Changes in Physiology and Stress Responses of Pellet‐Reared Largemouth Bass Fed Live‐Forage Diets

Abstract

Advanced-sized Largemouth Bass Micropterus salmoides to be used for stocking and experimentation can be efficiently reared on prepared feed in intensive culture conditions, but formulated diets containing high levels (≥20%) of dietary carbohydrates may lead to high liver and muscle lipid and high liver glycogen levels, which may affect survival and stress responses. Largemouth Bass were raised to a size of 240-344 mm TL on formulated diets and then were fed live forage (i.e., naturalization); the effects of naturalization on liver, blood, and muscle health indices and physiological stress measures were evaluated, and indices were compared with those of wild Largemouth Bass from three different reservoirs. Hepatosomatic index (HSI) decreased by week 1 of naturalization; liver glycogen decreased by week 2; liver lightness, yellowness, and steatosis decreased by week 4; and liver moisture and lipid concentration stabilized after 4 weeks. Plasma cortisol was higher by week 1 of naturalization than by week 6 and onward, and plasma pH decreased after 1 week. Muscle color showed changes by week 1 of naturalization, muscle collagen stabilized by week 4, and muscle lipids decreased more gradually compared to the liver. The magnitude of stress response in fish subjected to a 60-s chasing stressor was unaffected by naturalization. Among populations of wild fish, many liver, blood, and muscle metrics were similar, with the exception of liver yellowness, glycogen, and HSI; muscle redness, lipids, and moisture; and the viscerosomatic index. Therefore, after rearing on a high-carbohydrate, high-lipid diet (i.e., 20% carbohydrates; 16% lipids), 4-6 weeks of naturalization can improve liver health, with most liver parameters being similar to those found in populations of wild fish.

Understanding Nutrition and Metabolism of Threatened, Data-Poor Rheophilic Fishes in Context of Riverine Stocking Success- Barbel as a Model for Major European Drainages?

“…Rearing of river stocking materials to larger sizes often has unintended adverse effects. When unscientifically chosen feed is used, there is a high chance of nutritional deficiencies or morphological alterations [ 56 , 57 , 58 , 59 ]. Although morphological alterations are visible to the naked eye, physiological alterations or deficiencies in the body’s nutrients pool remain subtle.…”

The Effects of Water Temperature and Simulated Angling on the Physiological Stress Response of Largemouth Bass

“…Fish were raised on a formulated diet (EXTR 450; 46% protein, 20% carbohydrates, 16% fat; Rangen, Inc., Buhl, Idaho) using the methods described by Dinken et al. (2020).…”

“…This process, TEMPERATURE AND ANGLING EFFECTS ON STRESS RESPONSE termed "naturalization," was used to reduce the physiological effects of high dietary carbohydrates on liver function (Goodwin et al 2002;Amoah et al 2008) and to improve overall health. A separate experiment found that a naturalization period of 4-6 weeks reduced many of the negative effects of high (20%) carbohydrate diets on liver health and physiology (Dinken et al 2020), and fish had high survival after a 60-s chasing stressor .…”

“…Seven-thousand Largemouth Bass fingerlings (~50 mm TL) that were trained to consume formulated feed were transported from a commercial supplier (J. M. Malone and Son, Inc., Lonoke, Arkansas) to the Mississippi State University South Farm Aquaculture Facility (Starkville, Mississippi) in June 2014. Fish were raised on a formulated diet (EXTR 450; 46% protein, 20% carbohydrates, 16% fat; Rangen, Inc., Buhl, Idaho) using the methods described by Dinken et al (2020).…”

Survival of Advanced‐Fingerlings of Florida Largemouth Bass Stocked in Small Florida Lakes

“…Given the expected effects of size on stocked fish survival, it is not surprising that fishery managers have recognized the benefits of advanced sizes to the supplemental stocking of Largemouth Bass (Hoxmeier and Wahl 2002; Porak et al 2002; Colvin et al 2008; Mesing et al 2008; Diana and Wahl 2009). In some cases, however, rearing Largemouth Bass to larger sizes may incur unintended negative effects, such as morphological alterations (Wintzer and Motta 2005) or, if pelleted feed is used, nutritional deficiencies (Porak et al 2002; Cardeilhac et al 2008; Dinken et al 2019). Together, these studies have suggested that size at stocking should matter and that generally larger stocked Largemouth Bass should be more likely to increase fish populations, but managers will face trade‐offs with production numbers and influences of rearing techniques.…”