Research in marine and estuarine aquaculture in Israel is centred at the Marine Biology Research Station at Eilat, where a small group of scientists of OLRL share facilities with faculty and students of the Hebrew University of Jerusalem. The projects under way or planned include the following! (1) edible oysters, Crassostrea cucullata, (2) rabbit fish, Siganus rivulatus, (3) gilthead bream, Sparus auratus, (4) seabass Dicentrarchus sp., (5) pearl oysters Pinctada fucata and P. margaritifera.
Other research groups have conducted or planned to conduct research on (1) the fresh/ brackishwater shrimp, Macrobrachium rosenbergii, (2) the marine shrimps Penaeus japonicus and P. semisulcatus, (3) mullet Mugil cephalus in brackish and marine water.
Studies have been conducted on the feasibility of establishing oyster culture in the Gulf of Aqaba adjacent to the city of Eilat. Small populations of oysters (probably Crassostrea cucullata) exist in the area, but there are not enough to support commercial exploitation. In 1971 (May to November) investigators of OLRL studied the condition and rate of spatfall of oysters near Eilat. More intensive studies of the feasibility of oyster culture were initiated with the help of Dr. Peter Walne of the U.K., who spent a brief period in Eilat as an FAO/UNDP consultant. Observations by OLRL biologists and by Dr. Walne may be summarized as follows.
The “condition factor” (an index of edible, commercial value) of over half the oysters fell below the satisfactory level.
The numbers of bivalve larvae settling on collectors placed in the water was mall-a maximum of 1.5 – 2.0/cm2, and of these, the desired commercial species was in the minority, and was frequently absent.
The seabed at Eilat is not suitable for oyster culture because of its restricted area, the unsuitable bottom of sand and gravel, the exposure to wave action, and the likelihood of human interference. Hacks or trays might be better, but labour costs are higher with these methods. Rafts appear to be the most suitable method for Eilat, despite the restricted area and the navigational hazards resulting.
There are no stocks of young oysters available in the area for transplantation to culture sites. Alternatives are: (i) catching of natural spatfall; this was unsuccessful in the trials conducted; (ii) purchase of young from outside Israel; (iii) hatchery production of young. Neither of the latter alternatives (especially the third) would be wise until it could be shown that culture is feasible, as the productivity of the seawater is low. Oysters are phytoplankton feeders and their rate of growth depends essentially on the quantities of these organisms in the water. The very clear water of the Gulf of Aqaba reflects low standing crops of phytoplankton, and while the annual productivity may be relatively high due to rapid turnover resulting from high temperatures, the supply of food available to the oysters is apparently too low to encourage growth fast enough to sustain commercial culture.
Following Dr. Walne's visit, and on his advice, a study was made of the growth rate of oysters, on the rate and seasonality of spatfall, and on the productivity of the water. The unsatisfactory conditions believed to exist were confirmed. Consequently the oyster culture project has been abandoned.
Siganus rivulatus occurs naturally in Israel waters, being common both in the Mediterranean and the Red Sea, where small fisheries exploit them. They tolerate rough handling, overcrowding, oxygen deficiency and wide ranges of ecological conditions. In nature they feed on seaweed; they accept a wide variety of food in captivity, and it may be that they could be raised on cheap feeds. Scientists of OLRL and the University of Tel Aviv succeeded in raising rabbit fish caught in the harbour of Eilat. They were fed algae (Ulva) at first; later commercial fish food pellets were used. Growth in 39 days was 3.01 g and 30 mm - a ten-fold increase in weight and two-fold in length. Of 50 individuals, 19 survived to this time. In a second experiment, one group of 100 rabbit fish were fed lettuce and an equal group fed fish pellets. The first group increased 40 percent in weight, the pellet-fed fish 300 percent.
In later experiments S. rivulatus larvae were hatched from eggs. Eggs were from Mediterranean and Red Sea individuals. On three occasions eggs were obtained from stripping mature individuals, on the fourth, eggs were spawned and fertilised naturally by captive fish in a 200-litre tank. The larvae were maintained in tanks at constant temperature and salinity. They began to feed four to five days later. The food offered was unicellular algae. The larvae died after four to five days. The large eyes of the larvae suggested that they were carnivorous (even though the adults are herbivorous). Fish fed copepods survived up to 13 days.
Temperature control of water in which captive fish are held appears to be a good method of obtaining ripe animals. Further, larval survival seemed to be related to the size of the holding tanks, with those in the largest tanks surviving longest. The small larvae require food items smaller than 120μ, the size of the mouth opening, but large enough to be seen by the larvae.
Rabbit fish raised in troughs showed good growth on diet* of pellets (75 percent wheat, 25 percent fish meal and vitamins) fed at the rate of 6 percent of body weight per day. Mortalities were high, and disease nay have been the cause.
Fish in cages in the sea also grew well. The experiment was terminated when holes appeared in the net cages and many fish escaped.
While work with rabbit fish culture at Eilat is preliminary, progress here and elsewhere (e.g., in the Pacific) encourages hope that this species can be successfully cultured. But in Israel the market demand and price is so low that even if a successful technology could be developed, the cost of production would probably exceed the selling price. The reluctance of the Jewish buyer to accept rabbit fish, presents a problem. These fish have such small scales that they appear to be non-existent, and the buyer is often afraid to purchase them in case they are not approved under Jewish dietary laws which do not condone scale-less fish. For these economic and marketing reasons, therefore, this project has been put aside by the OLRL group at Eilat, at least temporarily.
Sparus auratus is one of a small number of marine/estuarine fish species which has been raised commercially in France and Italy. While production is still very small and culture techniques require much improvement, progress has been encouraging. Work in Israel includes research on feeding and on hatchery production of young. The first experiments were on fry caught in the Bardawil Lagoon of the northern Sinai. Fish of about 0.1 g weight and 1.5 to 2.5 cm length were fed three diets: local clams, commercial carp food and commercial trout food. Growth was good with the latter two diets, but degenerative diseases caused about 30 percent mortality. Degeneration of the kidney, spleen and liver seemed to be the major cause; initially there was no bacterial, fungal or viral disease but later a secondary bacterial infection appeared. The problem may have been associated with rancidity of fat in the commercial feeds. A second series of experiments was conducted on the surviving fish. Comparisons were made of seven diets, each with four replications. The diets were all high in protein (40–55 percent) and were composed of various proportions of fish meal, corn meal, soy meal, fish oil, vitamin premix, mineral mix, yeast and gluten. There were differences in resulting growth rates but all diets appeared adequate. It seems likely, in fact, that the feeds were richer than necessary. Their cost would be high and perhaps uneconomic in commercial practice.
The largest fish resulting from the above feeding trials were selected out and are being held separately as “brood stock”. Some have grown to sizes considerably larger than fish of similar age in nature: 180–400 g (mode of 227 g) in ten months. The largest of these in the Mediterranean would probably be about two to three years old, according to observations by Ben-Tuvia, and ten-month-old fish there would weigh only 120–150 g. The difference probably relates to the temperature regimes (e.g., average temperatures are 13°–15°C in the Mediterranean in December–February, compared to 20°–25°C in the Bed Sea) and to the quantity of food supplied to the experimental fish.
Further experiments and feeding and feed preparation are planned. But a strong need is felt for advice and assistance from a nutrition expert. Dr. G.W. Kissil has adequate background in experimental design and statistical analyses to prepare, conduct and analyse feeding trials, but he would benefit from advice on amino-acid analysis and other technical aspects of basic nutrition studies.
In anticipation of possible difficulties in obtaining wild fry to stock ponds, work has been started at Eilat on laboratory production of young. In the Mediterranean the eggs of Sparus hatch at sea into larvae about one cm long, in December/January. In February/March both adults and young move into the Bardawil Lagoon. Prom 1½ to 2 years of age, in November/December, fish are mature for the first time at 100–120 g in weight, and they leave the lagoon to spawn. The fish are usually males first and probably after about two years of age, are females.
The largest fish raised in the feeding experiments were injected with human chorionic gonadotropin (HCG). Some fish produced milt; these may have been normal since fish of this size (but not this age?) can spawn as males, or it may have resulted from the injection. In some of the larger fish the gonad began to change to the active female phase, as detected by sacrificing the fish and sectioning the gonads. The rapid growth achieved in the tanks, the doses of HCG, or a combination of these may have caused this activity.
These results encourage the hope that fish may be brought to maturity and induced to spawn or produce viable sex products in captivity, and perhaps outside the normal spawning season. If fully successful, this could result in supplies of young as needed, over the full year. In France this has already been partly achieved, and the period of spawning prolonged by at least twice. Fish are kept in water of reduced temperature (14°C compared to 24° C) and light, to measure the full cycle. The temperature is then raised to 18°C and the fish are injected with HCG. They spawn in 24–48 hours. This manipulation is effective over a three month period compared to the normal spawning season of about six weeks. French workers now grow small quantities of S. auratus. They are geared to produce 400 000 fry in a new pilot plant in Sête.
The highly encouraging growth rates of Sparus at Eilat, and the good results of early experiments there and elsewhere with induced and controlled reproduction has resulted in the decision to concentrate considerable effort on this fish. The strong market and high price of this species in Israel and in Europe makes the decision economically sound. The most urgent research required is in the areas of reproduction, larvae feeding, nutrition of young and feed formulation.
Dicentrachus spp. can be raised in captivity to market size. Young fish captured in the wild grow to saleable size in a few months. Fish captured in the Bardawil Lagoon of the northern Sinai have been raised at the Eilat Laboratory.
In Lesina, Italy, seabass were spawned at water temperatures of 15°–17° C and salinities of 36 ppt. The larvae were fed phytoplankton and a few individuals survived for three months or more. The species has a good sale in Israel, at prices comparable to those of the gilthead bream. Hence, there is interest in its culture and while work will concentrate on the bream, some effort will be expended on the seabass. Techniques and problems of spawning and larval and juvenile feeding and growth will be similar.
Small populations of Pinctada fucata and the larger P. margaretifera exist in the Gulf of Aqaba near Eilat. A project is underway to test The feasibility of a snail pearl culture industry there. This has been initiated by encouragement of two experienced commercial pearl culturists (Mr. Dennis George of Hew Guinea and Mr. Bill Reed of Tahiti; the latter served as an FAO consultant on pearl culture in Sudan). In addition, early trials resulted in the reproduction of a half pearl from P. margaretifera, and a small round pearl from P. fucata both exhibiting good quality.
P. fucata is similar to the species used in Japan to produce pearls. It grows to about 10 cm. In the Gulf of Aqaba it is fairly common. P. margaretifera, the black lipped oyster, is less common. It grows to about 20 cm and can produce larger pearls than fucata. It produces good quality half pearls.
Work at Eilat has included collection and confinement of adult P. margaretifera, spat collection, and trial production of pearls. Although P. margaretifera is not common, collections of 40 adults were made in two days. It is estimated that 500 could be gathered in a month and this is the minimum number suggested by Reed as required for a pilot farm. The oysters are drilled through the “heel” and suspended from lines anchored in the water. Growth of such suspended animals is good, comparing favourably with that in Donganab Bay, Sudan, and with growth of oysters in commercial farms in Tahiti (this despite the poor growth of Crassostrea here, which is also a filter feeder).
As a second way of accumulating stock, spat have been collected. Heavy stock of P. fucata have been made on nylon fish nets under a raft and it is thought that supplies of spat of this species will not be limiting. For P. margaretifera 42 spat were obtained on a Japanese style collection and some on large oysters. Water temperatures in the upper layers of the Gulf are 20°–;21°C in January to 25°–26°C in August. P. margaretifera is said to spawn at 25°C and, settling can thus be expected in May–January.
Hatchery production of spat is possible but the procedures are complicated and not fully developed. The building and operation of a hatchery is not feasible at this point.
P. fucata can produce round pearls of white, yellow or pinkish colour, of small size. P. margaretifera can produce larger round pearls and those over 10 mm diameter have a good market. Moreover, this species readily produces half pearls.
Mr. Hughes-Games has succeeded in raising two pearls. He implanted half round nuclei in four P. margaretifera and round nuclei in 40 P. fucata. In six months one half pearl of 16 mm and one round pearl of 4 mm resulted. These were described by Mr. Reed as exhibiting “excellent growth”, (0.5 mm per month) with the “colour and the quality of the nacre good”. Mr. George commented that the half pearl showed “an excellent rate of deposition of nacre, colour, lustre and orient excellent”, for the round pearl, “nacre deposit rate most satisfactory; lustre colour, orient most desirable”.
Mr. Reed and Mr. George believe the market for pearls produced in Israel would be good. According to Mr. Reed, small round pearls which compete with the enormous Japanese production would not be worth much. Those larger than 10 mm in diameter are much more valuable; these cannot be produced by P. fucata, but can be by P. margaretifera. In addition the latter species produces valuable black pearls. The export wholesale price of Australian pearls is about U.S.$ 50 each, ranging from U.S.I 10 to U.S.$ 100. In Polynesia, black pearls sold for an average of U.S.$ 200. Half pearls bring U.S.I 5–80 each. He believed that Israeli-produced pearls sold locally would fetch higher than market prices; this is the case in Tahiti. Half pearls from 500 oysters would be worth about U.S.I 10 000. They would be ready about a year after induction.
The success with first trials on pearl culture have encouraged the OLRL to include this as a culture project on a small scale. It is hoped to develop artisanal industries, principally for local markets, at least in the beginning. Emphasis will be on the half pearls.