Feeding behaviour of yearling and older hybrid grass carp

Abstract

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.