Preliminary investigations on rabbitfish, Siganus canalicullatus, cultivation in Tanzania

Preliminary investigation on the culture of Siganus canalicullatus in floating cages in Tanzania coastal water has revealed that the fish has high culture potential in the region. It is euryhaline, inhabiting areas where salinities range from 23‰ to 35.8‰. The fish grows faster on pelletted diets than on ordinary seaweeds. It is estimated that the fish would reach a marketable size of 20 cm fork length in 6 months; hence two crops can be harvested in a year.     

Induced spawning of sea bass, Lates calcarifer, and rabbitfish, Siganus guttatus, after implantation of pelleted LHRH analogue

Captive Lates calcarifer broodstock at Tigbauan, Iloilo (Philippines) were implanted with cholesterol-based pellets of the LHRH analogue D-Trp⁶-desGly¹⁰-LHRH ethylamide or D-hArg(Et₂)⁶,Pro⁹-NHet-LHRH at doses between 9.0 and 23.5 μg/kg body weight. In May, one of ten LHRH-treated females released partially hydrated ova into the tank 4 days after implantation. In July, at least one (and probably four) of five LHRH-treated females spawned in the tank 2 days after implantation; 2.6 million hatchlings were collected. In August, both LHRH-treated females spawned in the tank 2 days after implantation; 978 000 hatchlings were collected. None of the sham-operated control fish spawned in any of the experiments.Captive Siganus guttatus broodstock implanted with silastic-based pellets of the LHRH analogue D-Nal (2)⁶ LHRH spawned 1–2 days earlier than sham-operated controls.     

An experiment in rearing larval Siganus vermiculatus (Valenciennes) and some observations on its spawning cycle

Siganus vermiculatus spawned in captivity on three occasions, and limited numbers of newly hatched larvae were stocked in an 80-m³ outdoor concrete tank and a 2000-m² fish pond in Fiji. Survival through the larval stage was 9% in the tank, in spite of high temperatures and relatively low food densities. No larvae survived in the pond.Data collected on the appearance of fry, spawning, and the gonadal state of adults suggest that S. vermiculatus in Fiji spawns monthly on or around the first lunar quarter during its spawning season.Possible ways to solve problems encountered in this experiment are discussed.     

Larval rearing and development of Siganus lineatus (Pisces: Siganidae) from hatching through metamorphosis

Larvae of Siganus lineatus were hatched and reared through metamorphosis in a 7 000-1 tank covered with a translucent roof. The larvae were fed phytoplankton (mixed cultures), rotifers (Brachionus plicatilis), copepods (Oithona sp.), and Artemia nauplii. Thirty-five days were required for all the larvae to metamorphose; survival was 800 out of 5 000 (16%). The rearing period and rearing criteria are identical to those required for S. canaliculatus. Three important developmental stages were identified: the dark-head carnivorous stage (the gut is a simple coil), the brown-head omnivorous stage (the gut is elongated and convoluted), and the juvenile herbivorous stage (the gut is highly elongated and convoluted into a complex coil). Over-feeding on Artemia nauplii may result in deaths among brown-head and juvenile fishes; adjustment of the feeding regime when larvae begin to develop into the brown-head stage is considered important. Copepods are an excellent substitute for Artemia nauplii during this period     

Breeding and larval rearing of the rabbitfish,Siganus guttatus (Bloch)

Females of Siganus guttatus reared to sexual maturity in canvas tanks were induced to spawn by using human chorionic gonadotropin (HCG, Ayerst) at 500 IU/fish or about 2 IU/g body weight. The amount of HCG used depended on the initial mean egg diameter; the smaller the diameter, the more HCG was used. Fish with oocytes characterized by germinal vesicle migration (mean egg diameter ≥ 0.47 mm) spawned without HCG injection. Fertilization and hatching rates for both treated and untreated fish were more than 90%. The larvae were reared to metamorphosis using rotifers from day 2–17, rotifers + newly hatched Artemia nauplii from day 18–20 and rotifers + newly hatched Artemia nauplii + artificial feed from day 21–35. In addition, Isochrysis galbana was introduced to the rearing tanks from day 1–10 and Chlorella sp. and/or Tetraselmis sp. from day 1–35. Survival rates of larvae tended to be lower as the broodstock became older.     

The pseudo-green water technique for intensive rearing of sea bream (Sparus aurata) larvae

The “pseudo green water” technology for sea bream(Sparus aurata) larval rearing was evaluated by analyzingresults of a 2-year study, performed in a pilot scale system. Thetechnology is characterized by the daily addition of phytoplankton in therearing tanks during the first month of rearing. Effects of egg origin,spawningseason and initial larval density on the larval rearing were investigated. Fishreared in “pseudo green water” systems for 60 days, presented highbiological performance in terms of survival (56 ± 16%), meanweight (62 ± 12 mg), total length (20 ± 1mm), conformity with wild standard (88 ± 9%), andfunctional swim bladder (93 ± 4%). The results present homogenitybetween the categories (origin of eggs, time of spawning, initial egg density)studied, proving the stability of the technology.     

The pseudo-green water technique for intensive rearing of sea bream (Sparus aurata) larvae

The pseudo green water technology for sea bream(Sparus aurata) larval rearing was evaluated by analyzingresults of a 2-year study, performed in a pilot scale system. Thetechnology is characterized by the daily addition of phytoplankton in therearing tanks during the first month of rearing. Effects of egg origin,spawningseason and initial larval density on the larval rearing were investigated. Fishreared in pseudo green water systems for 60 days, presented highbiological performance in terms of survival (56 ± 16%), meanweight (62 ± 12 mg), total length (20 ± 1mm), conformity with wild standard (88 ± 9%), andfunctional swim bladder (93 ± 4%). The results present homogenitybetween the categories (origin of eggs, time of spawning, initial egg density)studied, proving the stability of the technology.     

Experiments of the rearing of larval turbot, Scophthalmus maximus L.

Experiments on the live food requirements of cultured turbot larvae are described. A mixture of six species of unicellular algae did not sustain early larvae, but the growth and survival of larvae fed with rotifers were considerably improved when the rotifers were feeding on Isochrysis galbana rather than on Dunaliella tertiolecta. Oyster (Crassostrea gigas) larvae offered alone or with rotifers, did not produce higher larval growth or survival than rotifers alone. Black tanks were found to be more suitable than white tanks for rearing larval turbot.     

Hatching and rearing lobster larvae (Homarus americanus) in a disease situation

Lobster rearing facilities in the United States suffered severe losses of larval stages during the summer of 1974 hatching season. The organisms responsible for losses at the Bodega Marine Laboratory were the fungus Lagenidium sp. and epiphytic contaminants. Various systems and treatments were used in attempts to overcome the problems encountered. Postlarval lobsters were produced successfully in a semi-closed system using ultraviolet-irradiated sea water and a malachite green dip for eggs and larvae.     

浅析褶皱臂尾轮虫室内人工海水的培育方法

对室内人工海水培养褶皱臂尾轮虫的用水、盐度、温度、接种密度、饵料等方面问题进行探讨。结果表明:人工海水尽可能采用无机盐全面的配方,盐度1.5%左右,温度25~30℃,接种密度20~50个/mL,每100万轮虫投喂酵母0.5~1.0g。     

Experiments on the culture in the sea of the butterfish Venerupis decussata L.

Eight batches of hatchery reared V. decussata were reared to market size at two sites in England and one in Wales. The mortality rate varied between 10 and 40% per year in different populations with an average of 23% per year. The growth rates were rather similar at the three sites and it was estimated that after 3 years a population planted at 10 mm shell length would have reached about 50 mm. Calculations on the yield of market sized animals showed that at the average mortality rate it would be necessary to plant 10⁵ 10-mm spat to yield 1 tonne of V. decussata after 3 years; at a mortality rate of 40% per year it would be necessary to plant 2 × 10⁵ 10-mm spat to achieve the same yield. Growth started in late April and ceased by mid-October; the condition factor was at its highest in June and July. Samples planted at different densities suggested that V. decussata could be cultivated at up to 500/m².     

罗氏沼虾育苗人工配制海水重复使用试验

罗氏沼虾育苗人工配制海水经过1次使用后,应用生物净化技术处理,水中主要有毒有害物质(NH3-Nm、NO2-N)得到去除,盐度调整到1.2%左右,水质符合罗沼虾幼体生长发育的要求,可重复使用。出苗28万尾,3.95万尾/m3,成活率80%,质量符合有关标准。     

Preliminary studies on rearing of the gilthead seabream, Sparus aurata (L.), in brackish water ponds

The first attempt to rear the gilthead seabream, Sparus aurata, in brackish water ponds in Egypt was conducted from April 1976 to February 1977. Experimental ponds were stocked with Sparus aurata fry of about 32 mm and 1.5 g average length and weight respectively at a rate of 3000 fry per one feddan of pond water (i.e. 0.42 ha). The growth rate was recorded monthly. An average length and weight of 190 mm and 78 g respectively was attained after 8 months without supplementary feeding or fertilization of pond water. mathematical equations expressing length-weight relationship and condition factor were derived for both wild and reared fish. The higher values of condition factor obtained for the reared fish in comparison to the wild fish signify their improved condition and hence their suitability for farming in Egypt.     

The effects of photoperiod and water exchange rate on growth and survival of gilthead sea bream (Sparus aurata, Linnaeus; Sparidae) from hatching to metamorphosis in mass rearing systems

The effects of photoperiod and water exchange rate on the larvae of gilthead sea bream, Sparus aurata, from hatching to metamorphosis, 60–70 days later, were tested. Survival, growth rate and condition factor were determined with photoperiods of 12 and 24 h, and water exchange rates of 0 and 25%/day.Continuous light supported the highest mean survival (3.25%), with a maximum of 7.8% from hatching to metamorphosis. Growth rate in dry weight was best under continuous light in a water system with no exchange, up to 20 days post-hatching. Highest growth rates of larvae 40–60 days old were obtained in tanks with 25% of their water exchanged daily, along with a 12-h photoperiod. Condition factor was directly correlated with larval age. For the first 30 days after hatching, condition factor was affected by photoperiod and was highest for larvae exposed to continuous light.     

Oxytetracycline (OTC) uptake following bath treatment in gilthead sea bream (Sparus aurata)

The uptake and elimination profile of oxytetracycline (OTC) following a prolong bath treatment in gilthhead sea bream (Sparus aurata) were investigated in this study. The bath experiment was carried out using a OTC concentration of 50 μg/ml for 24 h at 17-18 °C water temperature. Plasma and muscle fish samples were analysed at 1, 3, 6 and 24 h during and at 1, 2, 3, 4 and 6 d following the bath. Detectable OTC levels were revealed only at the end of bath treatment (24 h) in examined tissues of gilthead sea bream, where drug concentration was measured to be as low as 0.096 and 0.047 μg/g or ml in muscle plus skin and plasma, respectively. The findings of the present study indicate that OTC bath treatment under this dosage schedule is unlikely to confront systemic bacterial infections.     

A genetic analysis of egg,alevin and fry mortality in salmon (Salmo salar), sea trout (Salmo trutta) and rainbow trout (Salmo gairdneri)

Heritability of mortality in eggs, alevins and fry were estimated using data from salmon, sea trout and rainbow trout. The highest value (average for all species and both estimation methods) based on the sire component was obtained for the eyed egg stage, h² = 0.08, followed by the alevin stage, h² = 0.05, while estimates for fry mortality did not differ significantly from zero.The maternal effect was rather large for uneyed eggs and eyed eggs, while it was low for alevin mortality. Maternal effects were also found to have a significant influence on the mortality of salmon fry. It was, however, not possible to separate maternal effects from tank effects.     

Effects of water temperature and body weight on anaesthetic efficiency in marbled rabbitfish (Siganus rivulatus)

The effects of four anaesthetic agents, tricaine methanesulphonate (MS‐222) (112.5 mg L^?1), 2‐phenoxyethanol (400 μL L^?1), clove oil (70 mg L^?1) and benzocaine (65 mg L^?1) on juvenile marbled spinefoot (Siganus rivulatus) of three mean body weights (7.3 g, 19.1 g, 55.5 g) and at three temperatures (20, 25, 30°C) were evaluated. In addition, the relationship between body lipid content and efficacy of the four anaesthetic agents was evaluated in juvenile S. rivulatus. Times necessary for induction and recovery were recorded. Significant effects of temperature on induction and recovery times were observed. Induction and recovery times decreased with increasing water temperature. No uniform relationship between body weight of juvenile marbled spinefoot and anaesthetic efficacy was observed. Body fat content was positively correlated with induction time only when MS‐222 was used but did not affect induction times of fish exposed to 2‐phenoxyethanol, clove oil or benzocaine. Recovery times were generally longer for all fish containing more body fat. Results of the study show that anaesthetic efficiency increases with increasing water temperature but is not strongly affected by body weight for juvenile marbled spinefoot. In addition, body fat in fish affected the efficacy of the various anaesthetic agents tested in this study, generally slowing down recovery.     

刺参养殖技术之三利用海带育苗池进行刺参亲参培育技术

近几年,随着北方地区刺参养殖面积的不断扩大,养殖户对大规格苗种的需求不断增加,刺参控温育苗应运而生,其关键技术之一就是亲参的培育技术.在此,笔者将利用海带育苗池进行刺参亲参培育技术介绍如下.