STUDIES ON LEVELS OF STOCKING DENSITY FOR MULLET, RABBIT FISH AND PAGURUS FRY FOR FINGERLINGS PRODUCTION

by Magdy A. Saleh
EGYPT

Abstract : The effect of different stocking density of three fish species (Liza ramada; Risso, Siganus rivulatus and Pagurus haffara; C&V) fry fingerlings production was studied, Fish fry of the different species were stocked in 16 m2-bottom pens made of 2 mm mesh plastic netting materials in the nursing pond at lake Qaroun, El-Fayoum province, Fish fry (16–24 mm long) were stocked in five different stocking densities, 250/m2, 200/m2,150/m2,100/m2, and 50/m2, Feeding of fry was basically on green water and fermented-dried pigeon droppings.

Results of the study have shows that the best-highest stocking density was 150/m2 for mullet, 50/m2 for both rabbit fish and pagrus. Further studies are requires for studying the performance of fry of these species in mixed nursing at different stocking rates.

INTRODUCTION

Marine fish were introduced to lake Quaroun, an agriculture waste water recipient at EL-Fayoum province, since the early 20s (Faouzi, 1936). Mullet species were the first marine fishes introduced there, and on the contrary to what was published before (El-Zarka, 1968), no concrete evidence on natural propagation of any of the transplanted species was observed of found. Consequently, mullet fry must be transplanted regularly to the lake to maintain the local stock.

The operation of mullet fry transplantation to lake Qaroun, although conducted on a commercial scale since the early 30s, no solid informations are available on the suitable stocking density of fry during nursing. Mullet fry use to be stocked directly to the lake or to near shore pens and enclosures. This system was associated with great losses of fry (El-Zarka and Kamel, 1967) and a true figure of released fingerlings cannot be obtained.

An experimental nursing pond 32km2) was constructed lake Quaroun in the winter of 1988. The mullet fry requirement of lake Quaroun for 1988 season was calculated to be 11.5 mil, 2.5 mil, were stocked in two enclosures at Abu-Nemma and Shak-shouk, and 9 mil were stocked in the nursing pond.

Trials were conducted before to transplant other marine species (gilthead seabream-Sparus aurata; L-and the European seabass-Morone labrax; L) but the shortage of fry supply of those species seems to be the main obstacle that hindered the potentiality of these species as a part of the commercial catch of the lake.

Studying the availability of different natural food components, it was found that there is a great potential for introducing other marine species in the lake. A review of the quantitative and qualitative fry catch from 12 different fry collection stations on the Mediterranean, gulf of Suez and the bitter lakes, revealed that, a sufficient supply of rabbit fish and hafara fry can be obtained for stocking the lake in addition to mullet. Taking into consideration that the performance of any fish species in a new environment and production system should be studied soundly, especially if the information on the cultue biology of such species is still not completely studied, only 300k fry of rabbit fish and 150k fry of hafara were decided.

MATERIAL AND METHODS

Fishes : Liza ramada fry collected from El-Gerby fry collection. Siganus and Pagurus fry collected from Shandora collection station on the bitter lakes near Suez.

Two DAF, 1600 fry transport trucks, each with 6 built on double-walled insulated, 1m3 glass-fibre tanks supplied with air with a diesel runned compressor with dust and oil traps. 15, 16m2 each, bottom pens of 2mm mesh plastic netting. A sartorius, electronic top balance with DCD screen. A standard micro-fish measuring scale.

Two earthern ponds each of 16k m2 supplied by a water flow of 648m3day and a working water level of 80–95 cm.

Pens were fixed in the nursing ponds by four corner poles/ pens, the bottom nets were fixed by intertangling it with the bottom soil and bags filled earth along the sides. An equal depth of water with pond water was kept and a free board of 35 cm above water surface.

Fry were transported with the fry transport truck in a stocking density of 20k and 25k fry/m3for mullet and the other two species respectively.

Random samples of fry were collected and 500 of each species were weight and measured. Fry were stocked in pens at five different stocking rates, 250,200, 150, 100 and 50 fry/m2.

Soil samples were taken, dried, extracted and analysed according to the standard techniques and the fertilizer requirement (in terms of mg/l available Nitrogen, Phosphorus and other minor nutrients) was calculated, Ponds were plowed and traditional old cattle manure(cow dung mixed with stall dust and kept in heaps for fermentation for more than 60 days) and pilled in small heaps fro fermentation for more than 60 days) and pilled in small heaps in the ponds.

Two cement glazed brick tanks, 16m2 each were constructed on the pond dyke near the pumps. Tanks were designed a s in fig.1 mainly for pigeon dropping fementation and the production of nutrients and plankton enriched water, Fermented pigeon dropping were sun dried and supplied to the nursing ponds as food and fertilizer.

A weekly samples of 100 fry from each pen were taken, weighed in water-filled plastic bags of known weight and the mean weight was calculated. A sub-sample of 10 fry from each weekly sample were taken, length (TL) was measured and discarded.

RESULTS AND DISCUSSION

Liza ramada fry used in this study were 19.45mm + 1.16 having an average weight of 0.64 gr + 0.08. The experiment was started Feb. 15 th. and finished June 1 st.; 10 weeks.
Table 1 and fig 2 shows the increase in length during the experiment time for the different used stocking density.

Table 1; increase in length during the 10 weeks experiment time at differ-stocking densities. D 1–5 = different used densities, T = time

Table 2 and fig, 3 shows the increase in weight during the experiment time, weight increment is also shown for each density.

At the end of the experiment, fry were gathered, counted and surivival was calculated for each stocking density.

It was found that mortality, on the contrary to what was expected, is not consitent with the stocking density. Survival % is shown with each increment for each stocking density.

Table 2; increase in body at the different stocking densities during the experiment time.
* 1 – 5 are the different densities, 1=50/m2…5 = 250/m2

Weight increment at a density of 50/m2 = 855 g/m2, Survival 86%.
Weight increment at a density of 100/m2 = 1238 g/m2, Survival 88%.
Weight increment at a density of 150/m2 = 1373 g/m2, Survival 87%.
Weight increment at a density of 200/m2 = 1390 g/m2, Survival 78%.
Weight increment at a density of 250/m2 = 913 g/m2. Survival 74%.

Siganus rivulatus fry used for this study were 23.73 mm + 1.09 mm and having an average weight of 1.06 g + 0.76 g. The experiment started March 20th. and finished June 1st.; ie 9 weeks, Table 3 and fig. 4 show the increase in length and weight during the experiment time.

Table 3.