Snrub, overall length of a FHM seemed to play a big role in whether or not my aquarium RES would actually eat a FHM or not. Mine definitely had a size/length preference for eating smaller and shorter fish.

If the FHM was too long and the tail stuck out of the RES mouth they would spit the FHM out most of the time, if they could fit the entire FHM in their mouth they would pop their jaw several times, crush it, and eat it. When they were smaller and eating night crawler pieces I inadvertently cut some night crawler chunks that were longer than normal, and they simply refused to eat the longer pieces. My thought was that maybe they needed to have their mouth closed completely in order to utilize their crusher teeth in the back of their throat.

I do know there has been at least one study done on RES and size preferences of snails that they eat. Journal of the World Aquaculture Society - Article first published online: 3 APR 2007

http://onlinelibrary.wiley.com/doi/10.1111/j.1749-7345.2003.tb00075.x/abstract

Prey-size Preference, Maximum Handling Size, and Consumption Rates for Redear Sunfish Lepomis microlophus Feeding on Two Gastropods Common to Aquaculture Ponds

Abstract
Maximum handling sizes, prey size and species preferences, and ad libitum consumption rates were determined for three size classes of redear sunfish Lepomis microlophus feeding on Physa gyrina and Helisoma trivolvis, two common aquaculture-pond snails which serve as intermediate hosts for fish parasites. Maximum handling-size experiments indicated that redear sunfish as small as 14-cm total length were capable of consuming all sizes of Physa typically observed in ponds, whereas only redear sunfish of at least 32-cm total length are capable of consuming all commonly observed sizes of pond-dwelling Helisoma. When presented with a range of sizes of both snail species, redear sunfish consumed higher proportions of smaller- and medium-sized snails; the largest snails offered were uneaten or consumed in relatively small quantities. Multiple linear regression was applied to consumption data to develop a simple model for predicting mean daily ad libitum consumption rate (g/g per d) for redear sunfish feeding on snails with temperature (20–27 C) and fish total length (9–24 cm) as independent variables. Our findings will facilitate prediction of numbers of redear sunfish of a given size required to control populations of Physa and Helisoma in ponds. Such predictions will enable pond owners to quickly evaluate whether stocking redear sunfish as a control agent for undesirable snail populations will be economically and logistically feasible. Findings also indicate potential limitations in the use of redear sunfish to control populations of Helisoma due to the inability of redear sunfish as large as 24-cm total length to consume the largest 30–40% of Helisoma commonly observed in ponds and to the expense of stocking larger fish (32-cm total length) capable of consuming all sizes of Helisoma.


Thank you Dr. Willis. wink

PDF link to the entire article

Last edited by Shorty; 08/27/14 03:08 PM.