Evaluation of Mass Mortalities of Trout Fry at Nanmenxia Hatchery




Title of Report:FIELD DOCUMENT NO. 11
Author:David EDWARDS
Project Code:CPR/88/077

1)Dr Armin Lindquist, ADG, FI
1)David Lubin Library - Room A-010
1)Fisheries Library
2)Technical Officers   T. PETR - X. LU - T. MATSUSATO
1)Dr Y. Kato, Director FIO(for circulation)
1)Dr S. Garcia, Director FIR"
1)Dr W. Krone, Director FII"
1)Mr B.F. Dada, Director FIP"
1)Chief, FIDI

Project Operations Officer:         W.L. CHAN         Date: 20 MARCH 1992

Field Document 11
December 1991


Report prepared for the project
Fisheries Development in Qinghai Province
People's Republic of China


David Edwards

This report was prepared during the course of the project identified on the title page. The conclusions and recommendations given in the report are those considered appropriate at the time of its preparation. They may be modified in the light of further knowledge gained at subsequent stages of the project.

The designations employed and the presentation of the material in this document do not imply the expression of any opinion whatsoever on the part of the United Nations or the Food and Agriculture Organization of the United Nations concerning the legal or constitutional status of any country, territory or sea area, or concerning the delimitation of frontiers.

Rome, 1991

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1. Trout fry mortalities at Nanmenxia hatchery

2. Progress in other aspects of the fish culture work

2.1 Longyangxia cage site

2.2 Naked carp hatchery

2.3 Trout feed meel


Annex 1


Following the mass mortalities of trout fry which occurred at the project's Nanmenxia hatchery during summer/autumn 1991, the CTA was assigned ahead of schedule for a short mission to Qinghai from 22 October - 7 November 1991. This brief account is intended as an interim summary of the current status, problems, progress and future plans for the coldwater fish culture work of CPR/88/077. Further details will be given later in the CTA's year end report.

1. Trout fry mortalities at Nanmenxia hatchery

Mortality of eggs and fry in the hatchery was normal throughout incubation, hatching, first feeding, and subsequent development until the end of June 1991, when a large number of dead fish were found in one of the 20 2×2m fry tanks inside the hatchery building. Initially staff suspected a nutritional problem, and the dry diets made by the local Xining Mixed Feeds Factory were therefore supplemented with fresh pig liver, fresh fish (naked carp), and boiled chicken egg. Despite this, the losses soon spread to other fry tanks inside the building, and eventually to 16 indoor troughs and eight outdoor 8m-diameter fish tanks. Mortality rate increased rapidly, until by mid-August it was estimated that almost 80% of the fish had been lost.

The main symptoms exhibited by sick fish were extreme blackening of the skin, swelling of the abdomen, presence of fluid in the gut, loss of appetite and lethargic swimming. These symptoms, combined with the pattern of spread of the problem through the farm, suggested infectious disease was responsible. Consequently fish disease specialists from Wuhan, Shanghai, and other scientific institutes in China were brought to the farm to give their opinions, and they also took away samples for parasitological, bacteriological and viral investigations at their laboratories. The consensus of opinion amongst the specialists was that a viral disease was responsible, probably IPN. However, to date no virus has yet been isolated and positively identified.

Analyses of feeds for rancidity of fats, etc., were all negative, and fish at other farms fed on diets made in the same factory to the same formulations experienced no exceptional losses. Water samples showed no components which could have been responsible for the problem. Also fish which had escaped from the farm were found to be thriving in the stream adjacent to the hatchery, which is fed by the same water supply.

By the time the CTA was able to visit Qinghai, in late October, over 90% of the fry were dead. The remaining fish are all black, lethargic and feeding poorly. Though of no value for future culture, they are being kept alive in hapas in a nearby stream until the cause of death is definitely established. To this end the trout culture team leader, Mr. Zhao Yimin, will shortly go to Japan to study preparation of samples, fish viral isolation and identification at the laboratory of Professor Touo Sano, Tokyo University of Fisheries. Prof. Sano is a world-renowned expert in fish viral diseases. After two weeks training, Mr. Zhao will return to Xining to collect samples of the sick fish, then carry them to Tokyo for detailed investigation. It is hope that this will finally established the causative agent of the losses, and thus help to ensure the problem does not occur again in future.

However, whatever the outcome of these investigations, plans for the future course of action at Nanmenxia are unlikely to be greatly affected, i.e., the hatchery must now be thoroughly disinfected, taking extreme care to avoid risk of chemical injury to staff or local inhabitants and their animals downstream. Subsequently the unit can be re-stocked with new eggs/fish. Once they are no longer needed, the surviving fry will be killed and hygienically disposed of. A programme for hatchery disinfection, re-stocking and subsequent activities at Nanmenxia, as well as plans for work at the project's cage farm and naked carp hatchery, is attached as Annex 1.

Negotiations are now under way with trout producers in neighbouring Gansu Province for purchase of sufficient fingerlings to enable the project's market fish output targets for next year to be met. It is considered advisable to buy fish now, rather than waiting until spring of next year (when fingerlings would normally be transferred to on-growing units), because by that time the fingerlings' owners need only keep them on for a few months to produce market fish themselves. Therefore they can be expected to be more reluctant to sell. Their price would certainly also be much higher at that time, especially so because they know the project has no alternative source of fingerling supply within easy transport distance.

It is hoped that approx. 250,000 fingerlings averaging between 5 and 10g can be obtained and transported to the project's Nanmenxia hatchery/ raceway unit and Longyangxia cage farm before the end of the year. The results of these purchases and transfers will be given in the CTA's year end report.

Since the source of the infectious disease at Nanmenxia is not known, the possibility exists that it was introduced with the eggs imported from Denmark in March 1991. Project staff are therefore reluctant to buy from the same source again in 1992, and an alternative supplier from whom disease-free status can be better guaranteed is being sought.

2. Progress in other aspects of the fish culture work

In other respects, the fish culture work of CPR/88/077 has made very good progress during 1991. At Nanmenxia itself, building of eight 100 cubic metre concrete raceways and associated canals is now virtually complete, ready for on-growing trout next year to produce a target output of at least 20 tonnes by autumn 1992. With the exception of work in progress to improve staff accommodation (by addition of bathroom and toilet facilities) and addition of more storage space, building at Nanmenxia was therefore finished on schedule.

2.1 Longyangxia cage site

It will be recalled that fish were being grown-on in floating cages at Longyangxia Reservoir during 1991, a full year ahead of the project's original plan (see Edwards 1991, Field Document 7). An arbitrary target output of five tonnes of market trout was set for autumn 1991, mainly to provide fish to the Longyangxia Hydro-Power Company's staff. Due to excellent growth rates, this target has been exceeded by over 100%. During the CTA's present visit, all fish at the cage site were weighed and counted. The approx. 20,000 fish stocked into cages in spring 1991 at an average weight of 50g have given a harvest of 11,367kg averaging about 650g five months later. This size of a little over one jin (1 jin=0.5kg) is considered optimal for the Chinese market.

As a result of this unexpectedly high production, the company has sufficient fish above its own needs to support a trial marketing exercise in Xining. Fish are now being brought into the provincial capital alive, and offered for sale at a price of 10Yuan/jin (approx. $4/kg). The outcome of this initial marketing trial will be reported later, together with details of feed conversions and fish production costs.

The Longyangxia Power Company has also agreed to retain approx. one tonne of trout as future broodstock for the project, and is keen to increase its production target for 1992 from the 25 tonnes originally planned: probably to around 40 tonnes.

2.2 Naked carp hatchery

The project's naked carp hatchery also performed well up to target during 1991. In total, approx. 1.2 million eggs were obtained in spring (against an arbitrary goal of 1 million) from 1,130 broodfish. Hatching rate was 64.7%. After first feeding in tanks with chicken egg, trout feed and soya flour, approx. 320,000 juveniles were released into the Buha River (from where their parents came), and the rest transferred to nursing ponds in Xining, where they spent the summer. Counting and weighing of surviving fry is not yet complete, but to date their average size is estimated at 8cm length and 2g weight. Full results of the year's work, including details of timing and dosages of hormone injections used to induce ovulation, yields of eggs per kg of female broodfish, fry survival and growth in nursing ponds etc. will be given in the CTA's year end report.

2.3 Trout feed mill

A complete new fish feeds factory has been established during 1991 on a site adjacent to the project's office. Trial batches of trout diets have already been made, and the facility will begin routine production of grower pellets early next year. The plant is equipped with Chinese machinery purchased with project funds.


Despite the major setback at Nanmenxia hatchery, the fish culture work of CPR/88/077 has made substantial progress during 1991. If sufficient of the lost fry/fingerlings can be replaced by purchases from Gansu Province, project outputs need still suffer no delays. Thus it is hoped that the project can be brought back onto schedule by the end of the year.

It is of particular importance at this time that staff morale and confidence be maintained. All project personnel have worked hard on the fish farming programme this year, and therefore no blame should be attached to individuals when problems occur.



1) Nanmenxia trout farm. 
Sell broodfish.1st week Nov. 1991
Divide staff into three working groups for hatchery, tanks and raceways.Nov. 1991
Disinfect all incubators, fry tanks, outdoor fibreglass tanks, and drains with 5% formalin, taking care to safeguard staff with breathing apparatus incorporating eye protection.2nd week Nov. 1991
Following disinfection, flush all tanks with clean water for several days.3rd week Nov. 1991
Order and arrange delivery of feeds for trout."
Purchase and transport trout fry/fingerlings from Lanzhou to 8m-diameter outdoor tanks.4th week Nov. 1991
Complete construction of 8 × 100 cubic metre concrete raceways.2nd week Nov. 1991
Flush raceways with water for one month.Mid-Nov. - Mid-Dec, '91
Prepare one earth pond for on-growing trout.By end 1991
Transfer half fingerlings from circular tanks to raceways and earth pond.Mid-Dec '91-Mid-Jan '92
Complete building toilets/bathrooms.End 1991
Construct small concrete raceways inside hatchery building.By March 1992
Import one million eyed eggs (of these, ca. 100,000 will go to Gansu and 100,000 to Longyangxia).March 1992
Transfer remaining fingerlings from circular tanks to cages at Longyangxia.March - May 1992
Modify screens for outdoor tanks.Summer 1992
Rear fingerlings and market fish.Nov. 1991-Oct. 1992
Harvest minimum 20 tonnes market fish.Oct. - Dec. 1992
2) Longyangxia cage farm.
Complete harvesting/marketing of 1991 fish crop, retaining one tonne for broodstock.End 1991
Improve anchoring of cages/working platform.Mid-Nov. 1991
Prepare small-mesh cages suitable for 5–10g fish.Mid-Nov. 1991
Purchase/transport fingerlings from Lanzhou to cages.By end Nov. 1991
Order/purchase feeds for small fish.Mid-Nov. 1991
Prepare small experimental floating hatchery for 200,000 trout eggs.By end 1991
Build minimum 26 cages and moor in lake.By end May 1992
Introduce eggs to experimental incubators.March 1992
Experimental hatching and fry rearing in cages.March - Autumn 1992.
Transfer fingerlings from Nanmenxia to cages.March - May 1992
Set up ice machine/fish packing facility.Summer 1992
Rear fish to market size.Nov. 1991-Nov. 1992
Harvest/sale of minimum 30 tonnes fish.Oct. - Dec. 1992
3) Trout feed manufacture.
Begin production of on-growing pellets at Bureau of Aquatic Products' new feeds factory in Xining.Spring 1992
4) Naked carp hatchery.
Prepare equipment/facilities for 1992 season, including min. 10 mu of nursing ponds.By March 1992
Capture sufficient broodfish from Buha River to provide 1 million eggs. Transport to broodfish ponds in Xining.April - July 1992
Induce spawning by hypophysation. Strip 1 million eggs.April - Aug. 1992
Hatch eggs, feed larvae in tanks, and transfer to nursing ponds.April - Aug. 1992
Rear fry in nursing ponds.May - Oct. 1992
Harvest fry, transport to Buha River for release and/or to ponds for experimental on-growing.Autumn 1992
5) Plans for future work.
Detailed plans/proposals for future coldwater fish culture work in Qinghai prepared.By end Oct. 1992

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