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%.     

细基江蓠繁枝变种与遮目鱼的混养试验

细基江蓠繁枝变种 (GracilariatenuistipitataV .liui)俗称细江蓠 ,在我国主要分布在海南岛 ,也是海南省海藻栽培的重要品种 ,细江蓠生长快 ,产量高。遮目鱼 [ChanosChanos(Forstal) ],生长迅速、饵料易得 ,鱼苗病害较少 ,易于饲养 ,是咸淡水养殖的重要对象。关于细江蓠与遮目鱼的混养迄今尚未见报道。 2 0 0 1～ 2 0 0 2年我们在兴发养殖场进行了细江蓠与遮目鱼混养的探索性试验 ,现将其初步结果总结如下。1　材料与方法1 .1　池塘条件　池塘面积 0 .2ha,池深 1 .2m ,底质为泥砂底 ,池端设有一进排水闸门 ,有海淡水水源。1 .2　清塘放苗…     

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.     

Requirement for tryptophan by milkfish (Chanos chanos Forsskal) juveniles

Groups of milkfish juveniles (mean initial weight 7.7 g) were fed semipurified diets containing 0.9, 1.4, 2.1, 3.1, 4.1 and 6.1 g tryptophan/kg dry diet for 12 weeks. The mean crude protein content of the diets (containing white fishmeal, gelatin and free amino acid mixture to simulate the pattern of hydrolysed milkfish protein) was 49%. On the basis of the growth response, the tryptophan requirement of milkfish juveniles was estimated to be 3.1 g/kg diet. Fish fed low levels of tryptophan exhibited low weight gains and poor feed conversion ratios. Survival (92–100%) was consistently high in all treatments. Fish fed diets containing tryptophan levels greater than 3.1 g/kg had slightly lower survival rates. The activity of hepatic tryptophan pyrrolase showed no significant differences with increasing dietary tryptophan levels. No nutritional deficiency signs were observed other than the depression in growth rates in fish given the tryptophan deficient diets.     

The essential fatty acid requirement of milkfish (Chanos chanos Forsskal)

The essential fatty acid (EFA) requirement of milkfish was examined by a 12-week feeding trial using defined, purified diets at water temperature of 28–29°C and salinity of 32. The test diets contained varying levels of 18:0 (triglyceride form, TG), 18:3(n–3), 18:2(n–6) and (n–3) highly unsaturated fatty acids (n–3 HUFA). Milkfish juveniles were starved for 7 days and were than fed lipid-free diet for 30 days before the initiation of feeding trials. Low growth and feed efficiency together with high mortalities were observed in fish fed the lipid-free diet as well as in the EFA-deficient diet. Supplementation of 2% 18:2(n–6) to the tristearin based diet did not improve growth rate of milkfish as effectively as feeding with (n–3) fatty acids. The highest weight gain was obtained in milkfish fed a combination of 5% 18:0 + 1.0% 18:3(n–3) + 0.5% 20:5(n–3) + 0.5% 22:6(n–3) although the supplementation of 2% 18:3(n–3) alone or combination of 0.5% 20:5(n–3) + 0.5% 22:6(n–3) to the tristearin based diets were also effective for improvement of growth. Thus, (n–3) fatty acids, such as 18:3(n–3) and (n–3)HUFA were nutritionally more important than 18:2(n–6) for milkfish. The fatty acid composition of the polar lipids from whole body of milkfish juveniles fed the various test diets were influenced by the composition of the dietary fatty acids.     

Acute nitrite toxicity and methemoglobinemia in juvenile milkfish (Chanos chanos Forsskal)

Nitrite was about 55 times more toxic to milkfish juveniles in fresh water than in 16% brackish water: the 48-h median lethal concentrations were 12 mg NO₂N/l (95% confidence limit=7.4–19.6) and 675 mg NO₂N/l (95% confidence limit = 435.8–1,045.4) respectively. Methemoglobin levels were higher for a given concentration of nitrite in milkfish kept in fresh water than in the brackish water. Methemoglobin decreased to a normal level within 24–26 hours of the removal of nitrite.     

Broodstock management and egg production of milkfish, Chanos chanos Forsskal

Abstract. The milkfish, Chanos chanos Forsskal, industry in the Philippines suffers from a limited supply of wild fry. The demand for milkfish fry has spurred research in artificial propagation to supplement the natural seed supply. Spontaneous maturation and spawning of milkfish beginning at 5 years of rearing in floating net cages or concrete tanks coupled with improved egg collection technique have increased daily egg collection to a maximum of 3 million eggs and provided adequate volumes of eggs for mass fry production. Annual egg collection and number of spawnings were markedly higher in cage-reared stocks older than 9 years old than stocks less than 9 years old. Egg collection of tank-reared stocks were comparable to those collected in cages. As feed constitutes a major portion of the operating expenses for establishing and maintaining milkfish broodstock, further studies must be geared towards defining optimum dietary requirements and ration size for gonadal maturation and spawning. Also environmental manipulation studies must be conducted for year-round spawning. Developments in these areas should ensure the production of maximum numbers of high quality eggs and fry year-round.     

Hormonal changes accompanying sexual maturation in captive milkfish (Chanos chanos Forsskal)

Steroid hormone profiles accompanying sexual maturation in captive milkfish are described. There were no significant differences in levels of serum estradiol 17- (E₂) and testosterone (T) between immature male and female fish. Mean E₂ levels rose from 0.54±0.11 ng/ml in immature females (Stage 1) to 4.53±1.16 ng/ml in vitellogenic females (Stage 5), while T levels increased from 2.06±0.28 ng/ml to 38.4±9.26 ng/ml. E₂ and T levels were positively correlated to GSI and oocyte diameter. In males, serum T levels increased from 2.5±0.40 ng/ml in immature males to 27.73±5.02 ng/ml in spermiating males. A significantly higher T level was found in males with thick and scantly milt (spermiation index, SPI, 2) compared to males with scanty milt (SPI, 1) or males with copious, fluid milt (SPI, 3).Serum levels of E₂ and T, and the GSI in females rose significantly during the breeding season (April–June 1983). The levels of both steroids dropped below 1 ng/ml in spent females sampled in succeeding months. In immature males, T levels ranged from 1.11 ng/ml to 2.78 ng/ml and rose significantly to 21.52±8.38 ng/ml during the breeding season when GSI peaked. Serum T levels dropped to around 10 ng/ml in the succeeding months when only spent or regressed males were sampled.     

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.     

Digestibility in milkfish,Chanos chanos (Forsskal): Effects of protein source,fish size and salinity

The true digestibility of casein, gelatin, fish meal, defatted soybean meal and Leucaena leucocephala leaf meal was measured in 60- and 175-g milkfish (Chanos chanos Forsskal) in fresh- and seawater. The diets contained 45% of these feedstuffs and 1.3% of the indicator substance, chromic oxide. The intestinal dissection method was used to collect fecal material. Results showed that the length of time between initial feeding and fish sacrifice did not significantly affect digestibility. Gelatin was the most digestible (90–98%) protein, regardless of size. Casein, defatted soybean meal and fish meal were moderately digestible (50–90%) and digestibility coefficients tended to increase as a function of fish size. L. leucocephala was the least digestible (−10–40%). The digestibility of most of these feedstuffs was less in the anterior than in the posterior intestine, and tended to be lower in seawater than in freshwater. Rate of food movement was similar in both size groups, but was significantly faster when milkfish were in seawater rather than in freshwater. The effect of salinity on digestibility may in part be due to food motility changes necessitated by alterations in osmoregulatory processes when fish are in seawater.     

A preliminary study on the protein requirements of Chanos chanos (Forskal) fry in a controlled environment

Milkfish (Chanos chanos) fry with an average weight of 40 mg per fish were stocked in 60-l wooden-glass aquaria filled with 30 l of filtered sea water with a salinity of 32–34 p.p.t. and a temperature of 25–28°C. They were fed diets containing 20, 30, 40, 50 and 60% protein and 2740 kcal of digestible energy per kg at a daily rate of 10% of the biomass for a period of 30 days. Fish which were fed the diet containing 40% protein had the highest weight gain which was significantly higher (P < 0.05) than those of fish receiving the lower dietary levels of protein. Slightly lower weight gains were obtained when fish were fed diets containing 50 and 60% protein. Although feed conversion values were not statistically different (P < 0.05) among all treatments, the value for the 40% protein diet (1.96) was the best. The mean survival rates were low for all treatments but was highest for the 40% protein diet. No significant difference (P < 0.05) was found in the survival rates of fish receiving different treatments. Results show that a dietary level of 40% protein was required by milkfish fry for maximum growth, efficient feed conversion and high survival rate.     

Dietary vitamin C and E supplementation and reproduction of milkfish Chanos chanos Forsskal

Milkfish Chanos chanos Forsskal broodstock (11 years old, average body weight 5.23–5.73 kg) reared in 10‐m‐diameter by 3‐m‐deep floating net cages (31–36 fish per cage) at SEAFDEC AQD's Igang Marine Substation in Guimaras Island, central Philippines, were fed daily at 3% of total body weight formulated diets (36% protein, 7–8% lipid) supplemented with 0.1% vitamin C, 0.05% vitamin E, both vitamin C and E or no vitamin supplementation (control) for 3 years. Reproductive performance was assessed in an attempt to determine the optimum nutrition for successful spawning of milkfish. The total egg production, mean number of eggs per spawning, number of spawns and mean egg diameter were not affected by dietary vitamin C and E supplementation. However, broodstock given dietary supplementation of vitamin C alone or in combination with vitamin E had a higher percentage of spawns with higher (> 90%) percentage egg viability, hatching and cumulative survival rate than those of the control. Broodstock given dietary vitamin E supplementation alone had few spawns, which made the results difficult to analyse. The results confirm the essentiality of vitamin C supplementation in producing more spawns with good egg and larval quality. The production of an adequate volume of good quality eggs and larvae to support hatchery operation is necessary to offset the huge investment in broodstock development, as it takes at least 5 years for milkfish to attain sexual maturation and spawning.     

Survival of captive milkfish Chanos chanos Forsskal broodstock subjected to handling and transport

The survival of milkfish broodstock (body weight range 1–11 kg) was determined until 30 days after handling and transport in open tanks or in sealed oxygenated bags containing chilled sea water (20–25 °C). Maintenance of cool sea water was achieved by the gradual addition of ice chunks or frozen gel packs. A survival rate of 50% after transporting fish at a loading density of 45 kg m^?3 for 4 h in open tanks was not significantly different from those that were handled but not transported (86%). Similarly, survival rates (67–83%) among broodstock confined for 8 h in chilled sea water at 40 and 60 kg m^?3 were not significantly different from each other or from a group not subjected to confinement. Nevertheless, low dissolved oxygen (DO) and accumulation of total ammonia–nitrogen beginning 1 h after transport and confinement may be responsible for low survival rates of milkfish in open tanks. In contrast, all milkfish survived 10 h of overland transport in sealed bags with chilled and diluted (28 g L^?1) sea water. Likewise, all milkfish survived after being bagged and immediately transferred to a communal rearing tank, or bagged and placed in a styrofoam box for 10 h. Except for total ammonia–nitrogen levels, which increased slightly (0.7–0.8 mg L^?1) above background, seawater temperature (20–24 °C), salinity (28 g L^?1) and DO (6 to > 20 mg mL^?1) titres in transport bags were maintained during the 10‐h test. The effectiveness of handling and transporting milkfish broodstock in sealed bags containing chilled sea water was verified in actual field trials. Spawning of sexually mature milkfish subjected to these stressors was not impaired. These results demonstrate that mortalities of large milkfish broodstock can be minimized when fish are handled and transported in sealed oxygenated bags containing chilled sea water.     

An immunohistochemical study on endocrine cells in the neuroendocrine system of the digestive tract of milkfish Chanos chanos (Forsskal, 1775)

In this study, several kinds of endocrine cells which produce neuropeptides and hormones have been identified and located in the digestive tract of milkfish (Chanos chanos) by the immunohistochemical technique. The oesophagus, stomach (cardiacus, fundic and pyloric regions), pyloric caeca, intestine (anterior, middle and posterior regions) and rectum were divided from the digestive tract of milkfish. The distribution and frequency of the endocrine cells produced these neuropeptides and hormones including gastrin, cholecystokinin, leu‐enkephalin, neuropeptide Y and somatostatin were described in these segments. Endocrine cells containing all neuropeptides and hormones immunoreactivities were present in the anterior intestine region, but no reaction was found in oesophagus. Only a few L‐ENK‐ and SST‐immunoreactive cells were detected in the pyloric caeca. Large numbers of SST‐immunoreactive cells were observed in the stomach with no immunoreactivities to other neuropeptides and hormones. Two different types of endocrine cells were founded in the intestine and pyloric caeca. These results indicate that the anterior intestine region may be the main region of food digestion and absorption, and the neuropeptides and hormones regulate the food intake process by different ways in milkfish.     

Comparisons of physiological and biochemical responses between milkfish (Chanos chanos) and grass carp (Ctenopharyngodon idella) to cold shock

Temporal changes in physiological parameters and enzyme activities related to carbohydrate metabolism in the milkfish (Chanos chanos) and the grass carp (Ctenopharyngodon idella) under cold shock at 15 °C were examined in order to better understand thermal compensation mechanisms of teleosts with different cold tolerances. The plasma glucose, lactate, and lipid contents as well as enzyme activities of citrate synthase, glucose-6-phosphate dehydrogenase, fructose-1,6-bisphosphatase, phosphorylase a, and lactate dehydrogenase at varying time intervals were monitored. The results show that changes in plasma glucose and lipid contents of the milkfish were more notable than those of the grass carp, but the elevation in plasma lactate contents in the grass carp occurred earlier and was much greater than that in the milkfish. Furthermore, changes in plasma glucose contents in the milkfish were correlated with the enzyme activities of phosphorylase a and fructose-1,6-bisphosphatase, but in the grass carp they were correlated with glucose-6-phosphate dehydrogenase and lactate dehydrogenase activities instead. In addition, the change in lactate dehydrogenase activity in the grass carp was more notable than those of other enzymes, but lactate dehydrogenase activities in the milkfish steadily decreased during cold compensation. The results demonstrate that the two species (milkfish and grass carp) respond quite differently to cold shock, and this may be related to their differences in cold tolerance.