Paul A. Sandifer

The role of pelagic larvae in recruitment to populations of adult decapod crustaceans in the York River estuary and adjacent lower Chesapeake Bay, Virginia☆

Abstract The distribution patterns exhibited by some larval decapod crustaceans within the York River system and adjacent lower Chesapeake Bay, Virginia, suggest means by which young stages can be recruited to the adult benthic and bentho-pelagic populations. Species considered are four caridean shrimp (Crangon septemspinosa, Hippolyte pleuracantha, Ogyrides limicola and Palaemonetes spp.) and 12 brachyuran crabs (Callinectes sapidus, Cancer irroratus, Hexapanopeus angustifrons, Neopanope sayi, Ovalipes ocellatus, Pinnixa chaetopterana, Pinnixa sayana, Pinnotheres maculatus, Pinnotheres ostreum, Rhithropanopeus harrisii, Sesarma reticulatum and Uca spp.). Larvae of the species which are heavily dependent on estuarine habitats were more abundant in the lower layer of the water column where net transport is upstream than near the surface and thus tended to be retained within the estuary. For these species, retention of larvae in the estuary may be the primary mechanism of recruitment to estuarine adult populations. No distributional adaptations for retention within the bay were apparent among larvae of Cancer irroratus, Crangon septemspinosa and O. ocellatus, species not restricted to estuarine habitats, nor for Callinectes sapidus, a migratory estuarine species which also occurs on the inner continental shelf. While chance retention of larvae may affect recruitment, especially of C. septemspinosa, the major mechanism by which the bay populations of these species are restocked is probably the immigration of juveniles or adults from inner shelf waters. Thus, there appear to be two basic mechanisms of recruitment of young to estuarine decapod crustacean populations: (1) recruitment by retention of larvae and (2) recruitment by immigration of juveniles and adults. Various combinations of the two mechanisms are expressed among the different populations of an estuary, and the tendency of a species to exhibit one more than the other is influenced primarily by the degree of its dependence upon the estuary.

Meiotic chromosome complements and nuclear DNA contents of four species of shrimps of the genus Penaeus

Meiotic chromosome spreads were prepared from testicular lobes of 4 species of penaeid shrimps to determine numbers of chromosomes and meiotic phases. DNA content of nuclei isolated from shrimp hemocytes of these species was estimated by flow cytometry. Meiotic chromosome spreads indicated that the haploid chromosome number of Penaeus aztecus, P. duorarum, and P. vannamei was 44, while that ofP. setiferus was 45. These counts are consistent with diploid chromosome numbers reported previously for each of these species. No trivalents or quadrivalents were found in meiotic prophase. These 4 species had approximately the same genome size (approximately 70% of the human genome) as measured by flow cytometry. It is suggested that Robertsonian chromosome rearrangement has accompanied the speciation process in the genus Penaeus without polyploidization. Chromosome research in the decapod Crustacea has advanced slowly (Farmer, 1974; Milligan, 1976; Hughes, 1982; Hayashi and Fujiwara, 1988). Milligan (1976) and Hayashi and Fujiwara (1988) provided new techniques to obtain mitotic chromosome metaphase preparations in penaeid shrimps, but these works are still concerned only with chromosome counts and comparison of chromosome numbers between species. Thus, no karyotype has ever been described in this animal group. Although the small size and large numbers of chromosomes present some difficulty, determination of the genome size and examination of meiotic chromosome phase may provide additional information. In this paper, we report observations on meiotic chromosome phases in 4 species of shrimps of the genus Penaeus, with determinations of their genome size.

The relationship between feeding rate, paddlewheel aeration rate and expected dawn dissolved oxygen in intensive shrimp ponds

Abstract Determination of the proper level of supplemental aeration in intensive shrimp culture is critical for maintaining adequate concentrations of dissolved oxygen while minimizing equipment and operating costs. Little quantitative information is available on sizing the amount of aeration equipment to various levels of intensification. Results indicate that dawn dissolved oxygen (mg/liter) can be predicted based upon the amount of feed applied (kg/ha day) per unit aeration (hpday/ha). The amount of feed which can be applied with a given amount of supplemental aeration and a reasonable expectation that dawn dissolved oxygen will not be below a targeted concentration is expressed by the equation F A = 28·83 − (4·31 × DO ) .

Effects of mercury on survival and development of the larval grass shrimp Palaemonetes vulgaris

Effects of 7 concentrations of mercury from 0.0 (control) to 0.056 ppm on survival and development of the larval grass shrimp Palaemonetes vulgaris (Say) were investigated. A concentration of 0.056 ppm Hg was toxic to all larvae within 24 h, but below a threshold level (≤0.0056 ppm) no lethal effect occurred within 48 h. Feeding appeared to increase slightly the resistance of P. vulgaris larvae to mercury, and 48-h TLms (median tolerance limits) for fed and unfed larvae were 0.0156 and 0.0100 ppm, respectively. Delayed effects of 48-h exposure to sublethal mercury concentrations which appeared in later post-exposure rearing of the larvae included (1) reduced survival to the postlarval stage, (2) delayed molting, (3) extended development time, (4) increased numbers of larval instars, and (5) morphological deforment

SPERMATOPHORE FORMATION IN THE WHITE SHRIMPS PENAEUS SETIFERUS AND P. VANNAMEI

The medial and distal vasa deferentia and terminal ampullae of Penaeus setiferus and P. vannamei were studied by light and electron microscopy to assess their roles in spermatophore formation. The ascending medial vas deferens of each species consisted of 2 parallel epitheliumlined ducts, referred to as the spermatophoric and accessory ducts, with the accessory duct fitting into a groove along the spermatophoric duct. In the spermatophoric duct, the sperm mass was surrounded by a thick primary spermatophore layer secreted by the epithelial lining. Two secretions forming accessory layers 1 and 2 were deposited by the epithelial cells of the accessory duct. The lumina of the two ducts partially merged at the flexure between the ascending and descending portions of the medial vas deferens. Upon confluence, accessory layer 1 flowed into the spermatophoric duct and formed an additional layer around the primary spermatophore layer. Additional spermatophore components were deposited in the terminal ampulla, which consisted of 5 interconnecting chambers or lumina in P. setiferus and 4 in P. vannamei, respectively. The spermatophoric and accessory ducts terminated in chambers I and II, respectively. New secretions from chamber I were a thick dorsal plate and a thin adhesive layer. In chamber II, structural alteration of accessory layer 2 into corky reticulate and collapsed or fibrous reticulate portions occurred. Chamber III was a branching duct and contained glutinous material. Chamber IV seemed to be an extension of chamber II, but formed a distinct large lumen located in the proximal to medial regions of the terminal ampulla. This chamber contained a large amount offibrous reticulate substance similar to that observed in chamber II. Chamber V of P. setiferus contained the wing portion of the spermatophore. The terminal ampulla of P. vannamei possessed neither this chamber nor wing material. Upon ejaculation, each spermatophore joined mesially along the adhesive layer and formed a compound spermatophore. Accessory layer 1 and the corky reticulate layer were hard and functioned as a sheath for the sperm mass. These layers also supported the structure of the compound spermatophore. The dorsal plate, glutinous material, fibrous reticulate layer, and wing served to attach the compound spermatophore to the open thelycum.

Physical, chemical and biological characteristics of distinctive regions in paddlewheel aerated shrimp ponds

Intensive shrimp ponds are commonly aerated by placing paddlewheel aerators parallel to the pond dikes. This placement creates a relatively rapid water current along the pond banks, while leaving a center region with much slower flow. Implications of this flow mode were studied in three 0.25-ha ponds. Measurements of water flow, sludge depth, dissolved oxygen and pH were taken throughout a pond, and contour graphs were created and verified by several transect measurements on different dates in the same pond and in two other ponds. The distribution of the measured parameters suggests these ponds have two primary regions: a relatively well-mixed and aerated outer region, and a virtually stagnant, vertically stratified inner region. During the early morning, the inner region had significantly lower DO than the outer region in all ponds and on all dates. In contrast, during the afternoon, inner surface water DO ranged from nearly twice to nearly half that of outer surface water. This wide range in the inner region was facilitated by the minimal effect of mechanical aeration in this region and the consequentially larger affect of variable photosynthesis and oxygen demand. The separation between inner and outer regions was very distinct, and characterized by a drop in water speed from about 10 cm/s to less than 2 cm/s within 5 m. Sludge depth and organic matter accumulation were higher in the inner region, facilitating the lowest DO and pH measurements in the bottom water of this region. Shrimp abundance, as indicated by trap catches, was significantly lower in the center region, suggesting conditions may have been less favorable for shrimp growth and health over as much as 30% of the pond area. The results obtained in this work raise the need for renewed thought, development and assessment of alternative aeration strategies in intensive shrimp ponds.

Hydrozoans as pests in closed-system culture of larval decapod crustaceans☆

Abstract Three species of hydrozoans, Moerisia lyonsi, Stylactis arge , and Clytia gracilis , were accidentally introduced into closed system culture tanks used for rearing larval decapod crustaceans. The cnidarians were highly successful in competing with prawn and crab larvae for food (nauplii of Artemia salina ), and their numbers increased rapidly. Medusae of M. lyonsi were particularly troublesome as they also preyed directly on the decapod larvae. Although a 1-h treatment with a 250 ppm formalin solution was effective against medusae, the best method for eradicating the hydrozoans involves sacrificing the infested cultures, scrubbing and flushing the tanks and filter beds with hot water and allowing them to dry for several days. Neither M. lyonsi nor S. arge has been reported previously in South Carolina.

SPERM PRODUCTION AND THE EFFECTS OF ELECTRICALLY INDUCED SPERMATOPHORE EXPULSION IN THE PRAWN MACROBRACHIUM ROSENBERGII (DE MAN)

ABSTRACT The effects of electroejaculation techniques upon sperm cell and spermatophore production in the giant prawn Macrobrachium rosenbergii were investigated extensively. Animals received electrical stimuli according to various regimes: fixed 24-h interval between stimuli; decreasing interval between stimuli; increasing interval between stimuli; stimulation postmolt only; daily abdominal stimulation; and no electrical stimulation. The mean percentages of successful electroejaculation attempts for the 29-day period ranged from 81.1-100%. Of the individuals tested, 45% were capable of extruding some portion of a spermatophore after as little as 3 h postejaculation. While mean ejaculum size decreased significantly over the experimental period, no structural or ultrastructural abnormalities were observed in either sperm cell or spermatophore morphology. The spawns of 44 female prawns artifically inseminated with study-group ejacula exhibited normal percentages of fertilization. Several undesirable conditions resulted from the use of electroejaculation, including coxal ulcerations, limited muscle necrosis, and melanization of reproductive tissues. The relevance of these results for increased profitability in and feasibility of commercial aquaculture and selective breeding programs is considered.

Unusual testicular lobe system in the white shrimps, Penaeus Setiferus (Linnaeus, 1761) and P. Vannamei Boone, 1931 (Decapoda, Penaeidae) ; a new character for dendrobranchiata ?

[Contrairement aux testicules de la plupart des Crustaces Decapodes, ceux de deux especes de crevettes peneidcs, Penaeus setiferus et P. vannamei, sont composes de seize lobes independants, chacun dentre eux etant constitue par un tubule seminifere tres replie sur lui-meme. Les lobes testiculaires sont relies un par un au canal deferent anterieur proximal grâce a un canal collecteur court et fin. Le canal deferent anterieur proximal a la forme dun U renverse et passe a la base de chaque lobe testiculaire. Ces observations suggerent que ce systeme de testicules composes de multiples lobes independants pourrait etre une caracteristique nouvelle du sous-ordre des Dendrobranchiata. Des observations histologiques indiquent que la population de spermatogonies (zone germinale) se trouve toujours a la peripherie du tubule seminifere. Ces tubules seminiieres apparaissent soit dans une phase pleine, dite en corde, composee de cellules germinales (spermatocytes ou spermatides jeunes ou vieux) et de cellules sustentatrices soit dans une phase tubulaire dite a lumen composee de spermatides vieux, soit encore comme une phase intermediaire entre les deux precedentes. Ainsi les deux phases, en corde et a lumen semblent etre reversibles, les cellules sustentatrices sorganisant en matrice pour former la lumiere (epitheliation) et se desorganisant pour la supprimer (de-epitheliation)., Contrairement aux testicules de la plupart des Crustaces Decapodes, ceux de deux especes de crevettes peneidcs, Penaeus setiferus et P. vannamei, sont composes de seize lobes independants, chacun dentre eux etant constitue par un tubule seminifere tres replie sur lui-meme. Les lobes testiculaires sont relies un par un au canal deferent anterieur proximal grâce a un canal collecteur court et fin. Le canal deferent anterieur proximal a la forme dun U renverse et passe a la base de chaque lobe testiculaire. Ces observations suggerent que ce systeme de testicules composes de multiples lobes independants pourrait etre une caracteristique nouvelle du sous-ordre des Dendrobranchiata. Des observations histologiques indiquent que la population de spermatogonies (zone germinale) se trouve toujours a la peripherie du tubule seminifere. Ces tubules seminiieres apparaissent soit dans une phase pleine, dite en corde, composee de cellules germinales (spermatocytes ou spermatides jeunes ou vieux) et de cellules sustentatrices soit dans une phase tubulaire dite a lumen composee de spermatides vieux, soit encore comme une phase intermediaire entre les deux precedentes. Ainsi les deux phases, en corde et a lumen semblent etre reversibles, les cellules sustentatrices sorganisant en matrice pour former la lumiere (epitheliation) et se desorganisant pour la supprimer (de-epitheliation).]

A simple airlift-operated tank for closed-system culture of decapod crustacean larvae and other small aquatic animals

KurzfassungEin Kultursystem wird beschrieben, das zur Zucht von Decapodenlarven und anderen kleineren Wassertieren geeignet ist. Es besteht aus einem rechteckigen Zuchtgefäß mit schräg abfallendem Boden, an dessen seichtem Ende Wasser einströmt, so daß eine abwärtsgerichtete Bodenströmung entsteht. An dem tiefen Ende des Zuchtbeckens wird durch eingeleitete Luft das Bodenwasser nach oben transportiert, wobei an der Oberfläche ein Gegenstrom erzeugt wird. Das Wasser zirkuliert kontinuierlich durch ein Kiesfilter, das von dem eigentlichen Zuchtgefäß abgegrenzt ist. Nahrungspartikel und Planktonorganismen werden durch den hierbei erzeugten Wasserumlauf in Suspension gehalten. Die Larven des DecapodenMacrobrachium rosenbergii konnten mit Hilfe dieses Kultursystems erfolgreich aufgezogen werden.Summary1. A rectangular tank for culture of decapod crustacean larvae with continuous water recirculation is described. The tank has a sloped bottom and an attached gravel filter unit. Water circulation through the filter serves at the same time for maintaining food particles in suspension and for dispersing the larvae; it is accomplished by airlift pumps.2. Tanks of this design have been used successfully for closed system culture of larvae of the prawnMacrobrachium rosenbergii and are expected to be satisfactory for other small aquatic animals.