Growth and Morphological Development of Laboratory-Reared Yellowfin Tuna <i>Thunnus albacares</i> Larvae and Early Juveniles, with Special Emphasis on the Digestive System

Abstract

Yellowfin tuna Thunnus albacares larvae were reared from hatching beyond metamorphosis in May and June 1996. The larval size was 2.65mm SL at just after hatching and 27.68mm SL on Day 37. Transformation to juveniles occurred around 30 days after hatching at about 13mm SL. The larvae ini tially fed on rotifers since Day 4, on fish larvae and Artemia nauplii since Day 16, and then on frozen fish and minced fish meat. The primitive digestive system differentiated on Day 4. The gastric gland and pyloric caeca first appeared on Day 14 and 16, respectively. The pharyngeal and jaw teeth became fully functional synchronized with gastric gland differentiation. The number of gastric glands and pyloric caeca and volume of the gastric blind sac increased markedly toward the juvenile stage. Although exter nal morphological development of yellowfin tuna resembled to that of other marine fishes hatched from pelagic eggs, the digestive system developed precociously. The rapid development of the digestive sys tem allows the early appearance of piscivory which can support the high growth potential as shown in other scombrid fishes.

First data on growth and nucleic acid and protein content of field-captured Mediterranean bluefin (<em>Thunnus thynnus</em>) and albacore (<em>Thunnus alalunga</em>) tuna larvae: a comparative study

“…In studies focusing on the analysis of nutritional status of tuna larvae, the existing techniques have tended towards histological methods, mainly focusing on histological characteristics and appearance of the digestive tract (Margulies, 1993;Kaji et al, 1996Kaji et al, , 1999. However, nutritional condition studies by nucleic acid and protein content estimation are practically lacking in larval tuna.…”

“…Most studies have used histological methods to track the nutritional status of tuna larvae (Margulies, 1993;Kaji et al, 1996Kaji et al, , 1999. The only study in which nucleic acid and protein content was analysed refers to the species T. maccoyi (Carter et al, 1998), for which the differences of specific growth rates and nutritional status in farmed juveniles subject to diet variations were assessed.…”

Tuna Nutrition and Feeds: Current Status and Future Perspectives

“…This precocious timing of digestive system differentiation in scombrids may suggest an adaptation allowing the early appearance of piscivorous habits and high growth rates during the early life stages. Changing the feeding schedule from invertebrate zooplankton to fish larvae (see section 4.2.1) is therefore associated with the functional development of the digestive system and seems to be reasonably effective in the rearing of Thunnus larvae (Kaji et al, 1999). These studies on the development of digestive capacity of larval and juvenile tunas have shown that, after commencing feeding, trypsin-like and amylase-like activities increased as larvae grew, and pepsin-like activity increased and stomach and pyloric caeca functions developed from the post-flexion phase to juvenile transition (Miyashita et al, 1998;Kaji, 2002).…”

“…Most marine fish larvae have poorly developed digestive systems at first feeding (Sargent et al, 2002), although the larval type-gut has a considerable processing capacity that can support high growth rates, and the adult-type of digestive system (including a functional acid-producing stomach) only develops at metamorphosis, weeks to months after first feeding. However, several studies have revealed that in scombrid larvae such as Spanish mackerel (Scomberomerus niphonius), chub mackerel (Scomber japonicus) and striped bonito (Sarda orientalis), and also NBT and YFT, the adult-type digestive system is established at the mid phase of the larval period or around the first feeding stage, during scombriform-type metamorphosis (Kaji et al, 1996;Miyashita et al, 1998;Kaji et al, 1999;Kaji, 2002;Kaji et al, 2002). Moreover, and in contrast to straight gut teleost fish larvae, bluefin tuna present a rotated gut, which permits retention of ingested food for some time in the anterior midgut, and retrograde peristalsis as a mechanism for filling the pyloric caeca .…”

Fisheries oceanography and the ecology of early life histories of fishes: a perspective over fifty years

“…Kaji et al, 1999;Govoni et al, 2003) is another area for fruitful research that will aid in the resolution of growth and mortality.…”