Chikara Kitajima

Nutritional values of live organisms used in Japan for mass propagation of fish: A review

Abstract The mass production of zooplankton, in particular the rotifer, Brachionus plicatilis, and the brine shrimp, Artemia salina, is considered to be of vital importance for the rearing of larval fish (up to 30–50 mm total body length) in Japan. Data on the proximal, mineral, protein and essential fatty acid (EFA) contents of live food organisms are reviewed: the EFA content chiefly determines the dietary value for fish larvae. The EFA content of rotifers supplied with yeast during the culture period was less favourable for larval fish growth than that of rotifers given marine Chlorella. The nutritional value of yeast-fed rotifers may be improved either by the use of the recently developed ω-yeast (indirect method) or by feeding with a mixture of homogenized lipids and bakers yeast (direct method). Artemia could be classified into two types, marine — containing a high content of 20:5ω3 (an EFA for marine fish), and freshwater — containing a high content of 18:3ω3 (an EFA for freshwater fish). The fish mortalities sometimes encountered with Artemia may be related to this difference. Either type may be used for freshwater fish larval nutrition. For marine fish, the marine Artemia type is adequate but the freshwater type should be fed together with marine copepods or should be enriched by feeding on lipids with high ω3 HUFA contents.

Recent development of a high density mass culture system for the rotifer Brachionus rotundiformis Tschugunoff

Feeding rotifer mass cultures condensed Chlorella made it possible toculture rotifers at 103 ind. ml−1 Subsequently,it was realized that to raise the culture density of rotifers to104 ind. ml−1, inhibitory factors (low dissolvedoxygen, foaming separation, and NH3-N toxicity) needed to bereduced through oxygen gas supplementation and regulation of pH at 7.However, even after these improvements, problems remained to be solved. Oneis controlling debris, particulate organic matter and microbes which oftenclog the collection nets during harvest. Another problem is the developmentof a more accurate quantitative method for determining Chlorella and rotiferdensities that could replace the conventional counting method. Theseproblems have been resolved in the following manner. (1) Filtering equipmentfor removing particulate debris in the culture media: Filtering equipmentmade of a nylon mat and a stainless steel frame was developed to increasethe surface area for debris removal. Using this filter, the harvest of highdensity culture at 104 rotifers ml−1 waspossible without clogging of the collection net. (2) Quantitativedetermination of rotifers by a centrifugation method: We determined theabundance of rotifers by centrifuging samples and measuring their packedvolume (PV, ml l−1). PV of rotifers was easier to and moreaccurate to measure (coefficient of variation, 4%) than a directcount of the density (coefficient of variation, 15%). Organic wastesin rotifer cultures made the measurement of rotifer PV difficult. By placinga filter in the mass culture tank, however, the boundary between rotifersand other organic wastes in a centrifuge tube was easily visualized.

Annual reproductive cycle of the captive female Japanese sardineSardinops melanostictus: Relationship to ovarian development and serum levels of gonadal steroid hormones

Gonad and blood samples were taken from the captive female Japanese sardineSardinops melanostictus between 1988 and 1989, and changes in serum levels of gonadal steroids were correlated with the annual gonadal cycle. Under captive conditions, female fish did not mature and spawn spontaneously, although oocytes developed up to the end of vitellogenic growth. Based on evidence from ovarian histology, the annual gonadal cycle of the Japanese sardine was divisible into four periods, i.e., immature (June to October), vitellogenesis (November to December), spawning (January to March), and post-spawning (April to May). The pattern of seasonal change in the gonadosomatic index (GSI) showed an inverse correlation to change in water temperature and reflected the degree of ovarian maturity. The serum estradiol-17β level increased from its lowest concentration (0.12 ng ml−1) in September to a peak (1.14 ng ml−1) in March. Serum 17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-P) was detectable at low levels (<0.3 ng ml−1) between October and February, but was below the assay detection limit (0.06 ng ml−1) at all other times. Testosterone was not detectable (<0.06 ng ml−1) in the serum of any fish throughout the year. The effects of several steroids on the maturation of follicle-enclosed oocytes of sardine were examined in vitro, and 17α,20β-P was found to be the most potent inducer of maturation. This suggests that post-vitellogenic oocytes of the Japanese sardine in captivity have an ability to respond to an appropriate hormonal effector and subsequently to resume meiotic maturation.

Effects of salinity and temperature on incubation period, hatching rate, and morphogenesis of the silver sea bream, Sparus sarba (Forskål, 1775)

Abstract Effects of salinity and temperature on eggs of silver sea bream (Sparus sarba) were studied in laboratory experiments. Naturally fertilized eggs were incubated under 60 different combinations of constant temperature (13.0, 15.0, 18.5, 22.0 and 23.5°C) and salinity (8, 12, 16, 20, 24, 28, 32, 36, 40, 44, 48 and 52‰). Incubation period, hatching period, hatching rate, abnormalities and total length of newly hatched larvae were investigated. The relation between incubation period and temperature was expressed for salinity levels of 24, 28, 32, 36, 40 and 44‰. Hatching occurred between 12 and 52‰ and between 13.0 and 23.5°C. Higher hatching rates of normal larvae were observed at 18.5°C between 20 and 36‰ and at 22.0°C between 28 and 32‰. Largest larval size was observed at 22.0°C and between 28 and 36‰. Using multiple regression analysis the calculated maximum yield of normal larvae was 66.7% at 19.4°C and 31.4‰.

Testicular development and serum levels of gonadal steroids during the annual reproductive cycle of captive Japanese sardine

Gonad and blood samples were taken throughout the year from captive males of the Japanese sardine,Sardinops melanostictus, and changes in serum levels of gonadal steroids were examined in relation to the annual gonadal cycle. On the basis of testicular histology, the annual gonadal cycle was divisible into four periods: immature (July–September), spermatogenesis (October–December), spermiation (January–April), and post-spawning (May–June). The pattern of seasonal changes in the gonadosomatic index (GSI) was inversely correlated with that of water temperature, and reflected the degree of testicular maturity. The serum testosterone level was relatively low during spermatogenesis (2.2–2.5 ng/ml), rose markedly around the time of spermiation (7.7–24.6 ng/ml), and became low after spawning and during immature periods (0.6–0.7 ng/ml). The serum 17α,20β-dihydroxy-4-pregnen-3-one level was high in males with spermatogenic or spermiating testes (0.6–1.0 ng/ml), but became low (0.2 ng/ ml during the post-spawning period and was undetectable in immature fish. Although 11-ketotestosterone was detectable in some fish, the values obtained were thought to reflect cross-reactivity of the antiserum employed with testosterone. These findings are discussed in relation to male reproduction of the Japanese sardine and steroidal regulation of spermatogenesis and spermiation in other teleosts.

Early development of laboratory-reared redlip mullet, Liza haematocheila

Abstract Eggs and sperm of Liza haematocheila were obtained from mature adults under natural conditions, fertilized artificially and incubated in the laboratory. Larvae and juveniles were reared for about 3 months by feeding with rotifers, Artemia nauplii and artificial feed. Early development and growth were described from a series of live specimens of larvae and juveniles. Fertilized eggs hatched after 80–95 h incubation at 15.6–21.2 °C. Feeding began on the 6th day after hatching, when some yolk still remained. Absorption of the oil globule was completed on the 13th day. The notochord staned to flex on the 15th day. The morphological transition from the larval to the juvenile stage occurred during the 25th to 29th days between 12.0 and 14.0 mm in total length (TL). When the larvae transformed to juveniles, the third anal fin ray had not yet transformed into a spine. The formation of the third anal spine occurred during the 40th to 76th days, between 21.6 and 45.5 mm TL; during this period juveniles transformed to young adults. Changes in proportion of the body parts to total length were observed at approximately 13 mm and 30 mm TL, corresponding to the transformations from larva to juvenile and from juvenile to adult, respectively.

Induction of ovarian maturation and development of eggs, larvae and juveniles of the tonguefish,Cynoglossus abbreviates, reared in the laboratory

Cynoglossus abbreviatus spawns from mid-March to mid-April in the Sea of Shimabara in Kyushu. During the spawning season ovarian maturation was successfully induced by injection of the pituitary homogenate ofHypophthalmichthys molitrix. The dose of the aceton-dried pituitary homogenate was 6.5 mg/kg body weight ofC. abbreviatus. It took about 2 days for ovulation after injection at a water temperature of 14 to 16°C. Artificial fertilizations were accomplished on March 29, 1974 and again on April 7, 1984, using the females matured by hormone injection in the latter case only. The larvae were reared on the rotifers,Artemia nauplii,Tigriopus japonicus and copepods collected from the sea over a period of 113 days in 1974 and 58 days in 1984. The eggs were pelagic, spherical, 1.19–1.23 mm in diameter and had 30–50 oilglobules of 0.068–0.095 mm in diameter, and the perivitelline space was narrow. The incubation period was 90–98 hours at a water temperature of 14 to 16°C. The newly hatched larvae were 3.18–3.45 mm TL and had 61–64 myomeres. The larvae had many melanophores and xanthophores on the body, forming three bands on the caudal region, but were lacking chromatophores on the finfolds. The yolk was completely absorbed when the larvae attained a size of 4.7–5.6 mm TL 8 days after hatching. A single elongated dosai fin ray developed on the head in the 8-day old larvae. The ray was reduced in size as long as the other rays 1 or 2 days after metamorphosis. The rudiment of pectoral fins were found on the both sides of the body in the 2-day old larvae, but two of them disappeared after metamorphosis. A pelvic fin first appeared as a ventral bud just anterior to the gut in the larva of 8.39 mm TL. The full count of 4 rays was observed on the larva of 10.83 mm TL. Metamorphosis began 22 days after hatching when the larvae were 11.20 mm TL. The right eye began to shift the left side of the head at night and reached to the final place after 8.5 hours. It took about 36 hours to complete the metamorphosis, including the eye movement and fusion of the hole in the rostral beak. At the last stage of metamorphosis, the dosal, caudal, anal and ventral fins became confluent. The larvae reached the juvenile stage at a size of 13.5–14.0 mm TL, approximately 28 days after hatchling. The growth of larvae reared in 1974 is expressed by the following equations: Y1 = 3.448 · 1.0507x (8≦X≦28) Y2 = 6.3322 · 1.0275x (28≦X≦75) where Y is the total length (mm) and X is the number of days after hatching. Growth rate changed after metamorphosis.