Studies on the biology of young grey mullet, Mugil cephalus L. II. Food and Feeding

This is the second of a series of investigations into the biology of young grey mullet, Mugil cephalus L., and the feasibility of its culture in the coastal, estuarine waters of Sri Lanka. The food and feeding habits of mullet, 20–55 mm in length, from the coastal Negombo Lagoon (7° 10′ N; 79° 50′ E) were studied from November 1974 to October 1975.The feeding intensity, estimated as the number of food organisms found in stomachs per feeding individual, followed a seasonal pattern with the intensity increasing from April onward and reaching a peak during June–August. Over 80% of the individuals were found to feed throughout the year. The diet consisted of 18 genera of diatoms, eight genera of green algae, some desmids, six genera of blue-green algae and eight other food groups. No sand or detritus was found to occur in fish smaller than 25 mm in length, and the percentage occurrence of detritus and/or sand particles increased with increase in body length. Quantitatively and qualitatively, diatoms were the most predominant food items, accounting for more than 50% of the total diet. Although only one genus of Xanthophyceae was found to occur in the diet, its contribution was significant.M. cephalus was found to show diurnal periodicity in feeding activity; peaks of activity occurred at dawn and around midday and were unrelated to the state of the tide.The significance of the nature of the diet and the occurrence of two peaks of feeding activity within a 24-h period is evaluated in the light of present knowledge of the food and feeding behaviour of M. cephalus at various stages of growth, and the possibilities of polyculture with other herbivorous species is discussed briefly.     

Operational procedures for rearing larvae of the grey mullet (Mugil cephalus L.)

Larvae of the grey mullet Mugil cephalus L. can be reared successfully using careful procedures following induced spawning of the adults with purified salmon gonadotropin or human chorionic gonadotropin.Preliminary incubation of the eggs to the gastrula stage at high density for 12 h at 22°C is preferred, using stirred irradiated seawater (32‰ salinity) and the antibiotics penicillin (80 IU/ml) and streptomycin (0.05 mg/ml). The eggs are transferred before hatching to circular rearing tanks at a density of 250 eggs/l.The mouths of the larvae are open and ossified and the eyes are sufficiently pigmented for the larvae to begin feeding on the third day. The larvae are fed cultured phytoplankton and rotifers supplemented with available natural plankton. Nauplii of Artemia are provided on the seventh day.The migratory behavior of the larvae during early development and their physiology are discussed, being relevant to the procedures and the techniques applied.Mass propagation in large (over 12-ft diameter) circular tanks with total light control is recommended.     

Factors influencing the efficacy of MS-222 to striped mullet (Mugil cephalus)

Some responses of juvenile striped mullet (Mugil cephalus) to the anesthetic MS-222 were investigated. Induction times to total loss of equilibrium decreased with increasing anesthetic concentration over the range of 40–120 ppm. Temperature, pH, and oxygen concentrations all significantly affected induction times to total loss of equilibrium in freshwater-adapted fish at a concentration of 80 ppm MS-222. Anesthetic toxicity was less for saltwater-acclimated fish than for freshwater-acclimated fish. The 24-h 50% mortality (LC₅₀) in fresh water was 33.1 ppm; in salt water it was 39.8 ppm. The results suggest that anesthetic action may be intensified in fish acclimated to conditions other than those near their physiological optima.     

The culture of striped mullet (Mugil cephalus Linnaeus) in ponds receiving heated effluent from a power plant

During 1972 and 1973, striped mullet (Mugil cephalus Linnaeus) were stocked into six ponds (located on the upper end of the Galveston Bay system, Texas, U.S.A.) receiving heated effluent. Fish were fed commercially prepared feeds. In 1972, mean daily weight and standard length gains in two ponds were 0.71 and 0.66 g and 0.65 and 0.59 mm. In 1973, mean daily weight and standard length gains in four ponds were 0.64, 0.36, 0.67, and 0.59 g and 1.03, 0.81, 0.71, and 0.67 mm. During the two year study, survival rates ranged from 50 to 85%; production, from 293 to 804 kg/ha. Food conversion fluctuated from 2.24 to 3.31; commercial feed costs, from $0.61 to $0.87 per kg of fish.     

Recent progress on the control of ovarian development and induced spawning of the grey mullet (Mugil cephalus L.)

The paper describes some past and current work for the control and regulation of ovarian development. It reports on the induction of ovarian maturation out of season by manipulation of photoperiod and temperature cycle, and recommends conditions of constant temperature control at 21°C and photoperiod of $\text{6L}\text{18D}$ for the best results using fish with oocytes in the refractory period. It also recommends salmon pituitary gonadotropin SG-G100 as the best ovulating agent for reliable results, but suggests further research with alternative gonadotropins and steroids. The paper describes some recent progress with the latter.     

On the induced spawning and larval rearing of milkfish,Chanos chanos (Forskal)

A female milkfish, captured at sea, was injected with two hormonal injections of acetone-dried salmon pituitary powder and human chorionic gonadotropin, plus Vitamin B complex. It was stripped, and produced 128,000 ripe eggs with an average diameter of 1.15 mm. Fertilization rate was 38% following artificial fertilization with milt from an uninjected male. A total of 36,000 larvae hatched (74% of fertile eggs) after 26–32 h at 34 ‰ salinity and 27–32°C. The newly hatched larvae measured 3.4 mm in mean total length and possessed a large yolk sac. The mouth of the larvae opened about 54 h after hatching. The larvae were fed with fertilized oyster eggs, rotifers, copepods, brine shrimp, flour and prepared feed, together with Chlorella. A critical period was between the 4th and 6th days with mortality over 80%. The larvae started increasing in length by Day 8, and had the appearance of the wild fry by Day 11. On Day 13 a pigmentation pattern developed and the biggest larva measured 10.0 mm. By Day 18 the larvae measured 12.5 mm, and 14.5 mm by Day 21. A total of 2,859 fry was obtained; the highest larval survival rate obtained from different experimental groups was 46.8%.     

An experiment in rearing larval Siganus vermiculatus (Valenciennes) and some observations on its spawning cycle

Siganus vermiculatus spawned in captivity on three occasions, and limited numbers of newly hatched larvae were stocked in an 80-m³ outdoor concrete tank and a 2000-m² fish pond in Fiji. Survival through the larval stage was 9% in the tank, in spite of high temperatures and relatively low food densities. No larvae survived in the pond.Data collected on the appearance of fry, spawning, and the gonadal state of adults suggest that S. vermiculatus in Fiji spawns monthly on or around the first lunar quarter during its spawning season.Possible ways to solve problems encountered in this experiment are discussed.     

Induced spawning and larval rearing of the white seabream, Mylio berda

The white seabream, Mylio berda, was induced to spawn spontaneously by hormone injections of synahorin or human chorionic gonadotropin for over 3 months between December and April in Hong Kong. Fertilized eggs were also obtained during the peak spawning period between February and March through natural spawning or artificial insemination. The hatched larvae were reared in 500-1 circular tanks and fed initially on rotifers, Brachionus sp., followed by brine shrimp nauplii or copepod nauplii and finally weaned onto fish meat. Larval rearing trials for growth and survival to 60 days produced larvae of average length, 26.2 mm, at survival rates ranging from 1.32 to 11.62%.     

Hatching and rearing lobster larvae (Homarus americanus) in a disease situation

Lobster rearing facilities in the United States suffered severe losses of larval stages during the summer of 1974 hatching season. The organisms responsible for losses at the Bodega Marine Laboratory were the fungus Lagenidium sp. and epiphytic contaminants. Various systems and treatments were used in attempts to overcome the problems encountered. Postlarval lobsters were produced successfully in a semi-closed system using ultraviolet-irradiated sea water and a malachite green dip for eggs and larvae.     

Photoperiod induced off-season spawning of pink salmon (Oncorhynchus gorbuscha)

Four groups of pink salmon, which had been reared under artificial light, became sexually mature and produced viable gametes: 59 days prior to, and 19 – 32 days, 115 days and 220 days after their expected date of reaching sexual maturity. Altered times of sexual maturation were obtained by accelerating, leaving unchanged, or decelerating the rate of change of photoperiod which each group of fish would normally receive during its first year of life. All groups of fish were exposed to a normal rate of change in photoperiod during their final year of life. Mean fecundity was reduced from the 800–2000 ova observed in wild stocks, and ranged from 629 for the 59 day advanced fish, to 862 for the 115 day delayed fish. Egg mortality during the period from fertilization to eyeing was much greater in the three groups of fish subjected to accelerated or decelerated rates of change in photoperiod than in the fish subjected to the normal rate of change in photoperiod. Some of the progeny of the 220 day delayed fish, which were reared under artificial light with the normal rate of change in photoperiod set 220 days out-of-phase, became sexually mature 2 years after they had begun life as fertilized eggs.     

Experimental raising of golden grey mullet (Liza aurata (Risso)) in saltwater ponds

The growth and feeding habits of the grey mullet Liza aurata, raised together with Sparus auratus and Trachinotus ovatus in experimental saltwater ponds were studied. The results show that L. aurata can be stocked in saltwater ponds, and though their growth rate does not compare favourably with those of the other fishes further studies are recommended.     

Growth of the golden grey mullet (Liza aurata (Risso)) in saltwater ponds during 1974

The growth rates of Liza aurata in saltwater ponds were measured during 1972, 1973 and 1974. The growth rate of L. aurata young of the year was 0.6–0.95 g per fish per day and that of fish in their second year of life was 0.85–1.0 g per fish per day.Body composition analyses were conducted on L. aurata in both the first and second years of life.A significant difference in length and weight was found between males and females of L. aurata in their second year of life.The results show that L. aurata can be stocked in saltwater ponds but that they will not be the main crop of fish.     

Induced winter spawning and culture of larvae of the blue crab, Callinectes sapidus rathbun

Female blue crabs were induced to produce eggs out of their normal spawning season. One group of crabs, held in the laboratory at 19° C, was fed every 7 days; another group, held at 15° C, was offered food at the same interval. Photoperiod simulated ambient winter conditions in both groups. Of ten crabs held at 19° C, two produced egg masses and one died when spawning was about to commence. Among those crabs not producing egg masses during the experiment, ovarian development at 19° C proceeded further than among those held at 15° C.Survivorship of larvae from induced eggs raised on a rotifer diet was comparable with that for naturally spawned larvae through the first 28 days of development.Zoeae survived well to metamorphosis when fed a diet of rotifers during the first two stages, followed by Artemia salina nauplii. However, only six zoeal stages were present instead of the usual seven. Possible explanations for this observation include genetically controlled variation, variation due to origin of eggs (induced), or effect of diet.Survivorship and growth were not adversely affected when synthetic sea water was used as the culture medium.     

Body composition of Mugil cephalus,Liza dumerili,Liza richardsoni and Liza tricuspidens (Teleostei: Mugilidae) caught in the Swartkops Estuary

Body composition (protein, fat, ash and moisture) and energy content of four mullet species Mugil cephalus, Liza dumerili, Liza richardsoni and Liza tricuspidens were determined monthly for 13 months in specimens taken from the Swartkops Estuary. Six size classes (<2.5, 2.6–6.0, 6.1–10.0, 10.1–15.0, 15.1–23.0 and > 23 cm SL) were analysed separately. Statistical analyses of results could only be performed on three size classes of M. cephalus, L. dumerili and L. richardsoni due to inavailability of fish during certain months. Regression equations were calculated for those body components that were significantly correlated, viz.: energy and moisture, fat and moisture, protein and moisture and energy and fat. The influence of species, size as well as seasonal effects and reproductive cycle on body composition were investigated. It was found that in general Liza dumerili had the lowest mean body energy and fat values and Liza tricuspidens the highest. Smaller size fish were lower in energy and fat and larger size fish lower in moisture. Overall mean values showed that body energy reserves were the highest during the winter. Sexually mature specimens of Liza dumerili showed a build-up of energy before the commencement of the spawning season.     

Captive spawning and larval rearing of California yellowtail (Seriola lalandi)

A captive population of California yellowtail (Seriola lalandi) was used to document spawning patterns, including measures of egg production, population fecundity and egg and larval quality from 2007 to 2010. Spawned eggs were also used to document larval development and to develop rearing techniques for aquaculture in the region. Broodstock growth and condition factor were best when feeding rations were maintained at 10–15% body weight week^?1 during the warm summer months. A winter ration based on satiation feeding was typically 4% body weight week^?1. During the 4‐year study period, the only broodstock health issue was an infestation by the parasitic gill fluke Zeuxapta seriolae, which was readily treated. Spawning occurred naturally in the 140 m³ tank when the ambient water temperature reached 16°C and ended when the temperature exceeded 22°C. Egg production reached a maximum in 2010 when 43 spawn events were recorded from a pool of nine females yielding 36.8 million eggs in total. The average female size at this time was 20 kg, which equated to a total annual population fecundity of approximately 226 000 eggs kg^?1 female year^?1. Larval rearing trials yielded survival rates as high as 5.8% from egg to 50 days post‐hatch (dph). Successful larval culture methods included the addition of algae paste for green water culture, rotifers (20 rotifers mL^?1) at 2 dph and Artemia (5 Artemia mL^?1) at 6 dph. Larvae were transferred from the incubation tank at 10 dph to a shallower tank with 33% greater surface area to accommodate the larvae's strong orientation to surface waters. This research represents the first documentation of successful spawning and larval rearing for S. lalandi in the eastern Pacific.     

Influence of temperature and salinity on survival of the freshwater mullet, Rhinomugil corsula (Hamilton)

The upper incipient lethal temperatures of the freshwater mullet, Rhinomugil corsula, acclimated to 15, 20, 25, 30 and 35°C in fresh water, were 32.4, 34.1, 36.0, 36.2 and 36.5°C respectively, and the corresponding lower lethal temperatures were 10.5, 11.5, 13.2, 15.8 and 19.5°C. The mullet has a total tolerance (area of thermal polygon) of 569°C with an upper and lower thermal tolerance of 253 and 316°C². Likewise, the total resistance of the mullet was 391°C², with upper and lower resistance zones of 181 and 210°C respectively. The upper critical temperatures of swimming inhibition of R. corsula (17.2 cm; acclimation 30°C), determined in a swimming tunnel, were 35.2, 34.6 and 34.2 for water current velocities of 38, 62 and 77 cm s^?1 respectively. The corresponding lower critical temperatures were 26.2, 27.5 and 28.1°C. These results indicated the stenothermal nature of the mullet by comparison with other fishes, e.g. Tilapia mossambica.In tests on the influence of ambient salinity on thermal resistance, R. corsula survived longest at 7‰ (iso-osmotic salinity). At salinities above and below this point, survival times were shorter at any lethal temperature. In a tentative scheme for quantification of stress due to temperature and salinity at death (after acclimation to 30°C and tested at 37°C), the hypo-osmotic and hyper-osmotic stress were estimated to be 50 and 31% of the thermal stress (100%) respectively.     

Ontogeny of the digestive tract of thick lipped grey mullet (Chelon labrosus) larvae reared in “mesocosms”

This work describes the ontogeny of the digestive tract in thick lipped grey mullet (Chelon labrosus) larvae reared until day 36 post-hatching with the semi-extensive technology in mesocosms. Diet was constituted by live preys, rotifers, Artemia and wild zooplankton, then compound diet was added from day 20 (p. h.). Linear growth, weight growth and digestive enzymes specific activities were studied during larval ontogeny. Pancreatic enzymes (trypsin and amylase) and intestinal enzymes (leucine-alanine peptidase “Leu-ala”, aminopeptidase N “AN” and alkaline phosphatase “AP”) were assayed in larvae sampled throughout the rearing trial to evaluate gastrointestinal maturation along the development.The trypsin specific activities were very high during the first two weeks and then declined as observed in marine fish species. A following increase in trypsin specific activity from day 20 was attributed notably to ingestion of particle compound diet. In contrast to the pattern generally described in fish larvae, amylase specific activity showed a continuous increase. This could be attributed to the fact that C. labrosus is an omnivorous species and suggests that the fish might be able to use efficiently diets containing higher levels of starch or other carbohydrates since the end of larval development.Relative expression of intestinal brush border membrane enzymes (AP and AN) and cytosolic enzyme (Leu-ala), showed an abrupt increase of both AP/leu-ala and AN/leu-ala ratios at day 8 (p. h.), indicating that maturation of intestinal tract in C. labrosus larvae is particularly precocious. It is assumed that larvae of C. labrosus might support early co-feeding and weaning strategies, which could reasonably be initiated since mouth opening.     

Effect of heat-treated feed and exogenous zymogen on survival and growth of grey mullet, Liza ramada (Risso), larvae in Egypt

A preliminary trial and two experiments were carried out to study the effect of heat-treated feed and exogenous zymogen on the survival and growth of grey mullet, Liza ramada (Risso), larvae. The fish were held in glass aquaria supplied with continuous aeration and salt water, which was changed daily. Two test diets (40% crude protein) formulated from commercial ingredients were used. In the preliminary trial, diet A was either heat treated in an autoclave using a maximum pressure of 1.2 kg cm^–2 for 15 min, or supplemented with exogenous zymogen at rates of 0%, 2%, 4%, 6% or 8% of the diet. In experiments 2 and 3, four heat treatment times (0, 10, 20 or 30 min) using the previous pressure and three exogenous zymogen supplementation rates (0%, 2% or 4%) were evaluated in a 4 × 3 factorial arrangement for effects on the survival and growth of grey mullet using diet B. Zymogen and vitamins were added to the diets after heat treatment. In addition to survival and growth, dissolved oxygen, temperature and salinity were measured periodically through the study. The grey mullet larvae were introduced to the treatments 24 h after transportation to the laboratory in experiment 2 and after 3 weeks acclimatization in experiment 3. In the preliminary trial, significant differences in survival rates were observed after 7 days for larvae maintained at heat-treated diet A and diet A supplemented with 4% exogenous zymogen. In experiment 2, significant differences in weight gain corresponded to increasing dietary zymogen in diet B. Likewise, the percentage of survival rate increased significantly starting from week 2 as zymogen increased in diet B. Heat treatments in diet B had no significant effect on weight gain of grey mullet after 2 weeks. However, significant differences in survival rate corresponding to heat treatments were observed for grey mullet larvae after 4 weeks in experiment 2. Diet B heat-treated for 20 min with 4% zymogen gave the best results for larval survival rate and growth. Although the larvae were acclimatized for 3 weeks to salinity using the best diet of the second experiment before starting the third experiment, the same results were observed after 3 weeks. Further experiments must be performed to confirm the best conditions for acclimatization.