TROPHIC COMMUNITY CORRELATIONS IN FERTILIZED PONDS
FOR THE COMMERCIAL CULTURE OF THE KURUMA PRAWN
Penaeus japonicus Bate IN THE NORTH ADRIATIC SEA
(North-East Coast of Italy)

LUMARE F., ANDREOLI C., GUGLIELMO L., MASELLI M.A.
PISCITELLI G., SCOVACRICCHI T., TOLOMIO C.

INTRODUCTION

The Penaeus japonicus, a penaeid of Asian origin which was introduced into Italy and acclimatized in 1979 (LUMARE and PALMEGIANO, 1980), is now considered to be one of the most interesting species for Italian and Mediterranean aquaculture. Italy's environmental features and advanced biotechnological knowhow make it a favourable environment in which to develop prawn culture using this species (LUMARE, 1983; LUMARE, 1983 a).

One of the most promising approaches to prawn culture is through extensive breeding in fertilized ponds to increase the final production levels. An initial experiment has been conducted along these lines in a small area of a “valle da pesca” (Italian traditional extensive fish farm) in the venetian lagoon (l ha), which gave a final yield of 294, 2 Kg after 5 months'management (LUMARE et al., 1984).

This paper is a tentative initial interpretation of the main correlations at various levels in the trophic chain, in which the final link is prawn production, and is intended to provide preliminary indications for production purposes.

MATERIALS AND METHODS

The research was conducted in two “valli da pesca” in the Venetian Lagoon (fig. 1). the first, Valle Sparesera, covered 11 ha, and was divide into smaller ponds (fig. 2) in which the bed sloped at a gradient of about 0,40 %. The low water replacement rate was due to the weak effects of the tide (ponds A, B, C) and, in the case of ponds D end E, it was partly due to the fact the pump was only brought into service at the end of June, to ensure an exchange rate of 1 % of the whole volume par day. The bottom of the ponds were very high in sand content (45 ù) and low in organic matter (0,9 – 1,1 %).

In the second area, in Valle FOSSE, a l ha square pond was dug, shored up with earth and fitted with grilles for water replacement. The bed has a high lime content (70 %) and a high organic matter content (4,3 %). A pump provided a total water replacement rate of1,5 %. A considerable time before sowing, the valle SPARESERA ponds were completely drained to eliminate predators; since the pond in the Valle FOSSE could not be completely drained, sodium hypochlorite was added to remaining pools (0,015 litres/m²).

About a month before the Penaeus japonicus post-larvae sowing operation (table 1), the fertilization programme was started, following the schedule and using the quantities given in Fig. 3. Initial organic fertilization was effected in very shallow water (10 – 20 mm), while the subsequent phases were effected on the full ponds (0,60 – 1,30 m).

During fertilization, water samples were taken at regular intervals (every 1 – 4 hours for 1,5 – 3 consecutive days) at a preselected station on each pond, to measure the phosphate, nitrate, nitrite, ammoniacal nitrogen, O², pH and salinity levels and the temperature.

Every 15 days, in addition to the physical and chemical readings, phyto and zoo-plankton samples were taken from each pond. The phyto-plankton was collected at a depth of about 20 cm, and fixed in 4 % neutralized formation. The quantitative and qualitative study was conducted using the UTERMOL method, to calculate the cellular volume (ANDREOLI and FRICANO, 1983) and the wet biomass.

The zooplankton was collected by skimming the surface with a 200 um mesh net, and was fixed in 4 % neutralized formalin; Subsamples were analized to identify and count the species using the “DOLLFUF curve”. The dry weight and wet weight were established using the technique described by LOVEGROVE (1966). Phyto and zoo-plankton turbidity levels were periodically measured using a SECCHI disk, to from the partial basis for the fertilization programme.

Monthly measurements of the biotic communities on the pond bottom were taken on the basis of three samples taken from a station on each pond using a 0,04 m² VAN VEEN grab. The samples were passed through a serie of sieves with a minimum mesh of 0,5 mm. The organisms collected were fixed in 4 % neutralized formalin and then classified, counted and measured in terms of dry and wet biomass. At various stages in the breeding process, penaeid samples were taken and immediately fixed in 4 % formalin; Their stomach contents were examined and a qualitative analysis of their prey and percentage frequency was effected. Penaeid samples were periodically taken for the biometric analysis of sexual maturity levels, impregnation rates and sex ratios.

Periodic water temperature measurements were also made to establish the effect of temperature change as a conditioning factor on the growth of the penaeids.

The prawns were harvested using netted traps and an electric fishing system beginning early September in ponds D and F, and in October in the others, through to the end of November.

RESULTS

Fig. 4 gives the ammoniacal nitrogen, nitrite, nitrate and orthophosphate levels in the water of pond D in Valle SPARESERA. This pond was also considered representative of the other ponds (A, B, C, E) of which it reflected the general patterns, with slight variations.

Fig. 5 gives the readings for these parameters for pond F in Valle FOSSE, where fertilization was only effected at the beginning of the breeding phase.

Fig. 6 gives the temperature readings in pond D. But this situation may also be considered indicative of the other ponds in the two “Valli da pesca”. The same applies to the pH readings, which varied between 7,9 and 9,4 averaging 8,4, while salinity ranged from 26,6 to 38,5 %.

Fig. 7 gives the quantitative variations in the wet weights of the phyto and zoo-plankton and the corresponding chlorophyll a quantities in pond D in Valle SPARESERA; the same parameters are considered in fig. 8 in relation to pond F in Valle FOSSE.

Periodic water transparency readings were taken on the ponds when conditions were calm, to ensure that the reading expressed the quantities of phyto and zoo-plankton. A SECCHI disk was used to provide an empirical assessment of the state of eutrophication of the ponds, to relate this to prawn production and to see if it might in future be used by prawn farmers. Fig. 9 gives the water transparency reading for ponds D and F during the experimental period.

Fig 10 gives the histograms for the biomasses of the biotic communities on the pond bottoms, expressed in wet weight, allowing for the metabolized inert substances (molluscs shells and valves). Account was also taken of the edible fraction of these alone, namely the soft parts of Hydrobia sp and Cerastoderma glaucum (Brug.), with regard to the latter, only sizes below 3 mm were considered, being the size which the penaeid could attack because of their soft valves and because they are only found in the valle SPARESERA up to the end of May. In the following months, although C. glaucum were plentiful in the macrobenthonic communities in Valle SPARESERA, they did not form part of the P. japonicus diet because they were generally larger than three mm. in Valle FOSSE, Hydrobia sp constituted the main component of the fraction of mollusc utilized.

Table II gives the percentage composition of the prey found in the stomachs of the P. japonicus It shows the different natural diets, which reflects the different structures of the macrobenthos in the two “valli”.

Fig. 11 shows the growth pattern of the penaeid populations in the two ponds considered (D and F). One relevant finding is the fact that the size in terms of weight of the pond D population dropped during the final breeding phase, which is striking proof of the scarcity of trophic resources in the environment. This situation is corroborated by the final weight given in table III, which shows the production of penaeid in the ponds (A, B, C, D, E, F) in both “valli da pesca”.

The sex ratio of the different populations of P. japonicus was around l (table III), with a slight predominance of females: the impregnation rate (ie. the presence of spermatophore in the thelycum) was generally low in comparison with the 98 % found under normal breeding conditions (LUMARE, unpublished data). The percentage of females at an advanced stage of ovarian maturation (stages III – IV) was also very low indeed (0 – 8,6%).

DISUSSION

Water fertilization is practised in many forms of fresh-water fish culture (MOAV, et al., 1977: WAHBY, 1974: BISHARA, 1978; BISHARA, 1979) and sea water fish culture (CHEN, 1972). It is also practised in many forms of prawn farming; for example, the farming of Penaeus vannamei Boone and P. stylirostris Stimpson in Central America, and P. monodon Fabricius in polyculture in the Philippines (ELDANI and PRIMAVERA, 1981).

For penaeid production, KITTAKA (1975) emphasizes the value of this practice, coupled with predator control and improving the pond bed conditions.

In Italy, water fertilization was successfully adopted for the first culture experiments with P. japonicus (LUMARE end al., 1984).

It is vital to gain a better understanding of the relationship between the features of the pond bed, fertilization, and productivity at the various trophic levels, and final production, if this production approach is to be properly planned. The two areas used for the experiment were therefore chosen in terms of the differing features of the pond beds, and different fertilization programmes were designed accordingly. The effect of this diversity was measured more directly through the torbidity of the phyto and zooplankton. Yet this diversity was not matched by the expected diversity in the sizes of the phyto and zoo-plankton populations, because pond D was surprisingly found to have a larger biomasses than pond F. Probably one of the main reasons for this was the part played by the microbenthonic populations that were not measured in the experiment, although they will have to be taken into account in future. The macrobenthonic biomasses also appeared to be larger in pond D, yet for the purposes of counting the biomass relevant to the trophism of the penaeids, the curve superimposed on the histogram in Fig. 10 shows that the trophic base was larger in pond F (the average size of the biomass, calculated on the basis of the last three readings, was 113,6 kg/ha, compared with 41,2 kg/ha in pond D). To calculate this figure, the sizes of the zoological groups which were wholly utilizable were taken into account (mainly annelids, crustaceans, insects) and only the soft parts of the attackable molluscs (Hydrobia sp and others). No account was taken of the soft parts of the percentage of Cerastoderma glaucum which were too large (over 3 mm) to be used by the penaeids. A comparison of the stomach contents of the penaeid populations of the two ponds (D and F) also revealed different diets correlated to the differing biocetonic composition of the pond bottoms, probably due to the specific pedological features of the soil (high sand content in pond D, mainly lime in pond F, and different percentages of organic matter).

Table II shows that Chironomidae and Copepoda make up 81,5 % of the penaeids'diet in valle SPARESERA, while Hydrobia sp and Corophiidae account for 82,4% of the diet in valle FOSSE. The differing quantities of macrobenthonic biomasses in the two environments are also reflected in the final production in each case.

In this connection, it should be noted that the final yields (Kg/ha) in the two intercommunicating ponds D and E were different. This might be due to the fact that harvesting began on 3 September in pond D, while in pond E it began about one month later. Harvesting early in the first pond thinned out the population and provided a better distribution of the trophic resources, and hence reduced cannibalism which was much higher in pond E, and in nearly all the others. One may assume that the pattern of the environmental parameters of the water and the related trophic situation ensured sufficient nutritional levels in terms of the size of the penaeids, almost until September in pond F, and only until the end of July in pond D. In the following periods, the macrobenthonic populations were no longer able to meet the penaeids' feeding requirements (the daily requirements is about 20 % of their body weight, at the size and temperature levels considered here), thus causing cannibalism. This was even more evident in ponds which had a higher sowing density. In pond F, growing out trials with a lower sowing density (1,8 p 23/m²) had yielded a recovery rate of 48 % the year before (LUMARE and al., 1984)

Proof of the difficult dietary situation in Valle SPARESERA in the final breeding phase was the softening of the penaeids' carapax, attributable to the low content of mineral salts.

More evident proof of this was the unusually low impregnation percentages, expect in pond F, which was further evidenced by the extremely low ovarian maturation rate (stages III – IV) in all the ponds, where as in a previous experiment, pond F has produced an 84,6 % rate (LUMARE and al., 1984).

ACKNOWLEDGEMENTS

The authors wish to thank the Department of Ecology, the Environment and Fisheries of the VENICE Provinical Government for having placed “Valle SPARESERA” and the “Valle FOSSE” ponds at their disposal, and for their invaluable help in the management and harvesting operations.

They also thank the venetia Fisheries and Aquaculture Development Consortium COSPAV), CHIOGGIA, for its logistical support, and Mr. G CASOLINO, of “Istituto per lo Sfruttamento Biologico delle Lagune - CNR”, LESINA, for his help with the graphics.

Literature Cited

ANDREOLI C e G. FRICANO - 1983 -Il Po: Ulteriori osservazioni di densità e di biomassa del fitoplancton nel tratto di fiume prossimo alla centrale termonucleare, di CAORSO (Piacenza). Un ciclo annuale (settembre 1980 - agosto 1981). Riv. Idrobiol. (in press).

BISHARA, N.F. - 1978 - Fertilizing fish ponds. II - Growth of Mugil cephalus in Egypt by pond fertilization and feeding. Aquaculture, 13; 361 – 367.

BISHARA, N.F. - 1979 - Fertilizing fish ponds.III - Growth of Mugil cephalus in Egypt by pond fertilization and feeding. Aquaculture, 16; 47 – 45.

CHEN T.P. - 1972 - Fertilization and feeding in coastal fish farms in Taiwan. In “Coastal aquaculture in Indo-pacific Region”. PILLAY T.V.R.(Ed.); 410 – 416.

ELDANT A. and J.H. PRIMAVERA - 1981 - Effect of different stocking combinations on growth production and survival of milkfish (Chanos chanos (Forskäl) and prawn (Penaeus monodon Fabricius) in polyculture in brackishwater ponds. Aquaculture, 23, 59 – 72.

KITTAKA J.-1975 - Food and growth of Penaeid shrimp, Proceedings of the First International Conference on Aquaculture Nutrition, October, 1975; 249 – 285.

LOVEGROVE T. - 1966 - The determination of the dry weight of plankton and the effect of various factors on the values obtained. Some contemporary studies in marine science. Ed. H. Borners; LONDON.

LUMARE F. - 1983 - Italy farms kuruma prawn; Fish farming International, 10 (3); 10 – 11

LUMARE F. - 1983 a - Italian valliculture and its future development. Rapp. Comm. int Mer Medit., , 28 (6); 85 – 89.

LUMARE F.e G.B. PALMEGIANO - 1980 - Acclimatazione di Penaeus japonicus Bate nella laguna de LESINA (Italia Sud-Orientale). Riv. It. Piscic. Ittiop. A XV, 2; 53 – 58.

LUMARE F., T. SCOVACRICCHI, G. PISCITELLI, G. GRASSO - 1984 - Prime esperienze di allevamento commerciale a gestione controllata del peneide Penaeus japonicus Bast in una valle da pesca nella laguna di VENEZIA; XVI Congr, SOcv. It. Biol. Mar., 25 – 30 settembre 1984, LECCE; 1 – 18.

MOAV R., G. WOHLFARTH, G.L. SCHROEDER, G. HULATA and H. BARASH - 1977 - Intensive polyculture of fish in freshwater ponds. I. Substitution of expensive feeds by liquid cow manure. Aquaculture, 10; 25 – 43.

- Fig. 1 -

- Fig. 2 -

- Fig. 3 -

- FIG. 4 -

- FIG. 5 -

- FIG. 7 -

- FIG. 8 -

- FIG. 9 -

- FIG. 10 -

- FIG. 11 -

Tab. I - Sowing programme of Penaeus japonicus post larvae (P₂₃ - ₂₇) in Valle SPARESERA (A, B, C, D, E Ponds) and in valle FOSSE (F pond).

Tab.II - Percent of preys in stomach contents of Penaeus japonicus stocks in valle SPARESERA (D pond) and in Valle FOSSE (F pond) reared. Different qualitative pattern of preys are related to macrobenthonic biocenosis differentiation in the two “valli da pesca”.

Table III - Biometric, biological and production data on the penaeus japonicusbred in Valle SPARESERA (ponds A,B,C,D,E) and Valle FOSSE (pond F). The impregnation rate and ovarian maturation rate have been calculated as the average of the last four samples (September – October). The number in brackets indicate the numerical size of the samples. (1) the breeding period in days, from sowing date to the date the harvesting of the penaeids began.