WWW.WAS.ORG • WORLD AQUACULTURE • SEPTEMBER 2014 37 Body tissues of teleost fishes are denser than water, causing fish to sink, but a gas-filled swim bladder allows fish to attain neutral buoyancy and adjust their position in the water column. Swim bladder inflation is a fundamental developmental step during the early life history of many fish larvae and is also a major challenge in the larval rearing phase of commercial perch production. As with most teleosts, perch have a narrow window of opportunity to inflate the swim bladder. Successful swim bladder inflation occurs during a specific and likely temperature-dependent developmental interval associated with a transient physostomous swim bladder in early ontogeny (Bailey and Doroshov 1995). The swim bladder is formed in the perch embryo as a dorsal branch of the gut that, during the larval stage, loses its connection with the gut. Two to three days after hatching, larvae rise to the water surface and swallow air to fill the swim bladder. Air gulped from the surface is forced into the pneumatic duct, a temporary opening to the swim bladder. This duct closes permanently 6-12 days after hatching (Summerfelt 1996). Swim bladder non-inflation can result in larval deformities (lordosis or stunting), slow growth and increased susceptibility to cannibalism and mortality (Overton and Paulsen 2005). Fish without a properly inflated swim bladder cannot maintain position in the water column without constant swimming, making it difficult to feed and use major energy reserves (Jacquemond 2004). However, in intensive aquaculture, fish with a non-inflated swim bladder can survive to adulthood. Swim bladder non-inflation in larval fish reared in captivity is common and usually attributed to constraints associated with artificial environments (Czesny et al. 2005). When swim bladder non-inflation, or sinker syndrome, was first recognized in teleost fishes, several hypotheses were proposed to explain its etiology, including nutrition, genetics and environmental factors. The primary hypothesis, proposed by Boggs and Summerfelt (1996), is that an oily layer on the water surface prevents larvae from breaking that surface. This may be from oil leaking from compressors or submersible pumps, leached from feed, or decomposition of dead fry (Boggs and Summerfelt 1996). An alternative mechanism is an aerocystitis bacterial infection of the swim bladder lining from bacteria in the water or at the water surface that interferes with the initial stage of swim bladder inflation. Evolutionary adaptive explanations for swim bladder noninflation have been proposed. McCune and Carlson (2004) reported a high frequency of mutations resulting in the loss of the swim bladder in zebrafish Danio rerio and widespread convergent loss of Effect of Body Size on Swim Bladder Inflation in Intensively Cultured Eurasian Perch Larvae from Different Locations Aleksey Pimakhin and Jakub ˘ák (CONTINUED ON PAGE 38) Aleksey Pimakhin and Jakub Zák TABLE 1. Sample origin and description of data. Country Location Designation 2011 Poland Masurian Lakes A Czech Republic Nove Hrady B Czech Republic Velke Mezirici C Poland Olsztyn Lake District C 2012 Germany Lake Ammer A Czech Republic Hodonin B Poland Zator C Germany Lake Starnberg D Czech Republic Velke Mezirici E Czech Republic Jistebnik F Czech Republic Lipno G Czech Republic Klatovy H Poland Mlynskie Stawy I Poland Olsztynek J Poland Lake Dejguny K Poland Gorjow L Czech Republic Litomysl M Bulgaria Lake Goljam N Germany Lake Muritz O Finland Lake Haukajarvi P Finland Lake Vajkjarvi Q Slovakia Strbske Pleso Lake R TABLE 2. Larval feeding protocol. Age dph Diet 1-10 Artemia nauplii (OceanNutrition Artemia Cysts) 11-14 Artemia nauplii + Frozen cyclops 15-24 Frozen Cyclops 25-28 Frozen Cyclops + dry starter feed BioMar Inicioplus 0.5 29-38 Dry starter feed BioMar Inicioplus 0.5 39-42 Dry starter feed BioMar Inicioplus 0.5 + pellets BioMar Inicioplus 1.1 42-56 Pellets BioMar Inicioplus 1.1
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