Daniel Margulies

Tank culture of yellowfin tuna, Thunnus albacares: developing a spawning population for research purposes

Abstract A land-based culture facility for research on yellowfin tuna, Thunnus albacares , was developed at the Achotines Laboratory in the Republic of Panama. Six concrete tanks, and seawater and life support systems were built to maintain a yellowfin broodstock. On average, 50% of the yellowfin caught survived capture and handling, and approximately 30% became broodstock in Tank 1 (17 m diameter, 6 m depth) or Tank 2 (8.5 m diameter, 3 m depth). Each fish was tagged with a microchip implant tag, then weighed, measured, and injected with oxytetracycline (OTC) prior to stocking. Daily rations of primarily market squid, Loligo opalescens , and Pacific thread herring, Opisthonema spp., were regulated based on the feeding activity and energy requirements of the fish. Feeding activity of the broodstock decreased when the water temperatures decreased, and the fish ate decreasing daily rations and increasing calories with increasing size. Spawning occurred in both tanks within 6–8 months of capture. Spawning first occurred in Tank 1 when 24 females ranged in size from 6 to 16 kg and 65 to 93 cm fork length (FL). Spawning was intermittent during the first 2 months and occurred near daily thereafter. Tank size appeared to affect survival rates, the types of mortalities that occurred, and the growth of the fish. Survival rates after 1 year in captivity were higher, and the fish were larger, on average, in Tank 1 than in Tank 2. Most of the mortalities in Tank 1 were the result of wall strikes, which occurred more frequently after the fish reached their highest density of 0.64 kg m −3 and sizes greater than 96 cm FL and 19 kg. Non-linear growth models were fitted to the initial stocking sizes and final sizes of fish that died or were removed from Tank 1 during 1996–1999. Estimated growth rates in length (11–48 cm year −1 ) for fish between 51 and 150 cm FL decreased with increasing length. Estimated growth rates in weight ranged from 9 to 19 kg year −1 for fish less than 19 kg and 20–23 kg year −1 for fish greater than 19 kg. The results of this work demonstrate that the stable environment of a land-based culture facility may be the preferred system for long-term maintenance of a yellowfin broodstock.

Developmental Changes in the Visual Pigments of the Yellowfin Tuna, Thunnus Albacares

Previous studies have suggested that adult tunas have only two visual pigments in their retinas - a rod pigment with a wavelength at maximum absorbance (u max) around 485 nm and one with similar u max in both twin and single cones inferred from extraction data. Using microspectrophotometry we confirm the presence of a u max 483 nm visual pigment in the rods of adult yellowfin tuna and a u max 485 nm pigment in both members of the twin cones. However, all single cones contain a previously undetected violet visual pigment with u max 426 nm making the adult yellowfin tuna a photopic dichromat. The situation for larvae and early juveniles is different from that of the adults. The all single-cone retina of preflexion larvae shows a wide distribution in individual cone absorbances suggesting not only mixtures of the two adult cone pigments, but the presence of at least a third visual pigment with u max greater than 560 nm. With growth, the variation in cone absorbances decreases with convergence to the adult condition coincident with cone twinning. The significance of u max variability, multiple visual pigment expression and age-related differences are discussed in terms of the visual ecology of larval, juvenile and adult tunas.

Development of the visual system and inferred performance capabilities of larval and early juvenile scombrids

Development of the visual system in larval and early juvenile Euthynnus lineatus, Auxis spp., and Scomberomorus sierra was examined histologically. First‐feeding larvae of all three taxa possess a pure cone retina, with theoretical acuities ranging from 50 min of arc in Scomberomorus sierra to about 60 min of arc in Euthynnus lineatus and Auxis spp. Accommodative structures (lens retractor muscle and suspensory ligament) first appear during the late preflexion stage. Rod precursors appear in the flexion and early postflexion stages. By the late postflexion stage, the appearance of retinomotor movements indicates functionality of rods. The optic tectum is prominent in the midbrain at the first‐feeding stage and exhibits rapid growth and differentiation. The torus longitudinalis, an important sensory integration center of the tectum, does not develop until the early postflexion stage. Development of the visual system in larval scombrids is advanced and is likely involved in rapid improvements in foraging ab...

Genetic monitoring for spawning ecology of captive yellowfin tuna (Thunnus albacares) using mitochondrial DNA variation

Abstract Mitochondrial DNA genotypes of captive broodstock of yellowfin tuna ( Thunnus albacares ) were compared with those of their offspring in order to monitor spawning frequency and periodicity. Among 38 broodstock individuals, 27 genotypes were observed, 18 of which established a single individuals identity. Spawned eggs and hatched larvae were collected on 48 sampling days over a period of 1 year. Among 538 eggs and larvae analyzed, 10 genotypes were observed; eight of them established a single females identity, and two types were shared by two females. The spawning profiles of these females were determined by observing the occurrence of these genotypes in the offspring. Based on the dates when genotypes first occurred and on growth trajectories estimated for individual fish, the size of a female at first spawning was estimated to be 12–28 kg and 75–112 cm. Usually, multiple females spawned on a given date. The same genotypes were observed on almost any sampling day throughout the year. The results indicated that some individual females were capable of spawning almost daily for extended periods of time as long as they remained in the appropriate range of water temperatures and had sufficient food.

Direct Evidence for Mendelian Inheritance of the Variations in the Ribosomal Protein Gene Introns in Yellowfin Tuna (Thunnus albacares)

Abstract: Restriction fragment length polymorphism found in the S7 ribosomal protein gene introns of yellowfin tuna (Thunnus albacares) was compared between a single pair of parents and their offspring. The sizes of the first intron (RP1) and second intron (RP2) amplified by polymerase chain reaction were 810 bp and 1400 bp, respectively. The dam and sire had different restriction types from one another in HhaI and RsaI digestions for RP1 and in DdeI, HhaI, and ScrFI digestions for RP2. Putative genotypes in both introns of 64 larvae were found to be segregated in Mendelian proportions. Genotype distributions in a wild yellowfin tuna sample (n= 34) were in Hardy-Weinberg proportions, and observed heterozygosity ranged from 0.149 to 0.388. This study presents novel Mendelian markers, which are feasible for tuna population genetic study and pedigree analysis.

Improvement of water chemistry with Bacillus probiotics inclusion during simulated transport of yellowfin tuna yolk sac larvae

Abstract The effects of adding a probiotic Bacillus spp. blend on shipping bag water quality and survival of yolk sac larvae of yellowfin tuna Thunnus albacares during a 24-h mock shipment were investigated. To better detect effects on water quality, the trial was designed without the utilization of available chemical water quality or temperature modulators. Shipping water salinity (30.7–31.0‰) and temperature (24.0–26.7°C) reflected conditions utilized during larval rearing. Probiotic incorporation (15 mL/L, about 1.5 × 106 colony-forming units/mL) resulted in significantly lower final concentrations of total ammonia nitrogen and un-ionized ammonia in comparison with the control. Significantly higher final mean dissolved oxygen concentration observed in the probiotic treatment could have resulted from stress reduction. Although no statistical difference was detected in larval survival upon termination of the trial, improvements in water quality (reduced total ammonia nitrogen and increased dissolved oxyg...

Gonadogenesis and slow proliferation of germ cells in juveniles of cultured yellowfin tuna, Thunnus albacares.

To develop techniques for seedling production of yellowfin tuna, the behavior of primordial germ cells (PGCs) and gonadogenesis were examined at 1-30 days post hatching (dph) using morphometric analysis, histological examination, and in situ hybridization. Immediately after hatching, PGCs were located on the dorsal side of the posterior end of the rectum under the peritoneum of the larvae, and at 3 dph they came into contact with stromal cells. PGCs and stromal cells gradually moved forward from the anus prior to 5 dph. At 7-10 dph, germ cells were surrounded by stromal cells and the gonadal primordia were formed. In individuals collected at 12 dph, PGCs were detected by in situ hybridization using a vasa mRNA probe that is a germ-cell-specific detection marker. The proliferation of germ cells in the gonadal primordia began at 7-10 dph. We observed double the number of germ cells at 30 dph (22 ± 3.2 cells), compared to that at 1 dph (11 ± 2.1 cells). Therefore, based on our data and previous reports, the initial germ cell proliferation of yellowfin tuna is relatively slower than that of other fish species.