Three improvements were found in the larval section, otherwise unchanged. First, a new electronic control of the heating system replaced the pneumatic system. Second, the heating system has been connected to the cooling system to give the staff the possibility to cool the rearing water if some conditioned spawnings are available earlier (September-October), when the natural seawater temperature is much higher than that of the conditioning unit. Third, each tank light has been connected to a single trimmer to give more flexibility in the illumination management.
Some fast joints have been installed along the water piping system (drains and main distribution line) in order to improve disassembling and make cleaning easier and more effective.
The cooling fans of the UV sterilizer board were found out of order because heavily corroded by salt. Since it was impossibile to have them repaired in Turkey, they have been removed, leaving a larger window to allow air exchange to cool the electronic component of the board.
However odd it can appears, no production planning was made at the beginning of the season by the Direction of the Beymelek Centre. A target of one million fingerlings was set without any selling evidence, most probably because it sounds well.
One larval cycle with seabream eggs was almost completed by the time the consultant left. There is the possibility of a second larval cycle with seabass egg in March, if a larger number of seabass fingerlings is requested by the farmers.
In order to increase production and to take advantage by the existing facilities (staff, tanks, live food availability, etc.), five weaning tanks have been stocked with seabream eggs and four ones with seabass eggs, together with five spawning tanks.
One weaning tank was stocked with eggs supplied by a private hatchery (Electrosan Deniz Ürünleri Üretim ve Pazarlama Ltd. Sti, Izmir) in exchange with rotifer and algal strains.
The larval rearing protocols of seabream provided last year have been followed without major changes this year. Concerning seabass, rotifers supplied as first food starting from day 8 were replaced by artemia nauplii supplied 24 hours earlier at day 7. The new feeding protocol worked at least as well as the old one, thus saving in production costs (rotifers, algae and labour).
Final data are not available since the consultant left before the larval rearing was over. It is however evident that this year the overall performance of the larval unit stocked with seabreams appears definitely better than that of last year in terms of average larval density per tank. Output should at least double the previous season results. The five weaning tanks stocked with seabream eggs perform in different ways: two tanks promise a good production close to that (101000 fry) got from one weaning tank the previous season, two other tanks could give half this figure, while the last one has a very low larval density. Since the rearing conditions are identical, these different outputs can be explained in terms of hatching rate and stocking density (Annex 15).
Being even younger than seabreams, no final survival rate is available for seabass larvae. However, their density in both weaning and spawning tanks (with the exception of tank W2, due to a very low hatching rate) looks higher than that obtained the previous season. Tank W1 needed to be diluted two times at age 30 and to keep oxygen under control. Tank W3 shows an even higher density and will required dilution at an earlier age. A final production of more than one million seabass fry should be safely guaranteed by the existing larval stock, provided that no serious technical failure or disease outbreak happen.
Hatching rates and percentage of viable larvae aged one day are presented separately for seabream (Annex 15) and for seabass (Annex 16). For an easier comparison, the main results of both seasons 1993–4 and 1994–5 are summarized in Table 17.
Average hatching rate remains low in both species, even if some improvements from the previous season have been observed, compared with the one usually obtainable from natural spawning.
In the larval tanks seabream showed a 47% hatching rate, roughly the same figure of the previous year (44%). The percentage of viable larvae one day after eclosion is however much higher (92% against 62%), probably because better rearing conditions of the parent fish. Due to the different geometry of the tanks (and the difficulty of homogeneus sampling), the weaning tanks presented a lower hatching rate (16%), but the presence of viable larvae remains almost constant.
In both types of tanks (weaning and spawning) seabass eggs improved significantly their hatching performance if compared with last year. The percentage of viable larvae was 77% on average, more or less the same of 1993–4 season.
At the beginning of the larval rearing the total number of viable larvae was about 5.0 million seabream and 4.8 million seabass.
Repletion rate of seabream was high from the first days of feeding controls, in particular in the larvae hosted in the weaning tanks (Annex 18). No appreciable difference was found in the larvae sampled in the days in which they were submitted to prophylactic treatments (Annex 18, bold values).
The inflation rate of swimbladder in seabream shows a delayed starting due to the low water temperatures (Annex 18). Its average value of 65% in larvae aged 20 days and more represents a light improvement of the activation rate observed last year (59%). It should have been higher since this season a new generation of more efficient skimmers was available. Even considering the possibility of some sampling errors (in 25% of tanks the greatest rate was not found in the older larvae as it should be since the swimbladder activation is a not reversible process), such a low performance is probably due to a manual cleaning of the skimmers not as efficient as requested, in particular after the distribution of rotifers, as pointed out many times by the consultants during his mission.
Urinary calculi were almost always found in larval seabreams, with a higher rate than previous season (Annex 18).
In seabass larvae repletion rate was 77% the first feeding day (7th) to increase further in the following days (Annex 19). Swimbladder inflation can be detected as earlier as the first day of light and feeding. Its rate was 97% in the oldest weaning tank at age 19. The spawning tanks are also proceeding quite well since the last available data show an average value of 61% at day 11th. Surface sampling probably overestimated the rate of nonactive swimbladders since the presence of poor quality larvae is higher near to the water surface, in particular close to the tank wall. The presence of urinary calculi was scarce (Annex 19).
In intensive fish farming, and the hatchery in particular, diseases represent one of the most important causes of production losses. Since their prevention or control play a vital role in any successful aquaculture enterprise, an experienced fish pathologist becames a key staff in the hatchery.
According to the Beymelek Centre director, a local veterinary should joint the hatchery staff in a short time. However he has no experience on fish and fish deseases and has to be trained accordingly. To that purpose my recommendation B.10 becames particularly useful.
This production season a larger use of prophylactic treatments was made, further to any appearance of even very light mortality or abnormal behaviour in fish larvae.
The bacteriostatic furanic Furazolidone was employed for 1-hour bath at dosages of 20 ppm for very young larvae and 30 ppm for larvae aged 20 or more days. Treatments were repeated three days every morning before feeding. Bottom left-over of Furazolidone were siphoned out at the end of the treatment cycle.
In some rare cases a large mortality occurred, mainly in the spawning tanks W1, W3, W10 and W11 due to a bacterial pathogen identified as vibrio by microbiological analysis. The subsequent antibiogramme analysis showed a good antibiotic activity by Flumequine, the furanics being almost useless. This drug was therefore subministered to the larvae by means of artemia metanauplii. Bioencapsulation was performed by mixing Flumequine to the enrichment diet Super Selco in a dose of 30% w/w for the first 2 days, then 20% w/w for the last three. The supply of the antibiotic by means of bioencapsulation presents many advantages: a constant supply of the drug with the feed, its reduced need if compared with bath treatments, a lower contamination of the environment and a greater effectiviness. Results were very good and mortality disappeared in a few days
Staff is composed by one head and four workers (Annex 22). A fifth worker from the life food section will joint them at the beginning of March.
Working hours were arranged to cover the feeding time: a normal shift (07.30–12.00 and 13.00–16.00) staffed by three workers and an afternoon shift (15.00–20.00) staffed by one worker. No change was made during weekends. The head usually inspects his section in the evening in concomitance with the last feeding.
The detailed instructions and forms concerning the daily management of the section supplid the last season were used without significant changes and are not quoted here.
The present experience has confirmed once more that both the spawning and weaning tanks can successfully be converted into larval rearing tanks. In this way the production capacity of the hatchery can at least double. This is now an true reality since its weaning capacity will double in a short time thanks to the new weaning unit, at present under construction in a covered area close to the hatchery.
