Induced multiple spawning of reared Siganus oramin (Schneider) (=S. canaliculatus Park)

Rabbit-fish, Siganus oramin, reared in a closed seawater system on an artificial diet, were brought to maturity and spawned artifically after human chorionic gonadotropin (HCG) injections. Eggs were incubated under different salinity regimes. Hatching success between 20.9 and 32.2‰ S was ≥95%.     

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.     

Some ecological and behavioural aspects of siganid populations in the Red Sea and Mediterranean coasts of Israel in relation to their suitability for aquaculture

A comparative study of five populations of fishes: Siganus rivulatus (Forskal) and Siganus luridus (Ruppell) from both the Red Sea and Mediterranean Sea and Siganus argenteus (Quoy and Gaimard) from the Red Sea was carried out during 1972. The study included ecological and behavioural aspects that may have significance in determination of suitability of the species for aquaculture. Emphasis has been put on the behaviour, reproduction, availability of fry and resistance to changes in salinity levels.     

Food preferences in cultured rabbitfishes (Siganidae)

Four species of rabbitfishes, Siganus concatenata, S. oramin, S. striolata and S. virgata were held in rearing tanks and fed with benthic algae. Out of 101 algae species and 4 vascular plants offered, the fishes ate only 67 species. The electivity indices E, for 23 algae were determined. The species Enteromorpha intestinalis, Gracilaria confervoides and G. cylindrica proved to have the highest indices with E = 0.594, E = 0.269 and E = 0.182, respectively.     

Report on the growth of rabbit fish in fish ponds in Fiji

Some data are presented about the gain in weight of rabbit fishes (Siganus vermiculatus) grown at different densities in dirt ponds.     

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.     

Importance of outer reef slopes for commercially important fishes: implications for designing a marine protected area in the Philippines

A passive acoustic telemetry survey was conducted to determine occurrence patterns of commercially important fishes on a steep reef slope along a marine protected area (MPA) in the southern Philippines, where the outer reef edge is often set as an offshore MPA boundary. Based on 4–61 days of tracking data from 21 detected individuals of five species (Lutjanus argentimaculatus, Lutjanus monostigma, Lethrinus atkinsoni, Lethrinus obsoletus, and Siganus guttatus; 20.7–69.2 cm fork length) caught near the reef slope of the MPA, S. guttatus occurred most frequently on the reef flat of the MPA, whereas all individuals of the four lutjanid and lethrinid species were primarily (99.4–100%) detected near the reef slope, and nine individuals (56.3% of these four species) of three of these species (not L. obsoletus) most likely used the shallow (≤10 m) and deep (≥20 m) layers, and thus, middle layers of the slope. These findings indicate that commercially important lutjanid and lethrinid species predominantly and vertically used the areas near the reef slope, suggesting the importance of fully including reef slopes in MPAs to enhance their effectiveness for the conservation of such fishes.     

Growth of Siganus rivulatus reared in sea cages in the Red Sea

Siganus rivulatus fry stocked in extensively managed sea cage systems grew from 3 to 105 g in 150 days.     

Effect of photoperiod on gonadal maturation in the rabbitfish,Siganus canaliculatus Park 1797

A long photoperiod of 18 hours light alternating with 6 hours darkness (18L 6D) was found to retard gonadal maturation in the rabbitfish (Siganus canaliculatus Park) compared to the normal photoperiod of 12L 12D. Thus, a long photoperiod may be used to delay the breeding season of the fish.     

The size composition of the eggs of curimbatá, Prochilodus scrofa Steindachner 1881, induced to spawn with human chorionic gonadotropin (HCG)

Curimbatá, Prochilodus scrofa, were examined and selected for induced spawning with human chorionic gonadotropin (HCG). Intra-ovarian eggs were sampled and size composition was analyzed.With 21 females, two doses of HCG were applied at 10-h intervals, 5 IU and 10 IU per gram of total weight. According to response, three distinct groups were identified. For the groups where eggs were successfully fertilized, followed by embryonic development, the percent frequency distribution of egg diameter was unimodal with a constant mode of 1111.15 μm. It is suggested that for P. scrofa, selection of recipient females can be made on egg frequency-diameter distribution.     

Automated identification of invasive rabbitfishes in underwater images from the Mediterranean Sea

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Lunar cycle in the reproductive activity in the forktail rabbitfish

Histological observations of the gonads of Siganus argenteus showed that gametes developed toward the last quarter moon from May to July. Weekly changes in plasma steroid hormones were correlated closely with gonadal development. Human chorionic gonadotropin (hCG) stimulated in vitro production of steroid hormones at the specific lunar phase. These results suggest that the concomitant physiological events in the gonads strictly changes with the lunar cycle.     

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.     

Field-induced breeding of the dorado,Salminus maxillosus Valenciennes

Induced breeding of the dorado was performed using broodfish held at capture sites near the river shore. Prochilodus platensis pituitary glands (Pit) and human chorionic gonadotropin (HCG) were used as stimulators of ovarian maturation and ovulation. Positive results, with the production of viable larvae, were obtained with single injections of 1 Pit/kg and with multiple injections of 0.5, 0.25 or 0.125 Pit/kg at 2.5-h intervals. Females ovulated after receiving between 0.5 and 1 Pit/kg. During the time period covered by the experiments the percentage of ovulatory responses improved from 36% in December to 86% in February.The threshold dose that triggers final maturation and ovulation was found to be between 0.125 and 0.25 Pit/kg. Latency between injection and ovulation varied from 7 to 9 h at 23.5°C. Viability of intraovarian ovulated eggs rapidly decreased to 0% in less than 4 h at 23.5–25°C.Hatching rates ranged from 0 to 63%; the best value was obtained when eggs were stripped immediately after ovulation from a female treated with five injections of 0.125 Pit/kg at 2.5-h intervals.     

Induced breeding experiments with milkfish, Chanos chanos Forskal,in Hawaii

The hormones SG-G100, CPH, and HCG were used to induce spawning of the milkfish. A total of 22 potentially receptive females were injected. Females with oocytes 0.7 mm in diameter or above offer the greatest chance for success. A priming dose of hormone injected immediately after capture reduces the effects of stress or atresia. Under optimal conditions, the spawning of milkfish can be induced by two or three injections of total dose up to 200 mg CPH with 25,000 IU HCG. Mature females respond more readily to injections without the added stress of salinity adjustment.     

Observations on induced breeding of the Amazonian fish tambaqui, Colossoma macropomum (Cuvier) using CPE and HCG treatments

Trials on induced breeding of the native Amazonian fish tambaqui, Colossoma macropomum (Cuvier), using CPE and HCG treatments, were carried out during 1992-93 at the Fish Culture Station in Natal, Brazil. Final maturation, ovulation and spermiation of tambaqui broodstock, reared in earthen ponds, were induced by injecting heteroplastic carp pituitary gland extracts (CPE) and human chorionic gonadotrophin (HCG) separately. The female spawners received double injections and the males received a single dose. Females were tranquillized using quinaldine and their genital openings were sutured before the resolving injection was administered. Latent period between the resolving injection and ovulation varied from 6 to 11 h according to the prevailing water temperature. Milt was obtained by extrusion. Stripping and dry fertilization of the eggs produced viable larvae. Relative fecundity was estimated at 140 000 eggs kg^-1. Mean fertilization and hatching rates varied from 50% to 70% and from 60% to 80%, respectively.     

Stable isotope analysis suggests the existence of multiple populations of streaked spinefoot (<Emphasis Type="Italic">Siganus javus</Emphasis> L.) in Bandon Bay,Southern Thailand

The stock unit used in fisheries resource assessment and management is generally based on the morphological and genetic characteristics of a particular population or species to avert problems caused by the treatment of multiple populations as one stock, which can lead to the overestimation of population sizes and genetic pollution. Furthermore, since the linkage of microhabitats is an important factor affecting the reproduction of marine organisms in coastal areas, an understanding of the food web in each microhabitat is essential to establish sustainable fisheries management practices. We investigated spatial variations in the food sources and feeding habits of immature stage of Siganus javus using genetic population analyses and stable isotope analyses (δ¹³C and δ¹⁵N). These species are commonly harvested by small-scale fisheries, and it inhabits Bandon Bay in the Surat Thani Province of Southern Thailand. Genetic variation within sampling sites was greater than that between sites. The δ¹³C values of S. javus differed between sites, which suggest that the different ecological habitats exhibit different rates and patterns of carbon flow even among sites located in the same bay. Our results suggest that studies combining genetic population analyses and stable isotope analyses are required to confirm the delineation of fine-scale management units intended for the development of coastal fishery resources.     

IHHN virus: Infectivity and pathogenicity studies in Penaeus stylirostris and Penaeus vannamei

Infectivity studies of infectious hypodermal and hematopoietic necrosis virus (IHHNV) were conducted on Penaeus stylirostris and P. vannamei (representing species highly susceptible and highly refractory to the disease) via intramuscular injections of the virus. Distinctive histological lesion patterns were observed between species. Six target organ systems were compared interspecifically. The gills and nerve cord/ganglia were shown to undergo significantly higher degrees of tissue damage in infected P. stylirostris compared with infected P. vannamei. Pathogenetic differences correlated well with observed differences in epizootiology between the two species.The infectivity study confirmed that IHHN disease is virus-caused. Cell-free extracts from IHHNV-infected shrimp, when injected into healthy, susceptible shrimp, produced mortalities and Cowdry type A intranuclear eosinophilic inclusion bodies presently considered pathognomonic for the disease.     

Delayed gametogenesis and spawning of sea bass (Dicentrarchus labrax L.) kept under different photoperiod and temperature regimes

The present work investigates the importance of day length and temperature in the control of reproduction of sea bass, as well as the effectiveness of LHRHa and HCG in inducing spawning out of season in this species. A controlled regime was produced and seasonal cycles with high components of temperature and photoperiod were extended from the summer solstice for at least 6 months, followed by a short photoperiod regime for 3 months before a new increase in these components. Natural spawning in the control fish occurred more frequently in mid February, although it was also observed in January and early March. Temperature manipulation delayed the spawning one month with respect to the controls, although some of the animals entered into gonadal regression. Photoperiodic manipulation delayed maturation for three months with respect to controls but it was necessary to perform hormonal induction of spawning. Although LHRHa and HCG were both applied, only intraperitoneal injections of LHRHa were effective in inducing spawning of sea bass out of season when the temperatures were 17°C. Dephasing between the annual changes in photoperiod in relation to the coordination of the different events of the sexual cycle of sea bass is considered.