Changes in density of under-yearling masu salmon <Emphasis Type="Italic">Oncorhynchus masou</Emphasis> in a natural stream after release

ABSTRACT:   The relation between the density of fish and parameters such as body weight, condition factor and the hepatic triglyceride (TG) content of masu salmon Oncorhynchus masou juveniles after release into a natural stream were studied. Hatchery-reared juveniles of different sizes and numbers were released in May 1999, 2000 and 2001, and investigations were carried out from July to September each year. The density of fish was relatively high in 1999, when juveniles of the largest size and number were released, but then continued to decrease during the investigation. The hepatic TG content remained considerably low in 1999, and there was a significant negative correlation between the density of fish and the hepatic TG content of the juveniles caught over three years. The initial fish size and number at release as well as the nutritional condition of the juveniles may affect the density of fish after release.     

Physio-Chemical Characteristics of Seminal Plasma and Development of Media and Methods for the Cryopreservation of European eel Sperm

The high sperm density, together with the short spermatozoa swimming time, makes European eel sperm manipulation and assessment for quality difficult. Two diluting media (K15 and K30) previously designed for Japanese eel sperm were tested. After 24 h, European eel sperm showed significant reduction in the percentage of motile spermatozoa after activation and different motility parameters (VAP, angular velocity; VCL, curvilinear velocity; VSL, straight line velocity; BCF, beating cross frequency), concluding that these media are not suitable to preserve the sperm of this species. After a hormonal treatment to induce spermiation, sperm volume, density and motility were recorded at weekly samplings. The variation of the osmolality (325–330 mOsm kg⁻¹), pH (8.4–8.6) and the ionic composition (concentration of Na⁺, K⁺, Mg²⁺ and Ca²⁺) of the seminal plasma were registered. Physio-chemical results were related with sperm quality throughout the treatment, to determine which must be the suitable characteristics of one extender for the sperm of this species, and to find the best conditions to obtain suitable cryopreservation media for European eel sperm. K⁺ concentration increased, while Ca²⁺ and Mg²⁺ concentrations showed a progressive reduction in correlation with the sperm quality improvement. Na⁺ showed a decreasing, but not significant tendency. P1 and P2 freezing media were designed considering the physio-chemical parameters as well as the ionic composition shown by the best quality sperm samples, and then compared with the previously described solutions, TNK and K30. Sperm quality was determined, checking the percentage of motile spermatozoa and motility parameters using computer-assisted sperm analysis (CASA) software. Samples were frozen after dilution (1:5, 1:20, 1:100) in different freezing media supplemented with 10% dimethyl sulfoxide (DMSO). After thawing, samples frozen with low dilution ratio (1:5) in TNK and P1 media showed higher, although not significant, spermatozoa survival (35.5 ± 14.5 and 36.6 ± 6.7%). The addition of l-α-phosphatidylcholine to the media seems to have a positive effect, as reported in the Japanese eel.     

Isoëtes sabatina (Isoëtaceae,Lycopodiopsida): Taxonomic distinctness and preliminary ecological insights

1. Isoëtes sabatina is the rarest aquatic quillwort in Europe. Although recently found (2013) in Lake Bracciano (central Italy), the species is just one step away from extinction with an estimated population not exceeding 400 individuals and a spatial range of a few hundred square metres.
2. Lake Bracciano is a deep, oligo-mesotrophic Mediterranean volcanic lake that has been subjected to human activities. From January to October 2017, the lake experienced a dramatic water level decrease (up to −1.50 m), which significantly affected the littoral zone and the habitat of I. sabatina.
3. To improve the chances of survival of I. sabatina, the first eco-taxonomic investigation on this species was carried out to describe its genetic distinctness, physical and chemical requirements and companion species.
4. The phylogenetic position of I. sabatina was investigated by applying standard DNA barcoding methods. Simultaneously, during summer 2019, the physical and chemical features of water and sediments of the I. sabatina population and five small Alpine lakes colonized by Isoëtes echinospora – a supposed close relative – were characterized. These data were then compared with the available data on the trophic requirements of the target obligate aquatic Isoëtes, together with Isoëtes lacustris and Isoëtes malinverniana.
5. The present survey confirmed the taxonomic and ecological distinctness of I. sabatina – providing the first evidence of genetic differentiation from I. echinospora. Isoëtes sabatina grows in waters with temperature, conductivity and total alkalinity up to 30°C, 561 μS cm⁻¹ and 3.45 meq L⁻¹, respectively.
6. The edaphic requirements of I. sabatina confirm its outstanding conservation value, and this study offers a basic understanding of how to prevent its extinction. Now, all possible actions must be taken immediately to save this species.

     

Accumulation of organotin compounds and marine birnavirus detection in Korean ascidians

ABSTRACT:   Recently, a serious disease spread extensively in aquaculture sites of the ascidian Halocynthia roretzi in Korea. To understand circumstances of ascidians in Korean aquaculture sites, residue levels of organotin compounds were analyzed, and detection of a marine birnavirus (MABV) in tissues of H. roretzi was attempted. Korean H. roretzi showed high concentrations of butyltins (mono, di, and tributyltins), especially in the gill, hepatopancreas, and digestive tract. However, there was no significant difference in the residues of butyltins in the hepatopancreas between diseased and non-diseased ascidians. The positive rate of MABV detection was high in the hepatopancreas, but also no significant difference was observed between diseased and non-diseased individuals. These observations suggest that an accumulation of tributyltin and a latency of MABV in H. roretzi tissues does not directly relate to the occurrence of the disease.     

Vegetative propagation of the carrageenophytic red alga Gigartina skottsbergii Setchell et Gardner: Indoor and field experiments

The carrageenophytic red alga Gigartina skottsbergii presents several biological constraints for its cultivation such as restricted temporal availability and high spore mortalities that affect the development of its mass cultivation. For this reason, research to develop alternative propagation methods has been undertaken. Previous laboratory studies demonstrated that manipulating temperature, light and nutrients could enhance healing and regeneration of this seaweed. In this study nursery and field experiments were undertaken to establish the possibility to regrow G. skottsbergii in conditions similar to those applied in mass cultivation practices. Frond fragments and rhizoids were tested as alternative ways to obtain new plants. Our results indicate that regeneration occurs in the field, and can be managed in nursery conditions. The addition of a nitrogen source enhances the growth from 0.6 to 1.0% d^− 1 of the healed fragments and the use of a photon flux density above 50 μmol m^− 2 s^− 1 increases the growth rate but decrease the survival of the explants. Explants can be transferred to field conditions and grow at similar rates to those registered in the nursery (0.5% d^− 1). It is also possible to propagate rhizoids of G. skottsbergii and it seems that the attachment of a frond portion to the substratum, enhanced its survival and regeneration capacity. Finally, this study demonstrated that rhizoids attached to rocks can regenerate complete plants in nature, a feature which could be a useful for developing a sustainable harvesting methodology.     

Sensory evaluation of farmed sharpsnout seabream (Diplodus puntazzo)

The first attempts at applying aquacultural techniques to sharpsnoutseabream (Diplodus puntazzo) have proved very promising.One of the factors to keep in mind when analysing the viability of a speciesforindustrial farming is that of consumer acceptance of the product, a variablethat can be measured by sensory evaluation tests. To that end, 107 participantsfrom a number of work centres were assessed with hedonic sensory tests usingsharpsnout seabream samples. For reference purposes, the tasting also includedgilthead seabream samples. Participants were asked to fill out a questionnairethat included questions concerning their preferences for any one fish. Weanalysed the sensory attributes of both fish species using a hedonic scale, andalso their acceptability (disposition to purchase) to consumers. The resultsproved fairly encouraging with a view to sharpsnout seabream large-scaleproduction. All attributes tested in the sensory profile analysis werepositively rated. About 60% of the surveyed population would consider buyingsharpsnout seabream at a price similar to that of gilthead seabream (10),and 85% found it to be pleasing to the eye. Aside from flavour, its texture,juiciness and fat level are the most important appraisal attributes. Efforts toimprove the organoleptic characteristics of the species should focus mainly onthese attributes.