Copepods enhance nutritional status, growth and development in Atlantic cod (Gadus morhuaL.) larvae — can we identify the underlying factors?

Abstract

The current commercial production protocols for Atlantic cod depend on enriched rotifers and Artemia during first-feeding, but development and growth remain inferior to fish fed natural zooplankton. Two experiments were conducted in order to identify the underlying factors for this phenomenon. In the first experiment (Exp-1), groups of cod larvae were fed either (a) natural zooplankton, mainly copepods, increasing the size of prey as the larvae grew or (b) enriched rotifers followed by Artemia (the intensive group). In the second experiment (Exp-2), two groups of larvae were fed as in Exp-1, while a third group was fed copepod nauplii (approximately the size of rotifers) throughout the larval stage. In both experiments, growth was not significantly different between the groups during the first three weeks after hatching, but from the last part of the rotifer feeding period and onwards, the growth of the larvae fed copepods was higher than that of the intensive group. In Exp-2, the growth was similar between the two copepod groups during the expeimental period, indicating that nutrient composition, not prey size caused the better growth on copepods. Analyses of the prey showed that total fatty acid composition and the ratio of phospholipids to total lipids was slightly different in the prey organisms, and that protein, taurine, astaxanthin and zinc were lower on a dry weight basis in rotifers than in copepods. Other measured nutrients as DHA, all analysed vitamins, manganese, copper and selenium were similar or higher in the rotifers. When compared to the present knowledge on nutrient requirements, protein and taurine appeared to be the most likely limiting nutrients for growth in cod larvae fed rotifers and Artemia. Larvae fed rotifers/Artemia had a higher whole body lipid content than larvae fed copepods at the end of the experiment (stage 5) after the fish had been fed the same formulated diet for approximately 2 weeks.

Weaning of Burbot, Lota lota (L.) from Live to Dry Feed Using NaCl as Dietary Attractant

“…Generally, it is unknown which components of zooplankton have positive impacts on fish nutrition. Feeding studies conducted on cod larvae with copepod nauplii in comparison to rotifers revealed that copepod fed fish performed better (Karlsen, van der Meeren, & Rønnestad, 2015). Biochemical analyses of the feed showed that from all analyzed compounds protein, taurine, astaxanthin and zinc were higher on a dry weight basis in copepods than in rotifers and might be components responsible for better performance (Karlsen, van der Meeren, & Rønnestad, 2015).…”

“…Feeding studies conducted on cod larvae with copepod nauplii in comparison to rotifers revealed that copepod fed fish performed better (Karlsen, van der Meeren, & Rønnestad, 2015). Biochemical analyses of the feed showed that from all analyzed compounds protein, taurine, astaxanthin and zinc were higher on a dry weight basis in copepods than in rotifers and might be components responsible for better performance (Karlsen, van der Meeren, & Rønnestad, 2015). Also chitin, a main component of cladocerans and copepods, might play a role either as nutrient or as dietary fibre (Gutowska, Drazen, & Robison, 2004).…”

“…These aspects are important to obtain an accurate and solid data base on weaning parameters of L. lota. In previous studies where Artemia was used as starter feed, weaning was tested in earlier life stages (35-50 dph -Wocher, Harsányi, & Schwarz, 2012; Palińska-Żarska, Żarski, Krejszeff, Kupren, Łączyńska, & Kucharczyk, 2015) as this type of live feed is suitable for nutriton of larvae only for limited periods (Karlsen, van der Meeren, & Rønnestad, 2015). Weaning time points as tested in the present study are practicable when high quality and low cost live feeds are used.…”

Diet affects the redox system in developing Atlantic cod (Gadus morhua) larvae

“…The growth and development of marine fish larvae is superior when fed zooplankton consisting of their natural diet of copepods rather than the rotifers fed in commercial hatcheries [1][2][3][4]. This difference appears to be linked to differences in nutritional composition between the two zooplankton types, with rotifers having low levels of several nutrients, such as zinc, taurine and/or protein, compared to copepods [3,[5][6][7][8][9].…”

“…This difference appears to be linked to differences in nutritional composition between the two zooplankton types, with rotifers having low levels of several nutrients, such as zinc, taurine and/or protein, compared to copepods [3,[5][6][7][8][9]. The lower levels of certain nutrients in rotifers are probably deficient to sustain the high growth rates and successful metamorphosis of larval fish evolutionary adapted to the elevated levels of nutrients typical of copepods in their natural habitat [10,11].…”