Robert R. Stickney

Tilapia Tolerance of Saline Waters: A Review

Abstract Members of the family Cichlidae that are generally referred to as tilapias (Tilapia spp.) characteristically demonstrate some degree of euryhalinity. A survey of existing literature indicates that Tilapia zilli and Tilapia mossambica are among the most salinity-tolerant species, although neither is among the most desirable for culture. A tolerance for high salinity has been demonstrated in at least some crosses that produce red hybrid tilapia. Most known heritage crosses with that result to date have involved T. mossambica. The red hybrid may become a preferred culture fish in brackish and seawater systems as well as in fresh water.

A new method for force-feeding larval fish

Abstract Knowledge of digestive function in fish larvae may provide insight into the problem of poor survival of first feeding larvae, but research approaches to investigate digestion in larvae are limited. To compare the functional development of the digestive system in altricial and precocious larvae, we developed a method for force-feeding radio-labeled nutrients to fish larvae. The method involves micro-injection of diets into the gut of anesthetized and immobilized larvae in a petri dish under a dissecting microscope. Three protocols are described illustrating the application of this method to studies of larval digestive function. To determine the development of acid digestion, pH indicator solution was injected and the gut of the transparent larvae was monitored for color change. To determine nutrient assimilation efficiency, radio-labeled nutrients were injected. After a period of time, counts of the recovery water and the larvae were made using liquid scintillation counting. Finally, to determine sites of nutrient uptake, radio-labeled nutrients were force fed to larvae that were subsequently examined by microscopic autoradiography. The utility of this method is illustrated with observations of protein, polypeptide and free amino acid assimilation in larval walleye (Stizostedion vitreum) and pH changes in larval striped bass (Morone saxatilis).

Vitamin E requirements of the blue tilapia, Oreochromis aureus (Steindachner), in relation to dietary lipid level

Abstract The vitamin E requirement of the blue tilapia, Oreochromis aureus (Steindachner), was evaluated in semipurified diets containing two lipid levels (3% and 6% corn oil) and five levels (0, 10, 20, 40, and 80 mg/kg) of dl-α-tocopheryl acetate. Vitamin E-deficient fish exhibited significantly lower weight gains and feed conversion efficiencies compared to the other fish. In addition, the following vitamin E deficiency signs were observed; skin and fin hemorrhages, anorexia, impaired erythropoiesis, muscle degeneration, ceroid depositions in liver and spleen, and lack of skin color. The vitamin E requirement of the blue tilapia was estimated at 10 mg dl-α-tocopheryl acetate/kg of diet at 3% dietary lipid and at 25 mg/kg of diet at 6% dietary lipid when diets contained 120 mg/kg BHA. It is recommended that vitamin E requirements be expressed as a function of dietary lipid level; 3–4 mg α-tocopheryl acetate per percent corn oil per kg of diet for the blue tilapia.

Lipid requirements of some warmwater species

Abstract Some fish, such as rainbow trout and certain marine species, require n−3 fatty acids, while other species have a requirement for n−6 fatty acids and may also require at least low levels of n−3 fatty acids for proper nutrition. Channel catfish appear to require fatty acids from both the n−3 and n−6 families, though the proper ratio between the two, while apparently important, has not been precisely determined. Tilapia have a demonstrated requirement for n−6 fatty acids and grow poorly on diets containing high levels of linolenic acid. Both catfish and tilapia may have a requirement for n−3 fatty acids that can best be met from high molecular weight fatty acids such as 20:5n−3 and 22:6n−3. Ambiguities in data collected to date indicate the need for protracted studies and evaluation of the fatty acid patterns of polar lipids rather than total lipids if the actual fatty acid requirements of warmwater fish species are to be properly characterized.

Responses of Red Drum (Sciaenops ocellatus) to Calcium and Magnesium Concentrations in Fresh and Salt Water

Abstract Experiments were conducted to determine some of the chemical aspects of water quality required by cultured red drum in fresh or salt water. Two studies were conducted in fresh and two in salt water differing in concentrations of calcium and magnesium. Red drum weighing 1–3 g each were stocked at 15 fish per 114-l tank. Treatments were replicated three times. Environmental calcium significantly affected red drum survival in fresh and salt water; magnesium produced no discernible effect on performance. In saltwater [35 g/l total dissolved solids (TDS)] experiments, fish in experimental water containing less than 176 mg/l calcium exhibited 100% mortality within 96 h. Highest survivals were observed in water containing 340–465 mg/l calcium. Red drum stocked in fresh water (0.56–1.9 g/l TDS) with calcium concentrations 1.7 mg/l or less performed poorly (0–33% survival after 96 h). Growth and survival were not significantly affected when calcium was between 9 and 407 mg/l. These data are consistent with the recognized physiological effects of calcium on membrane permeability and its postulated function in pore or channel mechanisms. Generally, fish from the first fresh- and saltwater experiments had significantly better longterm (42 days) survival than those from the second set of experiments. This appeared to be related to the use of acid-washed biofiltration media (hypothetically related to the removal of essential trace components) in the second trials.

The effectiveness of tricaine, quinaldine sulfate and metomidate as anesthetics for larval fish

Abstract Tricaine, quinaldine sulfate, and metomidate were compared as anesthetics for larvae of two species of fish, red drum (Sciaenops ocellatus) and goldfish (Carassius auratus). Larvae were exposed to various concentrations of each anesthetic and the percentages of fish reaching stage 4 of anesthesia, post-exposure recovery, and survival were recorded. Effective concentrations were defined as those which induced stage 4 of anesthesia within 3 min after exposure with a recovery time of 10 min or less. Post-exposure survival of 100% was an additional criteria used to define effective anesthetic concentrations. The lowest effective concentration of tricaine for red drum was 55 mg/l (26 °C), while 50 mg/l (24 °C) was the lowest effective concentration for goldfish. The lowest effective concentration of quinaldine sulfate for red drum was 35 mg/l (26 °C), while 60 mg/l (24 °C) was the lowest effective concentration for goldfish. Metomidate was found to be an ineffective anesthetic for both red drum and goldfish larvae based upon survival and recovery times. Mortality occurred in red drum larvae at all tested concentrations of metomidate. Larvae of both species that survived anesthesia with metomidate had longer induction and recovery times compared to larvae exposed to tricaine and quinaldine sulfate.

Use of Hatchery Fish in Enhancement Programs

Abstract The practice of stocking hatchery fish is coming under increasing criticism. Views that genetic integrity may be altered by the intermingling of wild and hatchery fish originating from different stocks and that hatchery fish have been genetically altered as a result of generations of selection are widely held. Past breeding and hatchery management practices have produced instances wherein hatchery fish were poorly prepared to compete in the wild.

Dietary Pantothenic Acid Requirement of the Blue Tilapia

Abstract The minimum dietary requirement of the blue tilapia (Tilapia aurea) for pantothenic acid was determined. Five semipurified diets supplemented with 0, 5, 10, 20, or 40 mg calcium D-pantothenate per kilogram of diet were evaluated. Fish fed unsupplemented diets showed significantly poorer (P < 0.05) weight gain, feed conversion efficiency (fish weight gained/dry weight fed), and survival after 12 weeks than fish that received the vitamin. Deficiency signs included exudated gills, fusion of gill filaments and lamellae, and severe fin erosion. Deficient fish recovered completely when fed a diet supplemented with 40 mg calcium D-pantothenate/kg. The minimum pantothenic acid requirement was estimated at 6 mg/kg based on growth. However, based on survival and lack of pathology, a level of 10 mg/kg of diet is recommended.

Vitamin Requirements of Blue Tilapias in a Recirculating Water System

Abstract Fingerling blue tilapias (Tilapia aurea) were offered vitamin-complete semipurified diets supplemented with different levels of either pantothenic acid or choline during three studies. A vitamin-free control diet was included in one study. Fish were kept in aquaria and supplied with recirculated water from a downflow gravel filter. No differences in weight gain, survival, or feed utilization were detected among fish in the different treatments, except for fish fed the vitamin-free diet. Those fish became lethargic and anorexic, lost equilibrium, developed hemorrhagic areas in the skin and fins, and exhibited poor growth and low survival. It is suggested by the results of this study that tilapias could satisfy their requirement for pantothenic acid, choline, and possibly other (but not all) vitamins by feeding on bacteria in a recirculating system.

A global overview of aquaculture production

Abstract Aquaculture, or underwater agriculture, is an art that has been practiced for some 4000 years. Largely within the past three decades, it has developed into a science. Aquacultured plants, molluscs, crustaceans, and fishes contribute significantly to mans food supply, though total production from wild harvest continues to greatly exceed the contribution from aquaculture. In the United States, development of the channel catfish industry since 1960 is an example of one of the major success stories of aquaculture. U.S. aquaculture is almost insignificant, however, in comparison with production levels that have been achieved in Asia. Constraints associated with user conflicts, availability of water, and a pending crisis in the worlds fish meal supply exist, but modern technology may find solutions to these problems. Aquaculture, while not the total answer to providing food for a hungry planet, will continue to make an important contribution. One of the major challenges to further aquaculture growth ...