fibre cross-sectional area than when eggs were transported shortly after the blastopore closure. A higher survival until 230 degree days after hatching was also observed in the former group. All eggs incubated at 1° C died before hatching and all larvae incubated at 1° C died before 45 degree days after hatching. From hatching until 230 degree days the total white cross-sectional area increased threefold in all temperature groups. The increase in white cross-sectional area was entirely due to hypertrophy between hatching and 150 degree days (10 mm L _S). Recruitment of new white fibres increased in germinal zones at the dorsal, ventral and lateral borders of the myotome from 150 degree days onwards, but at 230 degree days (12–13 mm L _S) the recruitment fibre zone constituted <10% of the total white cross-sectional area. Larval incubation at 8° C gave slightly longer larvae with a significantly larger cross-sectional area of recruitment fibres at 230 degree days than incubation at 5° C. The larval group incubated at 8° C also had a significantly lower survival until 230 degree days than did the 5° C group. Incubation temperature regimes did not affect the volume density of myofibrils in the axial muscle fibres at 230 degree days. Thus hypertrophy is the predominant mechanism of axial white muscle growth in Atlantic halibut yolk-sac larvae and an increased rearing temperature during the yolk-sac stage increases white muscle fibre hyperplasia.     

Influence of light intensity and photoperiod on embryonic development,survival and growth of threatened catfish Ompok bimaculatus early larvae

Larval growth and survival of catfishes are largely influenced by the various biotic and abiotic factors. The present study investigated the effect of different light intensities and photoperiods on growth and survival of Ompok bimaculatus larvae. Three separate trials of 21 days each were carried out in an aquarium tank. The first trial investigated the embryonic changes (based on hatching rate and time) upon exposure to varied light intensity (0, 300, 500, 900 and 1200 lx) and photoperiodic regime (24l:0d, 16l:8d, 12l:12d, 8l:16d and 0l:24d). Subsequently, hatched-out larvae were subjected to the aforementioned intensities (Trial II) and photoperiod (Trial III, intensity of 300 lx) for growth and survival attributes. Eight hundred healthy larvae (average body weight = 0.003 g) were randomly distributed into five treatment groups for the last two trials. Results suggest a higher embryo hatching rate and larval survival at 0 and 300 lx, whereas the largest larval growth was observed at 900 lx. In Trial III, survival was highest in 0l:24d and growth in 24l:0d and 16l:8d was higher (P < 0.05). Performance index was higher (P < 0.05) in both 0 and 300 lx light and decreased at higher intensities. The overall interpretation from the present study concludes that a completely dark rearing environment is recommended for better survival of O. bimaculatus although growth was compromised.     

Development of eggs,larvae and juveniles of the puffer,Takifugu chrysops,reared in the laboratory

The artificial fertilization of the puffer,Takifugu chrysops (Hilgendorf), was carried out at Sajima in Yokosuka City on May 22, 1984. Hatched larvae were reared for a period of about 150 days. The spawning period seems to extend from mid to late May in the eastern part of Sagami Bay. The eggs were spherical, pale milky white and semitransparent, demersal and adhesive in nature, measuring 1.32±0.04 mm in diamter, and with a cluster of small oil-globules. The incubation period was about 162 hours at a water temperature of 17.4 to 21.8°C. During embryonic development, the only pigment cells that appeared on the embryo were the black chromatophores. The newly hatched larvae measured from 2.72 to 3.06 mm TL, averaging 2.87±0.1 mm TL, and 22–23 (9 + 13?14) myomeres. At yolk absorption, 4 days after hatching, the larvae attained 3.64–3.79 mm TL. On the 11th day, postlarvae averaged 4.69±0.24 mm TL. Larval finfolds disappeared and rudimental dorsal, anal and caudal fins were formed. There were two large clusters of melanophores, one on the back, exteding from the mid-base of the dorsal fin to the caudal peduncle region, the other along the anal fin base. The color of the body began to turn pale green to brownish-orange and spinelike scales appeared on the belly. Eighteen days after hatching (7.02±0.27 mm TL), the caudal notochord began to turn up and a “constriction” appeared on the posterior margin of the caudal fin membrane. This notch moved upwards as the notochord upturning advances. The larvae attained full fin ray counts and reached the juvenile stage at 9.1-9.5 mm TL, 24 days after hatching. Characteristic black blotches on the back and specific brownish orange body color appeared at the stage of 20 mm TL, 24 days after hatching. The growth during the larval stage and early juvenile stage (24 to 51 days after hatching) were expressed by the following equations, wherey is total length (mm) andx is days after hatching.y ₁=2.8424× 1.0509⁹ (0≦x≦24)y ₂ = 3.7872×1.0372^x (24≦x≦51)     

Larval retention and dynamics of the prawns Palaemon longirostris H. Milne Edwards and Crangon crangon Linnaeus (Decapoda,Caridea) in the Mira estuary,Portugal

Summary

Palaemon longirostris and Crangon crangon larval and post-larval stages were collected intensively in two 24-h cycles during neap and spring tidal periods in a fixed station located in the mid-Mira estuary (southwest Portugal). In each case, on the previous day, horizontal distribution of larval stages was studied in a series of 20 stations from the mouth of the estuary to near freshwater. Horizontal distribution of the discrete instars of both species were similar, suggesting larval retention. Results from the 24-h cycles indicate a semilunar cycle of larval release activity, and an initial displacement of the larvae from the parental stock, as newly-hatched larvae concentrate in the surface layer of the water column on post-crepuscular ebbing tides. The sequence of larval stages tends to be progressively more dependent of the bottom layers, and the whole larval and post-larval development is accomplished within the estuarine boundaries. Larval release cycles, coupled with duration of development and progressive change in vertical position, induce mutual exclusion of different aged larvae, which may minimise cannibalistic behaviour and competition between larvae with different capabilities.     

Egg production, hatching rates, and abbreviated larval development of Campylonotus vagans Bate, 1888 (Crustacea: Decapoda: Caridea), in subantarctic waters

Early life history patterns were studied in the caridean shrimp, Campylonotus vagans Bate, 1888, from the subantarctic Beagle Channel (Tierra del Fuego). As a consequence of very large egg size (minimum 1.4 mm), fecundity was low, ranging from 83 to 608 eggs per female (carapace length [CL] 11-22.5 mm). Egg size increased continuously throughout embryonic development, reaching prior to hatching about 175% of the initial diameter. Due to low daily numbers of larval release, hatching of an egg batch lasted for about 2-3 weeks. The complete larval and early juvenile development was studied in laboratory cultures fed with Artemia sp. nauplii. At 7.0±0.5 °C, development from hatching to metamorphosis lasted for about 6 weeks. It comprised invariably two large zoeal stages and one decapodid, with mean stage durations of 12, 17, and 15 days, respectively. Larvae maintained without food survived on average for 18 days (maximum: 29 days), but did not reach the moult to the zoea II stage. Size increments at ecdysis were low in all larval stages (2.1-3.9%), indicating partial utilisation of internal energy reserves. A clearly higher increment (14%) was observed in the moult from the first to the second juvenile stage. Low fecundity, large size of eggs and larvae, an abbreviated mode of larval development, high larval survival rates during absence of food, demersal behaviour of the early life history stages, and an extended hatching period with low daily release rates are interpreted as adaptations to conditions typically prevailing in subantarctic regions, namely low temperatures (causing long durations of development) in combination with a pronounced seasonality in plankton production (i.e., short periods of food availability).     

Early development of milkfish: effects of salinity on embryonic and larval metabolism, yolk absorption and growth

During embryogenesis of Chanos chanos , more than half of the yolk was consumed and the majority of it was converted into larval tissue. Salinity affected both yolk absorption and embryonic and larval growth. Larvae hatched in 20% had larger yolk reserves but were smaller and grew more slowly than larvae in 35 and 50%. Larvae hatched in 35 and 50% had equal amounts of yolk but those from 35% were larger. Oxygen consumption rates increased during development (from 0.06 ± 0.01 μl O₂ egg^–1 h^–1 by blastulae to 0.37 ± 0-01 μl O₂ egg^–1 h^–1 by prehatch embryos and 0–43 ± 0–03 μl O₂ larva ^–1 h ^–1 by newly-hatched larvae) and were significantly affected by salinity. Eggs and yolk-sac larvae incubated in 35% consumed more oxygen than those in the low and high salinities. Salinity affected both the rate and pattern of yolk utilization but salinity-related differences in metabolism, yolk absorption, and growth were not related directly to the osmotic gradient. Low salinity retarded yolk absorption while high salinity reduced yolk utilization efficiencies. Differences in oxygen consumption rates were probably related to variations in the relative amounts of metabolically active embryonic and larval tissue and/or higher activity levels rather than differential osmoregulatory costs. 35% is probably the most suitable salinity for incubation and larval rearing of milkfish.     

A preliminary report on the development, growth and survival of laboratory reared larvae of the grey mullet, Mugil cephalus L.

Larvae from artificially bred grey mullet were reared in the laboratory and survival rates of 0.2 %, 5 % and 5 % achieved in three of six trials. Food consisted of wild zooplankton and Anemia nauplii. Feeding began on the fifth day, when the yolk sac was depleted, and intensified on the ninth day. The rate of yolk absorption and feeding intensity were reflected in the growth curve. Larval survival was not affected by withholding food from the larvae till the seventh day from hatching. Two critical periods associated with high larval mortality were apparent on the 2nd–3rd and 8th–11th days after hatching. These were preceded by an increase in specific gravity of larvae followed by passive sinking to the bottom of the rearing tank. Larval length increased from 2.63 mm at hatching to 17.69 mm at the end of the 42-day larval period. The larvae survived on benthic diatoms therefter. Maximum survival rates were achieved at 22°C. (Oceanic Institute Contribution No. 101).     

Embryonic development and newly hatched larvae of the little dragon sculpinBlepsias cirrhosus

This paper describes both embryonic development and newly hatched larval morphology of the little dragon sculpinBlepsias cirrhosus. The eggs ofB. cirrhosus are almost spherical, 3.0–3.2 mm in diameter, and have a yolk color of burnt orange. Development is very slow, being especially sluggish once the embryo appears. The embryo begins forming from the 10th day. In size, the early embryo is less than 1/6 of the yolk’s circumference. Incubation at 10°C takes about 200 days, 50 days shorter than the incubation period in a natural environment, with a mean water temperature of 11°C. The notochord length of newly-hatched larvae averages 11.1 mm. The larvae are developed so fully that the notochord is already flexing and the caudal and pectoral rays are forming.