Development of Improved Growout Culture for Chinese Catfish Through Ploidy and Feed Applications |
The overall goal of this two-year project, which was initiated under the CTSA Eighth Annual Plan of Work, is to develop improved Chinese catfish culture techniques that result in reduced production costs, greater growth and survival rates, lower feed conversion ratios (FCR) and more reliable production. Specific objectives related to that goal are to:
A successful outcome from this project would result in decreased production costs for Chinese catfish and greater profits to farmers. Opportunities for a successful outcome to this project include increased growth and survival rates of triploids and improved FCRs of diploid and/or triploid fish through better feed applications and formulations.
Objective: Develop methods for reliably producing triploid catfish using cold shock treatment of fertilized eggs.
Cold shock treatment for inducing triploidy was evaluated at two different temperatures-4øC or 5øC-for shock durations of 0, 5, 10, 15, 20, 25 and 30 minutes. Hatch rates did not differ between temperature treatments but dropped as cold treatment time increased. Hatch rates did not change significantly between cold shock times of 20 and 30 minutes. Based on this and previous experiments, cold shock treatment at 4øC to 5øC for 20 to 30 minutes seem most effective at inducing triploidy.
An experiment was conducted to compare the effectiveness of two methods of inducing triploidy. After eggs were mixed with sperm for three minutes, the fertilized eggs were divided into three portions-control, cold shock and pressure shock for treatments with four replicates of each. Cold shock at 4øC was applied for 20 minutes; pressure shock at 8,000 psi was applied for 8 minutes. Hatch rates were higher in the control group than in either the cold shock or pressure shock groups. Pressure shock yielded a higher hatch rate than cold shock.
Objective: Based on intrinsic feeding patterns observed during Year 1, alter feeding patterns to coincide with those commonly used at commercial production facilities and observe the effect on comparative growth rates, survival and FCR.
During Year 1, juvenile Chinese catfish were found to have two
distinct feeding peaks. An experiment was begun February 1997 to
test whether fish growth and survival would be affected by
feeding schedules that did not coincide with their intrinsic
feeding patterns. Fish are fed on three schedules:
(1) once daily at noon,
(2) once daily at midnight, and
(3) twice daily at 8 a.m. and 6 p.m.
Three 1.5-meter-diameter, 0.8-meter-high tanks each stocked with
150 20-gram fish are being used for each feeding schedule. Daily
ration, which is adjusted monthly according to fish weight gain,
is 5 percent of fish weight.
Objective: Using cold and/or pressure shock, attempt to produce tetraploid (4N) Chinese catfish and rear them fish to reproductive age. If successful, tetraploids could be cross-bred with diploids to produce 100 percent triploids.
Fertilized eggs were cold shocked at 5øC to 6øC for 17 minutes at 3, 15, 30, 45, 60, 75 and 105 minutes post-fertilization. A control group was not shocked. The nuclear diameters of red blood cells (rbc) in the developing larvae were then measured. As expected, control fish (c0) all had rbc nuclear diameters of <35pt. More than 70 percent of fish shocked at 3 minutes post-fertilization (c3) had rbc nuclear diameters of>35m, while those shocked at 15 minutes post-fertilization (c15) were similar to the control group. Eggs shocked at 30 minutes post-fertilization (c3O) indicated >50% with nuclear diameters >35m.
The data indicate that control fish were normal diploids (2N), while 70 percent of those shocked at 3 minutes post-fertilization were triploids (3N) due to polar body retention. Shocking at 15 minutes post-fertilization resulted in normal diploids since the polar body was lost, but the first cell division was not affected. Shocking at 30 minutes post-fertilization resulted in production of tetraploids (4N) due to disruption of first cell division after chromosome replication. To a lesser extent, this may have also occurred with fish shocked at 45 minutes post-fertilization but not at 60 minutes post-fertilization. Shocking later than 60 minutes probably resulted in mosaics, with some cells being 2N and some 4N.
Due to low survival of these fish, trials are being continued with efforts focused on shocking during the period from 25 to 40 minutes post-fertilization. If this succeeds in producing sufficient quantities of fish that appear to be 4N, their condition will be verified by chromosome spread (count) techniques.
During the remainder of this project, investigators plan to:
No publications or manuscripts were produced nor were any papers presented during the reporting period.