Morphological development of larval cobia Rachycentron canadum and the influence of dietary taurine supplementation

Abstract

The morphological development of larval cobia Rachycentron canadum from 3 days post hatch (dph) until weaning (27 dph) was examined using S.E.M. Two groups of fish were studied: a control group (CF), reared under standard feeding protocol, and a group in which prey items were enriched with supplemental taurine (4 g l(-1) day(-1) ; TF). TF fish grew faster (P < 0·001), attained greater size (mean ±s.e. 55·1 ± 1·5 v. 33·9 ± 1·0 mm total length) and had better survival (mean ±s.e. 29·3 ± 0·4 v. 7·1 ± 1·2 %) than CF fish. Canonical variance analysis confirmed findings with respect to differences in growth between the treatment groups with separation being explained by two cranial measurements. S.E.M. revealed that 3 dph larvae of R. canadum (in both groups) possess preopercular spines, superficial neuromasts on the head and body, taste buds in the mouth, an olfactory epithelium which takes the form of simple concave depressions, and primordial gill arches. Gill filaments start to form as early as 6 dph and lamellae buds are visible at 8 dph in both groups. In CF fish, the cephalic lateral line system continues its development at 12-14 dph with invagination of both supra- and infraorbital canals. At the same time, a thorn-like or acanthoid crest forms above the eye. At 14 dph, invaginations of the mandibular and preopercular canals are visible and around 22 dph enclosure of all cranial canals nears completion. In CF larvae, however, completely enclosed cranial canals were not observed within the course of the trial, i.e. 27 dph. In TF larvae, grooves of the cephalic lateral line system form 4 days earlier than observed in CF larvae of R. canadum (i.e. at 8 dph), with enclosure commencing at 16 dph, and completed by 27 dph. Along the flanks of 6 dph larvae of either treatment, four to five equally spaced neuromasts delineate the future position of the trunk lateral line. As myomeres are added to the growing larvae, new neuromasts appear such that at 16 dph a neuromast is associated with each myomere. By 27 dph, the trunk lateral line starts to invaginate in CF larvae, while it initiates closure in TF larvae. These findings elucidate important features of the larval development of R. canadum and show that dietary taurine supplementation benefits larval development, growth and survival in this species. Moreover, they suggest a conditional requirement for taurine in larval R. canadum.

Taurine: a critical nutrient for future fish feeds

“…10 2004; Kim et al, 2005a;Kim et al, 2005b;Lunger et al, 2007;Matsunari et al, 2005;Pinto et al, 2010;Rossi Jr and Davis, 2012;Salze et al, 2011;Salze et al, 2012;Takagi et al, 2008), as well as in shrimps (Shiau and Chou, 1994). Because fishmeal is a significant source of essential minerals, it was hypothesized that growth reduction in low-fishmeal diets were due to a low mineral bioavailability, and that taurine acted as an organic acid, improving the bioavailability of minerals (Baruah et al, 2007;Khajepour and Hosseini, 2012;Vielma et al, 1999).…”

“…Pepsin activity also was higher in taurine-supplemented larvae, although the time of onset of pepsin activity was not altered by dietary treatment. Benefits to morphological development and metamorphosis have also been attributed to dietary taurine in R. canadum and S. senegalensis (Pinto et al, 2010;Salze et al, 2011). As it is for the other observed effects of taurine, the mechanisms underlying these effects on larval growth, survival and development remain obscure.…”

Investigation of biomarkers of early taurine deficiency in Florida pompano Trachinotus carolinus

“…It emerged as an essential nutrient in a number of teleost species including Florida pompano Trachinotus carolinus (Salze and Davis, 2015). Taurine deficiency induces a reduction in growth and feed efficiency (Brotons Martinez et al, 2004;Chatzifotis et al, 2008;Salze et al, 2011;Takagi et al, 2008;Takeuchi, 2001) which can dramatically affect commercial operations and in some circumstances may cause mass mortality. Taurine deficiencies are typically seen in species with limited ability to synthesize taurine and occur when natural sources of taurine are removed from the diet.…”

Biochemical composition of the promising live feed tropical calanoid copepod Pseudodiaptomus annandalei (Sewell 1919) cultured in Taiwanese outdoor aquaculture ponds

“…Overall, P. annandalei adult females and late stage nauplii show favourable contents of essential AAs needed for fish larvae growth, with more than half of their AA pool pertaining to essential AAs. Additionally, an abundance of free taurine and its precursor methionine in fish feed has resulted in increased growth in some fish species after intake (Salze et al 2011;Luo et al 2005;Matsunari et al 2013). Free taurine observed in P. annandalei nauplii and adult females revealed modest contents in comparison to what has been observed in e.g.…”