Movements and behaviors of swordfish in the Atlantic and Pacific Oceans examined using pop‐up satellite archival tags

Swordfish are highly specialized top‐level predators that have been challenging to study. In this paper, data from 31 pop‐up satellite archival tags attached to swordfish from (i) the eastern Pacific, (ii) central Pacific, and (iii) western North Atlantic‐Caribbean were analyzed. Common across locations was a pronounced diel vertical pattern with daytime hours spent primarily below the thermocline and nighttime hours spent in warmer waters, close to the surface. One exception to this pattern was periodic daytime basking events which were most common in cooler waters off California. Maximum daytime depths were significantly correlated with light penetration as measured by the diffuse attenuation coefficient at 490 nm. Temperature did not appear to influence daytime depths, and swordfish tolerated both extremely low temperatures (4°C) and rapid and dramatic temperature changes (>20°C). Temperature did appear to influence the nighttime depths in the Pacific where fish typically remained in the surface mixed layer. In contrast, in the warm tropical Atlantic this was not the case, and nighttime depths were much deeper. In all areas, nighttime depth increased around the full moon. Given the parallels between the vertical movement patterns of swordfish and those of the deep sound scattering layer we suggest that swordfish vertical distribution patterns, especially during daytime, are influenced largely by resource availability. At night, when swordfish are typically targeted by fisheries, both ambient light and temperature influence movements. Understanding vertical movement patterns of swordfish can help evaluate gear vulnerability, improve population assessments, and potentially reduce fisheries bycatch.     

Pectin purified from pomelo (Citrus maxima) peel as a natural hatching agent for fish embryos

Pectin is a biodegradable polysaccharide, and it has been recently applied as a gene delivery, drug delivery, wound healing and tissue engineering agent. In this study, pectin was extracted from pomelo (Citrus maxima) peel and characterized. The extraction recovery of pectin form pomelo peel was 14.5%, and it had 72.56% degree of esterification, 1,245.56 equivalent weight, 7.82% methoxyl and 68.27% anhydrouronic acid contents. Use of pomelo pectin as a hatching enhancing agent for fish embryos and its effect on hatching enzyme 1 (ZHE1) was investigated. The pectin‐exposed zebrafish embryos (100 µg/ml) showed significantly (p < .05) higher hatching rate (96.6%) compared with untreated (control) embryos (66.6%) at 60 hpf. The mRNA expression of ZHE1 was also significantly (p < .05) elevated up to 55.6‐fold in pectin‐exposed embryos at 24 hpf. In situ hybridization results revealed remarkably strong expression of ZHE1 in pectin‐exposed embryos compared with the control group. In addition, considerably larger size of the hatching gland was observed in pectin‐exposed larvae than that of the unexposed larvae group. These results clearly indicate that pectin isolated from pomelo peel has an ability to enhance the hatching process of zebrafish embryos via upregulation of ZHE1.     

Long-term changes in the smolt size and age of Atlantic salmon, Salmo salar L., in a northern Baltic river related to parr density, growth opportunity and postsmolt survival

Abstract –  The size of wild Atlantic salmon ( Salmo salar L.) smolts in 1972–2004 was studied in relation to parr density, smolt age, growth opportunity and postsmolt survival in the Simojoki River. There was a significant negative regression between the annual mean smolt size and the density of wild >1 year parr in the previous autumn, but not between the annual mean smolt size and age. The density of reared parr released into the river or the growth opportunity, based on the day length and air temperature during the previous summer, did not affect the size of wild smolts. The data on postsmolt survival based on recaptures of Carlin-tagged smolts showed a significant positive relationship ( P  < 0.01) between the survival of postsmolts and the annual size of wild smolts. It is hypothesised that the increased density of wild >1 year parr could have contributed to the decreased smolt size since the 1990s, and the reduced size of wild smolts could be included among the factors resulting in their declined postsmolt survival in the Baltic Sea.     

Natural and artificially-induced habitat complexity and freshwater fish species composition

Abstract  The effects of habitat complexity, induced by construction of artificial reefs, on the fish assemblages in the Barra Bonita reservoir, Brazil, and in the lotic zone immediately below the dam were studied. Four artificial reefs were constructed in each habitat at variable distances from the shore. Multiple correspondence analysis showed that the factors distance from the shore and type of habitat were determinants for the group formation, and artificial reefs had a lesser effect. Fish species composition was about the same at locations with and without reefs.     

Molecular cloning and gene expression of the riboflavin-binding protein in the Nile tilapia, Oreochromis niloticus

Tilapia riboflavin-binding protein (RfBP) cDNA was isolated by library screening. Even though it shows only 31～35% similarity to the reported RfBPs, tilapia RfBP is conserved in amino acid residues that are known to be essential for its protein function. The exclusive expression of RfBP in the brain-pituitary-gonadal axis, as revealed by both RT-PCR and Northern blot, suggested a possible role for RfBP in fish reproduction.     

Cultivation of Trypanosoma danilewskyi (Laveran & Mesnil, 1904) in serum-free medium and assessment of the course of infection in goldfish, Carassius auratus (L.)

Abstract. Purification and in vitro cultivation techniques were developed for the fish haemoflagellate, Trypanosoma danilewskyi. The parasites were isolated and purified from the peripheral blood of experimentally infected goldfish, using a combination of Ficolt-paque gradient centrifugation to remove fish red blood cells and in vitro incubation to remove the remaining fish leucocytes. A serum-free culture medium for T. danilewskyi supported both short- and long-term cultivation of the haemoflagellates. The serum-free medium is a mixture of reagents available commercially: Leibovitz's L-15 medium, Dulbecco's Modified Eagle Medium and Hank's balanced salt solution. The doubling time was calculated to be 44.4 × 7.8h. Typically, a two- to five-fold increase in the number of cultured parasites was observed on day 7 after subculture with 1 × 10⁶ and 5 × 10⁵ trypanosomes ml⁻¹, respectively. When administered to fish, the in vitro -derived parasites caused an infection and pathology whose characteristics were similar to those observed following infection with trypanosomes obtained from infected goldfish. The freshly isolated and in vitro -grown parasites were successfully cryoprescrvcd in the culture medium containing 10% glycerine at −80°C for at least 3 months. Although the viability of the parasite decreased by 40–50% after thawing, cryoprcserved parasites retained the ability to infect goldfish.
Correspondence: Dr M. Belosevic, Associate Professor, Department of Zoology, CW-312 Biological Sciences Building, University of Alberta, Edmonton, AB, Canada T6G 2E9.     

The utilization of clam waste meal as a protein source for rainbow trout Salmo gairdneri

Solid waste recovered from clam processing wash water was evaluated for its utilization as a replacement protein for fish meal. Three diets, diets 1 and 2 formulated to simulate the Oregon Moist Pellet (OMP) and diet 3 (Rangen), were fed to rainbow trout (Salmo gairdneri) for eight weeks. The effects of the clam waste meal on fish growth, food conversion, carcass composition and whole body fatty acid content were determined. The clam waste diet supported maximum growth and food conversion. Carcass analysis of moisture, protein and lipid contents were similar among the moist feeds. The dietary levels of 20:5w3 + 22:6w3 and total polyunsaturated fatty acids (PUFAs) were significantly higher in the clam waste diet pellet.     

Gene Expression in Black Tiger Prawns Following Intramuscular Injection of β-gal Plasmid

Gene expression in black tiger prawns (Penaeus monodon) was studied following intra-muscular injection of CMVGal plasmid into the second abdominal segment. We used an in situ staining technique to detect -gal expression in one- and three-month-old injected prawns. We found that only one of the three-month-old prawns expressed the marker gene (2 days after injection), and the site of expression was confined to the sixth abdominal segment away from the injection site. We repeated the experiment on a new batch of three-month-old prawns, but using fluorometric determination technique. This time we found that -gal expression was detected (6/42) at the site of injection after 2, 7, and 14 days. In two other test samples, transgene expression was detected in the sixth abdominal segment only, further confirming the possibility of injected DNA dispersal. The results of the study also suggest that direct gene transfer is a feasible technique in black tiger prawns.     

Induced breeding and larval rearing of the endangered Australian freshwater fish trout cod, Maccullochella macquariensis (Cuvier) (Percichthyidae)

Abstract. The endangered Australian freshwater fish trout cod, Maccullochella macquariensis (Cuvier), was the subject of a captive breeding programme to produce fry for reintroduction into the wild. Trout cod broodfish were maintained in earthen ponds for up to 5 years and underwent gonadal maturation each spring but did not spawn in the ponds. Infestations of the protozoan parasite Chilodonella hexasticha caused the death of at least 21 broodfish. Mature fish, removed from ponds when water temperatures had reached or exceeded 16°C, had a higher proportion of atretic oocytes and fewer fish spawned successfully compared to fish removed at lower temperatures. Ovulation was induced by a single injection of 1000–3000 iu/kg HCG. Between 1188 and 11338 eggs ranging from 2·5 to 3·6 mm in diameter were stripped from individual fish. Hatching commenced on days 5–9 and continued for up to 10 days (at 15·5–23°C). Larvae commenced feeding on days 21–25. Trout cod larvae were grown out to fry (363.3–48.6mm total length [TL]) in fertilized fry rearing ponds then released. Between 1986 and 1989, 8420 trout cod fry were released into several sites in the upper Murray River and upper Murrumbidgee River, and reports indicate that released fish are surviving.