Annual reproductive cycle of milkfish, Chanos chanos Forskal,in Hawaiian waters

The monthly mean values of gonadosomatic index (GSI) over a continuous 36-month period show that the population of milkfish, C.chanos Forskal, in Hawaiian waters has a short breeding season between June and August. In these months, the GSIs of the mature individual males are between 3.19 and 5.36%, and of the mature individual females between 7.07 and 9.76%.These figures plus histological data suggest a synchronous spawning behavior for the species. Mature oocytes (stage III) are larger than 0.7 mm in diameter, which increases to about 1.2 mm at the time of ovulation and about 1.35 mm at the time of spawning     

Effects of several factors on growth of milkfish (Chanos chanos Forskal) fingerlings reared with artificial diets in aquaria

This paper presents the effects of feeding level, feeding frequency, salinity of water, kind and particle size of diets, and stocking density on the growth of milkfish (Chanos chanos Forskal) fingerlings which were reared with artificial diets in laboratory tanks. Experimental groups were designed using orthogonal array L₈, and the results were evaluated statistically. Growth of the milkfish fingerlings varied markedly with the kind of diets used and feeding level. The feeding frequency and particle size of the diets also affected growth of the fingerlings significantly, but the salinity of the water did not. The weight gain of the fingerlings did not vary with the stocking densities significantly, whereas the increase (%) in body length was greater at a lower stocking density. The milkfish fingerlings showed the best growth in terms of both weight gain and increase in body length when reared on a purified diet containing 35% casein and 15% gelatin as protein sources under the following conditions: feeding level, 30–35% of body weight; feeding frequency, twice a day; particle size of diets, 125–250 μm diameter; and stocking density, $\text{5 fish}\text{5-liter}$ tank. The means and confidence limits of the weight gain (%) and increase (%) in body length of milkfish fingerlings under the best conditions adopted were estimated to be 360 ± 63.7 and 62.1 ± 10.6, respectively.     

Preliminary analysis of the performance of the fry industry of the milkfish (Chanos chanos Forskal) in the Philippines

The fry industry of the milkfish (Chanos chanos Forskal) in the Philippines is alleged to suffer from certain inefficiencies, principal among which are an annual shortage to meet the stock requirements of the 176 000 ha of fishponds in the country, and the failure of the pricing system to direct and allocate the fry resources geographically. Contrary to these and other allegations, this paper presents a preliminary analysis that indicates a higher level of performance for the industry than hitherto supposed. Specifically, fry catch is estimated to be 1.35 billion, sufficiently high to meet present stocking requirements; less than 3% of trade flows between regions overlap; and monthly average fry prices between trading regions are significantly correlated, indicating the system responds to supply and demand changes and other stimuli.     

Effect of thyroxine on growth and development in post-yolk-sac larvae of milkfish, Chanos chanos

Post-yolk-sac larvae of milkfish, Chanos chanos (commonly referred to as “fry”) were collected along the shore in the Philippines. Treatment of these long, slender and transparent larvae with L-thyroxine-sodium (Eltroxin, Glaxo) by immersion in 0.5 ppm solution (changed daily) markedly accelerated their growth and development. By day 15 of the treatment, the treated larvae had become silvery, opaque and adult-like in form, whereas the control larvae were still slender and transparent (or at best translucent) with incomplete silvering of the body. 0.1 ppm thyroxine was less effective. Discontinuation of the treatment after 8 days was also less effective as judged by the appearance and weight of the larvae on day 15.     

The effect of duration of feeding on survival,growth and production of milkfish, Chanos chanos (Forskal), in brackishwater ponds in The Philippines

Milkfish (Chanos chanos) fingerlings with an average weight of 16.3 g were stocked at 4000 per ha in twelve 500-m² experimental brackishwater ponds. The duration of supplementary feeding using pelletized chick starter (21.15% protein) at a ration of 5% of the biomass, was varied between 0 and 3 months. The duration of supplementary feeding had no significant effect on the survival, growth and production of milkfish. The results indicated that supplementary feeding of milkfish was not necessary at a stocking level of 4000 fish/ha, when adequate pond fertilization was carried out.     

Polyculture of milkfish (Chanos chanos Forskal), all-male Nile tilapia (Tilapia nilotica) and snakehead (Ophicephalus striatus) in freshwater ponds with supplemental feeding

Results showed that all-male Nile tilapia can be cultured in milkfish ponds without affecting the growth and production of milkfish, at ratios of 1–3 tilapia to 5 milkfish; 2:5 is the optimum ratio.Supplemental feeding with fine rice bran or copra meal at a daily rate of 5% of the biomass increased the net production of milkfish but had no influence on all-male Nile tilapia. Standing crop of about 890 kg/ha in 135 days was obtained in a polyculture system of milkfish, all-male Nile tilapia and snakehead when fed rice bran.     

Induced spawning of maturing milkfish (Chanos chanos Forsskal) with gonadotropin-releasing hormone (GnRH) analogues administered in various ways

The response of mature female captive milkfish to mammalian and salmon gonadotropin-releasing hormone analogues (mGnRH-A and sGnRH-A) was investigated. Prior to spawning, six groups of three females received (1) 10–16 μg mGnRH-A from an osmotic pump implanted intraperitoneally (IP); (2) 100 μg mGnRH-A from a cholesterol/cellulose pellet implanted IP; (3) 10 μg/kg mGnRH-A as an intramuscular (IM) injection; (4) 10–16 μg sGnRH-A from an osmotic pump implanted IP; (5) 100 μg sGnRH-A from a cholesterol/cellulose pellet implanted IP, and (6) a cholesterol/cellulose pellet without analogue implanted IP.

The most effective treatment was 100 μg sGnRH-A/fish given in a cholesterol/cellulose pellet; all (3/3) of the fish spawned. However, mGnRH-A was more effective (2/3) compared with sGnRH-A (1/3) if osmotic pumps were used to administer GnRH-A. If the dose and method of administration were not considered, then the salmon and mammalian GnRH analogues were equally effective (62–67%) for induction of ovulation and natural spawning in milkfish. Gonads of control fish regressed.

At the doses tested, injections or pellet implantations were more effective compared with osmotic pumps. All pellet-implanted and injected females responded to treatment and 75% (6/8) spawned; half (3/6) of the pump-implanted females spawned. Spawning occurred from 18 to 36 h after treatment.     

Physiological responses, desaturase activity, and fatty acid composition in milkfish (Chanos chanos) under cold acclimation

Physiological responses of milkfish (Chanos chanos) under cold shock and acclimation were investigated. The experimental milkfish, a warm-water teleost, were initially acclimated at 25 °C and then transferred directly to 15 °C; stress responses of this species were monitored for 1 week. Parameters monitored included plasma glucose, lactate, and lipids, as well as stearoyl-CoA desaturase activity and fatty acid compositions of hepatic membranes. All parameters showed significant changes in the process of cold acclimation. A hyperglycemic response indicated by a notable and steady increase in plasma glucose levels from 85 mg dl⁻¹ to the highest level of 458.2 mg dl⁻¹ in 24 h was followed by a rapid decline thereafter. The elevation in plasma glucose content under cold shock resulted from gluconeogenesis and glycogenolysis, indicated by correlated changes in plasma glucose with fructose-1,6-biphosphatase and phosphorylase a activities. Plasma lactate concentrations remarkably increased from 47 mg dl⁻¹ on day 0 to 149.6 and 120.4 mg dl⁻¹ on days 1 and 2, respectively, and then rapidly declined to the same level as the control thereafter. In contrast, plasma lipids increased gradually from 44.8 mg dl⁻¹ to 191 mg dl⁻¹ over the 5-day acclimation period, followed by a declining trend from day 6 on. Furthermore, changes in monounsaturated fatty acids were highly correlated with those of stearoyl-CoA desaturase activities in hepatic microsomes of milkfish during cold acclimation. Results indicate that in milkfish subjected to cold stress, plasma hyperglycemic and hyperlactemic responses can be used as acute stress indicators, and plasma lipids can be used as a chronic stress indicator.     

On the induced spawning and larval rearing of milkfish,Chanos chanos (Forskal)

A female milkfish, captured at sea, was injected with two hormonal injections of acetone-dried salmon pituitary powder and human chorionic gonadotropin, plus Vitamin B complex. It was stripped, and produced 128,000 ripe eggs with an average diameter of 1.15 mm. Fertilization rate was 38% following artificial fertilization with milt from an uninjected male. A total of 36,000 larvae hatched (74% of fertile eggs) after 26–32 h at 34 ‰ salinity and 27–32°C. The newly hatched larvae measured 3.4 mm in mean total length and possessed a large yolk sac. The mouth of the larvae opened about 54 h after hatching. The larvae were fed with fertilized oyster eggs, rotifers, copepods, brine shrimp, flour and prepared feed, together with Chlorella. A critical period was between the 4th and 6th days with mortality over 80%. The larvae started increasing in length by Day 8, and had the appearance of the wild fry by Day 11. On Day 13 a pigmentation pattern developed and the biggest larva measured 10.0 mm. By Day 18 the larvae measured 12.5 mm, and 14.5 mm by Day 21. A total of 2,859 fry was obtained; the highest larval survival rate obtained from different experimental groups was 46.8%.     

Use of duckweed (Lemna sp.) grown in sugarmill effluent for milkfish, Chanos chanos Forskal, production

Abstract. Oxidation treatment of sugarmill waste using duckweed ( Lemna sp.) as part of the system, to reduce effluent nutrient concentrations and biological oxygen demand (BOD), was evaluated during a 6 month milling season in Negros Oriental, Philippines. Mean ammonia concentration in effluent water was reduced from 0·87 to 0·31 mg/l NH₃-N and orthophosphate from 0·93 to 0·51 mg/l P₂O₅, while mean BOD was reduced from 611 to 143mg/t BOD₅, after treatment. Seasonal mass fish kills in the adjoining bay no longer occurred during the 3 years following introduction of this treatment. The mean duckweed production (dry weight) was 8–8g/m²/day. Duckweed was harvested from a 1·9ha area of the system and transferred to an adjacent milkfish, Chanos chanos Forskal, farm. Its fertilization effect, in terms of lablab production ( lablab is the biological complex of bluegreen algae, diatoms, bacteria and various animals which forms a mat at the bottom or floats in patches), was evaluated in the milkfish ponds. This was compared with ponds fertilized with either inorganic fertilizers or cow manure, in the traditional way. Lablab growth was significantly increased using duckweed, with ash-free dry weight production averaging 32g/m²/day following fertilization with duckweed compared with 4g/m²/day using inorganic fertilizers. Milkfish net production averaged 320 kg/ha/90-day crop in inorganically fertilized ponds. 545kg/ha/90-day crop for cow manure and 820kg/ha/90-day crop in duckweed-fertilized ponds. The system is described and the benefits of this integrated waste treatment-fish production facility are discussed.     

Economics of milkfish (Chanos chanos) production in Hawaii*

Abstract

Economic evaluations of commercial milkfish (Chanos chanos) growout systems were made based on current Hawaiian fishpond, pond and tank culture techniques in Hawaii. Based on the observed practices of milkfish culture as a secondary or tertiary crop, capital costs and several operating costs were pro‐rated to accurately depict current farm practices. For a target harvest weight of 0.80 lb, the study estimates the total production cost for milkfish production at $3.31/lb for the pond system, $3.81/lb for the tank system and $1.84/lb for the Hawaiian fishpond system. At a sale price of $3.00/lb and seed cost of $0.25/fingerling, only the Hawaiian fishpond system is profitable under a 20‐year project life. When considering variable costs alone, the production cost is $1.78/lb for the pond system, $2.33/lb for the tank system and $1.53 for the Hawaiian fishpond system, yielding returns on variable costs of 67%, 30% and 59% respectively. Analyses of profit sensitivity to sale price, production yield, labor, feed and stocking indicate that sale price, as expected, has the largest impact on profitability, followed by feed. The results of this study are consistent with the Hawaii farmers’ view of milkfish as a secondary specie to core production based upon current market conditions and input requirements.     

Observations on artificial fertilization of eggs and the embryonic and larval development of milkfish,Chanos chanos (Forskal)

Hydrated eggs obtained from a female milkfish, Chanos chanos, were artificially fertilized with the milt collected from a male injected with acetone-dried pituitaries of salmon. The fertilized eggs (1.1–1.25 mm in diameter) developed normally in seawater in basins and petri dishes at a salinity of 30–34‰, and successfully hatched in 25–28.5 hours at a temperature of 26.4–29.9°C. The yolk was completely absorbed in about 2.5 days and during this period many postlarvae died. A few larvae were reared up to 5 days but all died on the 6th day. Attempts were made to feed the postlarvae with freshly hatched trochophore larvae of oysters obtained from eggs artificially fertilized in the laboratory.     

Technical efficiency analysis of milkfish (Chanos chanos) production in Taiwan—an application of the stochastic frontier production function

Milkfish has been farmed in Taiwan for over 300 years. Faced with limited land resources, a labor shortage, decreasing demand, and growth of imported fisheries products, the industry is looking at the problem of how to maintain a sustainable and efficient production. This study specifies a stochastic production frontier function to estimate potential milkfish farm output and efficiency by using 1997–1999 data from a survey of 433 aquaculture milkfish farms. Both Translog and Cobb–Douglas frontier production models are estimated using the maximum likelihood estimation method. Empirical results show that the Translog stochastic production function model fits the data better and that milkfish farming in Taiwan exhibits diminishing returns to scale. We also compare estimated maximum potential milkfish production per hectare under various pond conditions to provide managers with information about how to boost efficiency. In addition, this study estimates substitution elasticities and complementarity of input factors for milkfish farms to provide helpful information for milkfish farmers on how to reallocate input resources and help raise milkfish productivity through improvements in technical efficiency.     

Induced breeding of the South American catfish, Rhamdia sapo (C. & V.)

Pituitary suspensions from the characin, Prochilodus platensis, were injected intraperitoneally into male and female Rhamdia sapo at doses between 0.37 and 6 mg dry weight per kg of body weight. Doses from 0.75 to 6.0 mg/kg effectively induced ovulation. The latent period between injection and ovulation for females held at different temperatures (17 to 27°C) decreased with increasing temperature.Stripping of gametes from both sexes, and dry method fertilization were successful and produced viable eggs. The period between ovulation and stripping for the highest hatching rates decreased from about 9 h at 20°C, to 5 h at 24°C. No viable eggs remained in samples obtained after 15 h at 20°C, or 8 h at 24°C. Hatching percentage and the fraction of deformed fry were negatively correlated (r = ?0.75; P < 0.001).     

Induced maturation and spawning of milkfish,Chanos chanos Forssakal,by hormone implantation

The milkfish, Chanos chanos Forsskal, does not reach gonadal maturity easily in captivity. In an attempt to induce maturation, exogenous hormones, LHRH-A and 17α-methyl-testosterone, were implanted into adult milkfish either alone or in combination. The hormones were delivered using cholesterol pellets (LHRH-A) or silastic tubing sealed with elastomer (17α-methyl-testosterone). The fish were implanted three times at monthly intervals between March and May of 1985. The combination of LHRH-A and 17α-methyl-testosterone induced significantly more maturing fish (P < 0.05) than LHRH-A alone or sham controls; 88%, 38%, and 13%, respectively.Fish with average egg diameters between 768 μm and 905 μm, spawned 48 h after hormone implantation. These results indicate that the maturation and spawning of milkfish in tanks can be induced and accelerated 1–2 months earlier than the beginning of the normal spawning season through hormone implantation.     

Induced triploidy in grass carp, Ctenopharyngodon idella Val

Induction of triploidy in grass carp was accomplished by means of thermal shocks to eggs shortly after fertilization. Triploidy occurred most often with cold shocks at 5–7°C and at durations of 25–30 min starting 2.0–4.5 min after fertilization. Estimated percent triploid ranged from 50 to 100% on five occasions. With one exception, cold shocks of 5–7°C for less than 25 min did not induce triploidy, and cold shock durations of 30 min or longer generally resulted in 100% mortality. A heat shock of 40°C for 1 min, 4.75 min after activation, was the only heat treatment which produced triploidy (8%) with 81% surviving to the blastula stage. Fertilized eggs immersed in a solution of cytochalasin B (10 mg/l, 0.1% DMSO) for 10 min, 12 min after activation, resulted in 54% of the eggs surviving to the blastula stage with none found to be triploid.     

Preliminary results of experiments on the rearing of Tasmanian flounders, Rhombosolea tapirina and Ammotretis rostratus

Tasmanian species of flounder were cultured successfully following stripping and fertilizing eggs after hormone-induced ovulation. The larvae were fed rotifers followed by Artemia nauplii. Survival rates of larvae from first-feeding to metamorphosis, which were as high as 94–98% for R. tapirina and 65% for A. rostratus, indicate that both species can be readily cultured in captivity.     

Induced breeding of the sabalo,Prochilodus platensis Holmberg

Maturation and ovulation were induced in female Prochilodus platensis with multiple homologous pituitary extract injections (total dose 0.9 to 1.4 hypophysis/kg) or single injections of pituitary extract combined with human chorionic gonadotrophin ((1 hypophysis + 500 I.U.)/kg). One of the females given the latter treatment produced viable eggs. Latency time from injection to ovulation was 9 h (at 28°C). Hatching occurred 12 h after fertilization. Survival after 30 days of rearing was 96%.     

Pimozide-LHRHa-induced breeding of the African catfish, Clarias gariepinus (Burchell)

Reproduction of the African catfish under hatchery conditions depends on the artificial induction of egg maturation and ovulation. In this study the combination of pimozide/LHRHa as ovulation-inducing substance has been evaluated. At a dosage, given as one single injection, of 5 mg pimozide + 0.05 mg LHRHa per kilogram body weight, 100% ovulation was achieved. Most of the eggs, collected after stripping, could be fertilized and hatched normally.