Effects of fertilization and stocking rate on the performance of Penaeus japonicus (Bate) in pond culture

83 (1989) 269-279 Elsevier Science Publishers B.V., Amsterdam -

Aquaculture,

269

Printed in The Netherlands

Effects of Fertilization and Stocking Rate on the Performance of Penaeus japonicus (Bate) in Pond Culture D. LANARI, R. BALLESTRAZZI and E. TIBALDI Istituto di Prod&one 33010 Pugnacco

Animale,

Universita’degli

Studi di Udine,

Via S. Mauro 2,

(UD) (Italy)

(Accepted 30 January 1989)

ABSTRACT Lanari, D., Ballestrazzi, R. and Tibaldi, E., 1989. Effects of fertilization and stocking rate on the performance of Penaeus japonicus (Bate) in pond culture. Aquaculture, 83: 269-279. The effects of fertilization and stocking rate on the grow-out phase (123 days) of Penaeus were studied in earth ponds in a ‘valle’ of the Grado Lagoon (north Adriatic Sea). Water was fertilized by broadcasting poultry manure (2000 kg/ha), ammonium nitrate (8 kg N/ha) and mineral superphosphate (10 kg P,O,/ha) in drained ponds. During the trial, half of the initial dose of -inorganic fertilizers was also spread fortnightly. Stocking shrimp at 3/m’ as opposed to 1.5/m’ lowered the average final weight of the shrimps and negatively influenced the distribution of live-weight classes. Fertilization significantly increased the live weight of the shrimps (P < 0.01) after the 42nd day of rearing. It also significantly lowered the incidence of shrimp weighing less than 16 g but did not affect survival rate. Stomach content analysis confirmed the benthic omnivore habits of P. japonicus, although, within each class, few species were shrimp prey. Both fertilization and stocking density affected shrimp stomach contents.

japonicus

INTRODUCTION

Penaeus juponicus (Bate) was introduced into Italy in 1979. Initially trials were performed to study its adaptability to the lagoons in the south and north of Italy (Lumare and Palmegiano, 1980; Lanari et al., 1985). Following the encouraging results obtained, restocking tests were performed in brackishwater areas and growth trials were performed in net enclosures within lagoons. The experiments showed that restocking could be performed in areas characterized by a low natural fish yield (Lumare, 1984). Net enclosures gave good results, although yields varied from year to year and management costs were high ( Lumare et al., 1986). Consequently, monoculture experiments in earth ponds, using the technique of water fertilization, were performed (Lumare et al., 1985). This practice is widely employed in extensive or semi-extensive

0044-8486/89/$03.50

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D. LANARI ET AL.

shrimp production (Hanson and Goodwin, 1977; Perrot, 1979; Wyban et al., 1987). We studied the effects of water fertilization and stocking rate on the performance of P. japonicus in ‘valle’ of the north Adriatic Sea. MATERIALS AND METHODS

The trial started in 1983, in a small ‘valle’ of the Grado Lagoon. Two water treatments - fertilization (E) vs. no fertilization (NE) - and two initial stocking rates - low = 1.5 specimens/m’ (LSR) vs. high = 3.0 specimens/m’ (HSR) - were compared in a 2 x 2 factorial design. Four earth ponds of 810 + 80 m2 surface area and 1 m deep, divided into two parts by a net and connected to two independent canals by seaward sluices, were used. Dried poultry manure (2000 kg/ha), ammonium nitrate (8 kg N/ha) and superphosphate (10 kg P,O,/ha) were spread on the bottom of the drained and cleaned ponds and the water level was returned to normal. The inorganic fertilizers were also added eight times during the trial, each time at half of the initial amount. The water level in fertilized ponds was maintained by means of a motor-pump while other ponds were subject to tidal exchange. Once a fortnight, water surface temperature (portable digital thermometer HI 8053 ) , pH (portable pH meter PHM 80 Radiometer ) , salinity (Salimeter Atago SC28), oxygen, nitrate, orthophosphate and bicarbonate levels (Strickland and Parsons, 1972) were measured in each pond. Once a month, bottom samples were taken from each pond with a VanVeen grab of 500 cm2 gape to perform macrozoobenthos analysis. On 7 June, 7350 P25 larvae (live weight 0.031 g) were released in the experimental units at the pre-arranged stocking rates, and fed 300 g of mussels once per experimental unit. Shrimps were sampled once a fortnight to study growth rate and stomach contents. Data on stomach contents are expressed, following the methodology of Klumpp and Nichols (1983), as: F= (&/St) x 100 where F is the percentage frequency of occurrence, S, is the number of stomachs containing a prey species and S, is the total number of stomachs, including empty ones; and N= (I,/& ) x 100 where N is the percentage number, 1, is the number of individuals of a prey species, and It is the total number of prey individuals. Final catches were performed after 123 days, by picking out the shrimps that had gathered in the deepest water following pond drainage. Total yield, total

FERTIL12,ATION,‘STOCKINC RATE EFFECTS ON F! JAPOMCUS

IN POND CULTURE

271

number of shrimps and the sex of each shrimp were determined for each experimental unit, while 200 shrimps from each treatment were weighed. Statistical analyses were made using the SPSS statistical package, installed on VAX (Nie et al., 1975), using two-way analysis of variance. The growth curves were determined according to the equation: a Y=G&h(x-c)l where Y is live weight, X is time in days after release, a is the asymptote of the function, b represents the growth rate, and c is the point of inversion of growth tendency (quick phase for X< c, slow phase for X> c). The parameters a, b, c were estimated using Gauss’ method of subsequential approximation (Nie et al., 1975). Water parameters were submitted to one-way analysis of variance. RESULTS

Temperature and salinity averaged 24.6 ? 3.0” C and 32.6 + 2.9%0 with no differe:nce between treatments, while pH and oxygen were significantly higher (PcO.05) in fertilized ponds (pH 8.3 vs. 8.1 and D.O. 10.8 vs. 8.1 mg/l). This was probably due to sampling time (11 a.m.) and to a higher algal population, as indirectly shown by a significantly lower bicarbonate concentration in fertilized ponds (2.49 vs. 3.16 meq/l). Phosphate level was higher in fertilized water (PC 0.05). The concentration of water nutrients was lower than expected:, indicating fast absorption by phytoplankton, as reported by Wahby (1974). Both experimental factors significantly influenced shrimp growth rate (Fig. 1). These effects became evident at the 42nd day of the trial and increased thereafter. Taking the point of inflection of the growth curve as an index of food scarcity, and using the equation parameters of Table 1 (see also Fig. l), it was possible to compute the point when growth rate declined. This occurred on the 38th day of the trial in the NE-HSR treatment and on the 64th day in E-LSR. Intermediate values (49.2 and 46.6 days respectively) were obtained in the NE-LSR and E-HSR treatments. Shrimp live weights at the point of inflection were 6.83 g (NE-HSR), 11.04 g (NE-LSR), 10.26 g (E-HSR) and 19.15 g (E-LSR) . Final live weight was positively and significantly affected (P < 0.01) by low stocking rate (30 vs. 17 g respectively for LSR and HSR) and water enrichment (29.2 vs. 17.8 g for E and NE respectively) (Table 2 ). Because of the market preference for large shrimps ( > 25 g), the whole catch within each treatment was divided into three classes of live weight ( < 16,1625 and > 25 g ) , corresponding to three different market prices (Table 2 ) . The LSR treatment yielded over 68% of shrimps in the high price class ( > 25 g),

D. LANARI ET AL.

272

-

E-LSR -

/’

NE-LSR /’

E-HSR -.-

NE - HSR

/

/“’

!F 0 20 i ’ 16 9 ; 12 6 4

li!

24

36

48

60

72

64

96

106

12 DAYS

Fig. 1. Effect of fertilization and stocking rate on growth curves of Penaeus japonicus. E, ization; NE, no fertilization; LSR, low stocking rate; HSR, high stocking rate.

fertil-

TABLE 1 Estimated parameters of the exponential growth curve Y = 1 + e[ _:CX_eJI Treatments

E-LSR E-HSR NE-LSR NE-HSR

Observations (n) 375 419 388 470

a asymptote

b

c point of

(9)

growth rate

inflection (days)

38.3000 20.5364 22.0982 13.6757

0.0487 0.0986 0.0850 0.1853

64.5392 46.6413 49.2267 37.6382

Residual mean square

N”

6.2519 3.1799 8.0943 3.6756

17 15 13 18

“N=number of interactions necessary to fit the equation. LSR= 1.5/m2; HSR= 3.0/m’; E = fertilized; NE = not fertilized.

but the HSR treatment produced less than 10% in that class. Water treatment also affected the distribution of the weight classes: over 56% of the shrimps reared in E were heavier than 25 g vs. 19.8% of the shrimps reared in NE basins. The high stocking rate or unfertilized water produced shrimps mostly in the low-price class, lowering yields and negatively influencing economic output. Table 2 shows shrimp performance and yield per hectare. Although not significant, catching rate appeared higher in LSR (59.8%) compared to HSR (38.1%), while fertilization did not influence this parameter. Due to the limited surface area of the basins and the great care taken when picking out the

FERTILIZ~ATION,‘STOCKING RATE EFFECTS ON P. JAPONfCffS

273

IN POND CULTURE

TABLE 2 Effects of fertilization and stocking rate on final live weight, live weight class distribution, ing rate and yield of Penaeus japonicus

catch-

Treatments Stocking rate LSR Average final weight Specimen distribution <16g 16-25 g >25g Final stocking rate Catching rate Yield

(g) within weight classes (%) (So) (%) (specimens/m’) (So) (kg/ha)

30.0** 17.8 14.0 68.2 0.90 59.8 257

Water enrichment

HSR 17.0** 43.8 48.8 7.4 1.14 38.1 198

E 29.2** 3.8 40.2 56.0 1.06 47.3 262

NE 17.8** 57.8 22.4 19.8 1.13 50.6 193

shrimps, differences in catching rate should only be ascribed to experimental treatments. Yield was higher at the low stocking rate and when fertilization occurred. The values obtained (from 193 to 262 kg/ha) were typical for the region, classified by Ravagnan ( 1981) as suitable for shrimp farming. The species found in pond sediments were less numerous than those normally recorded in open sea beds (Vatova, 1963; Brambati and Zucchi Stolfa, 1971; Esonaduce et al., 1974; Zucchi Stolfa, 1977). Among the Mollusca, twelve species of Gastropoda and three species of Bivalvia were present (Table 3); among the Annelida five families were counted within the Polychaeta. Two classes of Arthropoda were identified: Crustacea (with three subclasses and five orders in the subclass Malacostraca) and Insecta with one family (Chironom idae ) (Table 3 ) . A total of 133 stomachs from P. japonicus was examined. The stomachs contained 16 identified animal food components, showing that a limited number of species was preyed upon within each phylum and class (see Table 3). Among the Mollusca, only Hydrobia sp. within the class Gastropoda, and Cerastoderma e&de and Abru sp. within the class Bivalvia, were captured by shrimps. Among the Annelida, only two species were preyed upon, while in the phylum Arthropoda, Crustacea and Insecta were actively preyed upon. The latter were represented only by Chironomidae larvae, while among Crustacea, the Ostracoda, Copepoda and Malacostraca were of interest as food for P. japonicus. Among the subclass Malacostraca the prey belonged to the orders Decapoda (two families, Hippoidea and Palaemonidae ) , Tanaidacea, Mysidacea, Amphipoda (the family Gammaridae with two species) and Isopoda (the family

Polychaeta

Pterygota

Ostracoda* Copepoda* Malacostraca

Errantia Errantia Sedentaria

Basommatophora

Pulmonata

Diptera

Tanaidacea* Mysidacea* Amphipoda Amphipoda Isopoda

Decapoda

Filibranchia

Eulamellibranchia

Cephalaspidea

Neogastropoda

Archaeogastropoda Mesogastropoda

Order

Opisthobranchia

Prosobranchia

Subclass

Systematic keys: Barnes (1987); Gras& (1965).

Insecta

Arthropoda Crustacea

Annelida

Gastropoda

Mollusca

Bivalvia

Class

Phylum

Mysidae Gammaridae Gammaridae Sphaeromidae Sphaeromidae Chironomidae’

Hippoidea* Palaemonidae’

Mesopodopsis slabberi Gammarus aequicauda* Corophium insidiosum’ Sphaeroma serratum’ Cyathura carinata*

Hippolite longirostris Palaemon elegans

Polydora sp. Scolelepis sp. Ficopomatus enigmaticus*

Nereis diuersicolor Platynereis dumerilii Cirriformia sp.

Nereidae* Cirratulidae Terebellidae Spionidae Spionidae Serpulidae

Gibbula sp. Bittium reticulaturn Cerithium oulgatum Turbonilla la&a Rissoa uentricosa Hydrobia sp.’ Cyclope neritea Nassarius corniculus Retusa semisulcata Ham&a sp. Ouatella myosotis Leucophytia bidentate Abra sp.* Cerastoderma edule* Mytilaster minimus

Trochidae Cerithiidae Cerithiidae Pyramidellidae Rissoidae Hydrobiidae Nassariidae Nassariidae Retusidae Atyidae Ellobiidae Ellobiidae Scrobiculariidae Cardiidae Mytilidae

Trochoidea Cerithioidea Cerithioidea Aglossa Rissoidea Rissoidea Buccinoidea Buccinoidea

Siphonarioidea Siphonarioidea Tellinoidea Cardioidea Mytiloidea

Species

Family

Superfamily

Systematic categories found in bottom samples of the ponds and their presence in stomach contents*

TABLE 3

FERTILIZATION/STOCKING

RATE EFFECTS ON P. JAPONICUS

LSR

IN POND CULTURE E

HSR

275 NE

75

FREQUENCY

Fig. 2. Effect of fertilization

OF

OCCURRENCE

I%1

and stocking rate on relative importance

of prey items.

Sphaeromidae with two species). Sea grass fragments were also present in the stomachs. The effects of experimental factors on the natural diet of Penaeus japonicus are summarized in Fig. 2. Stocking rate affected frequencies (F) and numbers (N) data, especially for Crustacea and Insecta, whose importance decreased from LSR to HSR, and for Mollusca, which was a much more important class of food in the HSR treatment, whilst the data for Annelida and other phyla were unchanged. Fertilization affected the frequency and numbers of the different prey categories: for Mollusca and Insecta both values were higher in the E treatment than in NE. On the contrary, Crustacea and Annelida F and N values were larger in unfertilized ponds. Data on Macrophyta were not included in Fig. 2 due to the impossibility of calculating Nvalues. However, stocking rate affected Fvalues which decreased from 63.1% in LSR to 56.2 in HSR. Fertilization did not change this parameter (56.2 and 55.6% for E and NE, respectively). DISCU!ISION

Water fertilization in pond aquaculture is a practice (Hanson and Goodwin, 1977; IBoyd, 1979; Perrot, 1979; Stickney, 1979) that enhances shrimp performance and natural pond productivity (Schroeder, 1978; Furness and Aldrich, 1979; Stickney, 1979; Rubright et al., 1981; Geiger, 1983; Perschbacher and Strawn, 1984; Garson et al., 1986). The results of this experiment under-

276

D. LANARI ET AL.

line the importance of fertilization for shrimp growth rate, at least in temperate areas. The values obtained (1.49 g/week in E vs. 0.9 g/week in NE) were similar to those observed by Lanari et al. (1985,1987a,b) on P. japonicus, and by Lee and Shleser (1984) with P. uannamei in fertilized or unfertilized waters. In the experiments performed by Chakraborti et al. (1986) with P. monodon, fertilization and feed distribution did not enhance final weight, however. The difference between this and our results may be explained by the lower natural biomass productivity in northern Adriatic lagoons compared to tropical and subtropical areas. Weekly gains were inversely related to stocking rate, as already noted by Forster and Beard (1974), Chamberlain et al. (1981), and AQUACOP (1984). However, in our environment, stocking rate appeared to be an important factor at lower densities ( 1.5-3/m2) than those used in subtropical or tropical areas (6-9 to 15/m2). Live weights and growth curves were strongly affected by the treatments and showed a clear two-phase growth, as noted by Lee and Shleser (1984) for P. vannamei and by Chakraborti et al. (1986) for length development in P. monodon. Both fertilization and low stocking rate delayed the inflection point of the curves, indicating a higher food availability. Survival rates obtained in this research did not show a clear treatment effect. They were higher than those reported by Chakraborti et al. (1986) with P. monodon, and by Lanari et al. (1987a,b) with P. japonicus, and lower than the values noted by Rubright et al. (1981) and Lee and Shleser (1984). However, both the latter authors obtained an improvement in survival rate by means of fertilization or food distribution, and Tatum and Trimble (1978) and Lee and Shleser (1984) were able to reach 70-80% catching rate, stocking shrimps at juvenile stage (0.7-3 g ) and feeding them. It is worth emphasising that, in all the previously cited trials, the rearing period was shorter than the one adopted in this experiment (61-80 days vs. 123 days); moreover, the average final weights were lower than the ones reached in this trial. Final yield varied from 193 to 262 kg/ha: it was not statistically different because of the low number of replicates. However, both treatments appeared to affect the final yield, which was increased by fertilization ( + 36% ) and by low stocking rate ( + 30% ). Previous experiments performed in the valli of the north Adriatic Sea, in fertilized ponds, gave yields varying from loo-180 kg/ha (Lanari et al., 1987a,b ) to a maximum of 312 kg/ha (Lumare et al., 1985). Rubright et al. (1981) noted an increase of 88% in yield with water fertilization in comparison to the control (465 vs. 245 kg/ha), while Chakraborti et al. (1986) and Garson et al. (1986) obtained lower improvements ( +23% and 50%, respectively). Our experiment confirmed the data on feeding habits of P. japonicus previously reported (Lanari et al., 1985). The predatory activity of P. japonicus

FERTILIZATION/STOCKING

RATE EFFECTS ON P. JAPONICUS

IN POND CULTURE

277

towards Insecta larvae was observed also by Gundermann and Popper (1977 ), Rubright et al. (1981) and Lumare et al. ( 1985). Piscitelli (1986), in a survey on feeding habits of P. juponicus reared in different environments of south, central and north Italy, noted that stomach contents varied between rearing sites, clearly indicating the ability of this shrimp to adjust its feeding habits to natural productivity. However, no data were available in the literature on the effect of fertilization and/or stocking density on the feeding habits of this shrimp. Our work showed that changing stocking rate caused a shift in the normal food preference of P. juponicus which, when heavily stocked, was forced to prey upon Mollusca. The higher F and N values for Insecta and Mollusca noted in the stomach content of shrimps reared in fertilized ponds could be explained by an increase in the biomass if these two phyla, due to the positive effect of fertilization. In conclusion, in the environment of the northern Adriatic lagoons, water fertilization appeared to be useful in enhancing the growth rate, live weight and final yield of P. juponicw, with no apparent effect on survival rate. A stocking rate of 1.5/m2 gave better results than 3.0/m2. The results of this trial indicate that natural pond productivity of north Adriatic lagoons can sustain satisfactory growth of shrimps stocked at 3.0 and 1.5/m2 for no longer than 40 and 50 days, respectively. Thereafter, shrimp performance can be improved only with feed distribution. In fertilized water, pond productivity can sustain a satisfactory growth rate of the shrimps up to the end of the rearing period at 1.5/m’, while at the higher stocking rate feed is needed 50 days after release. Measuring shrimp live weight 40 to 50 days after their release could be a simple tool for the producer to evaluate the productivity of his ponds and to decide the optimum time to begin food distribution. Treatments affected the stomach contents of P. juponicus, reflecting different food availability following waiter fertilization and a change in food preference when high stocking rates are used. ACKNOWLEDGMENTS

This research was performed within the “Project on Development of National Aquaculture”, sub-project “Shrimp Production” of the Ministry of Agriculture and Forestry (Italy). The authors wish to thank Prof. G. Piscitelli who carried out benthos and stomach contents analyses.

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