Development of hatchery methods for fathead minnows.

Ignacio Masson (now a Ph.D. candidate at the University of Southern Mississippi) conducted his Master’s research on developing mew hatchery methods for fathead minnows. Fathead minnows Pimephales promelas traditionally have been produced using the wild spawning method, where eggs and young are retained in the same pond as the adults. Some producers also use the fry transfer method, where juvenile fish are partial harvested from brood ponds and transferred to others for grow-out. Rarely, the egg transfer method is also used. Disadvantages of these methods include overpopulation and a mixture of fish of different ages (in the case of the wild spawning) or they entail considerable labor to grade fish in order to collect the juveniles (fry transfer method). The egg transfer method results in uncertainty in the number of resulting fry stocked due to egg incubation without parental care after the transfer. New hatchery techniques have been developed for golden shiners and goldfish, consisting of the collection of eggs on spawning material, followed by transfer to indoor tanks to improve hatching rate and survival. Golden shiner eggs can also be detached with sodium sulfite solution for jar incubation, reducing hatchery space requirements. A similar system may have potential for commercial fathead minnow production. 

Fathead minnows lay adhesive eggs on the undersides of hard substrates. Male fatheads set up nesting sites and care for incubating eggs. Simple transfer of eggs to indoor tanks is problematic because relatively few eggs are spawned per unit of area and a great number of large tanks would be necessary to hold substrates for indoor incubation. A logical alternative is to remove eggs from substrate and hatch them in jars. Sodium sulfite (1.5%) was found to be effective at removing eggs without affecting the developing embryos. Up to 67% of the eggs were removed in 10 min with uniform agitation. Remaining eggs were easily removed by washing. Eggs that were exposed to 1.5% sodium sulfite for up to 30 min had hatching rates and percent deformities that were not significantly different from the control. If developed, cost-effective hatchery techniques could improve fathead minnow culture methods, enabling producers to utilize their facilities more effectively and to increase production of desired fish sizes. A manuscript is on internal review: Masson, I., and N. Stone. Developing methods for harvesting rosy red fathead minnow eggs. 

A cooperative project with Dr. Rebecca Lochmann, the thesis research of her graduate student Sathyanand Kumaran examines the effect of baitfish broodstock diet on egg production and the quality of eggs and resulting larvae. Methods are being developed to spawn and hatch baitfish eggs in indoor tanks. This significantly increases egg survival and can be used to obtain eggs out of season, allowing producers access to young (small) fish nearly year-round. Maternal broodstock nutrition is known to affect egg and larval quantity and quality in fishes. The fatty acid composition of the maternal lipid reserves is strongly influenced by her diet. A complete, balanced amino acid profile is also essential to allow vitellogenin production and other synthetic processes during egg formation. The composition of artificial diets is easy to manipulate. Therefore, there is tremendous potential to influence spawning success and larval quality and quantity of tank-held baitfish broodstock by manipulating the diet composition.

This project is being conducted in collaboration with Dr. Gerald Ludwig of the USDA/ARS H. K. Dupree Stuttgart National Aquaculture Laboratory. Arkansas leads the nation in baitfish production, and the majority of the six billion baitfish sold each year are golden shiners. New hatchery technologies provide farmers with many benefits, including reduced labor costs and water use, but basic production information for tank-hatched fish is lacking. Farmers desire consistency in fry survival and production. 

Two pond trials have been conducted and data are currently being analyzed. This study will provide farmers with information on the appropriate stocking densities of fry in order to obtain specific desired sizes of fish for market. In addition, the role of initial zooplankton populations on fry growth and survival will be investigated in order to develop appropriate pond preparation methods for tank-hatched fry. These trials will also strengthen the research base for the baitfish production verification program. Project goals are:

1) To determine the effect of stocking density on the growth and production of tank-hatched golden shiner fry.
 
2) To evaluate the relationship between zooplankton populations and golden shiner growth and survival for fry stocked at different densities.

New Studies

This study will be conducted in cooperation with Dr. Andy Goodwin. Golden shiners are the primary baitfish species raised in the US. Arkansas farmers produce more than 80% of the US crop with annual sales and economic impact to the state in the millions of dollars. With improvements in hatchery technology, the largest remaining bottleneck is that farmers must use young broodfish because older fish may be rendered sterile by the microsporidean parasite Ovipleistophora ovariae. This project will utilize recent advances in hatchery technology and diagnostic molecular biology to produce broodfish free of this parasite. Molecular diagnostic techniques, antiparasitic treatments, and biosecurity measures will be used together to produce specific pathogen free golden shiners.

Fish farmers in 36 states produce a total of  $37.5 million worth of baitfish annually (NASS 2000). Arkansas leads the nation in baitfish production (NASS 2000), and golden shiners comprise the majority of the six billion baitfish sold each year. A concern common to all producers is how best to promote or restrain fish growth. For example, feeder goldfish producers must hold their fish at a small size, while golden shiner producers want a portion of their crop to grow to a large size as fast as possible. Information on the roles and interrelationships of the various factors involved in fish growth is essential to the development of new techniques for baitfish production. Producers must supply a sufficient volume of each of the various size classes of fish (i.e., crappie, mediums, and jumbos) in order to meet market requirements. There is an unmet demand for large golden shiners (fish retained by a #25 or #27 grader, Stone et al. 1997). Production of large fish typically requires a second growing season, and fish farmers are particularly interested in strategies to reduce the time required to produce jumbo shiners. Farm-raised baitfish are valuable not only as a commercial product, but also because they provide an alternative to the harvest of billions of small wild fish from natural waters. 

Hepher (1978) listed the four main ecological factors controlling growth as water temperature, food, oxygen and metabolite production. Fish density is considered an important factor in fish growth, either directly or through indirect mechanisms, such as water quality (e.g., Backiel and LeCren. 1978, Shelton et al. 1981, Jodun et al. 2002). It has also been suggested that species-specific metabolites reduce fish growth with increasing density (Francis et al. 1974, Konstantinov and Yakovchuk 1994). Within a given set of culture conditions, stocking density clearly affects fish size at harvest, but the exact nature of the relationship between density and fish size is not well documented for golden shiners.  In a preliminary trial conducted in 12, 0.1-ha earthen ponds for 76 d, average harvest weight of golden shiners decreased exponentially with increasing stocking density, a = 262.42 b^-0.30645 (r² = 0.86), where a is average weight in grams and b is the number of fish per acre (Stone, unpublished data). The mechanisms responsible for the reduction in growth with increasing density are unclear. While it is overly simplistic to suggest a direct relationship between increasing fish density and the relative proportion of natural foods available to each fish, there is some relationship between the two factors. Based on the work of Ludwig (1989), it is possible that at higher densities golden shiners deplete populations of larger zooplankters to the point where recruitment is reduced.  Depletion of these larger zooplankters may also promote dense phytoplankton blooms dominated by cyanobacteria.

  Growth of golden shiners in indoor tanks and at higher densities in ponds is greatly reduced from that possible in ponds at low densities.  Why is this?  Is it food?  Golden shiners at low densities in ponds should have access to zooplankters, especially Cladocerans, the preferred food. This might result in exceptional growth. But golden shiners have been fed a high quality feed indoors and the growth is not equal.  Is it simply density, a crowding effect? One cannot imagine that this is really a factor in a schooling species like shiners. One difficulty in testing fish density effects in tanks is that ALL densities are higher than what fish experience in ponds, and yet growth is reduced in ponds at rates above 25,000 to 40,000/acre.

  Natural foods play an important role in golden shiner production even when prepared feeds are supplied (Ludwig 1989, Lochmann and Phillips 1996). To a certain limit, feed quantity influences growth. Stone et al. (1993) found that increasing the daily feeding rate from 3% bw/d to 4.5% increased average fish size. Rowan and Stone (1995) documented that satiation feeding of golden shiners resulted in a greater proportion by weight of larger fish (> #23 grader) than did feeding at reduced rates (75% or 50% of satiation). Golden shiners required approximately 40 minutes to satiate and consumed close to 3% body weight.  Feeding rate was also shown to be a major factor in the growth of small goldfish (Stone et al. 2003).  In a winter feeding study, golden shiners fed on warmer days at 2% bw/d grew faster than fish fed at a rate of 1% bw/d (McNulty et al. 2000). The importance of feeding frequency may depend upon the amount of feed fed and the stability of the feed form. No benefits were seen from dividing the daily ration (3% bw/d) into 1, 2, or 3 feedings per day (Stone et al. 1993). 

Temperature is a particularly critical factor in the growth of cold-blooded animals (Backiel and Stegman 1967, Weatherley 1990, Pickering 1993) and fish are known to have preferred temperature ranges (Coutant 1977).  Thomas (1958) examined the growth and food conversion ratio of golden shiners held at various temperatures. Results of his study suggested that weight gain peaked at 21 C, however, the data were highly variable, perhaps due to small sample size. While essentially all baitfish are raised in earthen ponds where temperature remains uncontrolled, producers are interested in off-season spawning, involving holding broodstock in indoor tanks and tank rearing of fry.  Water temperature can be controlled in tank culture, but crowding also becomes a factor.  

  Fish behavior may also influence fish growth.  Mann (1991) reviewed cyprinid growth and production, and noted that “Backiel and LeCren (1978) suggested that many species of cyprinids (and other schooling species) occur in dense populations with growth rates much lower than the potential for that species.” Shoaling fish subject to predation should not stand out in the “crowd,” to avoid being targeted. Golden shiners form shoals and individual fish size and location within the shoal is influenced by the size of cohorts. Larger fish are typically found towards the head of the shoal and are selectively targeted by predators (Reebs 2001, Ward et al. 2002). Johannes et al. (1989) concluded that golden shiner abundance in study lakes was predator-controlled, rather than limited by food availability. This implies that in the golden shiner, evolutionary pressure might have favored adoption of predatory avoidance mechanisms. An understanding of fish behavior could lead to modifications in culture methods (e.g., in-pond grading) to improve growth.

Backiel, T., and E. D. LeCren. 1978. Some density relationships for fish population parameters. Pages 279-302 in S. D. Gerking, editor. Ecology of freshwater fish production. Blackwell Scientific, London.

Backiel, T., and K. Stegman. 1967. Temperature and yield in carp ponds. Pages 334-342 in T. V. R. Pillay, editor. Proceedings of the FAO world symposium on warmwater pond fish culture, Rome, Italy, 18-25 May 1966. FAO Fisheries Reports 44(4).

Coutant, C. C. 1977. Compilation of temperature preference data. Journal of the Fisheries Research Board of Canada 34:739-745.

Francis, A. A., F. Smith, and P. Pfuderer. 1974. A heart-rate bioassay for crowding factors in goldfish. Progressive Fish-Culturist 36:196-200.

Hepher, B. 1978. Ecological aspects of warm-water fishpond management. Pages 447-468 in S. D. Gerking, editor. Ecology of freshwater fish production. Blackwell Scientific, London.

Jodun, W. A., M. J. Millard and J. Mohler.  2002.  The effect of rearing density on growth, survival and feed conversion of juvenile Atlantic sturgeon.  North American Journal of Aquaculture 64:10-15.

Konstantinov, A. S., and A. M. Yakovchuk. 1994. Species-specific metabolites as a limiting factor for fish stocking density. Journal of Ichthyology 34(4):39-46.

Lochmann, R., and H. Phillips. 1996. Stable isotopic evaluation of the relative assimilation of natural and artificial foods by golden shiners Notemigonus crysoleucas in ponds. Journal of the World Aquaculture Society 27:168-177.

Ludwig, G. M. 1989. Effect of golden shiners on plankton and water quality in ponds managed for intensive production. Journal of the World Aquaculture Society 20:46-52.

NASS (National Agricultural Statistics Service). 2000. Census of aquaculture (1998). National Agricultural Statistics Service, United States Department of Agriculture, Volume 3, Special Studies, Part 3, AC97-SP-3, Washington, D.C.

Pickering, A. D. 1993. Growth and stress in fish production. Aquaculture 111:51-63.

Shelton, W. L., R. O. Smitherman, and G. L. Jensen. 1981.  Density related growth of grass carp, Ctenopharyngodon idella (Val.) in managed small impoundments in Alabama.  Journal of Fish Biology 18:45-51.

Stone, N., E. Park, L. Dorman, and H. Thomforde. 1997. Baitfish culture in Arkansas: golden shiners, goldfish and fathead minnows. Cooperative Extension Program, University of Arkansas at Pine Bluff, Extension Publication MP 386, Pine Bluff, Arkansas.

Stone, N., E. McNulty and E. Park. 2003.  The effect of stocking and feeding rates on growth and production of feeder goldfish in pools.  North American Journal of Aquaculture 65:82-90. 

Thomas, J. C. 1958. A study of relationships of temperature to food consumption of the golden shiner, Notemigonus crysoleucas crysoleucas (Mitchill) with some field observations on feeding habits and rates of growth. M.S. Thesis, Rutgers – The State University, New Brunswick, New Jersey.

Weatherley, A. H. 1990. Approaches to understanding fish growth. Transactions of the American Fisheries Society 119:662-672.