Increased toxicity of Karenia brevis during phosphate limited growth: ecological and evolutionary implications

Karenia brevis is the dominant toxic red tide algal species in the Gulf of Mexico. It produces potent neurotoxins (brevetoxins [PbTxs]), which negatively impact human and animal health, local economies, and ecosystem function. Field measurements have shown that cellular brevetoxin contents vary from 1–68 pg/cell but the source of this variability is uncertain. Increases in cellular toxicity caused by nutrient-limitation and inter-strain differences have been observed in many algal species. This study examined the effect of P-limitation of growth rate on cellular toxin concentrations in five Karenia brevis strains from different geographic locations. Phosphorous was selected because of evidence for regional P-limitation of algal growth in the Gulf of Mexico. Depending on the isolate, P-limited cells had 2.3- to 7.3-fold higher PbTx per cell than P-replete cells. The percent of cellular carbon associated with brevetoxins (%C-PbTx) was ~ 0.7 to 2.1% in P-replete cells, but increased to 1.6–5% under P-limitation. Because PbTxs are potent anti-grazing compounds, this increased investment in PbTxs should enhance cellular survival during periods of nutrient-limited growth. The %C-PbTx was inversely related to the specific growth rate in both the nutrient-replete and P-limited cultures of all strains. This inverse relationship is consistent with an evolutionary tradeoff between carbon investment in PbTxs and other grazing defenses, and C investment in growth and reproduction. In aquatic environments where nutrient supply and grazing pressure often vary on different temporal and spatial scales, this tradeoff would be selectively advantageous as it would result in increased net population growth rates. The variation in PbTx/cell values observed in this study can account for the range of values observed in the field, including the highest values, which are not observed under N-limitation. These results suggest P-limitation is an important factor regulating cellular toxicity and adverse impacts during at least some K. brevis blooms.

Phosphate treatment of frozen prawns. Pt. 1. Screening of various phosphates for prevention of drip loss

Various phosphates and their mixtures were screened for their efficiency of preventing drip loss in frozen prawns. The effectiveness of the phosphates decreased in the following order: Sodium tripolyphosphate — Sodium pyrophosphate — Sodium hexametaphosphate Sodium metaphosphate — Sodium dihydrogen phosphate; the last two being ineffective. Even though thaw drip loss was reduced by the above treatments the organoleptic quality of the thawed as well as cooked products was unsatisfactory, discoloration being the major defect. A solution of a mixture of 12% sodium tripolyphosphate and 8.6% sodium dihydrogen phosphate or 2% citric acid in water when used as dip prevented thaw drip loss, improved cooked yield and organoleptic quality without adversely affecting the biochemical characteristics. Commercial scale trials showed that the results are highly reproducible.

Phosphate treatment of frozen prawns. Pt 2. Frozen storage characteristics of prawn meat treated with polyphosphates

This communication reports the changes in physical, organoleptic and biochemical characteristics of prawn meat dip-treated with alkaline and neutral solutions of polyphosphates during frozen storage. Results are presented on changes in thawed and cooked yields, water extractable nitrogen, non-protein nitrogen, free amino-nitrogen, salt solubility, myosin and moisture in the muscle and loss of soluble nitrogenous constituents in thaw drip during frozen storage up to seven months. The salt solubility remained unchanged during storage in samples treated with neutral polyphosphate solutions and the organoleptic quality was superior to control sample. It is concluded that dip treatment with neutralized solutions of tripolyphosphate not only maintains correct drained weight and improves cooked yield during prolonged frozen storage but also protects the frozen product from denaturation as measured by the salt solubility of the proteins.

Effect of zinc and manganese supplementation to tricalcium phosphate rich diet for tiger puffer (Takifugu rubripes)

Effects of zinc (Zn) and manganese (Mn) supplementation to a tricalcium phosphate (TCP) rich diet for tiger puffer have been investigated. A TCP supplement to the diet decreased the growth of fish compared to the control diet with a Ca supplementation from Ca-lactate. However, addition of either Zn or Mn to the TCP supplemented diet could not improve the growth of tiger puffer. Addition of both zinc and manganese to the TCP supplemented diet improved the growth of tiger puffer.

Bacterial aspects of quality of phosphate treated frozen prawns

Changes in physical, organoleptic and biochemical characteristics of phosphate treated prawns and frog legs during storage have been studied in detail by Mathen and Pillai, (1970). Adoption of the recommended method by the industry in the freezing of prawns made it necessary to assess the influence of such treatment on the bacterial quality. This aspect assumes more importance in view of the proposed compulsory bacterial standards for raw frozen prawns. This note gives an account of the results on the influence of phosphate treatment on bacterial quality of raw frozen shrimp meat.