Najas Guadalupensis Research Articles

Feeding behaviour of yearling and older hybrid grass carp

Hybrid grass carp resulting from the cross of a female grass carp, Ctenopharyngodon idella (Val.), and a male bighead carp, Hypophthalmichthys (Aristichthys) nobilis Rich., 12–18 months old (c. 300 mm T.L.) were studied in a two‐part experiment to determine feeding preference and total daily consumption fish‐1 on selected species of aquatic plants. Fish were maintained in circular pools with 6840·8 1 of water inside a temperature‐controlled greenhouse. Preference tests were conducted at three temperature ranges; 25–28° C, 17–20° C and 12–15° C. Based on the time to complete consumption or the relative quantity consumed, the most preferred plant was Lemna gibba when in combination with six other species. Chara sp., Najas guadalupensis and Potamogeton peciinatus were readily consumed and considered to be of about equal preference. Ceratophyllum demersum and Myriophyllum brasiliense were least preferred. Hybrid grass carp generally consumed as much plant material species‐1 and in the same order of preference at the 12–15°C range as they did at 25–28° C. In the second part, mean daily consumption (g) fish‐1 at 25·7–31·0° C for five plant species tested separately was as follows: Chara sp. 369·8; Lemna gibba 178·2; Najas guadalupensis 172·6; Hydrilla verticillata 106·4 and Ceratophyllum demersum 8·8.

Feeding behaviour of underyearling hybrids of the grass carp, Ctenopharyngodon idella♀ and the bighead, Hypophthalmicthys nobilis♂ on selected species of aquatic plants

Underyearling hybrids of the cross Ctenopharyngodon idella♀ (grass carp) and Hypophthalmichthys nobilis♂ (bighead), averaging 104.8 mm total length were stocked for two weeks in cement tanks holding 605 1 of water with various combinations of submersed or floating aquatic plants. The submersed species most preferred were Ceratophyllum demersum, Chara sp. and Najas guadalupensis. Hydrilla verticillata, Hygrophila polysperma, Myriophyllum pinnatum and Utricularia foliosa were fed on from a minor to moderate extent. No feeding damage was observed on Egeria densa and Potamogeton illinoensis. Azolla caroliniana, Lemna sp. and Wolffia columbiana were readily consumed while Salvinia rotundifolia was not preferred when in combination with these floating plant species. Feeding damage to the submersed roots of Eichhornia crassipes and Pistia stratiotes was minor during a 30 day period. Hybrid fingerlings readily fed on mosquito larvae and small leeches when offered to them in an aquarium on one occasion.

Plant Development and Sequence in Artificial Ponds with or without Phosphorus-Enriched Sediments

Plant Development and Sequence in Artificial Ponds with or without Phosphorus-Enriched Sediments

Nutrient Removal from Drainage Waters with Systems Containing Aquatic Macrophytes

ABSTRACT WATER quality parameters were measured at the inflow and outflow of three types of treatment systems for nutrient-enriched agricultural drainage water. The systems were a natural swamp, a 16.2 ha reservoir with Eichhornia crassipes (Mart.) Solms and a 0.40 ha reservoir containing Najas guadalupensis (Spreng.) Magnus. The Najas system was the most effective and the swamp system the least effective for removing nutrients. The aerobic Najas system was the most effective for removing phosphate and ammonia N, and the anaerobic Eichhornia system was the most effective for removing nitrate N. Periodic harvesting of the systems is necessary for op-timum removal of nutrients. A combination of plant systems may be more effective than single plant systems.

Digestion of an aquatic macrophyte by Tilapia zillii (Gervais)

The digestive efficiency of Tilapia zillii fed Najas guadalupensis was studied in the laboratory. Digestion was dependent on the ability of the fish to triturate the plant tissues. Based on a dietary reference, cellulose, the total digestibility of Najas was 29.3%. Digestive efficiency of the fish for non‐cellulose organic matter, protein and fat was 55.7%, 75.1% and 75.9%, respectively. Of the total caloric content of the plant, 45.4% was assimilated. An estimate was made of the amount of Najas necessary to satisfy the caloric expenditure of the fish.

Effects of nitrogen levels on rates of oxygen consumption during decay of aquatic plants

Oxygen consumption rates by microbial organisms during decomposition of Typha latifolia L., Eichhornia crassipes (Mart.) Solms, Najas guadalupensis (Spreng.) Morong, Pithophora kewensis Wittrock, Chara braunii Gmelin, Spirogyra sp., Euglena proxima Dangeard, and Anabaena circinalis (Kütz.) Rabenhorst were measured by a modified biochemical oxygen demand (BOD) technique. Rates of oxygen consumption were in the following order: Anabaena > ( Pithophora, Chara, Najas, Spirogyra, and Euglena) > Typha and Eichhornia. Oxygen consumption was positively correlated with nitrogen concentrations in the plants. Additions of inorganic nitrogen to the medium in BOD bottles increased the rate of oxygen consumption by microbial organisms decomposing plants of low nitrogen content.

Effect of Diquat on Uptake of Copper in Aquatic Plants

Combinations of copper sulfate pentahydrate (hereinafter referred to as CSP) at 1.0 ppmw copper plus 0.1 to 2.0 ppmw 6,7-dihydrodipyrido-(1,2-a:2′,1′-c)pyrazinediium ion (diquat) resulted in higher accumulations of copper in hydrilla (Hydrilla verticillata Casp.), egeria (Egeria densa Planch.), and southern naiad (Najas guadalupensis Spreng. Magnus) when compared to plants which received only CSP. A contact period greater than 24 hr was necessary before the higher amounts of copper were detected in those plants treated with the combinations. Water samples from outdoor, plastic pools 7 days after treatment with CSP at 1.0 ppmw of copper plus 1.0 ppmw of diquat contained 25% less copper than pools treated with CSP. Samples of hydrilla and southern naiad removed 7 days after treatment of the pools with the combination contained 77 and 38% more copper, respectively, than samples from those pools treated with only CSP.

Ecology of Submersed Aquatic Weeds in South Florida Canals

A 3-year ecological study of physical, chemical, and biological factors affecting the growth of submersed aquatic weeds was conducted in four irrigation and drainage canals in south Florida. Growth of aquatic vegetation was influenced by light intensity which decreased in a geometric ratio to water depth. The light penetration into the water was influenced by dissolved coloring matter and turbidity. A high concentration of nitrogen was found in three of the canals. Nitrogen entered the canals as sewage effluent discharged into the water and as fertilizer runoff from surrounding farmland. Density of aquatic vegetation harvested at intervals of 6 months from clipped plots varied from zero in a newly dug canal to 22,000 lb green weight/A in an old established canal. During the 3-year study, there was a complete shift of the vegetation from southern naiad (Najas guadalupensis(Spreng.) Magnus) to Florida elodea (Hydrilla verticillataCasp.) in two of the canals, but there was no change in plant species in two canals. No other chemical and physical factors evaluated in the study limited submersed aquatic weed growth in these canals.

The Use of Fertilizer for Controlling Several Submerged Aquatic Plants in Ponds

Abstract Various submerged weeds form tangled masses of vegetation in shallow, clear-water ponds in the Southeast. It is difficult or impossible to fish in such weed-infested ponds, and the weeds protect the small fish from carnivorous species so well that overcrowding develops and stunted populations result. Hence, the control of submerged weeds is an important problem in pond management. Commercial fertilizer has been used in the control of Najas guadalupensis, Potamogeton pusillus, P. angustifolius, and Chara sp. The following is the recommended procedure: Apply 100 pounds of 6–8–4 and 10 pounds of sodium nitrate per acre at each application, broadcasting the fertilizer over the weed-infested portion of the pond; make the first application in the winter and others at about monthly intervals until the weeds are covered with filamentous algae. The algae shade the weeds so that they become detached and float in large decaying masses. No fertilizer should be applied while the weeds and algae are decaying a...